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  #1   Report Post  
T
 
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Default Sub Amps - a Follow up Question


OK, I have been looking into an amp to go between my (new to me) passive
sub and my (6 mo old) A/V Receiver.

The Receiver has a single SUB output jack, but the speaker enclosure has
both L & R inputs, in fact it has outputs as well for I assume satellite
speakers if I so choose. (We'll ignore those.)

My plan is to add this sub to an existing setup that already had decent
Front, Center and Surround speakers.

My question this time around is how best to deal with a single Sub
Output from the source through an Amp and on to a Stereo (perhaps dual
voice coiled?) Subwoofer.

Here's what I've brainstormed already:

- Run just one channel of the Amp and the Sub, ignoring the other
winding in the speaker & the other channel of the amp.

- Find an Amp that will accept a single input and will in turn output to
stereo.

- Same as option #1, but use both speaker windings, basically changing
the Ohms rating.

- Find a Mono Amp and A) Use just one winding in the speaker, or of
course B) Single in, Single out but use both windings on the Sub.

What say ye?


TBerk
  #2   Report Post  
still learning
 
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OK, I have been looking into an amp to go between my (new to me)
passive
sub and my (6 mo old) A/V Receiver.


The Receiver has a single SUB output jack, but the speaker enclosure
has
both L & R inputs, in fact it has outputs as well for I assume
satellite
speakers if I so choose. (We'll ignore those.)
_________________________________________________
The Reciever has an RCA connection marked sub out, correct?
If so just connect the RCA cables from there to the sub input which I
assume are also RCA connectors. Just to be sure, we are talking about
a powered subwoofer, correct?

The sub out from the reciever should already sum the LF to mono so no
need to worry further.

The only other setups I've seen are when the connections on the sub
woofer are for speaker wire input from the amp/reciever and outputs to
the main front speakers.

________________________________________________
My plan is to add this sub to an existing setup that already had decent

Front, Center and Surround speakers.


My question this time around is how best to deal with a single Sub
Output from the source through an Amp and on to a Stereo (perhaps dual
voice coiled?) Subwoofer.
__________________________________________________ ____
Just connect form the sub output on the reciever, to the input on the
sub. then you go about setting up the crossover on the sub to blend
with the main front speakers. It would be best (if you haven't already
purchased the sub) to get a sub that has both adjustable high and low
pass filter sections, failing that a passive sub with a separate amp
that has, (as many proamps do) a low pass filter and then add a high
pass filter. The reason for this, is to limit the LF output from the
main speakers and save them from working in their most difficult area.
Not having paid any attention to what the abilities are of an A/V
reciever I can't say if these sort of features are already built in,
but I'm sure the owners manual will tell you.
__________________________________________________ ____

If you buy a passive sub, or build one then you need an amp that can be
bridged to mono and preferably you need both high pass and low pass
functions to send only frequencies below a certain point (80Hz or less,
although the sub out will likely be 150-200 Hz) and send only
frequencies above a variable point to the main speakers. They need to
be variable and preferably the slopes should be 24 dB/octave to keep
the bass in the sub and not leak out.

www.hypex.nl has some of the best sub amps around.
Do a search for pro amplifiers and you will find there are many
affordable choices for bridgeable amps that will provide you with ample
power at lower prices than the typical sub amp. Then if you want to be
thourough, add a parametric EQ to smooth out probable FR bumps imposed
by the room.

Adire's Shiva and Tempest drivers are some of the best subwoofer
drivers available, and plans for cabinets are easy enough to find
through them as well. Another option in the DIY sub area is Rhythmik
Audio which also have a very godd product. If yo go the DIY route look
into the possiblity of using sonotube instead of an MDF cabinet. You
might wind up with a sub that looks something like a water heater, but
it will be at least as strong as a conventional cabinet and much
cheaper.

Adire also makes finished subs. Other good subs that are already
assembled are, HSU, PSB, NHT (who also sell there 12" woofer to the DIY
market for use in a sealed enclosure, the absolute easiest DIY project
there is), and SVS. All of these are good products and will give you
excellent bass.

Lastly you will need something that generates test tones so you can
match the sub to the mains, and an SPL meter to measure the levels so
you can match them for smooth integration.

You might want to check with the subwoofer section of www.diyaudio.com
and check the archives for some of the projects that have been done by
the participants.

There are plenty of online resources if you go the DIY route, which is
what I did. I'll never buy a ready made sub again, since I know you
can get equal or better performance by doing it yourself.

  #3   Report Post  
Barry Mann
 
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In , on 04/10/05
at 11:08 AM, T said:


[ ... ]
The Receiver has a single SUB output jack

[ ... ]

The RCA subwoofer output jack on a surround sound receiver is MONO and
any frequencies that don't belong to the subwoofer have been removed.
In the setup menu for the receiver, claim that the front and/or rear
speakers are "small" if you want bass that normally would be routed to
them to be withheld and routed to the subwoofer instead.

Assuming you have an appropriate amount of power and a capable
subwoofer, it doesn't matter if you use an external amplifier or an
amplifier built into the subwoofer.

The subwoofer is MONO even if it has a left and a right input.
Connecting to only the left or right input decreases the output level a
bit, but you can easily compensate for that by turning up the level
adjustment. (You will have to adjust the level anyway so that the
subwoofer output matches the main channels.)

A dual coil passive subwoofer appears as if it is two speakers. If you
use both coils, your amplifier will behave as if a second speaker has
been added. (Depending on who is lurking on the news group, this
statement may create some "flames". If it does, draw your own
conclusions after the flames have died down a bit.)

Passive subwoofers don't usually include level controls. Hopefully, the
gain of the external amplifier is variable or compatible with the
subwoofer output adjustment range of your receiver and the subwoofer
efficiency. It's a complex discussion when debating if the power
handling capability of the subwoofer would be much different when
driving one or both coils. True, the impedance seen by the amplifier is
different, but all the heat from the subwoofer coils is being dumped
into the same confined space in any case.

Make sure that the subwoofer's internal crossover does not fight with
the signal sent by the receiver.

-----------------------------------------------------------
spam:
wordgame:123(abc):14 9 20 5 2 9 18 4 at 22 15 9 3 5 14 5 20 dot 3 15
13 (Barry Mann)
[sorry about the puzzle, spammers are ruining my mailbox]
-----------------------------------------------------------

  #4   Report Post  
T
 
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Thank you both (Learning & Mann).

Some clarification from my end.

- I KNOW the A/V output is MONO.

- I have a Passive prebuilt SUB.

- It is a Paradigm SB-100.

Currently I don't have a stand alone amp for it, I am leaning towards
running the SUB output of the A/V unit through a vintage Sony Receiver I
have on the AUX input.

My dilemma is wrapped around having both Left & Right binding posts on
the bottom of the Sub cabinet. I'll likely ignore one side and just hook
up one or the other only.


TBerk
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jakdedert
 
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T wrote:
Thank you both (Learning & Mann).

Some clarification from my end.

- I KNOW the A/V output is MONO.

- I have a Passive prebuilt SUB.

- It is a Paradigm SB-100.

Currently I don't have a stand alone amp for it, I am leaning towards
running the SUB output of the A/V unit through a vintage Sony
Receiver I have on the AUX input.

My dilemma is wrapped around having both Left & Right binding posts on
the bottom of the Sub cabinet. I'll likely ignore one side and just
hook up one or the other only.

Does it also have L & R *output* terminals? If so, it probably has a dual
coil subwoofer driver and passive crossover. It can be placed directly on
the outputs of your amplifier, with your L&R front speakers connected to the
subwoofer outs. The crossover will handle the job of filtering some of the
low frequencies out of the main speakers and directing them to the sub...a
workable solution, but inefficient...some power will be wasted in the
crossover, and you might not want to filter the lows from your mains.

****Main amp speaker outssub insL&R speakers OR Main amp speaker outs
parallel with sub ins and L&R speakers (possible impedance problem?)****

The setup you describe, using an auxiliary sub amp, will result in slightly
more volume (assuming enough power output from that amp). Use a 'Y' cable
(one RCA male to two RCA males) to route sub output from your main amp to
the AUX ins on your sub amp, and connect the L&R speaker outs to your sub
ins.

***Main amp sub out'Y' cableL&R sub amp AUX inssub amp L&R speaker
outssub***

jak

TBerk





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still learning
 
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T Apr 14, 4:45 am show options

Newsgroups: rec.audio.tech
From: T


Some clarification from my end.


- I KNOW the A/V output is MONO.


- I have a Passive prebuilt SUB.


- It is a Paradigm SB-100.


Currently I don't have a stand alone amp for it, I am leaning towards
running the SUB output of the A/V unit through a vintage Sony Receiver
I
have on the AUX input.


My dilemma is wrapped around having both Left & Right binding posts on
the bottom of the Sub cabinet. I'll likely ignore one side and just
hook
up one or the other only.


TBerk


T: Just go to www.svssubwoofers and click on amps and EQ's. You find
2 Sampson amps that shoudl do very nicely for your sub. I think best
results would be obtained by adding an electronci xover and parametric
EQ, to flatten out the response.

  #7   Report Post  
still learning
 
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Correction: make that www.svsubwoofers.com

  #8   Report Post  
T
 
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jakdedert wrote:

snip
Use a 'Y' cable (one RCA male to two RCA males)
to route sub output from your main amp to
the AUX ins on your sub amp, and connect the
L&R speaker outs to your sub ins.

***Main amp sub out'Y' cableL&R sub amp AUX inssub amp L&R speaker
outssub***

jak



MuHahahahahah. That was _exactly_ what I wanted to hear.

It's just to get the thing a little run. I'll be picking out a dedicated
stand alone amp down the line.


Thx everybody.
TBerk
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Engineer
 
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"T" wrote in message
m...
jakdedert wrote:

snip
Use a 'Y' cable (one RCA male to two RCA males) to route sub output
from your main amp to
the AUX ins on your sub amp, and connect the L&R speaker outs to
your sub ins.

***Main amp sub out'Y' cableL&R sub amp AUX inssub amp L&R
speaker
outssub***

jak



MuHahahahahah. That was _exactly_ what I wanted to hear.

It's just to get the thing a little run. I'll be picking out a
dedicated stand alone amp down the line.


Check out PartExpress linear FET class AB sub amps. Nice units, good
value - I have two in service (home theatre and stage piano keyboard)
.. BTW, I have no connection with this company.
Cheers,
Roger


  #10   Report Post  
T
 
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Engineer wrote:
"T" wrote in message
m...

jakdedert wrote:

snip

Use a 'Y' cable (one RCA male to two RCA males) to route sub output
from your main amp to
the AUX ins on your sub amp, and connect the L&R speaker outs to
your sub ins.

***Main amp sub out'Y' cableL&R sub amp AUX inssub amp L&R
speaker
outssub***

jak



MuHahahahahah. That was _exactly_ what I wanted to hear.

It's just to get the thing a little run. I'll be picking out a
dedicated stand alone amp down the line.



Check out PartExpress linear FET class AB sub amps. Nice units, good
value - I have two in service (home theatre and stage piano keyboard)
. BTW, I have no connection with this company.
Cheers,
Roger





Yeah, they seem to get a lot of recommendations.

I have know of them for awhile but just recently when i got up the
gumption to build a sub (and hence buy one of those amps) a friend
dropped this passive prebuilt sub on me for free so I was going to hook
it up and give it a run to see what I was working with.


Thx everybody,
TBerk


  #11   Report Post  
Cyrus
 
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In article ,
T wrote:





Yeah, they seem to get a lot of recommendations.

I have know of them for awhile but just recently when i got up the
gumption to build a sub (and hence buy one of those amps) a friend
dropped this passive prebuilt sub on me for free so I was going to hook
it up and give it a run to see what I was working with.


Thx everybody,
TBerk


Here's one more for a recommendation. My only beef is the 2nd order xo,
may not be enough in some situations. But for the price vs. performance
ratio, they can't be beat.

hth,

--
Cyrus

*coughcasaucedoprodigynetcough*


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still learning
 
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Here's one more for a recommendation. My only beef is the 2nd order xo,

may not be enough in some situations. But for the price vs. performance

ratio, they can't be beat.

hth,


________________________________________-

Absolutely, Do not consider anything less than a 4th order L/R xover.
The parts express plate amp I saw says nothing about it's xover. IMO
the Rythmik Audio or Adire Audio Hypex amps are a much better choice
for plate amps.

ZZsounds has a wide choice of freestanding proamps with lowpass xovers
built in. Pro audio seems to allow far more flexibility and much better
prices for things like parametric EQ's and xovers.

  #13   Report Post  
Cyrus
 
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In article .com,
"still learning" wrote:

Here's one more for a recommendation. My only beef is the 2nd order xo,

may not be enough in some situations. But for the price vs. performance

ratio, they can't be beat.

hth,


________________________________________-

Absolutely, Do not consider anything less than a 4th order L/R xover.
The parts express plate amp I saw says nothing about it's xover. IMO
the Rythmik Audio or Adire Audio Hypex amps are a much better choice
for plate amps.

ZZsounds has a wide choice of freestanding proamps with lowpass xovers
built in. Pro audio seems to allow far more flexibility and much better
prices for things like parametric EQ's and xovers.


The Rythmik amps *are* the PE amps, with upgraded caps/opamps and 4th
order xo's as opposed to PE's 2nd order. This is parroted information
though, I have no first hand experience. I can't see paying more than
$150us for an AB plate amp w/out at least one parametric band and 2nd
order xo's though.

Have you any experience with Adire's new ADA series plate amps?

--
Cyrus

*coughcasaucedoprodigynetcough*


  #14   Report Post  
Cyrus
 
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In article .com,
"still learning" wrote:

Cyrus said:

The Rythmik amps *are* the PE amps, with upgraded caps/opamps and 4th
order xo's as opposed to PE's 2nd order. This is parroted information
though, I have no first hand experience. I can't see paying more than
$150us for an AB plate amp w/out at least one parametric band and 2nd
order xo's though.

Have you any experience with Adire's new ADA series plate amps?
__________________________________________________ ______

No, my only experience is with the HS200, but I have seen many
favorabloe comments on the Rythmik gear at www.diyaudio.com subwoofer
section.


I've seen reviews of the same, can't go wrong with Rythmik it seems.

--
Cyrus

*coughcasaucedoprodigynetcough*


  #15   Report Post  
still learning
 
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Cyrus said:
The Rythmik amps *are* the PE amps, with upgraded caps/opamps and 4th
order xo's as opposed to PE's 2nd order. This is parroted information
though, I have no first hand experience. I can't see paying more than
$150us for an AB plate amp w/out at least one parametric band and 2nd
order xo's though.
-------------------------------------------------------------------------------------

I think the biggest bang for the buck with the greatest flexibility
would be the Behringer EP1500 with the parametric EQ I mentioned
earlier.
400 wpc@ 4 ohms or in bridged mono mode 900@ 8 ohms and 1400 @ 4 ohms.
It has a switchable LP filter for 30 Hz or 50 Hz and on/off muting. At
$249.00 for the amp and IIRC $89.00 for the EQ, think you'd be set for
the next 20 years or so and the only thing left to upgrade would be the
driver in the sub, but that's a whole 'nother story.



  #16   Report Post  
Cyrus
 
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In article .com,
"still learning" wrote:

I think the biggest bang for the buck with the greatest flexibility
would be the Behringer EP1500 with the parametric EQ I mentioned
earlier.
400 wpc@ 4 ohms or in bridged mono mode 900@ 8 ohms and 1400 @ 4 ohms.
It has a switchable LP filter for 30 Hz or 50 Hz and on/off muting. At
$249.00 for the amp and IIRC $89.00 for the EQ, think you'd be set for
the next 20 years or so and the only thing left to upgrade would be the
driver in the sub, but that's a whole 'nother story.


I concur about the Behringer amps. Keep in mind though, one should
derate them a bit as the wattage is measured at 1k. Hardly a measurement
for sub duties.

Personally, I'm done with plate amps and my next upgrade step will be a
noisy fan'ed Behringer or equivalent amp. Placed in an adjacent room
and/or amp rack of course.

Here come the NSB line arrays and Avalanche 18's IB'ed. *drool* Ah well,
one can dream till one can afford.

--
Cyrus

*coughcasaucedoprodigynetcough*


  #17   Report Post  
still learning
 
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Cyrus said:

I concur about the Behringer amps. Keep in mind though, one should
derate them a bit as the wattage is measured at 1k. Hardly a

measurement
for sub duties.


They give measurements for stereo and for mono that are for 10db below
rated output power @ 8ohms of 900 watts with distortion of .01% so I
think there'll be plenty of power for any sub currently available.

Personally, I'm done with plate amps and my next upgrade step will be

a
noisy fan'ed Behringer or equivalent amp. Placed in an adjacent room
and/or amp rack of course.



Here come the NSB line arrays and Avalanche 18's IB'ed. *drool* Ah

well,
one can dream till one can afford.



Have you any dealings with the Behringer and it's noise level from the
fan?
IB's have no interest for me, unless I get up into the attic. Perhaps
after the disk decompression heals, although mysingle Shiva is
currently filling my needs.
--
Cyrus

  #18   Report Post  
Cyrus
 
Posts: n/a
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In article .com,
"still learning" wrote:



They give measurements for stereo and for mono that are for 10db below
rated output power @ 8ohms of 900 watts with distortion of .01% so I
think there'll be plenty of power for any sub currently available.


I'm not doubting that they're enough power one bit. Just saying don't
accept printed specs as gospel.

Have you any dealings with the Behringer and it's noise level from the
fan?


In the installation the Behringer amp was in that I experienced, it was
never quiet enough to notice it. A home setting is where its been
reported to be a problem. IMO If one chooses to purchase, know its
downfalls and install around said problems.

Cult of the Infinitely Baffled has more info on PA amps, their fan noise
ratings in some cases, as well as other options and quieter fan
replacements on some amps. There are of course other resources, but the
Cult has the most condensed info in this department.

IB's have no interest for me, unless I get up into the attic. Perhaps
after the disk decompression heals, although mysingle Shiva is
currently filling my needs.


Ugh sorry to hear about the disk troubles.

An IB is well worth the effort IMO. Whether ceiling or adjacent room
mounted. I've had experience with one and helped set up another. I was
hooked before proper eq.

My Shiva did well until it was replaced with an Atlas12. No more
bottoming in the 88.5L sealed enclosure.

hth,

--
Cyrus

*coughcasaucedoprodigynetcough*


  #19   Report Post  
still learning
 
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Cyrus said:

Cyrus Apr 17, 1:22 am show options



In article ups.com,
"still learning" wrote:



They give measurements for stereo and for mono that are for 10db

below
rated output power @ 8ohms of 900 watts with distortion of .01% so I


think there'll be plenty of power for any sub currently available.




I'm not doubting that they're enough power one bit. Just saying don't


accept printed specs as gospel.


I just figure that for normal use they would be runing well below rated
output and distortion would not likely be a problem.

Have you any dealings with the Behringer and it's noise level from

the
fan?



In the installation the Behringer amp was in that I experienced, it

was
never quiet enough to notice it. A home setting is where its been
reported to be a problem. IMO If one chooses to purchase, know its
downfalls and install around said problems.


Cult of the Infinitely Baffled has more info on PA amps, their fan

noise
ratings in some cases, as well as other options and quieter fan
replacements on some amps. There are of course other resources, but

the
Cult has the most condensed info in this department.


Interesting, never heard of this group, I'll have to check them out.


IB's have no interest for me, unless I get up into the attic.

Perhaps
after the disk decompression heals, although mysingle Shiva is
currently filling my needs.



Ugh sorry to hear about the disk troubles.


Surgery is scheduled for the 10th of next month. I'm just glad that
the problem has been identified and will be resolved. My regular doc
seems to have given up caring much about his practice. He had been
telling me for a year that I needn't consult with a surgeon as there
was nothing that could be done. Finally I got him to give me a
referral and the Surgeon says not only can something be done but it
should be done ASAP.

An IB is well worth the effort IMO. Whether ceiling or adjacent room
mounted. I've had experience with one and helped set up another. I was


hooked before proper eq.



My Shiva did well until it was replaced with an Atlas12. No more
bottoming in the 88.5L sealed enclosure.


That is a bit small for a Shiva. 140 liters would be more suitable.

I'm looking to try mine in a sonotube, currently it's in a similar size
cabinet.



hth,=20


--

  #20   Report Post  
still learning
 
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Cyrus:

I went to the Cult of the Infinitely Baffled and found it to be a very
good place. Lots of useful info.
Anybody into DIY and subs should pay a visit.

Thanks.



  #21   Report Post  
Cyrus
 
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In article .com,
"still learning" wrote:


My Shiva did well until it was replaced with an Atlas12. No more
bottoming in the 88.5L sealed enclosure.


That is a bit small for a Shiva. 140 liters would be more suitable.


Really? In 88.5L, the Qtc is ~.64 IIRC. I found the Shiva sounded very
nice but was able to be bottomed out with ~250 watts. In my quest for
ruggedness, I was not happy.

A quick model sets the 140L enclosure at ~.56 Qtc. Both of these are
without Vdr taken into account, take that how you will. Let me know how
it sounds, I seriously dig low Q systems.

I'm looking to try mine in a sonotube, currently it's in a similar size
cabinet.


My Shiva was handed down to the needy, my buddy with a ****ty sub. I
tried to steer him into the sonotube route for space considerations and
the small footprint, he didn't like the endcaps idea for some reason..
ah well. He's happy with it in a ~.72 Qtc enclosure, its somewhat rugged
in this higher Q alignment.

I'm impressed with XBL and won't be going back to normal drivers without
a fight.

--
Cyrus

*coughcasaucedoprodigynetcough*


  #22   Report Post  
Cyrus
 
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In article . com,
"still learning" wrote:

Cyrus:

I went to the Cult of the Infinitely Baffled and found it to be a very
good place. Lots of useful info.
Anybody into DIY and subs should pay a visit.

Thanks.


Like ThomasW tries to instill in users/readers of the forum, pay it
forward somehow. Glad I could help.

--
Cyrus

*coughcasaucedoprodigynetcough*


  #23   Report Post  
still learning
 
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Cyrus daid:

My Shiva did well until it was replaced with an Atlas12. No more
bottoming in the 88.5L sealed enclosure.



That is a bit small for a Shiva. 140 liters would be more suitable.




Really? In 88.5L, the Qtc is ~.64 IIRC. I found the Shiva sounded very


nice but was able to be bottomed out with ~250 watts. In my quest for
ruggedness, I was not happy.


I'm sorry, are you saying you hade it in a sealed enclosure?
I just assumed ported which works well in a 5 cubic foot box, and
should not bottom out with that amount of power. At least that's my
understanding.

A quick model sets the 140L enclosure at ~.56 Qtc. Both of these are
without Vdr taken into account, take that how you will. Let me know

how
it sounds, I seriously dig low Q systems.


If I understand correctly and this was a sealed encousre, then a .5 Qtc
is supposed to be transient perfect.
I'm planning on the 5 cubic ft. enclosure based on Adire's box
recomendations which show 3 box sizes with 5 cu. ft being the largest
and supposedly allows it to play louder before bottoming out and
providing the lowest f3.

I would have most likely added a second woofer with compound loading to
increase the effective Xmax.


After I get my tax return, I'll be broaching it to the wife.

I'm looking to try mine in a sonotube, currently it's in a similar

size
cabinet.



My Shiva was handed down to the needy, my buddy with a ****ty sub. I
tried to steer him into the sonotube route for space considerations

and
the small footprint, he didn't like the endcaps idea for some reason..


ah well. He's happy with it in a ~.72 Qtc enclosure, its somewhat

rugged
in this higher Q alignment.


I'm impressed with XBL and won't be going back to normal drivers

without
a fight.



Isn't XBL Adire's technology? I see it being referenced in other
manufacturer's products.

  #24   Report Post  
Cyrus
 
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In article .com,
"still learning" wrote:


I'm sorry, are you saying you hade it in a sealed enclosure?
I just assumed ported which works well in a 5 cubic foot box, and
should not bottom out with that amount of power. At least that's my
understanding.


Yep sealed. I don't dig bass reflex boxes, but its personal.

If I understand correctly and this was a sealed encousre, then a .5 Qtc
is supposed to be transient perfect.
I'm planning on the 5 cubic ft. enclosure based on Adire's box
recomendations which show 3 box sizes with 5 cu. ft being the largest
and supposedly allows it to play louder before bottoming out and
providing the lowest f3.


The large sealed enclosure gave me the sensitivity. Just not the output
at higher spl levels. But I understand thats asking a bit much from a
single 12" sub in a sealed enclosure.


I would have most likely added a second woofer with compound loading to
increase the effective Xmax.


More drivers is always a good upgrade route. There's no replacement for
displacement IMO.


After I get my tax return, I'll be broaching it to the wife.


hehe This is a common hurdle for just about anybody into audio it seems.
Good luck.


Isn't XBL Adire's technology? I see it being referenced in other
manufacturer's products.


Adire licenses it out to whomever is willing to pay. Ascendant Audio, RE
Audio and Creative Sound Solutions to name a couple that I know of.

A byproduct of an XBL design is that there is more clearance between the
cone and the top plate of the motor structure even at high Xmax.. hence
harder to bottom out.

--
Cyrus

*coughcasaucedoprodigynetcough*


  #25   Report Post  
Tim Martin
 
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The Behringer EP1500 is a sound reinforcement amplifier, and presumably has
a fan in it. You should listen to it in your room with no signal before
buying, as you may find the fan noise irritating..

Behringer have just announced a new amplifier with no fan, the A500, list
price 240 dollars. It's not as powerful as the EP1500 - 500 watts bridged
into 8 ohms rather than 800.

Is EQ is a good idea for a single subwoofer? In my albeit limited
experience, LF sound intensity varies markedly as you move your head short
distances, due to room characteristics. You can't EQ that away, so it's not
clear that with a single subwoofer you can make the sound better with EQ
unless you stick to a single mall listening position.

Multiple subwoofers are another matter, as their room effects tend to smooth
each other out.

Tim Martin




  #26   Report Post  
Cyrus
 
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In article ,
"Tim Martin" wrote:

The Behringer EP1500 is a sound reinforcement amplifier, and presumably has
a fan in it. You should listen to it in your room with no signal before
buying, as you may find the fan noise irritating..

Behringer have just announced a new amplifier with no fan, the A500, list
price 240 dollars. It's not as powerful as the EP1500 - 500 watts bridged
into 8 ohms rather than 800.

Is EQ is a good idea for a single subwoofer? In my albeit limited
experience, LF sound intensity varies markedly as you move your head short
distances, due to room characteristics. You can't EQ that away, so it's not
clear that with a single subwoofer you can make the sound better with EQ
unless you stick to a single mall listening position.


I concur, in untreated rooms there tends to be a very small sweet spot.
Or as sweet as one can get in an untreated room that is.


Multiple subwoofers are another matter, as their room effects tend to smooth
each other out.


Even if placed next to each other? Or better yet, in the same
enclosure/manifold?

I'm thinking if spaced apart, multiple subs may be a problem.


Tim Martin



--
Cyrus

*coughcasaucedoprodigynetcough*


  #27   Report Post  
still learning
 
Posts: n/a
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Tim Martin said:



The Behringer EP1500 is a sound reinforcement amplifier, and

presumably has
a fan in it. You should listen to it in your room with no signal

before
buying, as you may find the fan noise irritating..


True it does have a fan and from comments I've seen elsewhere, a fairly
noisy one. It is however a rather trivial task to find a quieter
replacement for a couple bucks and still be way ahead of the game. SVS
recomends the Samson amp because it has a very quiet fan.

Behringer have just announced a new amplifier with no fan, the A500,

list
price 240 dollars. It's not as powerful as the EP1500 - 500 watts

bridged
into 8 ohms rather than 800.


Seems like that should fill the need for subwoofer power very nicely,
thanks for the heads up.

Is EQ is a good idea for a single subwoofer? In my albeit limited
experience, LF sound intensity varies markedly as you move your head

short
distances, due to room characteristics. You can't EQ that away, so

it's not
clear that with a single subwoofer you can make the sound better with

EQ
unless you stick to a single mall listening position.


Yet many sub amps come with a prametric EQ for just that purpose, so it
would seem that form of EQ works for some people.

Multiple subwoofers are another matter, as their room effects tend to

smooth
each other out.


Harman has a paper on the subject of multiple
subs._____________________________________________ _________________________=
__________________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
1
A New Laboratory for Evaluating
Multichannel Audio Components and Systems
SEAN E. OLIVE, AES Fellow, BRIAN CASTRO, AES Member, AND
FLOYD E. TOOLE, AES Fellow
R&D Group, Harman International Industries Inc., 8500 Balboa Blvd.,
Northridge, CA, 91329, USA
Email:
ABSTRACT
The design criteria, features and acoustic measurements of a new
listening laboratory
designed specifically for listening tests on multichannel loudspeakers
and components
are described. Among its features is a novel automated speaker shuffler
that eliminates
loudspeaker position effects or allows the variable to be efficiently
tested. Other features
include complete computer control of experimental design, control and
collection of
listener data, making listening tests more reliable and efficient.
1=2E0 INTRODUCTION
Listening tests are the final arbiter for determining whether an audio
product sounds
good, and they play a critical role in the research and development of
new products.
Designing and conducting listening tests that produce reliable and
accurate data is,
however, no simple task. There are many variables other than those
under test that unless
removed or controlled can seriously bias the results [1-9]. Two of the
more difficult
variables to control are the listening room [5],[7],[9] and the
position(s) of the
loudspeakers under test [5],[9] both of which can significantly
influence the sounds that
arrive at listeners' ears and listeners' perceptions of them.
Recently we had the opportunity to design and construct a new
state-of-the-art listening
laboratory to be used for developing and subjectively testing
multichannel loudspeakers
and other components. The goal from the outset was to build and equip a
listening
laboratory that could generate subjective measurements as accurate,
efficient and free of
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
2
bias as possible. To meet these goals, a large effort went into
developing hardware and
software that would automate the design and control of experiments,
including the
collection, storage and statistical analysis of listener data. Included
in the design is a
novel automated speaker shuffler that performs positional substitution
of 9 loudspeakers
so that positional biases can be eliminated or efficiently tested. By
eliminating position as
a variable, the speaker shuffler has reduced the length of a typical
multiple loudspeaker
listening test by a factor of 24:1 making product development faster
and less costly.
Another notable feature of the room is that the acoustics can be easily
varied from almost
hemi-anechoic to semi-reverberant by adding removable reflective panels
to the walls
and ceiling.
This paper describes the rationale, features and measurements of the
new listening
facility, which we call the Multichannel Listening Laboratory (MLL).
Finally, the results
are compared with several current international standards that
recommend performance
criteria for listening rooms intended for critical listening.
1=2E1 Listening Room Standards
Several standards recommend values for various acoustic parameters that
define listening
room performance. The goal of these standards is to facilitate the
replication of listening
evaluations in different rooms under the same test conditions. This is
particularly
important for radio and television broadcast corporations, audio
production facilities,
large audio equipment manufacturers, and international standards and
research
organizations, all of whom have multiple facilities in which critical
judgments are made
on the same program material or equipment. Ideally, if the listening
rooms and test
conditions in which these judgments are made are sufficiently similar,
and the listeners
have normal hearing are properly trained, then a consensus in opinion
should be possible.
If not, then there is likely something wrong with the test procedure
itself.
In reviewing these various standards, a serious problem common to many
is that while
they define tolerances for specific acoustic parameters, they do not
adequately define
how the parameter is to be measured. For example, IEC is the only
standard that specifies
how reverberation time should be measured, even though it has been
shown that RT60
can vary widely depending on the technique used. Unfortunately, this
rather defeats the
purpose of defining a standard in the first place! It is conceivable
that one measurement
method may show the room meets the standard, while another measurement
method may
not. Added to this is the belief, held by some authorities, that in
small rooms,
reverberation time is a parameter of little or no value.
A very good discussion and summary of standards as they relate to the
design of
multichannel listening room intended for loudspeaker listening tests
are given by
Jarvinen et al in [9].
The current standards that recommend listening room performance
include:
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
3
1=2E IEC Publication 268-13: Sound System Equipment, part 13. Listening
Tests on
Loudspeakers (1985) [10 ]
2=2E NR-12 A, Technical Recommendation: Sound Control Rooms and Listening
Rooms.
2nd Edition, The Nordic Public Broadcasting Corporation, (1992) [11]
3=2E ITU-R Recommendation BS.1116: Methods for Subjective Evaluation of
Small
Impairments in audio systems including multichannel sound systems, 2nd
Edition
(1997) [12]
4=2E ITU-R Recommendation BS.775: Multichannel stereophonic sound system
with and
without accompanying picture (1994) [13]
5=2E EBU Tech 3276 (2nd Edition, 1997 ) [ 14]
6=2E AES20-1996: Recommended Practice for Professional Audio -
Subjective Evaluation
of Loudspeakers (1996) [15 ]
The standards can be classified according to the intended application
of the listening
room and can be generally classified into two groups. The AES and IEC
standards were
intended for monophonic and stereophonic testing of loudspeakers in
typical domestic
listening rooms. Both these standards are now quite old and the
recommended room sizes
are too small to allow multiple comparison of multichannel systems.
The EBU, ITU and NR standards were drafted primarily by broadcasters
and allow for
much larger control rooms that can accommodate several listeners at a
time. Only the
AES, IEC and ITU standards include recommendations for listening test
methodology.
At the design stage, we did not intentionally set out to meet any of
the above standards.
However, in post-hoc examination have found that our listening room
meets both ITU
and EBU standards in its current configuration in which we have added
reflective and
diffractive surfaces to both the ceiling and walls.
In the following sections we show measurements made in the MLL and
compare these
with various acoustical properties recommended in the above standards.
These properties
include dimensions, floor area, volume, proportions, reverberation time
and background
noise. The values measured for the MLL are compared with the
recommended values in
Table 1 for each standard, and shows that the MLL meets both ITU and
EBU
recommendations.
2=2E0 MULTICHANNEL LISTENING LAB (MLL)
2=2E1 Room Dimensions
The listening room itself consists of double-wall constructed shell
built by Industrial
Acoustics Corporation (IAC). The dimensions of the MLL were largely
dictated by our
requirements to be able to evaluate up to 3 different 5.1 or 7.1
channel systems at a time
and accommodate 1-6 listeners. The room also had to be sufficiently
large to
accommodate our automated 9-loudspeaker shuffler that requires a space
of
approximately 9 m (L) x 1.5 m (W) x 1 m (D). This resulted the
following dimensions:
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
4
MLL Dimensions
Length 9.14 m
Width 6.58 m
Height 2.59 m
Floor Area 60.20 m 2
Volume 155.92 m 3
As shown in Table 1, the MLL satisfies the recommended volume and floor
area values
specified in ITU, EBU, and N12 standards. The MLL's volume exceeds
the IEC and AES
recommended limits of 110 m 3 and 120 m 3 respectively because the
standards were
intended for small domestic stereo listening rooms.
2=2E2 Room Proportions
The most problematic performance issue in small listening rooms is
non-uniform low
frequency reproduction caused by standing waves that produce large
pressure peaks and
nulls in the lower 3-4 octaves of the audio range. The distribution and
frequencies at
which these peaks and notches occur are directly related to the
geometry of the room. If
the ratio of the room dimensions is carefully chosen, a more uniform
response is possible.
Walker from the BBC [16] has created a room geometry criterion that has
been adopted
by both the EBU and ITU standards. The "Walker" criterion defines
the limits of the
ratios for length (l), width (w) and height (h) as:
1=2E1 =3D =3D 4.5 - 4
h
w
h
l
h
w
(1)
As shown in Table 1, the ratio of dimensions for the MLL meet the
"Walker" criterion
and therefore satisfies the EBU and ITU standards. The relatively large
size of the MLL
also benefit uniform frequency response in the lower octaves since the
first order width
and length modes are below 25 Hz.
2=2E3 Background Noise
Accurate and repeatable subjective measurements require a listening
room with low
background noise so those listeners are able to reliably judge the
quality of low-level
signals. Perception of timbre, nonlinear distortion, loudness and
spatial qualities are all
influenced by the presence and masking effects of background noise.
Minimizing background noise in the MLL was carefully considered during
the design and
construction. The IAC double-wall shell itself is located in a large
room that has limited
access to both people and noisy equipment. No part of the shell touches
the structural
walls of the building except the floor, which is mechanically floated.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
5
The inner walls and ceiling of the double-wall IAC shell are made of
heavy gauge steel
panels separated 10 cm and filled with fiberglass. The inner surfaces
are perforated with
2=2E34-mm openings to provide substantial sound absorption inside the
room. The inner
walls are entirely floated and separated from the outer wall of the
shell by a 10 cm space
to minimize mechanical and acoustic transmission of noise.
The room has its own dedicated HVAC system with ventilation silencers
and acoustically
lined ducts that create a comfortable and quiet environment. For
experiments that require
extremely low background noise the room can be cooled and the HVAC can
be
completely shut off during the test. The room requires minimal lighting
during the test
itself (i.e. 1 Halogen light) which means that noise from lights is not
an issue. All audio
equipment, other than the required amplifiers, is located outside the
room, and this also
helps to minimize electrical noise as well.
In an effort to simulate the construction of floors found in many
homes, a carpeted
"squeak-free" plywood floor was laid on 5 cm x 15 cm wooden joists
separated 41 cm
apart. The joists are mounted on 6.4 mm neoprene pads for isolation
from the concrete
floor beneath. The rationale for constructing this floor is to allow
transmission of low
bass from the loudspeaker through the floor to the listeners' feet,
since the perception of
bass depends on what is felt, as well as what is heard. The front and
middle sections of
the floor can be removed to allow easy access of audio, video and data
cables that run
underneath the floor to access panels both inside and outside the room.
In reviewing the various listening room standards there is a wide range
of recommended
levels for background noise. The most stringent requirements are
specified by the EBU
and ITU standards, which call for minimum level of NR10, not exceeding
NR15. These
rather demanding requirements are likely justified in broadcast
environments where
listeners are frequently required to evaluate small signal linearity,
for example in relation
to CODECS.
At the other extreme, the AES and IEC standards both have rather
liberal recommended
background noise limit of 35 dBA measured using a slow time constant.
The AES
standard has an additional limit of 50 dB C-weighted for low frequency
noise. The less
stringent requirements are likely justified on the basis that they are
aimed at loudspeaker
evaluations in typical domestic environments where background noise
levels are typically
higher.
Figure 1 shows the background noise measured in the MLL with the air
conditioner
turned both on and off. Also plotted are the NR curves 0 through 15.
The MLL noise
curves each represent an average of four measurements take at 4
different locations
around the listening area. The time over which each measurement was
averaged was 64 s.
The measurement was taken using a Bruel & Kjaer 4179, 1 inch
microphone, a Bruel &
Kjaer preamp Type 2660, and a Bruel & Kjaer real-time analyzer. The low
noise
microphone and preamp allow accurate measurement of sound pressure
levels below the
threshold of hearing, which is necessary at higher frequencies for
measuring rooms below
NR20. Figure 1 shows that with the air conditioning turned off, the MLL
meets NR5,
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
6
thus meeting the requirements of the EBU and ITU specification. With
the air
conditioning turned on the noise increases to NR15.
2=2E4 Reverberation Time
The reflected sounds and reverberation time in a room have been shown
to have an
important influence on the perception of loudness, timbre and spatial
qualities and speech
intelligibility in both live and reproduced sound. While this is a
complex phenomena, the
acoustic community sees fit to summarize it all in a T60 measurement.
Both the EBU and the ITU standards specify values for the average
reverberation time in
the room. ITU and EBU recommend the value (within a tolerance of =B1
0=2E05 s) be
determined using the following equation:
s
V
T V
ref
m
1/ 3
25 . 0 



 


=3D (2)
where Tm is the average reverberation time between 200 Hz to 4 kHz, V
is the volume of
the room, and Vref is the reference volume of 100 3 m. The EBU also put
limits on the
range of values specifying that the value should lie between 0.2 Tm
0=2E4 s.
The IEC standard specifies a Tm of 0.3 - 0.6 seconds which is very
similar to the AES
standard that recommends 0.45 s ( =B1 0.05 s). The N 12-A standard
specifies Tm be
measured in 1/3 octaves between 200 Hz to 2.5 kHz and be determined as
a function of
the floor area using the following equation:
0=2E35 =B1 0.05 s 



 


=3D
ref
m S
T S (3)
where S is the floor area of the room and S ref is the reference area
of 60 2 m.
In addition to specifying the average reverberation time, most of the
standards
recommend that Tm be relatively independent of frequency within a
certain bandwidth
and tolerance. For ITU and EBU standards, the Tm value for each octave
band between
200 Hz - 3.5 kHz should vary no more than =B1 0.05 s from the calculated
optimum value.
Below 200 Hz, Tm is allowed to increase monotonically with frequency to
0=2E3 s above the
optimum value. Above 3.5 kHz, the tolerance is increased to =B1 0.1 s
from the optimal
value.
By substituting the volume of the MLL (155.92 3 m) into equation (2),
we calculate that
Tm should be 0.29 s to meet ITU and EBU standards. According to N 12-A,
the Tm for the
MLL should be 0.35 s.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
7
The Tm of the MLL was measured using a MLSSA system from DRA
laboratory. The
microphone was a Bruel & Kjaer 4134 microphone. The sound source
consisted of four
JBL Synthesis satellite loudspeakers crossed at 80 Hz over to a JBL
Synthesis Two
subwoofer located in the corner of the room. Each of the four
satellites was located
approximately 2 m apart and aimed at a different corner in an attempt
to create a diffuse
sound field. The measurement shown in Figure 2 represents a spatial
average of four
microphone locations. The average Tm value for the MLL is about 0.23 s,
which is
slightly below the calculated ITU and EBU optimal value of 0.29 s.
However, the curve
falls within the minimum recommended value, and is quite uniform with
frequency, only
rising slightly below 125 Hz.
2=2E5 Control of Early Reflections
With the advent of 5.1 and 7.1 multichannel and 3D audio playback
systems, there is a
trend among professional and home theater listening room designs
towards lower
reverberation times and the control of early reflections. There are
sound scientific reasons
for doing this, since strong early reflections are known to influence
the perceived spatial
and timbral qualities of reproduced sound [7], [17]. In the new
generation of
multichannel recordings and video disks, the additional center and
surround channels
allow the producer and recording artist to create much more realistic
and spatiallyenriched
environments than ever before. There is less need to use the room's
boundaries
and the loudspeakers' directional characteristics to compensate for
the obvious spatial
deficiencies inherent to stereo.
The EBU standard recommends that all reflections within the first 15 ms
after the arrival
of sound be no greater than 10 dB in level relative to the direct sound
from each sound
source. With multichannel setups the early sound field is rather
complex given that there
are between 5-7 loudspeakers and several boundaries. For example with 5
loudspeakers
and 6 boundaries there are 30 first order reflections and 150 second
order reflections.
Measuring and separating out these reflections is no trivial task. The
reflections from the
floor are particularly problematic to treat since in most facilities,
the floor surfaces must
be hard and reflective to facilitate the movement of people and
equipment. Nonetheless,
several organizations [18], [19] are building such rooms that meet this
reflection-free part
of the specification with the exception of the floor bounce.
In the MLL room, the only significant first order reflections are from
the floor, and these
are attenuated at higher frequencies by the carpet. At
listener-loudspeaker distances
greater than 2 m any reflection with a path length greater than 6.34 m
will be attenuated
10 dB by spreading loss [18]. This effectively eliminates all second
order reflections
since their path length exceeds this value. For front channel sources,
first order
reflections from the side walls will also be sufficiently delayed
beyond the 15 ms time
gap. The main culprits are reflections from the front and back walls,
and the ceiling.
Fortunately these surfaces can be made absorptive by simply removing
the reflective
panels so that the absorptive surface is exposed. To reduce flutter
echoes from reflective
surfaces and to increase reverberation, 120 RPG Skylines, an
omnidirectional primitive
root number theory 2D diffusor, are placed on the reflective panels
located on the walls,
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
8
as well as on the ceiling and areas behind the loudspeaker as shown in
Figures 4 and 5.
These light-weight diffusors are easily removed or relocated, and help
reduce any other
specular reflections that may arrive after the direct sound.
2=2E6 Automated Speaker Mover
The position of a loudspeaker in a room has a significant impact on its
perceived sound
quality. Changing its position affects the way it couples to the
standing wave modes of
the room, and alters the physical characteristics of broadband
reflections that arrive at the
listener. In listening tests that involve multiple comparisons among
loudspeakers the
positional effects on listeners' ratings can be larger than the
differences between the
loudspeakers under test [8]. Unless these positional effects are
controlled, the results may
be contaminated by a nuisance variable.
For multiple comparison loudspeaker tests, asking human beings to sit
behind a doubleblind
screen and quickly and smoothly substitute the positions of 2-9
loudspeakers (some
weighing upwards to 100 kg) on command presents an obvious logistical
problem.
Clearly the problem of positional substitution calls for an automated
solution. This
realization led to the development of our own custom-built speaker
shuffler. Prior to
having a speaker shuffler, the positional effects in loudspeaker tests
had been balanced by
testing each loudspeaker in each position. Any position-related bias
would be equally
distributed or balanced across each loudspeaker. More scientifically
rigorous designs go
even further and test all possible loudspeaker-position permutations so
that any possible
context effects between loudspeaker and position are also balanced.
The disadvantage of not having a speaker mover is that an additional
number of trials are
required to balance the variable position. This relationship in
illustrated in Figures 3(a)-
(b), which compare the number of trials required to balance the
variable position in
multiple comparison tests, with and without a speaker mover. The number
of trials is
calculated using the following equation:
Number of Trials =3D N Speaker Positions ! =D7 N Programs =D7 N Repeats (4)
Where N Speaker Positions equals the number of speaker positions in the
test, N Programs equals
the number of program selections being used and N Repeats is the number
of repeats. In
Figure 3 we, the experimental design shows no repeats, that is N Repeat
=3D 1.
The graphs clearly shows that an automated speaker mover can
drastically reduce the
length of the experiment because the variable N Speaker Positions
always equals 1, regardless
of how many loudspeakers are compared. In comparing the two graphs we
see that there
is a 2:1 advantage for paired comparisons, a 6:1 advantage for triple
comparisons, and a
24:1 advantage for comparisons among four loudspeakers. When you
multiply these
ratios by the number of programs and repeats used in the experimental
design, the
number of trials quickly escalates. For multiple comparisons between
four loudspeakers
using 4 programs with no repeats, a total of 96 trials are required
without a speaker
mover. Having a speaker mover reduces the experiment to 4 trials. This
enormous
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
9
difference provided the justification to design and build a custom
speaker shuffler, since
over the long-term, it could afford considerable savings in
person-listening hours and
product development time.
A custom-built floor at the front of the room allows us to perform
positional substitution
of up to 9 different loudspeakers. A photograph of the speaker mover
set up for an A/B
stereo loudspeaker comparison is shown in Figure 4. Figure 5 shows a
photograph of the
speaker mover set up for a single comparison of a 5.1 loudspeaker
system. For the
purposes of the photograph the front, side and rear listening curtains
have been retraced
out of the way. Each loudspeaker is attached to one of nine pallets
that move in 1-inch
increments over a range of 4 feet forwards and backwards while the
entire array moves 4
feet to the left and right of the listener. The movement of the floor
can be controlled
manually from a programmable logic controller (PLC), or from a computer
that is linked
serially to the PLC via RS232. This allows all positions of
loudspeakers to be
programmed, stored and recalled quickly. The movement of the floor is
extremely quiet,
repeatable to within 1 inch, and fast. Transit time between positions
is no greater than 3 s,
and most positional changes are under 2 s. The transit speed is also
programmable and
can be decreased or increased if desired. As a safety measure, a light
fence is installed in
front of the moving floor so that if anyone crosses the light beam the
speaker mover
automatically stops.
The speaker shuffler allows position-controlled loudspeaker comparisons
in mono (up to
4 different systems), stereo (4 different systems) or three different
left/center/right
channel loudspeakers. At this time, positional substitution of surround
and rear channel
speakers must be done manually for multichannel experiments. The
speakers can be
placed away from the side and rear boundaries on stands, or placed on
adjustable shelves
that are mounted on baffles made of high-density board, that slide in a
track along the
perimeter of the room.
The moving floor gives us an efficient means to eliminate the effects
of loudspeaker
position, or it can do the reverse, and allow us to test the
interaction effects between
loudspeaker and position. By statistically-averaging a loudspeaker's
performance over a
number of different positions we can assess its off-axis performance,
and a number of
other parameters that are position dependent. All of this becomes
essential as we aim to
design loudspeakers that are 'room friendly' and develop digital
room equalization
systems.
Finally, the speaker mover also allows us to efficiently randomize
between each trial,
how the loudspeaker is identified to the listener (e.g. "A,B,C..).
This ensures that
listeners' judgments in each trial are statistically independent
between program
selections. Without a speaker mover, experimenters normally do not move
the
loudspeakers behind the screen until a complete block of programs has
been rated. These
are not independent judgments since the listener knows they are rating
the same
loudspeaker(s) within each block. The extent to which this biases the
results has not yet
been reported.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
10
2=2E7 Blind versus Sighted Listening Tests
It is generally accepted among scientists that psychometric experiments
must be
performed double blind. For audio tests, this means the identities of
the components
under test cannot be made known to the listener, and the experimenter
cannot not directly
control or administer the actual test.
In 1996 Toole and Olive in [2] conducted some blind versus sighted
loudspeaker tests
that showed both experienced and inexperienced listeners' judgments
were significantly
influenced by factors such as price, brand name, size and cosmetics. In
fact, the effect of
these biases in the sighted tests were larger than any other
significant factors found in the
blind tests, including loudspeaker, position and program interactions.
These experiments
clearly show that an accurate and unbiased measurement of sound quality
requires that
the tests be done blind.
To remove these biases from listening tests in the MLL an acoustically
transparent
curtain that is visually opaque is placed between the products and the
listeners so that
they do not know the identities of the products under test. All other
associated equipment
in the signal path is also out-of-sight and locked in an equipment
rack, since the
performance and paranoia of some listeners can be affected by simply
having knowledge
that a certain brand of interconnect or CD player is in the signal
path.
The front screen consists of a black open knit polyester knit cloth
chosen for its acoustic
transparency and used as grille clothe in many of our loudspeakers. The
material is
attached to a large automated curtain roller so it can be easily lifted
down and up with an
infrared remote control. Weights are attached to a seam in the bottom
so the cloth retains
its tautness when in use. Retractable curtains made of the same
material surround the
listeners to hide the identities of loudspeakers located at the sides
and rear of the listening
room. Figures 4 and 5 show the front, side and rear curtains fully
retracted when not in
use, and Figure 8 shows the curtains in place during an actual
listening test.
2=2E8 Video Playback
Video and audio are increasingly becoming recorded, processed and
distributed together.
There is a growing interest among researchers in studying how the
perceived quality of
one affects the perception of the other. Although much research still
needs to be done,
evidence suggests there are bimodal interactions between the two that
influence listeners'
expectations and judgments of the quality of the audio, and vice versa.
Keeping this in
mind, we were careful in selecting a video playback system within our
budget that had
sufficient quality, so that it would not negatively impact listeners'
opinions of the sound
quality.
We selected a three gun front projection CRT made by Audio Video Source
for its aboveaverage
picture quality and the additional advantage that is has no fan. The
picture is
projected on a 100 inch Stewart Microperf screen that is retractable so
it can be removed
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
11
for audio-only listening tests. The acoustical effect of the screen is
another factor that is
not completely understood, and will be a subject of investigation.
2=2E9 Automated Control, Collection and Analysis of Data
In designing the MLL, we wanted to automate as much as possible the
design and
running of experiments including the collection, storage and analysis
of data, in order to
reduce the time and costs of performing listening tests. Automation of
experiments has
the additional benefit of making listening tests more reproducible,
largely because it
reduces the risk of human errors and biases introduced by the
experimenter. Considerable
ongoing effort in software development is helping us to fulfill these
goals.
Automation begins at the experimental design stage where all important
experimental
parameters and details are defined by the experimenter as a "*.exp"
file that is stored in a
database that resides on the Windows NT server.
The experiment file contains the following information:
=B7 The name of the experiment and a brief description
=B7 Detailed information related to the experimental design and
protocol including
definition of scales and randomization of variables. Protocol choices
include single or
multiple comparisons, ABX, ABC(with hidden reference) and different
threshold
measurement protocols.
=B7 Instructions to the listeners
=B7 Equipment control information and operational parameters required
by the audio
switcher for level matching, switching and overall output level.
=B7 The file names or track information for each program selection.
This information is
sent to the appropriate signal source device.
=B7 Information related to the position and movement of loudspeakers
=B7 A list of trials which the software randomly selects
The Windows NT server controls the running of the experiment including
control of all
associated equipment in the signal path. A block diagram of the
equipment and signal
path for the MLL is shown in Appendix 1. The lines that connect each
block as well as
the signal paths are color coded and typed according to whether the
signals are audio
(either analog or digital), video, infrared or RF control, computer
data, MIDI control or
sent over PCI or serial buss. The signal sources are the blocks on the
top left of Appendix
1=2E They currently include DVD and Laser Disk player, an 8-channel PCM
digital
recorder, and an 8-channel PC-based hard disk recorder (Lexicon Studio)
and its
associated A/D and D/A I/O cards. The audio and video outputs of the
DVD and LD
players are sent to the Lexicon DC-1 which provides AC-3 and DTS
decoding when
required. The analog outputs are sent to the Spirit 328 digital mixer
which provides signal
switching and level matching (within 0.03 dB) for up to 16 analog or
digital inputs. The 8
channel sources are sent digitally to the Spirit mixer and remain
digital up to the power
amplifier before they are converted by the Studer D/A's.
All operational parameters of the Spirit mixer can be viewed, stored
and recalled from the
NT Server via MIDI control.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
12
The input of listener data, feedback and status information is done
using laptops
connected to the NT Server through a LAN. For single listener
experiments, the listener
can control switching of the stimulae remotely from their laptop. A
photograph of a
listener entering data on the laptop connected to the NT Server is
shown in Figure 6. For
multiple listener experiments, the NT Server controls the switching
either manually or
through software automation. During the experiment, all changes in
listener response data
can be viewed in real-time on the NT Server which performs running
statistical averages
and graphs of the results.
Remote access to the NT Server and control of the equipment from inside
the listening
room is also possible through a wireless RF mouse, keyboard and a flat
panel display, all
of which are connected to the Server. This might be required during set
up or for
informal listening sessions or product demonstrations. The flat panel
display also shows
status information to the listener(s) indicating what stimulus (i.e. A,
B, C...) is currently
selected, and any other necessary information.
Finally, all experimental data and information related to listeners
(date and time, name,
seat position, age) is stored in a relational data base which can be
formatted and imported
into various statistical packages we use for analysis of results.
Not shown in the block diagram is a video camera used for monitoring
subjects and to
detect and hopefully deter possible cheating. Also not shown is a
two-way intercom that
allows communication between the subject(s) and the experimenter.
3=2E0 CONTROL ROOM AND LISTENER TRAINING LAB
Outside the MLL is a lab area dedicated for audio and test equipment
used during the set
up, running and monitoring of listening experiments. Here a space is
also dedicated for
the training of listeners, which is done over headphones at computer
audio workstations.
Bech in [20] has shown that 6 trained listeners can provide data that
is as statistically
reliable as data gathered from 18 untrained listeners. Clearly,
considerable cost-savings in
time and money can be realized if listeners are trained before they
participate in formal
listening experiments. At Harman, listeners with normal hearing undergo
a listener
training program, which self-administered through a computer and custom
software
developed in-house [21]. The software teaches listeners to identify and
rate using
different scales, frequency response irregularities according to the
center frequency,
amplitude and Q of the distortion. The graphical user interface of the
training software is
shown in Figure 8.
The training focuses on frequency-related problems since these are the
common and most
serious audible problems found in most loudspeaker-related listening
tests, which many
untrained listeners find difficult to describe. The training solves
this problem by teaching
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
13
listeners to describe these phenomena in technical terms that design
engineers can
understand and use to correct any problematic audible artifacts in
product designs.
The training software has proved to be a valuable tool for teaching
listeners how to
describe and scale the various dimensions of sound quality in
meaningful terms, and
allows their performance to be quantified in terms that allow us to
discriminate good
listeners from bad ones. An additional, indirect, benefit accrued from
training is that we
have learned which program selections are most revealing of typical
frequency-related
artifacts introduced during the training exercises, and we now use
these in our product
evaluations.
4=2E0 CONCLUSIONS
In summary, we have described a new facility designed to test
multichannel components
efficiently and as bias-free as possible. The facility includes
acoustically transparent
listening screens that hide the identities of all multichannel
loudspeakers and equipment
within the audio path. Particular attention has been taken to address
the two of the most
problematic variables in listening tests: the listening room and the
position(s) of the
loudspeaker. Through the use of a computer automated speaker shuffler,
we have greatly
reduced the amount of time and effort required to set up and test
multiple comparisons
between loudspeakers by reducing the factor position to a one-dimension
or level
variable. Typical loudspeaker evaluations should be reduced in length
by a factor of 24:1.
The listening room itself is capable of testing up to three different
5=2E1 or 7.1 channel
systems and accommodate 1-6 listeners at a time. The measurements we
have shown in
this paper indicate its performance in its current form meets the very
highest standards set
out by the ITU and EBU recommendations, in terms of volume, geometry,
reverberation
time, and the control of early reflections. The acoustics of the room
can be easily altered
from hemi-anechoic to more typical domestic room conditions by adding
reflective
panels to the room's boundaries.
Finally, the experimental design, set up and control are
computer-automated so that
experiments can be easily repeated, and are less prone to human error.
The more timeconsuming
and mundane tasks such as collection and analysis of data have also
been
computer-automated, so that experiment report writing becomes a simple
cut-and-paste
operation.
5=2E0 ACKNOWLEDGEMENTS
The authors would like to thank Tom Roberts of Bruel & Kjaer for his
assistance and
loan of the equipment used to make the background noise measurements
shown in this
paper.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
14
6=2E0 REFERENCES
[1] F.E. Toole, "Listening Tests - Identifying and Controlling the
Variables", Proceedings
of the 8th International Conference, Audio Eng., Soc. (1990 May).
[2] F.E. Toole and S.E. Olive, "Hearing is Believing vs. Believing is
Hearing: Blind vs.
Sighted Listening Tests and Other Interesting Things", 97th Convention,
Audio Eng.
Soc., Preprint No. 3894 (1994 Nov.)
[3] F.E. Toole, "Listening Tests, Turning Opinion Into Fact", J.
Audio Eng. Soc., vol. 30,
pp. 431-445 (1982 June).
[4] F.E. Toole, "Subjective Measurements of Loudspeaker Sound Quality
and Listener
Performance", J. Audio Eng. Soc., vol. 33, pp. 2-32 (1985
January/February).
[5] Soren Bech, " Perception of Timbre of Reproduced Sound in Small
Rooms: Influence
of Room and Loudspeaker Position J AES, Vol. 42, Number 12 pp. 999
(1994).
[6] S.E. Olive, P. Schuck, J. Ryan, S. Sally, M. Bonneville, "The
Variability of
Loudspeaker Sound Quality Among Four Domestic-Sized Rooms", presented
at the 99th
AES Convention, preprint 4092 K-1 (1995 October).
[7] F.E. Toole, "Loudspeakers and Rooms for Stereophonic Sound
Reproduction",
Proceedings of the 8th International Conference, Audio Eng., Soc. (1990
May).
[8] S.E. Olive, P. Schuck, S. Sally, M. Bonneville, "The Effects of
Loudspeaker
Placement on Listener Preference Ratings", J. Audio Eng. Soc., Vol.
42, pp. 651-669
(1994 September).
[9] Antti Jarvinen, Lauri Savioja, Henrik Moller, Veijo Ikonen, Anssi
Ruusuvuori,
"Design of a Reference Listening Room - A Case Study", AES 103rd
Convention, New
York, Preprint 4559, September 26-29, 1997.
[10] IEC Publication 268-13: Sound System Equipment, part 13. Listening
Tests on
Loudspeakers (1985)
[11 NR-12 A, Technical Recommendation: Sound Control Rooms and
Listening Rooms.
2nd Edition, The Nordic Public Broadcasting Corporation, 1992.
[12] ITU-R Recommendation BS.1116: Methods for Subjective Evaluation of
Small
Impairments in audio systems including multichannel sound systems, 2nd
Edition (1997)
[13] ITU-R Recommendation BS.775: Multichannel stereophonic sound
system with and
without accompanying picture (1994).
[14] EBU Tech 3276 (2nd Edition, 1997).
[15] AES20-1996: Recommended Practice for Professional Audio -
Subjective
Evaluation of Loudspeakers (1996).
[16] Walker, R. "Optimum Dimension Ratios For Small Rooms". 100th
AES Convention.
Preprint 4191 (Copenhagen, Denmark, 1996).
[17] S.E. Olive and F.E. Toole, "The Detection of Reflections in
Typical Rooms", J.
Audio Eng., Soc., vol. 37, pp. 539-553 (1989 July/August).
[18] R.Walker," A controlled-reflection listening room for
multichannel sound", AES
104th Convention Amsterdam, The Netherlands, Preprint #4645, May 16-19,
1998
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
15
[19] E. Arat=F3 Borsi, T. P=F3th, and A. F=FCrjes," New Reference
Listening Room for Two-
Channel and Multichannel Stereophonic" AES 104th Convention
Amsterdam, The
Netherlands, Preprint #4732, May 16-19, 1998.
[20]Soren Bech,"Selection and Training of Subjects for Listening
Tests on Sound-
Reproducing Equipment" Vol. 40, Number 7 pp. 590 (1992).
[21] S. E. Olive, "A Method for Training of Listeners and Selecting
Program Material for
Listening Tests", 97th Convention, Audio Eng. Soc., Preprint No. 3893
(1994
November).
TABLE 1
Table 1: Dimensions and Acoustic Parameters of Harman MLL versus
Recommendations of Various Standards
Parameter Harman
MLL
ITU EBU N12-A IEC AES
Volume
( m 3 )
155.92 60-110
(80)
50-120
Floor area
( m 2 )
60.20 20-70 40 60 =B1 10 20
Height
h (m)
2=2E59 2.3 - 3.0 rec.
2=2E8
2.1

Length
l (m)
9=2E14 =3D 6
rec. 6.7
Width
w (m)
6=2E58 =3D 4
rec. 4.2
(1.1 w / h) 2.80
( l / h) 3.53
( 4.5w / h - 4 ) 7.44
T m (s) 0.23 0.29
=B1 0.05
0=2E29 0.35 0.3 -0.6
0=2E4 =B1 0.05
0=2E45 =B1 0.15
T 63 Hz Max
(s)
..34 Tm(s) 0.2 - 0.4 0.35 0.8
Noise Level NR 5 NR10;
abs. max
NR 15
NR10;
abs. max
NR 15
NR 10
or L pA
15 dB
L pA
35 dB
L pA 35 dB
and
L pC 50 dB
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
16
Figure 1 A spatially-averaged measurement showing the background noise
in the MLL
with the air conditioning off (dotted) and turned on (dashed) compared
to the NR curves:
0,5,10 and 15.
Figure 2 The Tm (RT60) values measured in the MLL compared to the
optimal,
maximum and minimum values recommended by the EBU and ITU standards.
0
0=2E1
0=2E2
0=2E3
0=2E4
0=2E5
0=2E6
0=2E7
63 125 250 500 1000 2000 4000 8000
Frequency (Hz)
T60 (seconds)
EBU & ITU OPT.
EBU & ITU Max
EBU & ITU Min
MLL
-10
0
10
20
30
40
50
60
70
32 63 125 250 500 1000 2000 4000 8000
Frequency (Hz)
SPL ( dB )
AC ON
AC OFF
NR0
NR5
NR10
NR15
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
17
Figure 3(A) The above graph shows the number of trials required for a
multiple
comparison loudspeaker experiment as a function of the number
loudspeaker positions
compared. The lines represent experiments in which 1-4 programs are
used. The design
balances all position and context effects and has no repeats.
Figure 3(B) The same experiment is shown as in Figure 3(A) above except
here a
speaker mover is used.
Minimum Number of Trials ( Without Speaker Mover)
0
20
40
60
80
100
120
1 2 3 4
Number of Loudspeaker Positions
Compared
1 program w/o
2 programs w/o
3 programs w/o
4 programs w/o
Minimum Number of Trials ( With Speaker Mover)
0
2
4
6
8
10
12
14
16
18
20
1 2 3 4
Number of Loudspeaker Positions
Compared
1 program w.
2 programs w.
3 programs w.
4 programs w.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
18
Figure 4 Shown is the automated speaker shuffler of the MLL set up for
A/B stereo testing of two stereo
loudspeakers. Here the front listening screen is pulled up.
Figure 5 A front-left wide-angle shot of the MLL with the listening
screens pulled back.
The automated speaker shuffler is in the foreground setup for 5.1
playback. Note the side
and rear channel speaker baffles in the background, and the audio and
computer data
control box on the back wall. The video projector is mounted on the
ceiling with a
retractable screen in front of the speaker mover.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
19
Figure 6 A listener performing a test by entering their data on a
laptop computer that is
networked to the NT Server. In this test, video is displayed and both
front, side and rear
curtains are drawn to hide the identifies of the 5.1 loudspeaker
systems under test.
Figure 7 Shown is the control room area outside the listening room
where all audio
equipment,experimental control and monitoring takes place. Shown here
is the NT Server
on the left, and two listener training workstations on the right.
__________________________________________________ _________________________=
_____________________________
Harman International Industries, Incorporated 8500 Balboa Blvd., PO Box
2200, Northridge, CA 91329 (818) 893-8411
20
Figure 8: The GUI of the listener training software. The listeners'
task is to match the 4 different
equalizations indicates by their frequency response curves that are
randomly assigned to Buttons A-D
Feedback is given on their responses. The "FLAT" button allows
listeners to audition the program
without any equalization added.
Figure 9: The GUI of the software used for a typical listening test or
training exercise. Listeners
enter their preference ratings for sounds A-D relative to a given
reference ("REF"). Ratings are also
given on spectral balance and distortion. Relevant comments are
optional.
__________________________________________________ ______________

Tim Martin


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