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ludovic mirabel
 
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Default transmission line bass

I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel

  #2   Report Post  
Michael Mckelvy
 
Posts: n/a
Default transmission line bass

"ludovic mirabel" wrote in message
news
I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel

Suggested reading: G.L. Augspurger, "Loudspeakers in Damped Pipes--Part
one: Modeling and Testing; and Part Two: Behavior," 107th JAES Convention,
24-27 September, 1999, prepring No. 5011.

G.L. Augspurger, Transmission Lines Updated, Part 1 Speaker Builder 2/00

G.L. Augspurger, Transmission Lines Updated Part 2
Speaker Builder 3/00

G.L. Augspurger, Transmission Lines Updated Part 3
Speaker Builder 4/00

J.A. D'Appolito, Testing Loudspeakers, Audio Amateur Corporation
Peterborough New Hampshire, 1998

Also the article in audioXpress from May 2002 describing the design of the
THOR TL kit for SEAS Mr. D'Appolito mentions that "after many months of
operation, the Dacron pillow filler settled in the second half of one of the
lines."

He says that this did not appear to affect performance but can be avoided by
using Acousta Stuf or Dcron Quilt padding. Read the full article for all
the details.

  #3   Report Post  
BEAR
 
Posts: n/a
Default transmission line bass

I would refer you to a google search and Martin J. King's site on
transmission lines, which includes some modeling software.

There are other sites with modelling software to be found for TLs.

If the FS of your 'mutt' drivers is not fairly low, then you may merely
have found a room node which you managed to excite. Try taking
the boxes (tubes) outside and see what they measure.

_-_-bear

ludovic mirabel wrote:

I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.


snip

The brief version is:

a) absorb all the backwave (in effect) making it an infinite baffle.
(usually called a labrynth, iirc)
or
b) tune the backwave to like a lowish Q organ pipe and excite it.
(usually called a "Tranmission Line", iirc)

iirc...

_-_-bear


(Please make it as simple as possible).
Ludovic Mirabel

  #4   Report Post  
Don Gortemiller
 
Posts: n/a
Default transmission line bass

Check out this link to nelson Pass's DIY site.
http://www.passdiy.com/speakers.htm

A very interesting big transmission line.

"ludovic mirabel" wrote in message
news
I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel

  #5   Report Post  
ludovic mirabel
 
Posts: n/a
Default transmission line bass

"Don Gortemiller" wrote in message ...
Check out this link to nelson Pass's DIY site.
http://www.passdiy.com/speakers.htm

A very interesting big transmission line.

Thanks for this link. Essentially what I have but mucho bigger.
Nice to know that professional designers use sonotubes as well.
What I wanted to and obviously failed to communicate was that with
very little expense and skill one can get extraordinary bass
performance. The cylindrical lines I set up are amazingly efficient. I
had to equalise downwards BOTH sides. The left "only" 16db. down at
80, 50, 40 and 30 Hz. The right 30 db down *over two octaves*. And the
bass is clean incomparably better sounding than what came from the
closed boxes, properly Thiele measured for my 12" woofers.
If all these cylindrical tubes do is go hunting for "room nodes"
of that magnitude on both sides over two octaves then good hunting.
Everyone should have nodes like that.
I should say that my Acoustats have 100 watts monoblocks to
produce 1000Hz while my bass comes fromm 200watts Bryston amp. But
the same amp served the closed boxes with nowhere near such output and
performance.
What still puzzles me is why should the output get stronger and
stronger while the filler was settling down. I read most of the links
offered but found no explanation
Ludovic Mirabel

"ludovic mirabel" wrote in message
news
I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel




  #6   Report Post  
Michael Mckelvy
 
Posts: n/a
Default transmission line bass

"ludovic mirabel" wrote in message
news
I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel

Having the 2 subs on opposite sides of the room is probably part of your
problem. Comb filtering is the most liely culprit, since your not getting
normal node excitation as I understand it.

Try placing them both in the same corner and then see what happens. I'd bet
you get a much smoother response.

  #7   Report Post  
BEAR
 
Posts: n/a
Default transmission line bass

Don Gortemiller wrote:

Check out this link to nelson Pass's DIY site.
http://www.passdiy.com/speakers.htm

A very interesting big transmission line.


Well, imho, not so very interesting.

Here's why.

First, Pass uses no less than TWO 21" pro sound woofers, with an Fs of 25Hz,
per channel.

Then he loads them into what is simply a very large long tube. The result is
not tuned particularly. So, he has to EQ the whole thing to get the response flat.
In effect throwing out the relative sensitivity (two 96dB woofies in parallel -
presumably getting 102dB/1w/1m/4 ohms) to achieve a "flat response."

The filter he calls for is a 2nd order LP @ 20 Hz!

One has to ask, would the effect be much different if he merely built what
has been so popular here, what-it-called? The EBS alignment? And, a
much smaller box.

Ok, so you might like the long delayed LF coming out of those smokestacks
in your listening room, I dunno.

Note also, the end of the pipes are actually 2 feet from what is basically a large
conic horn section - the peaked inside of the roof. Gain from this is possible too.

Then he goes and plays them with 4,000 w/ch amps! Yeah, ok.

As noted, check Martin King's method, I think it is likely superior.

_-_-bear



  #8   Report Post  
ludovic mirabel
 
Posts: n/a
Default transmission line bass

"Michael Mckelvy" wrote in message ...
"ludovic mirabel" wrote in message
news
I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel

Having the 2 subs on opposite sides of the room is probably part of your
problem. Comb filtering is the most liely culprit, since your not getting
normal node excitation as I understand it.

Try placing them both in the same corner and then see what happens. I'd bet
you get a much smoother response.


1) These are no subs. They are 12" bass speakers crossed over at
400 Hz. to complement my ESL Acoustats also crossed.
2) I have no problem unless you call oodles of clean bass to pad
down a problem. I just wanted to hear from people experienced with
transmission lines if getting so much more output from transmission
lines than from closed box is a common experience.
Ludovic Mirabel
  #10   Report Post  
Michael Mckelvy
 
Posts: n/a
Default transmission line bass

"ludovic mirabel" wrote in message
...
"Michael Mckelvy" wrote in message

...
"ludovic mirabel" wrote in message
news
I'd like to solicit the opinion(s) of knowledgeable readers.
As I recounted recently I made two transmission line woofers,
each consisting of two "sonotubes'" (compressed paper cylinders)one
inside the other with a 12" woofer (Electrovoice frame and Altec
Lansing cone). The whole enterprise is very primitive and just within
my very limited aptitude for jigsawing and so on.
The tubes are packed with Dacron pillow fill. They are 24db
Linkwitz Xovered at 400Hz.
Two things happened: 1) From the start I got clean bass and
low treble. And buckets of it. I use Radio Shack SPL meter with the
Stereophile warble 1/3 octave tones from my listening seat as a guide
to equalisation Behringer 2084 digital equaliser) From the start I
was getting more bass esp in the lower octaves, beginning with 100
Hz, than I ever got out of my old closed boxes (originally Magnat
made)
2) Over the succeeding weeks it became obvious
that the bass was getting obnoxiously too much. I remeasured. To cut
the long story short: on the right side of my room which opens into an
L dining room- (so no corner) I had to cut 80 Hz to 30 Hz range-
mostly by 30 db(yes- no typo) to get it to match my starting point of
ZERO db at 1000Hz. Even 20 Hz had to go 10 db down, And believe me I
hear plenty of bass. No mistake.
It would appear that as the filling settled down
the lower octaves got louder. Is it what should happen with
transmission line?
I should say that now the right side is the "strong"
side. When I had closed boxes I would blow the woofers trying to get
50 Hz up to mark. Hence my custom sturdy 12" made by a friendly
speaker repairsman who took pity on me.
The overall quality of my bass is the best I evar had
and possibly the best I can recall having heard. The cost of
sonotubes/pillowfill and one day's work is about the best return for
the expenditure I ever made in audio. But I still would like to know
HOW it works. (Please make it as simple as possible).
Ludovic Mirabel

Having the 2 subs on opposite sides of the room is probably part of your
problem. Comb filtering is the most liely culprit, since your not

getting
normal node excitation as I understand it.

Try placing them both in the same corner and then see what happens. I'd

bet
you get a much smoother response.


1) These are no subs. They are 12" bass speakers crossed over at
400 Hz. to complement my ESL Acoustats also crossed.


I guess the next question I would ask is were the ESL's lacking in that
area?

2) I have no problem unless you call oodles of clean bass to pad
down a problem.


Any time you have to make an adjustment it is a problem of sorts. The
frequencies you mentioned did not sound like room nodes so I was interested
in what sort of placement options you had experimented with.

If there's no lack in FR at the range yiou have them crossed over at, what
not try the TL's as subs? IME many rooms have dips at around 200 Hz and
bumps around 50Hz that can only be gotten rid through some sort of passive
(room treatment) or active EQ.

If your happy with the setup you have, enjoy.

I just wanted to hear from people experienced with
transmission lines if getting so much more output from transmission
lines than from closed box is a common experience.
Ludovic Mirabel




  #12   Report Post  
Michael Mckelvy
 
Posts: n/a
Default transmission line bass

"BEAR" wrote in message
...
Don Gortemiller wrote:

Check out this link to nelson Pass's DIY site.
http://www.passdiy.com/speakers.htm

A very interesting big transmission line.


Well, imho, not so very interesting.

Here's why.

First, Pass uses no less than TWO 21" pro sound woofers, with an Fs of

25Hz,
per channel.

Then he loads them into what is simply a very large long tube. The result

is
not tuned particularly. So, he has to EQ the whole thing to get the

response flat.
In effect throwing out the relative sensitivity (two 96dB woofies in

parallel -
presumably getting 102dB/1w/1m/4 ohms) to achieve a "flat response."

The filter he calls for is a 2nd order LP @ 20 Hz!

One has to ask, would the effect be much different if he merely built what
has been so popular here, what-it-called? The EBS alignment? And, a
much smaller box.

Ok, so you might like the long delayed LF coming out of those smokestacks
in your listening room, I dunno.

Note also, the end of the pipes are actually 2 feet from what is basically

a large
conic horn section - the peaked inside of the roof. Gain from this is

possible too.

Then he goes and plays them with 4,000 w/ch amps! Yeah, ok.

As noted, check Martin King's method, I think it is likely superior.

_-_-bear

So far as I know Augpurger's work is currently the best and most definitive
on TL's which is why i recomended it.
I know of nobody who has done more to refine TL theory.


  #13   Report Post  
BEAR
 
Posts: n/a
Default transmission line bass - addenum

Two corrections:

1. The "EBS alignment" is not popular *here*, it's popular on another forum
that I frequent. What it refers to is putting a long excursion/high power
woofer in a box that is actually a bit small, and then EQ'ing the thing to
get flat response down to some F3 (like 20Hz.) and then dropping the
response off below that with a HP filter to keep from really wasting more
power and heating the driver too much. It works nicely with the modern
drivers now available.

2. I forgot to mention that shows these "TLs" against a floor/wall
boundary, making it pi/4 space (that's right?), which provides boost.
And then as noted the "outlet" of these smokestacks is only 2 feet
from the sloped ceiling/wall boundary.

I dunno, maybe he should stick to amps...

_-_-bear

BEAR wrote:

Don Gortemiller wrote:

Check out this link to nelson Pass's DIY site.
http://www.passdiy.com/speakers.htm

A very interesting big transmission line.


Well, imho, not so very interesting.

Here's why.

First, Pass uses no less than TWO 21" pro sound woofers, with an Fs of 25Hz,
per channel.

Then he loads them into what is simply a very large long tube. The result is
not tuned particularly. So, he has to EQ the whole thing to get the response flat.
In effect throwing out the relative sensitivity (two 96dB woofies in parallel -
presumably getting 102dB/1w/1m/4 ohms) to achieve a "flat response."

The filter he calls for is a 2nd order LP @ 20 Hz!

One has to ask, would the effect be much different if he merely built what
has been so popular here, what-it-called? The EBS alignment? And, a
much smaller box.

Ok, so you might like the long delayed LF coming out of those smokestacks
in your listening room, I dunno.

Note also, the end of the pipes are actually 2 feet from what is basically a large
conic horn section - the peaked inside of the roof. Gain from this is possible too.

Then he goes and plays them with 4,000 w/ch amps! Yeah, ok.

As noted, check Martin King's method, I think it is likely superior.

_-_-bear

  #15   Report Post  
Nousaine
 
Posts: n/a
Default transmission line bass

(Stewart Pinkerton)
wrote:


On Fri, 03 Oct 2003 14:41:15 GMT,
(ludovic
mirabel) wrote:

What I wanted to and obviously failed to communicate was that with
very little expense and skill one can get extraordinary bass
performance. The cylindrical lines I set up are amazingly efficient.


No, they're not. Let's knock this one on the head right away. Even at
their very best, true transmission lines *cannot* be more efficient
than an infinite baffle. I canna' change the laws o' physics, cap'n.

I had to equalise downwards BOTH sides. The left "only" 16db. down at
80, 50, 40 and 30 Hz. The right 30 db down *over two octaves*. And the
bass is clean incomparably better sounding than what came from the
closed boxes, properly Thiele measured for my 12" woofers.
If all these cylindrical tubes do is go hunting for "room nodes"
of that magnitude on both sides over two octaves then good hunting.
Everyone should have nodes like that.


Consider the above, and then consider what *must* be happening in your
room. Also, please note that even in 1/8 space, you *cannot* get more
than 18dB of room gain, and 12dB is a much more likely maximum. I
canna' change the laws o' physics, cap'n.
--

Stewart Pinkerton | Music is Art - Audio is Engineering


The actual amount of cabin gain is 12 dB per octave as frequency falls below
that lowest axial room mode.

For example I can measure 30 dB of cabin gain in my Corvette at 8 Hz. But the
lowest axial mode in the subcompact car occurs at 60 Hz and the whole cabin is
sealed tightly with little low frequency absorption.

In a 2136 ft3 listening room (stick frame/ drywall) some room gain was evident
beginning near 25 Hz. In my current 7600 ft3 room (stick frame/drywall
construction; adjacent co-joined spaces) there appear to be a very small effect
starting at 17 Hz.

However to attain these benefits the woofer/subwoofer(s) must have the
dispacement to take advantage of cabin gain. Thus a long stroke 10-inch woofer
is a 1-ft3 sealed enclosure can produce 120 dB at from 12 to 62 Hz in a
Corvette. To get equivalent SPL in a 7600 ft3 room requires 8 long stroke (23.4
mm Xmax) 15-inch woofers and a 5000 watt amplifier.

Low frequency absorption can be a good thing at low frequencies (knocks down
the room mode peaks) but it also tends to offset cabin gain at very low
frequencies, meaning that woofer displacement and amplifier power are required
to compensate.


  #16   Report Post  
Dick Pierce
 
Posts: n/a
Default transmission line bass - addenum

BEAR wrote in message ...
Two corrections:

1. The "EBS alignment" is not popular *here*, it's popular on another forum
that I frequent. What it refers to is putting a long excursion/high power
woofer in a box that is actually a bit small, and then EQ'ing the thing to
get flat response down to some F3 (like 20Hz.) and then dropping the
response off below that with a HP filter to keep from really wasting more
power and heating the driver too much. It works nicely with the modern
drivers now available.


Actually, the excursion requirements for such an alignment are
no more stringent than for any other woofer for the bandwith and
SPL requirements. Driver excursion is determined by the frequency,
the radiating area and the total acoustic power, not by the aligment
of the system. In other words, to get, say, 100 dB SPL out of a 12"
woofer at 20 Hz requires an excursion of 1.35 cm, it makes NO difference
whether the system resonance is 15 Hz or 150 Hz.

However, here's the advantage of a very small box alignment. As you
approach resonance and, expecially, below, the driver is more and
more stiffness-controlled. That is, the mechanical and acoustical
stiffness control motion (above resonance, the system is mass-
controlled, the moving mass controls the movement). That means, at
low frequencies, where you are at or below resonance AND your
excursion requirements are increased, the linearity of motion is
more and more determined by the linearity, or more importantly,
lack thereof, of the driver suspension.

If you take a driver with a high compliance and a very low free-
air Qts, and place it in a VERY small enclosure, small enough that
it's system Qts is now raised to 0.707 (Butterworth 2nd order
rolloff), it is now no longer the driver suspension that dominates
the total system stiffness, it is the compression of the air in the
box, which is a WHOLE lot more linear than the driver suspension.
Further, since the volume of air is fixed and very accurately
determined by simple cabinet dimensions, it is the acoustical
stiffness that dominates over the mechnical stiffness, the latter
having very poor manufacturing tolerance.

These are precisely the arguments originally advanced by Villchur
for the AR-1 and subsequent speakers, the so-called "acoustic
suspension" principle. The technical arguments advanced are sound.

The twist here is that the original acoustic suspension systems
suffered from very poor efficiency. That problem is solved with the
use of active equalization. It's perfectly sound, technically, to
have a system that by itself has a system resonance of, oh, 150
Hz and a Qtc of 0.707, then be augmented with a +12 dB/octave boost
down to 20 Hz, with a rolloff below that. The result is a 4th order
system that's flat down to the system cutoff. The resulting system
has a 6 dB orn better advantage over an acoustic suspension system
of the same cutoff and bax volume.

But, again, the excursion requirements for a 12" acoustic suspension
and a 12" small-box, EQ'd design such as mentioned here are exactly
the same.
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