So-called (actually, mis-named) 'isobarik' systems are a way of
obtaining a given response in half the volume, since the arrangement
results in half the total equivalent compliance volume and thus
requires half the enclosure volume for the same response function.

My Isobric has been constructed to improve LF ouput (it seems) not reduces
size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic
secondary, I guess that they have decided that the cone mass of an 8 inch
drive in isobaric has advantages over that of an 12 inch driver (at the size
of the brute it could easily use a 12 inch drive, one thing did occur to me
is that perhaps due to its age that duel VC speakers were not avalible and
the only method of getting a phase and anti phase driver easily was to use
two drivers.

As to "true hifi response," such a term needs definition to be
anything but meaningless jargon, in precisely the same way that
a "specification" like "20Hz-20kHz" is meaningless without
qualification.

I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with
gradual roll off above and below. If that is 'hi fi' or not is questionable.
I spent some time years ago analysing CD's to find usual and lowest
frequency's (plus HF, lots of CD's have significant output above 15Khz
(components up to 25Khz+ can be present) but at my age thats starting to get
above what I can easily here!) LF it seems stops round the ~30 Hz, few
instraments produce much less than this (yes I know that alot can) a lot of
the very LF on disk is artificial (1/2 frequency echo and its that it is
possibly added to give 'space' to the recordings) unless you are a pipe
organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or
such as the LF in these type video recordings is huge it seems (and
unnatural in my books) )

THe fundamental efficiency/enclosure volume/cutoff frequency equation
will ALWAYS rule. But, interestingly enough, driver diameter simply
does not enter into that relation. Specifically, the relation:

n0 = kn Vb F3^3

where n0 is reference efficiency, Vb is enclosure volume, F3 is is
low frequency cutoff and kn is the efficiency constant has NO term
in it in any way depedent upon driver diameter. This directly refutes
your assertion that it's not possible to get your "unqualified" 'hifi
response from an 8 inch driver. One needs to simply balance the three
terms of efficiency, enclosure volume and cutoff frequency and you're
there. You seem to intimate that low efficiency is incompatible with
'hifi response," for example, an unjustifiable viewpoint in light
of the lack of qualification of 'hifi response.'

kn = efficiency constant derived from driver (this figure will improve with
driver diameter, thus a large driver will allow a a small enclosue to
produce the same output at the same frequency with less power - correct me
if wrong)

However in order to get usable (at say 32Hz) levels the enclosure volume
(8 inch) will become so large as to be impactical in a lot of cases. This
equates to the 'You can put an airplane engine in a submarine' but who wants
too?

An enclose that is over 32 cubic feet will meet significant resistance when
placed in the home! (Test this by asking you wife if you can shift 2 small
fridges into the lounge!)

I tend to deal with and try and work in what can be achieved reasonably
easily in real world situations, absolutes and what is theoretically
possible don't fit! (But are well worth knowing and considering (Hey I own a
leak stereo 30 once discribed as all the power a home stereo would ever need
and enough th have your neighbours complaining! This we all know not to be
true!))

As a side issue I see that companies are producing very large (24 inch
diametre) woofers now. how well do these work and are they worth the
premiums being asked for them?

Peter,

Good comments. Thanks.

--Ethan

Peter,

Good comments. Thanks.

--Ethan

"The Flash" wrote in message ...
So-called (actually, mis-named) 'isobarik' systems are a way of
obtaining a given response in half the volume, since the arrangement
results in half the total equivalent compliance volume and thus
requires half the enclosure volume for the same response function.

My Isobric has been constructed to improve LF ouput (it seems) not reduces
size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic
secondary, I guess that they have decided that the cone mass of an 8 inch
drive in isobaric has advantages over that of an 12 inch driver (at the size
of the brute it could easily use a 12 inch drive, one thing did occur to me
is that perhaps due to its age that duel VC speakers were not avalible and
the only method of getting a phase and anti phase driver easily was to use
two drivers.

That's NOT what an "isobarik" is for, more to the point, that's NOT
what the primary advantage to an isobarik is.

By using two drivers one behind the other in close proximity and
coupled in-phase both acoustically and electrically, the effective
moving mass is doubled, the Bl product is doubled, all of your Q
figures remain the same and, most significantly, you effective
compliance is halved. The result is a driver that will have the
same low frequency performance in an enclosure 1/2 the volume
required for a single driver. There will be the attendant change
in reference efficiency resulting from the fact that the effective
radiating area remain constant.

If that's not what your system is doing, it is not a so-called
"isobarik" system.

As to "true hifi response," such a term needs definition to be
anything but meaningless jargon, in precisely the same way that
a "specification" like "20Hz-20kHz" is meaningless without
qualification.

I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with
gradual roll off above and below. If that is 'hi fi' or not is questionable.
I spent some time years ago analysing CD's to find usual and lowest
frequency's (plus HF, lots of CD's have significant output above 15Khz
(components up to 25Khz+ can be present)

Really? On a CD? If you are seeing components at "25KkHz+", then
you have a broken CD player.


instraments produce much less than this (yes I know that alot can) a lot of
the very LF on disk is artificial (1/2 frequency echo and its that it is
possibly added to give 'space' to the recordings)

There is no such thing as "1/2 frequency echo" in any linear system.

unless you are a pipe
organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or
such as the LF in these type video recordings is huge it seems (and
unnatural in my books) )

In fact, having been involved in not an inconsiderable amount
of both organ building, recording and analysis, it's something
of unsubstantiated myth that organs have some unique amount of
very low frequency content. They simply do not.

THe fundamental efficiency/enclosure volume/cutoff frequency equation
will ALWAYS rule. But, interestingly enough, driver diameter simply
does not enter into that relation. Specifically, the relation:

n0 = kn Vb F3^3

where n0 is reference efficiency, Vb is enclosure volume, F3 is is
low frequency cutoff and kn is the efficiency constant has NO term
in it in any way depedent upon driver diameter. This directly refutes
your assertion that it's not possible to get your "unqualified" 'hifi
response from an 8 inch driver. One needs to simply balance the three
terms of efficiency, enclosure volume and cutoff frequency and you're
there. You seem to intimate that low efficiency is incompatible with
'hifi response," for example, an unjustifiable viewpoint in light
of the lack of qualification of 'hifi response.'

kn = efficiency constant derived from driver (this figure will improve with
driver diameter, thus a large driver will allow a a small enclosue to
produce the same output at the same frequency with less power - correct me
if wrong)

Well, you're right and you're wrong. One cannot arbitrarily increase
the radiating area of the driver without having some other effects.
For example, while the area goes as the suqare of the diameter, and
one might think that the efficiency would go up accordingly, the moving
mass ALSO increases at least as the square of the diameter, and thus
what you might think you gain in increased area, you lose in increased
mass, as far as efficiency is concerned. And, indeed, the effect is
often working against you, since larger cones are heavier in excess
to the propoerion of the simple square of diameter, since they also are
generally thicker as well.

Thus we find, in a completely practical sense, that all other things
being equal, increased diameter DOES NOT increase efficiency.

Larger drivers are more efficiency NOT because they have larger cones,
but because they have larger voice coils that have more wire in the
larger magnet gaps and thus larger Bl products. Look at the correlation,
for example, between diameter and Bl product: it's ALMOST a linear
relationship: it's not uncommon for a typical high-quality 8" woofer
to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A.
The correlation between the numbers, as uncanny as it may seem, is merely
a coincidence of mixing English (inches) and metric (Newtons per Amp)
units, but the trend is clear.

However in order to get usable (at say 32Hz) levels the enclosure volume
(8 inch) will become so large as to be impactical in a lot of cases.

No, or the efficiency has to be appropriate. For example, you can get
30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed
enclosure is ENTIRELY possible if you're willing to tolerate a
sensitivity on the order of 82 dB/watt.

On the other hand, if you want a system with the same cutoff frequency
with an efficiency of 90 dB/watt, you are fiorever condemned to an
enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER
WHAT SIZE DRIVER YOU USE.

This
equates to the 'You can put an airplane engine in a submarine' but who wants
too?

Well, actually, airplane engines work rather well in submarines, given
that there exist submarines with Allison V16 diesels, an engine also found
in some fighters.

An enclose that is over 32 cubic feet will meet significant resistance when
placed in the home! (Test this by asking you wife if you can shift 2 small
fridges into the lounge!)

But, clearly, you're simply not willing to entertain the notion
that you have SEVERAL variables to play with in the efficiency/volume
cuitoff frequency equation.

As a side issue I see that companies are producing very large (24 inch
diametre) woofers now.

They've been around, actualy, for a number of decades. EV, for example,
had a 30" woofer in the 60's and 70's, and the Hartley 24" was also
available in the 1970's

how well do these work and are they worth the
premiums being asked for them?

Well, of the two I site above, both are pretty awful woofers, having
quite high resonances due to their crude and stiff suspensions.
Low frequency systems built with more conventional woofers that
are designed to work well instead of look impressive perform FAR
better.

"The Flash" wrote in message ...
So-called (actually, mis-named) 'isobarik' systems are a way of
obtaining a given response in half the volume, since the arrangement
results in half the total equivalent compliance volume and thus
requires half the enclosure volume for the same response function.

My Isobric has been constructed to improve LF ouput (it seems) not reduces
size as i can tell as it has a ~12 cubic foot cubed primary with a ~ 6 cubic
secondary, I guess that they have decided that the cone mass of an 8 inch
drive in isobaric has advantages over that of an 12 inch driver (at the size
of the brute it could easily use a 12 inch drive, one thing did occur to me
is that perhaps due to its age that duel VC speakers were not avalible and
the only method of getting a phase and anti phase driver easily was to use
two drivers.

That's NOT what an "isobarik" is for, more to the point, that's NOT
what the primary advantage to an isobarik is.

By using two drivers one behind the other in close proximity and
coupled in-phase both acoustically and electrically, the effective
moving mass is doubled, the Bl product is doubled, all of your Q
figures remain the same and, most significantly, you effective
compliance is halved. The result is a driver that will have the
same low frequency performance in an enclosure 1/2 the volume
required for a single driver. There will be the attendant change
in reference efficiency resulting from the fact that the effective
radiating area remain constant.

If that's not what your system is doing, it is not a so-called
"isobarik" system.

As to "true hifi response," such a term needs definition to be
anything but meaningless jargon, in precisely the same way that
a "specification" like "20Hz-20kHz" is meaningless without
qualification.

I guess what I desire is a reasonably flat response fro 32 Hz to 15Khz with
gradual roll off above and below. If that is 'hi fi' or not is questionable.
I spent some time years ago analysing CD's to find usual and lowest
frequency's (plus HF, lots of CD's have significant output above 15Khz
(components up to 25Khz+ can be present)

Really? On a CD? If you are seeing components at "25KkHz+", then
you have a broken CD player.


instraments produce much less than this (yes I know that alot can) a lot of
the very LF on disk is artificial (1/2 frequency echo and its that it is
possibly added to give 'space' to the recordings)

There is no such thing as "1/2 frequency echo" in any linear system.

unless you are a pipe
organ freak under 30Hz seems to unused (but not in Dolby Prologic, ES or
such as the LF in these type video recordings is huge it seems (and
unnatural in my books) )

In fact, having been involved in not an inconsiderable amount
of both organ building, recording and analysis, it's something
of unsubstantiated myth that organs have some unique amount of
very low frequency content. They simply do not.

THe fundamental efficiency/enclosure volume/cutoff frequency equation
will ALWAYS rule. But, interestingly enough, driver diameter simply
does not enter into that relation. Specifically, the relation:

n0 = kn Vb F3^3

where n0 is reference efficiency, Vb is enclosure volume, F3 is is
low frequency cutoff and kn is the efficiency constant has NO term
in it in any way depedent upon driver diameter. This directly refutes
your assertion that it's not possible to get your "unqualified" 'hifi
response from an 8 inch driver. One needs to simply balance the three
terms of efficiency, enclosure volume and cutoff frequency and you're
there. You seem to intimate that low efficiency is incompatible with
'hifi response," for example, an unjustifiable viewpoint in light
of the lack of qualification of 'hifi response.'

kn = efficiency constant derived from driver (this figure will improve with
driver diameter, thus a large driver will allow a a small enclosue to
produce the same output at the same frequency with less power - correct me
if wrong)

Well, you're right and you're wrong. One cannot arbitrarily increase
the radiating area of the driver without having some other effects.
For example, while the area goes as the suqare of the diameter, and
one might think that the efficiency would go up accordingly, the moving
mass ALSO increases at least as the square of the diameter, and thus
what you might think you gain in increased area, you lose in increased
mass, as far as efficiency is concerned. And, indeed, the effect is
often working against you, since larger cones are heavier in excess
to the propoerion of the simple square of diameter, since they also are
generally thicker as well.

Thus we find, in a completely practical sense, that all other things
being equal, increased diameter DOES NOT increase efficiency.

Larger drivers are more efficiency NOT because they have larger cones,
but because they have larger voice coils that have more wire in the
larger magnet gaps and thus larger Bl products. Look at the correlation,
for example, between diameter and Bl product: it's ALMOST a linear
relationship: it's not uncommon for a typical high-quality 8" woofer
to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A.
The correlation between the numbers, as uncanny as it may seem, is merely
a coincidence of mixing English (inches) and metric (Newtons per Amp)
units, but the trend is clear.

However in order to get usable (at say 32Hz) levels the enclosure volume
(8 inch) will become so large as to be impactical in a lot of cases.

No, or the efficiency has to be appropriate. For example, you can get
30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed
enclosure is ENTIRELY possible if you're willing to tolerate a
sensitivity on the order of 82 dB/watt.

On the other hand, if you want a system with the same cutoff frequency
with an efficiency of 90 dB/watt, you are fiorever condemned to an
enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER
WHAT SIZE DRIVER YOU USE.

This
equates to the 'You can put an airplane engine in a submarine' but who wants
too?

Well, actually, airplane engines work rather well in submarines, given
that there exist submarines with Allison V16 diesels, an engine also found
in some fighters.

An enclose that is over 32 cubic feet will meet significant resistance when
placed in the home! (Test this by asking you wife if you can shift 2 small
fridges into the lounge!)

But, clearly, you're simply not willing to entertain the notion
that you have SEVERAL variables to play with in the efficiency/volume
cuitoff frequency equation.

As a side issue I see that companies are producing very large (24 inch
diametre) woofers now.

They've been around, actualy, for a number of decades. EV, for example,
had a 30" woofer in the 60's and 70's, and the Hartley 24" was also
available in the 1970's

how well do these work and are they worth the
premiums being asked for them?

Well, of the two I site above, both are pretty awful woofers, having
quite high resonances due to their crude and stiff suspensions.
Low frequency systems built with more conventional woofers that
are designed to work well instead of look impressive perform FAR
better.

Mark wrote:
In article ,
says...
I have had no luck in measuring speaker response at low frequency's,

Then you may not be using the right tools.



Almost any speaker system sold today claims 20Hz to 20Kz response yet this
is so far from the truth I cannot understand how they dare claim such
figures.

Because they (or you) are not providing all the information.

It isn't enough to say 20-20k, you must also include (for
the measurement to have Any validity) what the +/- dB range
is across the band.


I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know
at what frequec(ies) does the reponse vary most from 'flat'.
e.g., is there a 3 dB hump or depression somewhere in the midrange, or is it
just at the tail ends of the spectrum? Is there anything implied
in the common 'range +/- dB' spec about where the variation occurs?


--

-S.

"They've got God on their side. All we've got is science and reason."
-- Dawn Hulsey, Talent Director

Mark wrote:
In article ,
says...
I have had no luck in measuring speaker response at low frequency's,

Then you may not be using the right tools.



Almost any speaker system sold today claims 20Hz to 20Kz response yet this
is so far from the truth I cannot understand how they dare claim such
figures.

Because they (or you) are not providing all the information.

It isn't enough to say 20-20k, you must also include (for
the measurement to have Any validity) what the +/- dB range
is across the band.


I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know
at what frequec(ies) does the reponse vary most from 'flat'.
e.g., is there a 3 dB hump or depression somewhere in the midrange, or is it
just at the tail ends of the spectrum? Is there anything implied
in the common 'range +/- dB' spec about where the variation occurs?


--

-S.

"They've got God on their side. All we've got is science and reason."
-- Dawn Hulsey, Talent Director

Dick Pierce wrote:

As a side issue I see that companies are producing very large (24 inch
diametre) woofers now.

They've been around, actualy, for a number of decades. EV, for example,
had a 30" woofer in the 60's and 70's, and the Hartley 24" was also
available in the 1970's

At least recently Fostex had a 30" woofer on their menu, quite well
sounding, Ole Lund Christensen here in Copenhagen has built some
different custom monitor systems based on it. I have heard the system DR
has in a control room, maily used for popular and jazz music, and it
does a good job.


Kind regards

Peter Larsen



--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
************************************************** ***********

Dick Pierce wrote:

As a side issue I see that companies are producing very large (24 inch
diametre) woofers now.

They've been around, actualy, for a number of decades. EV, for example,
had a 30" woofer in the 60's and 70's, and the Hartley 24" was also
available in the 1970's

At least recently Fostex had a 30" woofer on their menu, quite well
sounding, Ole Lund Christensen here in Copenhagen has built some
different custom monitor systems based on it. I have heard the system DR
has in a control room, maily used for popular and jazz music, and it
does a good job.


Kind regards

Peter Larsen



--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
************************************************** ***********

In article ,
Steven Sullivan wrote:
I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know
at what frequec(ies) does the reponse vary most from 'flat'.

Is there anything implied
in the common 'range +/- dB' spec about where the variation occurs?

50Hz is -3dB from the average, which is relevant in determining whether you
need a sub-woofer and where you'd want to cross one over.

Otherwise nothing useful is implied.

Variations may be dips/peaks than span a small set of frequencies or
only affect the on-axis response so they aren't noticeable, or long
trends that will be perceived as a significant coloration.

--
a href="http://www.poohsticks.org/drew/"Home Page/a
Life is a terminal sexually transmitted disease.

In article ,
Steven Sullivan wrote:
I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know
at what frequec(ies) does the reponse vary most from 'flat'.

Is there anything implied
in the common 'range +/- dB' spec about where the variation occurs?

50Hz is -3dB from the average, which is relevant in determining whether you
need a sub-woofer and where you'd want to cross one over.

Otherwise nothing useful is implied.

Variations may be dips/peaks than span a small set of frequencies or
only affect the on-axis response so they aren't noticeable, or long
trends that will be perceived as a significant coloration.

--
a href="http://www.poohsticks.org/drew/"Home Page/a
Life is a terminal sexually transmitted disease.

Peter Larsen wrote in message ...
Rusty Boudreaux wrote:

I just downloaded the pdf. The stated response is 15Hz-20kHz but
no dB qualifier. The magnitude plot shows essentially flat down
to 60Hz but no data below. However, they do show response to
30kHz...down 10dB.

My incomplete understanding is that there is no reason why that type of
microphone should roll off early other than series capacitance.

Plenty of reasons. A pressure microphone works because of pressure
differences betwen the front and the rear of the diaphragm. Assume,
for the moment, that the rear chamber of the microphone is perfectly
sealed. What's now going to happen is that any changes in barometric
pressure is going to change the position of the diaphragm. So, for
that reason alone, you want to put a leak in the back chamber to
allow for equalization of pressure.

The problem that you then face is how big a leak. Make it too small
a leak, and you haven't solved the problem. Make it too big, and
it "leaks" at too high a frequency.

One reason why laboratory mics are expensive is that the manufacturing
of such involves VERY careful attention to such matters: the leak is
a high-precision hole drilled through the backplate, and they essentially
guarantee the time constant of that leak to within a fairly tight
margin. (There are other factors, such as quartz rear insulators to
ensure both very high isolation resistance and very stable mechanical
dimensions with temperature, and so on).

Take a microphone that is made from a $2.00 mass-produced electret
condensor capsule, where there is little or no attention paid in
manufacturing to the time constant of the equalization leak and
other factors, and you'll actually find very large variations in the
low-frequency cutoff of the capsule, simply because the capsule was
NEVER intended, designed or manufactured for precision, low frequency
use.

These microphones and their variants are good as far as they go: they
have reasonable high frequency response, reasonably flat response
through the midband, reasonable though not remarkable temperature
stability, sensitivity matching is a little, well, variable AND
inconsitent low frequency performance.

And, they're cheap. As always, you get what you pay for.

I have quite a few of these things in my lab, and I use them not
for any broadband measurements, but for moderate-sized arrays to
measure moderately wide-band power response. They're not very
rugged, but, what the hell, if I break 2 or 3 or 20, who cares?
For less than a moderately priced German wine, I can replace them
ALL.

For any real measurements, out comes one of the B&K's.

Peter Larsen wrote in message ...
Rusty Boudreaux wrote:

I just downloaded the pdf. The stated response is 15Hz-20kHz but
no dB qualifier. The magnitude plot shows essentially flat down
to 60Hz but no data below. However, they do show response to
30kHz...down 10dB.

My incomplete understanding is that there is no reason why that type of
microphone should roll off early other than series capacitance.

Plenty of reasons. A pressure microphone works because of pressure
differences betwen the front and the rear of the diaphragm. Assume,
for the moment, that the rear chamber of the microphone is perfectly
sealed. What's now going to happen is that any changes in barometric
pressure is going to change the position of the diaphragm. So, for
that reason alone, you want to put a leak in the back chamber to
allow for equalization of pressure.

The problem that you then face is how big a leak. Make it too small
a leak, and you haven't solved the problem. Make it too big, and
it "leaks" at too high a frequency.

One reason why laboratory mics are expensive is that the manufacturing
of such involves VERY careful attention to such matters: the leak is
a high-precision hole drilled through the backplate, and they essentially
guarantee the time constant of that leak to within a fairly tight
margin. (There are other factors, such as quartz rear insulators to
ensure both very high isolation resistance and very stable mechanical
dimensions with temperature, and so on).

Take a microphone that is made from a $2.00 mass-produced electret
condensor capsule, where there is little or no attention paid in
manufacturing to the time constant of the equalization leak and
other factors, and you'll actually find very large variations in the
low-frequency cutoff of the capsule, simply because the capsule was
NEVER intended, designed or manufactured for precision, low frequency
use.

These microphones and their variants are good as far as they go: they
have reasonable high frequency response, reasonably flat response
through the midband, reasonable though not remarkable temperature
stability, sensitivity matching is a little, well, variable AND
inconsitent low frequency performance.

And, they're cheap. As always, you get what you pay for.

I have quite a few of these things in my lab, and I use them not
for any broadband measurements, but for moderate-sized arrays to
measure moderately wide-band power response. They're not very
rugged, but, what the hell, if I break 2 or 3 or 20, who cares?
For less than a moderately priced German wine, I can replace them
ALL.

For any real measurements, out comes one of the B&K's.

Dick Pierce wrote:

Plenty of reasons. ....

Thanks!


Kind regards

Peter Larsen

--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
************************************************** ***********

Dick Pierce wrote:

Plenty of reasons. ....

Thanks!


Kind regards

Peter Larsen

--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
************************************************** ***********

(Dick Pierce) wrote:



And, they're cheap. As always, you get what you pay for.

Except in high-end audio where you get either 'what you asked for', 'what you
got coming to ya.' as long as sonic performance isn't what you desire.

Thank you for the insight on those microphones.

(Dick Pierce) wrote:



And, they're cheap. As always, you get what you pay for.

Except in high-end audio where you get either 'what you asked for', 'what you
got coming to ya.' as long as sonic performance isn't what you desire.

Thank you for the insight on those microphones.

Dick,

Great explanation. You're turning me into a fan. I especially liked:

the leak is a high-precision hole

--Ethan

Dick,

Great explanation. You're turning me into a fan. I especially liked:

the leak is a high-precision hole

--Ethan

"Ian" wrote in message
...

"Tony Pearce" wrote in message
u...
No mention of what the maximum SPL Vs distortion level is at 30 Hz
though, I see.
Simply disregard these and you can easily get 30 Hz from a single 4 inch
driver. Of course you can't actually HEAR it :-)

Tony, please note I said "bandpass enclosure". Some of the
excursion/output
relations change.

Yes but the laws of physics still apply. You provide no actual figures.

You (perhaps) cannot "hear" 30Hz, although that depends ;-)

You certainly can hear 30 Hz if the level is loud enough. Check the
Fletcher/Munsen curves for the required levels. Remember if the distortion
is high enough (comon with small speakers), you will probably be hearing the
distortion generated, not the 30Hz, since the ear is more sensitive at the
higher harmonic frequencies. Re-read what I actually wrote.

Maximum SPL vs distortion level is just fine for reasonable levels in a
reasonable
(UK) size room.

As long as you think so, that is all that matters for you anyway :-)

TonyP.

"Ian" wrote in message
...

"Tony Pearce" wrote in message
u...
No mention of what the maximum SPL Vs distortion level is at 30 Hz
though, I see.
Simply disregard these and you can easily get 30 Hz from a single 4 inch
driver. Of course you can't actually HEAR it :-)

Tony, please note I said "bandpass enclosure". Some of the
excursion/output
relations change.

Yes but the laws of physics still apply. You provide no actual figures.

You (perhaps) cannot "hear" 30Hz, although that depends ;-)

You certainly can hear 30 Hz if the level is loud enough. Check the
Fletcher/Munsen curves for the required levels. Remember if the distortion
is high enough (comon with small speakers), you will probably be hearing the
distortion generated, not the 30Hz, since the ear is more sensitive at the
higher harmonic frequencies. Re-read what I actually wrote.

Maximum SPL vs distortion level is just fine for reasonable levels in a
reasonable
(UK) size room.

As long as you think so, that is all that matters for you anyway :-)

TonyP.

(Dick Pierce) wrote in message

Plenty of reasons. A pressure microphone works because ..


Dick:

Good job of explaning. I must reluctantly say, thank you. :-)

Bob Stanton

(Dick Pierce) wrote in message

Plenty of reasons. A pressure microphone works because ..


Dick:

Good job of explaning. I must reluctantly say, thank you. :-)

Bob Stanton

ow (Goofball_star_dot_etal) wrote in message ...
On 24 Nov 2003 00:24:57 -0800, (Svante)
wrote:

Our students in electroacoustics use this method in a lab on
loudspeakers.

I hope you teach them "inverted thinking" at the same time. :-)


Well, some of them have a hard time with the 12 db tilt... :-)


There must be some restrictions on the accuracy of this method but
the only one I can think off at the moment is that the wavelength must
be large compared to the internal dimensions of the speaker. The
meaasurement includes the effect of any port and of the enclosure
flexing.

There is probably an assumption that the air is compressed
adiabatically. The pressures involved are, of course, small if the mic
is not to be overloaded.

No, the pressures involved are HUGE, typically there is no problems
reaching 140 dB inside the box at low frequencies. So keep the levels
low in order to avoid overloading the microphone. Or did I perhaps
misunderstand your statement?)

Yes I should have been more clear. I am economical with words to the
point of recklessness. I should have warned that it is possible to
damage the microphone, which is a good reason to use a cheap one to
perfect the setup. What I meant was that when the levels are adjusted
so that the mic. is operating linearly then it follows that the
physics will be right - the pressure changes inside the box will be
linear with volume displacement. It is a small signal measurement with
large mic signals. . . You may have to fit an attenuator (with low
output impedance between amp and speaker.

The actual compression/expansion will be somewhere between adiabatic
and isothermal and since isothermal involves heat exchange with the
mass of any stuffing I might expect the degree to which it tends
towards isothemal to change somewhat with frequency.

Hmmm, yes, the "adiabaticness" of the volume will affect the
compliance of the box, but not very much. I have noticed a few times
when measuring the impedance curve of loudspeakers, that the only way
to match the simlated impedance curve with reality is to use a larger
volume than the physical in the simulation. The simulation assumes
adiabatic compression in this case. But the magnitude of this has been
like 135 litres instead of the physical 130 litres, so i don't think
this gives raise to any large errors. This error, would be about
20*log(130/135)=-0.3 dB (since box pressure is inversively
proportional to box volume). Even more, in order to affect the
frequency response (neglecting a pure scale factor) the
"adiabaticness" would have to
vary with frequency, and this effect would be even smaller.

My students use no stuffing in the box, so obviously I have not seen
this effect there. Once in a while I throw a sweater into the box to
demonstrate the effect on the standing waves, but I can't recall
seeing that the apparent volume of the box changes.

So in order for the "adiabaticness" to have any significant effect on
the response curve, one would have to have A LOT of stuffing material
and its "adiabaticness" would also have to be frequency dependant.
Maybe someone could prove such an effect, but until then I feel
confident that the method is OK.

Actually the response curves we measure match the predicted behaviour
so well that we beleive that they are far more accurate than
measurements in the anechoic chamber (that we don't have any more,
sigh...).

And... About overloading the microphone; Yes it is easy to overload
the microphone, in fact it has proven impossible to measure distorsion
inside the box. The distorsion simply originates from the microphone.
But on the other hand the microphone (Sennheiser MKE2) has proven
robust in the sense that it is not DAMAGED by high pressures. We have
been running this lab for some 7 years now, and for sure the box
pressure has been high on occasions (I would assume up to 150-160 dB)
but the mic is still OK.

ow (Goofball_star_dot_etal) wrote in message ...
On 24 Nov 2003 00:24:57 -0800, (Svante)
wrote:

Our students in electroacoustics use this method in a lab on
loudspeakers.

I hope you teach them "inverted thinking" at the same time. :-)


Well, some of them have a hard time with the 12 db tilt... :-)


There must be some restrictions on the accuracy of this method but
the only one I can think off at the moment is that the wavelength must
be large compared to the internal dimensions of the speaker. The
meaasurement includes the effect of any port and of the enclosure
flexing.

There is probably an assumption that the air is compressed
adiabatically. The pressures involved are, of course, small if the mic
is not to be overloaded.

No, the pressures involved are HUGE, typically there is no problems
reaching 140 dB inside the box at low frequencies. So keep the levels
low in order to avoid overloading the microphone. Or did I perhaps
misunderstand your statement?)

Yes I should have been more clear. I am economical with words to the
point of recklessness. I should have warned that it is possible to
damage the microphone, which is a good reason to use a cheap one to
perfect the setup. What I meant was that when the levels are adjusted
so that the mic. is operating linearly then it follows that the
physics will be right - the pressure changes inside the box will be
linear with volume displacement. It is a small signal measurement with
large mic signals. . . You may have to fit an attenuator (with low
output impedance between amp and speaker.

The actual compression/expansion will be somewhere between adiabatic
and isothermal and since isothermal involves heat exchange with the
mass of any stuffing I might expect the degree to which it tends
towards isothemal to change somewhat with frequency.

Hmmm, yes, the "adiabaticness" of the volume will affect the
compliance of the box, but not very much. I have noticed a few times
when measuring the impedance curve of loudspeakers, that the only way
to match the simlated impedance curve with reality is to use a larger
volume than the physical in the simulation. The simulation assumes
adiabatic compression in this case. But the magnitude of this has been
like 135 litres instead of the physical 130 litres, so i don't think
this gives raise to any large errors. This error, would be about
20*log(130/135)=-0.3 dB (since box pressure is inversively
proportional to box volume). Even more, in order to affect the
frequency response (neglecting a pure scale factor) the
"adiabaticness" would have to
vary with frequency, and this effect would be even smaller.

My students use no stuffing in the box, so obviously I have not seen
this effect there. Once in a while I throw a sweater into the box to
demonstrate the effect on the standing waves, but I can't recall
seeing that the apparent volume of the box changes.

So in order for the "adiabaticness" to have any significant effect on
the response curve, one would have to have A LOT of stuffing material
and its "adiabaticness" would also have to be frequency dependant.
Maybe someone could prove such an effect, but until then I feel
confident that the method is OK.

Actually the response curves we measure match the predicted behaviour
so well that we beleive that they are far more accurate than
measurements in the anechoic chamber (that we don't have any more,
sigh...).

And... About overloading the microphone; Yes it is easy to overload
the microphone, in fact it has proven impossible to measure distorsion
inside the box. The distorsion simply originates from the microphone.
But on the other hand the microphone (Sennheiser MKE2) has proven
robust in the sense that it is not DAMAGED by high pressures. We have
been running this lab for some 7 years now, and for sure the box
pressure has been high on occasions (I would assume up to 150-160 dB)
but the mic is still OK.

Hey Dickie
You need to get a life!
You are still the annoying fraud you always were.
I have this image of you huddled over your PC
scouring this NG looking for any posting to which
you can latch onto and then act superior, frantically
typing, and fuming inside, stop being so silly and get
some fresh air now and again.

Hey Dickie
You need to get a life!
You are still the annoying fraud you always were.
I have this image of you huddled over your PC
scouring this NG looking for any posting to which
you can latch onto and then act superior, frantically
typing, and fuming inside, stop being so silly and get
some fresh air now and again.

By using two drivers one behind the other in close proximity and
coupled in-phase both acoustically and electrically, the effective
moving mass is doubled, the Bl product is doubled, all of your Q
figures remain the same and, most significantly, you effective
compliance is halved. The result is a driver that will have the
same low frequency performance in an enclosure 1/2 the volume
required for a single driver. There will be the attendant change
in reference efficiency resulting from the fact that the effective
radiating area remain constant.

There is no such thing as "1/2 frequency echo" in any linear system.


In fact, having been involved in not an inconsiderable amount
of both organ building, recording and analysis, it's something
of unsubstantiated myth that organs have some unique amount of
very low frequency content. They simply do not.


Well, you're right and you're wrong. One cannot arbitrarily increase
the radiating area of the driver without having some other effects.
For example, while the area goes as the suqare of the diameter, and
one might think that the efficiency would go up accordingly, the moving
mass ALSO increases at least as the square of the diameter, and thus
what you might think you gain in increased area, you lose in increased
mass, as far as efficiency is concerned. And, indeed, the effect is
often working against you, since larger cones are heavier in excess
to the propoerion of the simple square of diameter, since they also are
generally thicker as well.

Thus we find, in a completely practical sense, that all other things
being equal, increased diameter DOES NOT increase efficiency.

Larger drivers are more efficiency NOT because they have larger cones,
but because they have larger voice coils that have more wire in the
larger magnet gaps and thus larger Bl products. Look at the correlation,
for example, between diameter and Bl product: it's ALMOST a linear
relationship: it's not uncommon for a typical high-quality 8" woofer
to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A.
The correlation between the numbers, as uncanny as it may seem, is merely
a coincidence of mixing English (inches) and metric (Newtons per Amp)
units, but the trend is clear.


No, or the efficiency has to be appropriate. For example, you can get
30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed
enclosure is ENTIRELY possible if you're willing to tolerate a
sensitivity on the order of 82 dB/watt.

On the other hand, if you want a system with the same cutoff frequency
with an efficiency of 90 dB/watt, you are fiorever condemned to an
enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER
WHAT SIZE DRIVER YOU USE.


They've been around, actualy, for a number of decades. EV, for example,
had a 30" woofer in the 60's and 70's, and the Hartley 24" was also
available in the 1970's

how well do these work and are they worth the
premiums being asked for them?

Well, of the two I site (cite?) above, both are pretty awful woofers, having
quite high resonances due to their crude and stiff suspensions.
Low frequency systems built with more conventional woofers that
are designed to work well instead of look impressive perform FAR
better.

Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

By using two drivers one behind the other in close proximity and
coupled in-phase both acoustically and electrically, the effective
moving mass is doubled, the Bl product is doubled, all of your Q
figures remain the same and, most significantly, you effective
compliance is halved. The result is a driver that will have the
same low frequency performance in an enclosure 1/2 the volume
required for a single driver. There will be the attendant change
in reference efficiency resulting from the fact that the effective
radiating area remain constant.

There is no such thing as "1/2 frequency echo" in any linear system.


In fact, having been involved in not an inconsiderable amount
of both organ building, recording and analysis, it's something
of unsubstantiated myth that organs have some unique amount of
very low frequency content. They simply do not.


Well, you're right and you're wrong. One cannot arbitrarily increase
the radiating area of the driver without having some other effects.
For example, while the area goes as the suqare of the diameter, and
one might think that the efficiency would go up accordingly, the moving
mass ALSO increases at least as the square of the diameter, and thus
what you might think you gain in increased area, you lose in increased
mass, as far as efficiency is concerned. And, indeed, the effect is
often working against you, since larger cones are heavier in excess
to the propoerion of the simple square of diameter, since they also are
generally thicker as well.

Thus we find, in a completely practical sense, that all other things
being equal, increased diameter DOES NOT increase efficiency.

Larger drivers are more efficiency NOT because they have larger cones,
but because they have larger voice coils that have more wire in the
larger magnet gaps and thus larger Bl products. Look at the correlation,
for example, between diameter and Bl product: it's ALMOST a linear
relationship: it's not uncommon for a typical high-quality 8" woofer
to have an average Bl of around 8 N/A, while a 12" is up around 12 N/A.
The correlation between the numbers, as uncanny as it may seem, is merely
a coincidence of mixing English (inches) and metric (Newtons per Amp)
units, but the trend is clear.


No, or the efficiency has to be appropriate. For example, you can get
30 Hz out of ANY diameter driver in a 56 liter (2 cubic foot) sealed
enclosure is ENTIRELY possible if you're willing to tolerate a
sensitivity on the order of 82 dB/watt.

On the other hand, if you want a system with the same cutoff frequency
with an efficiency of 90 dB/watt, you are fiorever condemned to an
enclosure volume no smaller than 390 liters (13.6 cubic feet), NO MATTER
WHAT SIZE DRIVER YOU USE.


They've been around, actualy, for a number of decades. EV, for example,
had a 30" woofer in the 60's and 70's, and the Hartley 24" was also
available in the 1970's

how well do these work and are they worth the
premiums being asked for them?

Well, of the two I site (cite?) above, both are pretty awful woofers, having
quite high resonances due to their crude and stiff suspensions.
Low frequency systems built with more conventional woofers that
are designed to work well instead of look impressive perform FAR
better.

Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

BoredSilly wrote:

Hey Dickie
You need to get a life!
You are still the annoying fraud you always were.
I have this image of you huddled over your PC
scouring this NG looking for any posting to which
you can latch onto and then act superior,

He doesn't act, he is.


Kind regards

Peter Larsen

--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
************************************************** ***********

BoredSilly wrote:

Hey Dickie
You need to get a life!
You are still the annoying fraud you always were.
I have this image of you huddled over your PC
scouring this NG looking for any posting to which
you can latch onto and then act superior,

He doesn't act, he is.


Kind regards

Peter Larsen

--
************************************************** ***********
* My site is at: http://www.muyiovatki.dk *
************************************************** ***********

From: "BoredSilly"

Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

braindead,

But you added no meaningful comment. From Mr. Pierce, I've learned several
important concepts, the physics behind them, and their proper application to
the field of sound reproduction. From you, I see nothing but childish name
calling. If you have an issue with something that Mr.Pierce has stated here,
then:

1. Show your real name. Mr. Pierce does, I do, and so do others. Without your
real name, your words are nothing but the empty rantings of a deranged internet
troll.

2. If you really do have an issue with any statement made by Mr. Pierce, then
state it, and it can then be discussed by the group in a mature and intelligent
manner.

If you, or anyone else, can't see the benefits of such an approach, then I
suggest that you find somewhere else to vent your anger.

Stuart Welwood
http://members.aol.com/StuWelwood

From: "BoredSilly"

Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

braindead,

But you added no meaningful comment. From Mr. Pierce, I've learned several
important concepts, the physics behind them, and their proper application to
the field of sound reproduction. From you, I see nothing but childish name
calling. If you have an issue with something that Mr.Pierce has stated here,
then:

1. Show your real name. Mr. Pierce does, I do, and so do others. Without your
real name, your words are nothing but the empty rantings of a deranged internet
troll.

2. If you really do have an issue with any statement made by Mr. Pierce, then
state it, and it can then be discussed by the group in a mature and intelligent
manner.

If you, or anyone else, can't see the benefits of such an approach, then I
suggest that you find somewhere else to vent your anger.

Stuart Welwood
http://members.aol.com/StuWelwood

"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

Well, it should be very easy for Mr. BoredSilly to show this is
the case. All he need do is simply cite the text book and quote
the paragraphs he is accusing me of making word-for-sord copies
of.

How about it, Bored (or is it just Silly?), care to step up to
the plate?

Nah, let's make it at least sporting. How about betting some
real money on it? Just show us the paragraphs from the text
book that I copied, as you say "word-for-word."

Anyone else want to join in on the bet?

"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

Well, it should be very easy for Mr. BoredSilly to show this is
the case. All he need do is simply cite the text book and quote
the paragraphs he is accusing me of making word-for-sord copies
of.

How about it, Bored (or is it just Silly?), care to step up to
the plate?

Nah, let's make it at least sporting. How about betting some
real money on it? Just show us the paragraphs from the text
book that I copied, as you say "word-for-word."

Anyone else want to join in on the bet?

On 30 Nov 2003 15:58:13 -0800, (Dick Pierce)
wrote:

"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

Well, it should be very easy for Mr. BoredSilly to show this is
the case. All he need do is simply cite the text book and quote
the paragraphs he is accusing me of making word-for-sord copies
of.

How about it, Bored (or is it just Silly?), care to step up to
the plate?

Nah, let's make it at least sporting. How about betting some
real money on it? Just show us the paragraphs from the text
book that I copied, as you say "word-for-word."

Anyone else want to join in on the bet?

This post is not my style, Dick, in case you are speculating.

On 30 Nov 2003 15:58:13 -0800, (Dick Pierce)
wrote:

"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

Well, it should be very easy for Mr. BoredSilly to show this is
the case. All he need do is simply cite the text book and quote
the paragraphs he is accusing me of making word-for-sord copies
of.

How about it, Bored (or is it just Silly?), care to step up to
the plate?

Nah, let's make it at least sporting. How about betting some
real money on it? Just show us the paragraphs from the text
book that I copied, as you say "word-for-word."

Anyone else want to join in on the bet?

This post is not my style, Dick, in case you are speculating.

On Mon, 01 Dec 2003 00:07:33 GMT, ow
(Goofball_star_dot_etal) wrote:

On 30 Nov 2003 15:58:13 -0800, (Dick Pierce)
wrote:

"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

Well, it should be very easy for Mr. BoredSilly to show this is
the case. All he need do is simply cite the text book and quote
the paragraphs he is accusing me of making word-for-sord copies
of.

How about it, Bored (or is it just Silly?), care to step up to
the plate?

Nah, let's make it at least sporting. How about betting some
real money on it? Just show us the paragraphs from the text
book that I copied, as you say "word-for-word."

Anyone else want to join in on the bet?

This post is not my style, Dick, in case you are speculating.

Sounds like Bob the Moron, to me. And of course Dick's posts *read*
like text books, because they all quote the *same* laws of physics.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

On Mon, 01 Dec 2003 00:07:33 GMT, ow
(Goofball_star_dot_etal) wrote:

On 30 Nov 2003 15:58:13 -0800, (Dick Pierce)
wrote:

"BoredSilly" wrote in message ...
Dickie, you poured over the text books and some of your
paragraphs are word-for-word copies!

Well, it should be very easy for Mr. BoredSilly to show this is
the case. All he need do is simply cite the text book and quote
the paragraphs he is accusing me of making word-for-sord copies
of.

How about it, Bored (or is it just Silly?), care to step up to
the plate?

Nah, let's make it at least sporting. How about betting some
real money on it? Just show us the paragraphs from the text
book that I copied, as you say "word-for-word."

Anyone else want to join in on the bet?

This post is not my style, Dick, in case you are speculating.

Sounds like Bob the Moron, to me. And of course Dick's posts *read*
like text books, because they all quote the *same* laws of physics.
--

Stewart Pinkerton | Music is Art - Audio is Engineering

Drew Eckhardt wrote:
In article ,
Steven Sullivan wrote:
I'm curious about this spec. When I see '50-20kHz +/- 3dB, I'd like to know
at what frequec(ies) does the reponse vary most from 'flat'.

Is there anything implied
in the common 'range +/- dB' spec about where the variation occurs?

50Hz is -3dB from the average, which is relevant in determining whether you
need a sub-woofer and where you'd want to cross one over.

Is the lower limit of the range determined by the -3dB point in the
measuremnts , i.e., 50 Hz was the highest frequency below 20 kHz at
which output was down 3 dB?

Is the same implied for the other end of the stated range (20 kHz)?
I.e., is the resposne down 3 dB from average at 20 kHz too?



--

-S.

"They've got God on their side. All we've got is science and reason."
-- Dawn Hulsey, Talent Director