[[email protected]]

i want to build a box to house (4) 10" subs....should i seperate all
four subs or can i put them in all in one chamber? i will be running
them in mono.
another thought i had is to have them in diamond shape...with opposit
sides facing each other, but would i then have to reverse the polarity
on one the speakers in each pair?
i need some help and or advice

[Mr.T]

wrote in message
oups.com...
i want to build a box to house (4) 10" subs....should i seperate all
four subs or can i put them in all in one chamber? i will be running
them in mono.

All in one chamber is OK if they are identical and fed the same signal.
The size still needs to be four times that required for one though.

another thought i had is to have them in diamond shape...with opposit
sides facing each other, but would i then have to reverse the polarity
on one the speakers in each pair?

Not for sub woofer frequencies, you want them all in phase.

MrT.

[Don Pearce]

On 29 Jul 2006 01:54:24 -0700, wrote:

i want to build a box to house (4) 10" subs....should i seperate all
four subs or can i put them in all in one chamber? i will be running
them in mono.
another thought i had is to have them in diamond shape...with opposit
sides facing each other, but would i then have to reverse the polarity
on one the speakers in each pair?
i need some help and or advice

It essentially makes no difference whether you separate them or not.
You still nee to provide each one with its necessary volume for the
type of sub you are designing. As for the polarity - wire them all the
same, just as you would if they were side by side on the front panel.

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers, so you might well find
things greatly improved with a smaller number of larger drivers. I
have built my sub with a single fifteen inch Adire Tempest. It has its
resonance at about 18Hz and performs very well. Now, I don't know what
you are using and they may also be very suitable, but do have a think
about it.

If you are lucky, Dick Pierce will pick up this thread - listen hard,
he knows a great deal more about speaker design than me or probably
anyone else around here.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mr.T]

"Don Pearce" wrote in message
...
If you are lucky, Dick Pierce will pick up this thread - listen hard,
he knows a great deal more about speaker design than me or probably
anyone else around here.

The "probably" is surely redundant.

MrT.

[Don Pearce]

On Sat, 29 Jul 2006 19:38:54 +1000, "Mr.T" MrT@home wrote:


"Don Pearce" wrote in message
...
If you are lucky, Dick Pierce will pick up this thread - listen hard,
he knows a great deal more about speaker design than me or probably
anyone else around here.

The "probably" is surely redundant.

MrT.

Fair comment

d

--
Pearce Consulting
http://www.pearce.uk.com

[James Lehman]

"Don Pearce" wrote in message
...
On 29 Jul 2006 01:54:24 -0700, wrote:

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers .....

You can get high excursion drivers with small cones that have very low
resonances. The only problem is that it takes a large surface area to push
enough air at those freqs to produce any appreciable volume. That's where
using multiple drivers in the same baffle comes in.

I have designed a system that uses (4) 8 inch woofers in dual isobaric
pairs. It is -3dB at 19Hz and can produce well over 110dB at it's maximum
dispersion freq; which is about 23Hz.

Smaller cones usually mean more accurate response and much less cone ripple.
Isobaric coupling improves this even more.

http://www.akrobiz.com/james/estie1.html

James. )

[Don Pearce]

On Sat, 29 Jul 2006 20:03:29 GMT, "James Lehman"
wrote:


"Don Pearce" wrote in message
...
On 29 Jul 2006 01:54:24 -0700, wrote:

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers .....

You can get high excursion drivers with small cones that have very low
resonances. The only problem is that it takes a large surface area to push
enough air at those freqs to produce any appreciable volume. That's where
using multiple drivers in the same baffle comes in.

I have designed a system that uses (4) 8 inch woofers in dual isobaric
pairs. It is -3dB at 19Hz and can produce well over 110dB at it's maximum
dispersion freq; which is about 23Hz.

Smaller cones usually mean more accurate response and much less cone ripple.
Isobaric coupling improves this even more.

http://www.akrobiz.com/james/estie1.html

James. )



Well, with those drivers the resonance is at 33Hz - double that of the
Adires, and Xmax is a bare 3.8mm. That really isn't enough these days
- the Adire is more than 16mm. If you assume that for the Adire a cone
area is roughly equivalent to the four 8 inchers (and in practice it
is likely to be a great deal more), and Xmax is four times as great,
then the one big speaker will shift four times as much air as the four
small ones, and provide a complete octave extra bass. Sensitivity is
not an issue these days - just put in a suitable amp.

Actually, I have just realised you design is isobaric, so you only
have the area of two drivers shifting air - that means the one big
speaker will shift 8 times as much air as the four in your design.

And of course for the frequencies covered by a sub, cone ripple is a
non-problem.

For me that is no contest.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mr.T]

"Don Pearce" wrote in message
...
Actually, I have just realised you design is isobaric, so you only
have the area of two drivers shifting air - that means the one big
speaker will shift 8 times as much air as the four in your design.

And of course for the frequencies covered by a sub, cone ripple is a
non-problem.

Whilst I often prefer one big driver myself, you cannot say cone break-up is
a non issue just because it's a sub.
If you put in a 30 Hz sine wave, you do not want *any* other frequency
coming out. Something that will surely happen with any cone break-up.
Just because the speaker is operating in the piston area does not mean there
is no possibility of any spurious output.

The proof of any pudding is in the final result, not only the ingredients.
Theory is well and good, but proper measurement is the final proof.

MrT.

[Phil Allison]

"Mr.T"

"Don Pearce"

And of course for the frequencies covered by a sub, cone ripple is a
non-problem.


Whilst I often prefer one big driver myself, you cannot say cone break-up
is
a non issue just because it's a sub.


** ********.

Cone "break-up" ( = standing waves in the cone ) occurs only at mid range or
higher drive frequencies.

The neologism term "cone ripple " appears to have been invented by the OP.



If you put in a 30 Hz sine wave, you do not want *any* other frequency
coming out. Something that will surely happen with any cone break-up.


** Only sub woofers do not suffer cone "break- up".


Just because the speaker is operating in the piston area does not mean
there
is no possibility of any spurious output.


** Sure - the box it might rattle, the woofer's suspension might be
asymmetrical, the cone might flex a little under high forces, the port might
make chuffing noises.......

NONE of which is cone " break- up" !!



The proof of any pudding is in the final result, not only the ingredients.
Theory is well and good, but proper measurement is the final proof.


** Same old anal retentive hobby horse.





........ Phil

[Mr.T]

"Phil Allison" wrote in message
...
Cone "break-up" ( = standing waves in the cone ) occurs only at mid range
or
higher drive frequencies.

Actually it is usually considered to cover any spurious cone emmissions, not
just standing waves.

** Only sub woofers do not suffer cone "break- up".

The manufacturers that have used laser interferometry to show otherwise
would disagree I imagine.

MrT.

[Phil Allison]

"Mr.Turd "

Cone "break-up" ( = standing waves in the cone ) occurs only at mid range
or higher drive frequencies.

Actually it is usually considered to cover any spurious cone emmissions,



** Absolute ****ing ******** !!!!!!!!!!!!!!!!!





........... Phil

[James Lehman]

With large cone woofers it is not uncommon that the force that is applied at
the center of the cone causes forward motion that warps the cone for a brief
period of time before that force can propagate out to the edge of the cone.
A similar, but different distortion of the cone may occur as the cone is
pulled back into the magnet gap. Any distortion of the cone during its
travel will cause some kind of distortion in the sound that it produces.
Just about any malformation of a sine wave results in harmonics; which are
frequencies above the fundamental frequency of the sine wave. As a matter of
fact, a fairly large portion of the audible signal coming from most woofers
is going to be second and third harmonics. It just so happens that those
added tones are musically constructive; one octave and an octave and a
fifth. These same tones are a natural component in just about any musical
instrument that might play notes in that range, so we don't worry so much
about it. The A string on a bass guitar is 55Hz., The second harmonic is
110Hz (also A) and the third is 165Hz (approximately E). WOW! I managed to
write all of these words without insulting anyone or using any profanity!


James. )



"Phil Allison" wrote in message
...

"Mr.Turd "

Cone "break-up" ( = standing waves in the cone ) occurs only at mid
range
or higher drive frequencies.

Actually it is usually considered to cover any spurious cone emmissions,



** Absolute ****ing ******** !!!!!!!!!!!!!!!!!





.......... Phil

[Don Pearce]

On Sun, 30 Jul 2006 18:47:49 GMT, "James Lehman"
wrote:

With large cone woofers it is not uncommon that the force that is applied at
the center of the cone causes forward motion that warps the cone for a brief
period of time before that force can propagate out to the edge of the cone.
A similar, but different distortion of the cone may occur as the cone is
pulled back into the magnet gap. Any distortion of the cone during its
travel will cause some kind of distortion in the sound that it produces.
Just about any malformation of a sine wave results in harmonics; which are
frequencies above the fundamental frequency of the sine wave. As a matter of
fact, a fairly large portion of the audible signal coming from most woofers
is going to be second and third harmonics. It just so happens that those
added tones are musically constructive; one octave and an octave and a
fifth. These same tones are a natural component in just about any musical
instrument that might play notes in that range, so we don't worry so much
about it. The A string on a bass guitar is 55Hz., The second harmonic is
110Hz (also A) and the third is 165Hz (approximately E). WOW! I managed to
write all of these words without insulting anyone or using any profanity!


James. )

But we aren't talking about woofers, we are talking subwoofers. They
don't handle the kind of frequencies that might induce such behaviour.
I've checked the cone material used in my subwoofer for the internal
speed of sound, and the consequent propagation time of a pulse from
the centre to the edge, and it comes out at 0.15 milliseconds. I don't
really think we need worry about that. And what would happen if the
edge did lag a little? Nothing bad - you would just get a slightly
better polar dispersion, and I don't think we can call that too nasty.

But as I said, you are detailing potential problems with woofers which
have to handle all those harmonics, but the subject is subwoofers,
which don't.

d

--
Pearce Consulting
http://www.pearce.uk.com

[James Lehman]

But as I said, you are detailing potential problems with woofers which
have to handle all those harmonics, but the subject is subwoofers,
which don't.

If you put a 55Hz pure sine wave into your sub woofer it will create the
second and third harmonic as distortion. It has nothing to do with the
crossover or whether this woofer is supposed to cover these frequencies or
not. The woofer itself is creating those tones as distortion. It just so
happens, that at very low frequencies, human hearing is much less sensitive
and one octave up can make a big difference. So just because of that, the
second harmonic will sound even louder at lower frequencies. One of the
possible advantages of isobaric coupling is that the woofers can be
positioned in opposite directions and wired out-of-phase. This has the
effect of balancing the forces that act on the cone to be symmetrical in
their positive and negative motion. This means that any malformation of the
waveform they reproduce will be the same in both the negative and positive
swing, which dramatically reduces even order harmonics; the strongest of
which is the second; the octave.

James. )

[Don Pearce]

On Sun, 30 Jul 2006 20:20:44 GMT, "James Lehman"
wrote:

But as I said, you are detailing potential problems with woofers which
have to handle all those harmonics, but the subject is subwoofers,
which don't.

If you put a 55Hz pure sine wave into your sub woofer it will create the
second and third harmonic as distortion. It has nothing to do with the
crossover or whether this woofer is supposed to cover these frequencies or
not. The woofer itself is creating those tones as distortion. It just so
happens, that at very low frequencies, human hearing is much less sensitive
and one octave up can make a big difference. So just because of that, the
second harmonic will sound even louder at lower frequencies. One of the
possible advantages of isobaric coupling is that the woofers can be
positioned in opposite directions and wired out-of-phase. This has the
effect of balancing the forces that act on the cone to be symmetrical in
their positive and negative motion. This means that any malformation of the
waveform they reproduce will be the same in both the negative and positive
swing, which dramatically reduces even order harmonics; the strongest of
which is the second; the octave.

James. )



But if the cone is not malforming at 50Hz, then it won't be producing
that distortion. Add to that of course the fact that there will be
natural harmonics of that frequency in the music, coming at full
strength from the main speaker's woofer, and it won't be heard. The
big test is this - can you locate the sub in the room by listening? I
certainly can't.

d

--
Pearce Consulting
http://www.pearce.uk.com

[James Lehman]

But if the cone is not malforming at 50Hz.....

It is.

[Don Pearce]

On Sun, 30 Jul 2006 20:57:56 GMT, "James Lehman"
wrote:

But if the cone is not malforming at 50Hz.....

It is.



Mine isn't.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Phil Allison]

"James Lehman" = Top Posting PITA ******


With large cone woofers it is not uncommon that the force that is applied
at
the center of the cone causes forward motion that warps the cone for a
brief
period of time before that force can propagate out to the edge of the
cone.
A similar, but different distortion of the cone may occur as the cone is
pulled back into the magnet gap. Any distortion of the cone during its
travel will cause some kind of distortion in the sound that it produces.


** Hand waving, irrational tripe.





......... Phil

[Mr.T]

"Don Pearce" wrote in message
...
But we aren't talking about woofers, we are talking subwoofers. They
don't handle the kind of frequencies that might induce such behaviour.
I've checked the cone material used in my subwoofer for the internal
speed of sound, and the consequent propagation time of a pulse from
the centre to the edge, and it comes out at 0.15 milliseconds. I don't
really think we need worry about that. And what would happen if the
edge did lag a little? Nothing bad - you would just get a slightly
better polar dispersion, and I don't think we can call that too nasty.

But as I said, you are detailing potential problems with woofers which
have to handle all those harmonics, but the subject is subwoofers,
which don't.

Are you really suggesting you can use ANY cone material for a sub woofer
driver and not incur ANY deviation from the ideal pistionic motion?
Would be very nice if true.
I guess all those Laser measurements showing otherwise was a waste of time
then.

MrT.

[Don Pearce]

On Mon, 31 Jul 2006 16:31:44 +1000, "Mr.T" MrT@home wrote:


"Don Pearce" wrote in message
...
But we aren't talking about woofers, we are talking subwoofers. They
don't handle the kind of frequencies that might induce such behaviour.
I've checked the cone material used in my subwoofer for the internal
speed of sound, and the consequent propagation time of a pulse from
the centre to the edge, and it comes out at 0.15 milliseconds. I don't
really think we need worry about that. And what would happen if the
edge did lag a little? Nothing bad - you would just get a slightly
better polar dispersion, and I don't think we can call that too nasty.

But as I said, you are detailing potential problems with woofers which
have to handle all those harmonics, but the subject is subwoofers,
which don't.

Are you really suggesting you can use ANY cone material for a sub woofer
driver and not incur ANY deviation from the ideal pistionic motion?
Would be very nice if true.
I guess all those Laser measurements showing otherwise was a waste of time
then.


Look, if you want to continue this in a sensible way, you are going to
have to argue against what I actually say. If you are just going to
make up random gibberish, pretend that is what I meant and then argue
against that, we may as well stop now.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mr.T]

"Don Pearce" wrote in message
...
Look, if you want to continue this in a sensible way, you are going to
have to argue against what I actually say. If you are just going to
make up random gibberish, pretend that is what I meant and then argue
against that, we may as well stop now.

Agreed, I can't fathom how your gibberish proves cone break-up can not occur
in a sub woofer either.
If you now agree it can, then we have no disagreement.

MrT.

[Don Pearce]

On Mon, 31 Jul 2006 18:59:17 +1000, "Mr.T" MrT@home wrote:


"Don Pearce" wrote in message
...
Look, if you want to continue this in a sensible way, you are going to
have to argue against what I actually say. If you are just going to
make up random gibberish, pretend that is what I meant and then argue
against that, we may as well stop now.

Agreed, I can't fathom how your gibberish proves cone break-up can not occur
in a sub woofer either.
If you now agree it can, then we have no disagreement.

MrT.



You just need to look at the frequency response of a subwoofer driver
to see where cone breakup starts, and it is generally in the high
hundreds of Hz - perhaps 1kHz for some. Since the maximum frequency
you put into a subwoofer is below 100Hz, we are safe in assuming that
cone breakup is *not* a problem with subwoofers.

Woofer, on the other hand, are asked to cover the range right up to
where the tweeter starts working and they can indeed suffer cone
breakup.

And I'm not saying it *can't* happen. It is perfectly possible to make
one so poor that it will, but what I'm saying is that in any decently
designed subwoofer it doesn't happen.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mr.T]

"Don Pearce" wrote in message
...
You just need to look at the frequency response of a subwoofer driver
to see where cone breakup starts, and it is generally in the high
hundreds of Hz - perhaps 1kHz for some. Since the maximum frequency
you put into a subwoofer is below 100Hz, we are safe in assuming that
cone breakup is *not* a problem with subwoofers.

There's your problem. Instead of *"assuming"*, some makers use laser
interferometry to actually show the cone breakup for various materials, then
they can select what to use.

And I'm not saying it *can't* happen. It is perfectly possible to make
one so poor that it will, but what I'm saying is that in any decently
designed subwoofer it doesn't happen.

OK, we agree then. Any "decently" designed driver is one in which it doesn't
happen (or only minimally at least) by definition.
Pity you didn't say that in the first place.

MrT.

[Don Pearce]

On Mon, 31 Jul 2006 20:36:07 +1000, "Mr.T" MrT@home wrote:


"Don Pearce" wrote in message
...
You just need to look at the frequency response of a subwoofer driver
to see where cone breakup starts, and it is generally in the high
hundreds of Hz - perhaps 1kHz for some. Since the maximum frequency
you put into a subwoofer is below 100Hz, we are safe in assuming that
cone breakup is *not* a problem with subwoofers.

There's your problem. Instead of *"assuming"*, some makers use laser
interferometry to actually show the cone breakup for various materials, then
they can select what to use.

Laser interferometry is a useful diagnostic tool for fixing cone
breakup when it occurs, but it is not necessary for identifying it -
the frequency response will do that for you. And of course it is about
50/50 between materials and geometry. You do need to get both right.


And I'm not saying it *can't* happen. It is perfectly possible to make
one so poor that it will, but what I'm saying is that in any decently
designed subwoofer it doesn't happen.

OK, we agree then. Any "decently" designed driver is one in which it doesn't
happen (or only minimally at least) by definition.
Pity you didn't say that in the first place.

Well I could have said an awful lot of things in the first place, but
when I post I do tend to make the assumption that we are restricting
our discussions to normal, competent gear and not the pathological
stuff.

d

--
Pearce Consulting
http://www.pearce.uk.com

[[email protected]]

Mr.T wrote:
"Don Pearce" wrote in message
...
Actually, I have just realised you design is isobaric, so you only
have the area of two drivers shifting air - that means the one big
speaker will shift 8 times as much air as the four in your design.

And of course for the frequencies covered by a sub, cone ripple is a
non-problem.

Whilst I often prefer one big driver myself, you cannot say cone break-up is
a non issue just because it's a sub.
If you put in a 30 Hz sine wave, you do not want *any* other frequency
coming out. Something that will surely happen with any cone break-up.

No, it will NOT "surely happen." The production of other
frequencies is the result of non-linearities. "cone nreakup"
is simply the result of the fact that the material the cone is
made of is neither infinitely stiff nor does it have infinite
mechanical propogation velocity. That doesn't make it
nonlinear. It only makes it non-ideal in the frequency
domain.

You have a LOT more sources of nonlinearity vefore you
even have to worry about what the cone is doing

Just because the speaker is operating in the piston
area does not mean there is no possibility of any
spurious output.

That's true, and in a sense catradicts what you just said.

[[email protected]]

James Lehman wrote:
But as I said, you are detailing potential problems with woofers which
have to handle all those harmonics, but the subject is subwoofers,
which don't.

If you put a 55Hz pure sine wave into your sub woofer it will create the
second and third harmonic as distortion. It has nothing to do with the
crossover or whether this woofer is supposed to cover these frequencies or
not. The woofer itself is creating those tones as distortion.

That's true, and it's due primarily to the non-linear behavior
of the motor and suspension system,, so limiting the
incoming bandwidth DOES NOT reduce teir effects.

One of the
possible advantages of isobaric coupling is that the woofers can be
positioned in opposite directions and wired out-of-phase. This has the
effect of balancing the forces that act on the cone to be symmetrical in
their positive and negative motion. This means that any malformation of the
waveform they reproduce will be the same in both the negative and positive
swing, which dramatically reduces even order harmonics; the strongest of
which is the second; the octave.

Unfortunately, you failed to take the next step in your
analysis, which is that it converts the non-symmetrial
non-linearity, which produce even orders of distortion,
into symmetrical non-linearities, which produce ODD
order distortions. The use of face-to-face or back-to-
back isobarics is NOT the same as mirror config-
urations of square-law device, such as triodes. In
square law devices (those whose transfer functions
are continuous 2nd order functions of the input,
where the "square" term predominates) DO benefit
in reduced non-linearity by such mirror or "push-pull"
arrangements.

Unfortunately, the transfer function of the vast majority
of loudspeaker drivers is FAR from square-law, and,
in fact, are such that the push-pull arrangement merely
converts the problem from high-levevls of even to high
levels of odd distortion.

If, then, the premise is that the second order distortion
produced by subwoofers is bad because it falls at a
higher frequency that's more easily detected by ears,
than a push-pull arragement, by the same logic, can
be argued as worse, becuase it puts the distortion
products at even higher frequencies.

[[email protected]]

James Lehman wrote:
But if the cone is not malforming at 50Hz.....

It is.

It likely IS NOT. "Cone malformation" IS NOT the source
of the non-linearity. The predominate source is the
non-linearity of the motor and the non-linearity of the
suspension.

As you go lower in frequency, two things are happening:

1. The cone excursion for a given SPL increases, pushing
the motor and suspension farther into their non-linear
regions,

2. Getting closer and closer to the mechanicla resonance
means the speaker is moving closer to the stiffness
controlled region of operation. As you move higher and
higher above resonance, the speaker moves more into
the mass-controlled region of operation, and the non-
linearity of the suspension becomes less and less
relevant. Moving lower into the stiffness controlled region
means the suspesion nonlinearity becomes more and
more dominant.

One of you is right, it's NOT about "cone breakup." The
other is right, too, there are non-linearities that being a
"subwoofer" is no exemption from.

[[email protected]]

Don Pearce wrote:
On Mon, 31 Jul 2006 20:36:07 +1000, "Mr.T" MrT@home wrote:


"Don Pearce" wrote in message
...
You just need to look at the frequency response of a subwoofer driver
to see where cone breakup starts, and it is generally in the high
hundreds of Hz - perhaps 1kHz for some. Since the maximum frequency
you put into a subwoofer is below 100Hz, we are safe in assuming that
cone breakup is *not* a problem with subwoofers.

There's your problem. Instead of *"assuming"*, some makers use laser
interferometry to actually show the cone breakup for various materials, then
they can select what to use.

Laser interferometry is a useful diagnostic tool for fixing cone
breakup when it occurs, but it is not necessary for identifying it -
the frequency response will do that for you.

No, it can't. You can't look at a frequency response curve and
say "oh, that's cone breakup that's causing that." There are a
lot of things that affect frequency response and, indeed, simple
frequency response is among the least revealing of tests for
higher-order phenomenon.

Cone breakup effects, diffraction effects and interference
effects all can mimic one another and can and often do
occur over similar ranges of frequency. They also have
spacial variations as well.

So, what's in the frequency response that unambiguously
indicates cone breakup as the root cause?

[Don Pearce]

On 31 Jul 2006 07:41:15 -0700, wrote:


Don Pearce wrote:
On Mon, 31 Jul 2006 20:36:07 +1000, "Mr.T" MrT@home wrote:


"Don Pearce" wrote in message
...
You just need to look at the frequency response of a subwoofer driver
to see where cone breakup starts, and it is generally in the high
hundreds of Hz - perhaps 1kHz for some. Since the maximum frequency
you put into a subwoofer is below 100Hz, we are safe in assuming that
cone breakup is *not* a problem with subwoofers.

There's your problem. Instead of *"assuming"*, some makers use laser
interferometry to actually show the cone breakup for various materials, then
they can select what to use.

Laser interferometry is a useful diagnostic tool for fixing cone
breakup when it occurs, but it is not necessary for identifying it -
the frequency response will do that for you.

No, it can't. You can't look at a frequency response curve and
say "oh, that's cone breakup that's causing that." There are a
lot of things that affect frequency response and, indeed, simple
frequency response is among the least revealing of tests for
higher-order phenomenon.

Cone breakup effects, diffraction effects and interference
effects all can mimic one another and can and often do
occur over similar ranges of frequency. They also have
spacial variations as well.

So, what's in the frequency response that unambiguously
indicates cone breakup as the root cause?

OK- you're right. But it is possible to forecast probable modes in the
cone (I imagine bell modes would be the simplest) and match them to
bumps in the frequency response curve. Interferometry would confirm
what was going on.

d

--
Pearce Consulting
http://www.pearce.uk.com

[Mr.T]

wrote in message
oups.com...
And of course for the frequencies covered by a sub, cone ripple is a
non-problem.

Whilst I often prefer one big driver myself, you cannot say cone
break-up is
a non issue just because it's a sub.
If you put in a 30 Hz sine wave, you do not want *any* other frequency
coming out. Something that will surely happen with any cone break-up.

No, it will NOT "surely happen."

Fair point.

The production of other
frequencies is the result of non-linearities. "cone nreakup"
is simply the result of the fact that the material the cone is
made of is neither infinitely stiff nor does it have infinite
mechanical propogation velocity.

Exactly.

You have a LOT more sources of nonlinearity vefore you
even have to worry about what the cone is doing

So true, but I was only responding to the cone comment.

MrT.

[Arny Krueger]

"James Lehman" wrote in message
. ..

"Don Pearce" wrote in message
...
On 29 Jul 2006 01:54:24 -0700, wrote:

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers .....

You can get high excursion drivers with small cones that have very low
resonances.

Within limits. The maximum ratio of excursion to diameter of woofers tends
to be constant or increase as woofer diameter increases. IOW, smaller
woofers tend to have smaller excursions. This is because maximum excursion
is based on geometry, and as you make something larger, the maximum
excursion tends to incrase accordingly.

I don't believe that there are *any* 4" drivers with 1" Xmax, for example.
But, there are a number of drivers in the 12-18" range that do have 1" or
greater Xmax.

The only problem is that it takes a large surface area to push
enough air at those freqs to produce any appreciable volume.

That's not the only problem, for the reason just given.

That's where using multiple drivers in the same baffle comes in.

There aren't a lot of really good justifications for using multiple drivers.
One is availability. IOW, if you have 4 10 inchers on hand and can't easily
liquidate them, you just might want to use them. Another reason would be a
desire to minimize the depth of the enclosure.

[Arny Krueger]

"James Lehman" wrote in message
news
With large cone woofers it is not uncommon that the force that is applied
at
the center of the cone causes forward motion that warps the cone for a
brief
period of time before that force can propagate out to the edge of the
cone.

This happens with any diaphragm that is driven at a point, or a small
portion of the total area of the cone. Whether or not this causes a problem
depends on the equipment and the application.

Since the topic is subwoofers, it is safe to say that no driver under 18"
will have significant problems due to this.

A similar, but different distortion of the cone may occur as the cone is
pulled back into the magnet gap. Any distortion of the cone during its
travel will cause some kind of distortion in the sound that it produces.

Not generally true, as there can be either linear or nonlinear deformations
of the cone. Linear deformations don't cause nonlinear distortion.

Just about any malformation of a sine wave results in harmonics;

Absolutely false as stated.

As a matter of
fact, a fairly large portion of the audible signal coming from most
woofers
is going to be second and third harmonics.

Depends what you call "large" I call 10% large, and there are tons of
woofers that perform better than this.

[[email protected]]

Mr.T wrote:
wrote in message
oups.com...
And of course for the frequencies covered by a sub, cone ripple is a
non-problem.

Whilst I often prefer one big driver myself, you cannot say cone
break-up is
a non issue just because it's a sub.
If you put in a 30 Hz sine wave, you do not want *any* other frequency
coming out. Something that will surely happen with any cone break-up.

No, it will NOT "surely happen."
The production of other
frequencies is the result of non-linearities. "cone nreakup"
is simply the result of the fact that the material the cone is
made of is neither infinitely stiff nor does it have infinite
mechanical propogation velocity.

Exactly.

Exactly what?

Non-ideal materials, in that they do not have infinite stiffness
or propogation velocity, does NOT, a priori, mean that the
resulting flexure and deformation of the cone under stimulus
results in the production of spurious frequencies. This is
ONLY the case if such flexure is non-linear in nature.

[GregS]

In article , "Arny Krueger" wrote:

"James Lehman" wrote in message
...

"Don Pearce" wrote in message
...
On 29 Jul 2006 01:54:24 -0700, wrote:

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers .....

You can get high excursion drivers with small cones that have very low
resonances.

Within limits. The maximum ratio of excursion to diameter of woofers tends
to be constant or increase as woofer diameter increases. IOW, smaller
woofers tend to have smaller excursions. This is because maximum excursion
is based on geometry, and as you make something larger, the maximum
excursion tends to incrase accordingly.

I don't believe that there are *any* 4" drivers with 1" Xmax, for example.
But, there are a number of drivers in the 12-18" range that do have 1" or
greater Xmax.

The only problem is that it takes a large surface area to push
enough air at those freqs to produce any appreciable volume.

That's not the only problem, for the reason just given.

That's where using multiple drivers in the same baffle comes in.

There aren't a lot of really good justifications for using multiple drivers.
One is availability. IOW, if you have 4 10 inchers on hand and can't easily
liquidate them, you just might want to use them. Another reason would be a
desire to minimize the depth of the enclosure.


You might also buy 4- 12 or 15 inch drivers that are relatively cheap to
begin with and are on sale. So by using 4 rather than two or one, you can
get more efficiency, more power handling, and less distortion, than the one
alone. Of course the 4 10 inch isobarik can really be small in size, as is
also the case with the 12's or 15's.

greg

[[email protected]]

Don Pearce wrote:
On 31 Jul 2006 07:41:15 -0700, wrote:
Laser interferometry is a useful diagnostic tool for fixing cone
breakup when it occurs, but it is not necessary for identifying it -
the frequency response will do that for you.

No, it can't. You can't look at a frequency response curve and
say "oh, that's cone breakup that's causing that." There are a
lot of things that affect frequency response and, indeed, simple
frequency response is among the least revealing of tests for
higher-order phenomenon.

Cone breakup effects, diffraction effects and interference
effects all can mimic one another and can and often do
occur over similar ranges of frequency. They also have
spacial variations as well.

OK- you're right. But it is possible to forecast probable modes in the
cone (I imagine bell modes would be the simplest) and match them to
bumps in the frequency response curve.

Yeah, were it even remotely that simple and easy.

Prediction, simulation and analysis of non-ideal cone
behavior has been something that has occupied many
pages of hournals such as the JAES over several decades,
and the ability to do what you claim is only a fairly recent
moderate success using finite element and finite boundary
analysis techniques. It's devlishly difficult to do right, just
like loudspeaker measurements in general are.

Interferometry would confirm what was going on.

Interferometry was the early leader in DIAGNOSING non-
ideal cone behavior, NOT in confirming it. We knew LONG
before then it was happening, we just didn't know ANY
details. And attempts at simple analysis such as basing
things on bell mode assumptions resulted in guesses
that did not correlate well with reality. To be successful,
it requires intimate detailed knowledge of the behavior
of the materials being used, and we did not have sufficient
data in hand of such behavior for simple models such as
this to work.

[GregS]

In article , (GregS) wrote:
In article , "Arny Krueger"
wrote:

"James Lehman" wrote in message
m...

"Don Pearce" wrote in message
...
On 29 Jul 2006 01:54:24 -0700, wrote:

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers .....

You can get high excursion drivers with small cones that have very low
resonances.

Within limits. The maximum ratio of excursion to diameter of woofers tends
to be constant or increase as woofer diameter increases. IOW, smaller
woofers tend to have smaller excursions. This is because maximum excursion
is based on geometry, and as you make something larger, the maximum
excursion tends to incrase accordingly.

I don't believe that there are *any* 4" drivers with 1" Xmax, for example.
But, there are a number of drivers in the 12-18" range that do have 1" or
greater Xmax.

The only problem is that it takes a large surface area to push
enough air at those freqs to produce any appreciable volume.

That's not the only problem, for the reason just given.

That's where using multiple drivers in the same baffle comes in.

There aren't a lot of really good justifications for using multiple drivers.
One is availability. IOW, if you have 4 10 inchers on hand and can't easily
liquidate them, you just might want to use them. Another reason would be a
desire to minimize the depth of the enclosure.


You might also buy 4- 12 or 15 inch drivers that are relatively cheap to
begin with and are on sale. So by using 4 rather than two or one, you can
get more efficiency, more power handling, and less distortion, than the one
alone. Of course the 4 10 inch isobarik can really be small in size, as is
also the case with the 12's or 15's.

Its been said above, but I'll repeat. For a given driver, one way to sort of
make it bulletproof for power, is to put two in series. It vertually
quadruples the rating.

Another metod of using multiple woofers is to combine the outputs
into a common chamber, so the outputs combine and yet the exit
is much smaller than the total woofers area, and can be used to
get more even SPL out at and gain better dispersion.

greg

[GregS]

In article , (GregS) wrote:
In article , (GregS)
wrote:
In article , "Arny Krueger"
wrote:

"James Lehman" wrote in message
om...

"Don Pearce" wrote in message
...
On 29 Jul 2006 01:54:24 -0700, wrote:

But I have to ask - is there any particular reason why you need four
ten inch drivers? In subs, a low resonant frequency is very important,
and you just don't get that from small drivers .....

You can get high excursion drivers with small cones that have very low
resonances.

Within limits. The maximum ratio of excursion to diameter of woofers tends
to be constant or increase as woofer diameter increases. IOW, smaller
woofers tend to have smaller excursions. This is because maximum excursion
is based on geometry, and as you make something larger, the maximum
excursion tends to incrase accordingly.

I don't believe that there are *any* 4" drivers with 1" Xmax, for example.
But, there are a number of drivers in the 12-18" range that do have 1" or
greater Xmax.

The only problem is that it takes a large surface area to push
enough air at those freqs to produce any appreciable volume.

That's not the only problem, for the reason just given.

That's where using multiple drivers in the same baffle comes in.

There aren't a lot of really good justifications for using multiple drivers.
One is availability. IOW, if you have 4 10 inchers on hand and can't easily
liquidate them, you just might want to use them. Another reason would be a
desire to minimize the depth of the enclosure.


You might also buy 4- 12 or 15 inch drivers that are relatively cheap to
begin with and are on sale. So by using 4 rather than two or one, you can
get more efficiency, more power handling, and less distortion, than the one
alone. Of course the 4 10 inch isobarik can really be small in size, as is
also the case with the 12's or 15's.

Its been said above, but I'll repeat. For a given driver, one way to sort of
make it bulletproof for power, is to put two in series. It vertually
quadruples the rating.

Another metod of using multiple woofers is to combine the outputs
into a common chamber, so the outputs combine and yet the exit
is much smaller than the total woofers area, and can be used to
get more even SPL out at and gain better dispersion.

Manifold, was the term I was trying to think of, not chamber.

greg

[James Lehman]

If, then, the premise is that the second order distortion
produced by subwoofers is bad because it falls at a
higher frequency that's more easily detected by ears,
than a push-pull arragement, by the same logic, can
be argued as worse, becuase it puts the distortion
products at even higher frequencies.


Use a little imagination here.....

Wiki triangle wave:
....odd harmonics of the fundamental, multiplying every (4n?1)th harmonic by
?1 (or changing its phase by ?), and rolling off the harmonics by the
inverse square of their relative frequency to the fundamental.

Even if you deformed a pure sine wave into a triangle wave; which is a
discontinuous function and has sharp points in the transitions, the first
audible harmonic, the natural third, is only 1/9 th of the fundamental.

The point is that if you can eliminate even orders then your first audible
harmonic is one step farther away from the fundamental and therefore, is of
much less magnitude.

James. )

[James Lehman]

Just about any malformation of a sine wave results in harmonics;

Absolutely false as stated.

Prove it.

James. )

[[email protected]]

James Lehman wrote:
If, then, the premise is that the second order distortion
produced by subwoofers is bad because it falls at a
higher frequency that's more easily detected by ears,
than a push-pull arragement, by the same logic, can
be argued as worse, becuase it puts the distortion
products at even higher frequencies.
Use a little imagination here.....

Wiki triangle wave:
...odd harmonics of the fundamental, multiplying every (4n?1)th harmonic by
?1 (or changing its phase by ?), and rolling off the harmonics by the
inverse square of their relative frequency to the fundamental.

What does that have to do with the nonlinear behavior of
loudspeakers?

Even if you deformed a pure sine wave into a triangle wave; which is a
discontinuous function

Only if the series is carried to an infinite number of terms,
it is.

and has sharp points in the transitions, the first
audible harmonic, the natural third, is only 1/9 th of the fundamental.

That under the rather dubious assumption that the non-
linearities of a speaker approximate those of a triangle
wave. They most assuredly DO NOT.

The point is that if you can eliminate even orders then your first audible
harmonic is one step farther away from the fundamental and therefore, is of
much less magnitude.

Based on some rather dubious assumptions, that is.