I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so should it
be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.
TIA.
Mike.

What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the term
"wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows).

Here's the purpose, and I'm going to start at the basics:

Any cone type speaker (including subwoofers) produces soundwaves both
forward and behind. The sound waves produced behind are 180 degrees
out-of-phase with the sound waves produced in front. This makes sense if
you think about it, as the cone moves forward in the front of the sub, it is
moving backwards behind the sub. This produces a sound wave exactly out of
phase. If these two sound waves were allowed to interact, they would cancel
each other out. This is THE MAIN REASON why enclosures are necessary when
building subwoofer systems, to keep the rear sound waves from canceling out
the waves produced by the front. So inside the subwoofer enclosure,
obviously much sound is being created. The purpose of acoustic wadding or
polyfil is to absorb this sound energy. Why is this important? Because if
you don't you can have very strange acoustic phenomena going on in your
enclosure, the main concern being what are called "standing waves". This
can create strong reinforcement (boosts) at certain frequencies and effect
the motion (and sound) of the cone. Also, you can have cancellation effects
going on inside the enclosure which will again affect the motion of the
cone.

Remember, ideally, the subwoofer enclosure should JUST be a volume of air to
act as a kind of a spring for the subwoofer (acoustic suspension). Ported
enclosures are a little different as they utilize a tuned port to emphasize
certain frequency bands (bass reflex) and this port has the effect of
realigning the sound coming out of the port so they are in-phase with what
is being produced by the front of the sub. Ported enclosures can produce
more SOL (they are a little louder) because they are able to utilize some of
the sound energy that is always lost in a sealed enclosure.

But THE MAIN POINT of any kind of polyfil or "acoustic wadding" or whatever
you want to call it is to try and produce (as close as possible) an anechoic
(no echoes) chamber as echoes CAUSE PROBLEMS (as I already mentioned). I'm
not an engineer so I've probably flubbed a few things, but basically I think
what I have said is correct. I hope this helped.

MOSFET

"Mike G" wrote in message
reenews.net...
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so should
it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.
TIA.
Mike.

"MOSFET" wrote in message
m...
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the
term "wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows).

Here's the purpose, and I'm going to start at the basics:

Any cone type speaker (including subwoofers) produces soundwaves both
forward and behind. The sound waves produced behind are 180 degrees
out-of-phase with the sound waves produced in front. This makes sense if
you think about it, as the cone moves forward in the front of the sub, it
is moving backwards behind the sub. This produces a sound wave exactly
out of phase. If these two sound waves were allowed to interact, they
would cancel each other out. This is THE MAIN REASON why enclosures are
necessary when building subwoofer systems, to keep the rear sound waves
from canceling out the waves produced by the front. So inside the
subwoofer enclosure, obviously much sound is being created. The purpose
of acoustic wadding or polyfil is to absorb this sound energy. Why is
this important? Because if you don't you can have very strange acoustic
phenomena going on in your enclosure, the main concern being what are
called "standing waves". This can create strong reinforcement (boosts) at
certain frequencies and effect the motion (and sound) of the cone. Also,
you can have cancellation effects going on inside the enclosure which will
again affect the motion of the cone.

Remember, ideally, the subwoofer enclosure should JUST be a volume of air
to act as a kind of a spring for the subwoofer (acoustic suspension).
Ported enclosures are a little different as they utilize a tuned port to
emphasize certain frequency bands (bass reflex) and this port has the
effect of realigning the sound coming out of the port so they are in-phase
with what is being produced by the front of the sub. Ported enclosures
can produce more SOL (they are a little louder) because they are able to
utilize some of the sound energy that is always lost in a sealed
enclosure.

But THE MAIN POINT of any kind of polyfil or "acoustic wadding" or
whatever you want to call it is to try and produce (as close as possible)
an anechoic (no echoes) chamber as echoes CAUSE PROBLEMS (as I already
mentioned). I'm not an engineer so I've probably flubbed a few things,
but basically I think what I have said is correct. I hope this helped.

MOSFET

"Mike G" wrote in message
reenews.net...
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so should
it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.
TIA.
Mike.

As a side note, if the speaker is in a box, it isn't infinite baffle.

Rob

Mike G wrote:
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so
should it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.

Well first, you're confusing your terms... "infinite baffle"
installations don't have a cabinet. Such an installation would be like
a speaker mounted in the rear deck of a car. Door speakers are
typically infinite-baffle configuration.

Damping material in a speaker enclosure has the effect of slowing down
the internal sound waves and makes the speaker "think" it's got a larger
box behind it. It's useful in situations where the proper size box for
a given speaker is impractical or won't fit, although it's not an ideal
substitute for a properly sized box.

The stuff you've got would probably work best just lining the inner
walls of the box.

"MOSFET" wrote in message
m...
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the
term "wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows)

Speaker acoustic wadding was how it was described in the shop.

Here's the purpose, and I'm going to start at the basics:

Any cone type speaker (including subwoofers) produces soundwaves both
forward and behind. The sound waves produced behind are 180 degrees
out-of-phase with the sound waves produced in front. This makes sense if
you think about it, as the cone moves forward in the front of the sub, it
is moving backwards behind the sub. This produces a sound wave exactly
out of phase. If these two sound waves were allowed to interact, they
would cancel each other out. This is THE MAIN REASON why enclosures are
necessary when building subwoofer systems, to keep the rear sound waves
from canceling out the waves produced by the front. So inside the
subwoofer enclosure, obviously much sound is being created. The purpose
of acoustic wadding or polyfil is to absorb this sound energy. Why is
this important? Because if you don't you can have very strange acoustic
phenomena going on in your enclosure, the main concern being what are
called "standing waves". This can create strong reinforcement (boosts) at
certain frequencies and effect the motion (and sound) of the cone. Also,
you can have cancellation effects going on inside the enclosure which will
again affect the motion of the cone.

So far I'm with you. It all makes sense.

Remember, ideally, the subwoofer enclosure should JUST be a volume of air
to act as a kind of a spring for the subwoofer (acoustic suspension).
Ported enclosures are a little different as they utilize a tuned port to
emphasize certain frequency bands (bass reflex) and this port has the
effect of realigning the sound coming out of the port so they are in-phase
with what is being produced by the front of the sub. Ported enclosures
can produce more SOL (they are a little louder) because they are able to
utilize some of the sound energy that is always lost in a sealed
enclosure.

A little more technical, but I think I'm still with you. :-)

But THE MAIN POINT of any kind of polyfil or "acoustic wadding" or
whatever you want to call it is to try and produce (as close as possible)
an anechoic (no echoes) chamber as echoes CAUSE PROBLEMS (as I already
mentioned). I'm not an engineer so I've probably flubbed a few things,
but basically I think what I have said is correct. I hope this helped.

Certainly did. So If I've understood correctly. Ideally the volume behind
the cone should be filled as completely as possible without actually
interfering with the movement of the cone.

Thank you. I think I understand speakers a little better now.
Possibly it explains why, with the speaker in an empty cabinet, certain
frequencies seem distorted. Sort of boomy, without any clarity, for want of
a better discription.
Thanks again.
Mike.

"Mike G" wrote in message
reenews.net...
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so
should it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.
TIA.
Mike.

As a side note, if the speaker is in a box, it isn't infinite baffle.

I thaught that was the common name for a sealed speaker enclosure.
Although I understand that technically it is incorrect.
Mike.

"Matt Ion" wrote in message
news:CXGmg.78569$Mn5.60111@pd7tw3no...
Mike G wrote:
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so should
it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.

Well first, you're confusing your terms... "infinite baffle" installations
don't have a cabinet. Such an installation would be like a speaker
mounted in the rear deck of a car. Door speakers are typically
infinite-baffle configuration.

Looks like the terminology might have changed since I dabbled in building
simple home speaker cabinets a good few years ago. There were basically only
two types. Sealed and ported. where the sealed types were known as infinite
baffle.

Damping material in a speaker enclosure has the effect of slowing down the
internal sound waves and makes the speaker "think" it's got a larger box
behind it. It's useful in situations where the proper size box for a
given speaker is impractical or won't fit, although it's not an ideal
substitute for a properly sized box.

I made the box with the internal volume that the speaker manufacturer
recommended for a sealed cabinet.
Had some 20mm multiply wood knocking around so I used that.

The stuff you've got would probably work best just lining the inner walls
of the box.

Thanks. that sounds easy enough. :-)
Mike.

Mike G wrote:

I made the box with the internal volume that the speaker manufacturer
recommended for a sealed cabinet.
Had some 20mm multiply wood knocking around so I used that.

See, that's just asking for problems... plywood flexes too much and can
cause all kinds of nasty issues for a sub box, including weak and/or
boomy bass. The whole idea of enclosing the speaker in a box is so the
sound waves from the back don't cancel out those from the front, and if
the box is going to flex and produce sound waves itself, it sort of
negates the whole purpose.

Medium-density fiberboard (aka MDF or Medite) is the recommended
material. Glue well... don't use nails, use pre-drilled, counter-sunk
screws to put it together, but don't go too nuts with the screws:
they're really only there to hold everything together until the glue
sets up. A good wood glue should produce joints that are stronger than
the wood itself.

"Matt Ion" wrote in message
news:QyKmg.76925$iF6.35576@pd7tw2no...
Mike G wrote:

I made the box with the internal volume that the speaker manufacturer
recommended for a sealed cabinet.
Had some 20mm multiply wood knocking around so I used that.

See, that's just asking for problems... plywood flexes too much and can
cause all kinds of nasty issues for a sub box, including weak and/or boomy
bass.

I know what you mean. I remembered that much from previous experience.
It wasn't ordinary ply I used. It was good quality multi ply, made up of
maybe a dozen layers, and over 3/4" thick. Very strong and very stiff.

The whole idea of enclosing the speaker in a box is so the
sound waves from the back don't cancel out those from the front, and if
the box is going to flex and produce sound waves itself, it sort of
negates the whole purpose.

The box is about 14" square. Tailored to fit my BM. The sound coming through
the ski slot in the back seat.
It's extremely strong and heavy.You could jump up and down on it, and I
doubt it would flex at all..

Medium-density fiberboard (aka MDF or Medite) is the recommended material.
Glue well... don't use nails, use pre-drilled, counter-sunk screws to put
it together, but don't go too nuts with the screws: they're really only
there to hold everything together until the glue sets up. A good wood
glue should produce joints that are stronger than the wood itself.

You're right though. I should have used MDF. The box is far heavier than
than it needs to be, but seeing as I already had the ply I used it. It is
glued and screwed, with 1/2" quadrant glued to the internal corners. Then
sealed with varnish. On reflection its way OTT.
When I get round to it, I may replace it with a lighter box made from MDF.
Thanks for the info though. All useful stuff.
Mike.

In article , "MOSFET" wrote:
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the term
"wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows).

Here's the purpose, and I'm going to start at the basics:

Any cone type speaker (including subwoofers) produces soundwaves both
forward and behind. The sound waves produced behind are 180 degrees
out-of-phase with the sound waves produced in front. This makes sense if
you think about it, as the cone moves forward in the front of the sub, it is
moving backwards behind the sub. This produces a sound wave exactly out of
phase. If these two sound waves were allowed to interact, they would cancel
each other out. This is THE MAIN REASON why enclosures are necessary when
building subwoofer systems, to keep the rear sound waves from canceling out
the waves produced by the front. So inside the subwoofer enclosure,
obviously much sound is being created. The purpose of acoustic wadding or
polyfil is to absorb this sound energy. Why is this important? Because if
you don't you can have very strange acoustic phenomena going on in your
enclosure, the main concern being what are called "standing waves". This
can create strong reinforcement (boosts) at certain frequencies and effect
the motion (and sound) of the cone. Also, you can have cancellation effects
going on inside the enclosure which will again affect the motion of the
cone.

Unless the woofer is reproducing up into the midbass region, stuffing is not required.
The bass frequencies do not need to be damped.

Remember, ideally, the subwoofer enclosure should JUST be a volume of air to
act as a kind of a spring for the subwoofer (acoustic suspension). Ported
enclosures are a little different as they utilize a tuned port to emphasize
certain frequency bands (bass reflex) and this port has the effect of
realigning the sound coming out of the port so they are in-phase with what
is being produced by the front of the sub. Ported enclosures can produce
more SOL (they are a little louder) because they are able to utilize some of
the sound energy that is always lost in a sealed enclosure.

A port is not in phase with the drivers output. Below the frequency where they share
output, most all of the lower bass comes out of the port only.

But THE MAIN POINT of any kind of polyfil or "acoustic wadding" or whatever
you want to call it is to try and produce (as close as possible) an anechoic
(no echoes) chamber as echoes CAUSE PROBLEMS (as I already mentioned). I'm
not an engineer so I've probably flubbed a few things, but basically I think
what I have said is correct. I hope this helped.

Thats true, and stuffing can also damp flimsy enclosurers.
There is another effect of course, a very important one. In that stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important, FOAM.

greg


MOSFET

"Mike G" wrote in message
freenews.net...
I'm a novice as far as audio is concerned, so bear with me.
Have a 12" bass speaker fitted in a homemade infinite baffle cabinet.
Speaker manufacturer recommends cab is filled with acoustic wadding.
Got some wadding. Now I need to know how it should be fitted.
I notice the 3/4" thick stuff I bought is very open and springy. Just
stuffing it in would obviously interfere with the speaker cone, so should
it be cut so it doesn't touch the cone at all, or what?
If someone can point me at a website, or offer any advice.
As an aside what is the effect of having acoustic wadding in a speaker
cabinet?
As opposed to leaving it empty.
TIA.
Mike.

In article QyKmg.76925$iF6.35576@pd7tw2no, Matt Ion wrote:
Mike G wrote:

I made the box with the internal volume that the speaker manufacturer
recommended for a sealed cabinet.
Had some 20mm multiply wood knocking around so I used that.

See, that's just asking for problems... plywood flexes too much and can
cause all kinds of nasty issues for a sub box, including weak and/or
boomy bass. The whole idea of enclosing the speaker in a box is so the
sound waves from the back don't cancel out those from the front, and if
the box is going to flex and produce sound waves itself, it sort of
negates the whole purpose.

There is a factor in the formula for calculating boxes, specifically for
loss. However in sealed boxes, losses can often improve
things. Think if it as a very tiny port.


Medium-density fiberboard (aka MDF or Medite) is the recommended
material. Glue well... don't use nails, use pre-drilled, counter-sunk
screws to put it together, but don't go too nuts with the screws:
they're really only there to hold everything together until the glue
sets up. A good wood glue should produce joints that are stronger than
the wood itself.

I have been building speakers for a long time, and never have yet used MDF.
I'm not saying MDF is not good, its just that there are many considerations
when selecting materials including availability.

greg

In article , "MOSFET" wrote:
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the term


Remember, ideally, the subwoofer enclosure should JUST be a volume of air to
act as a kind of a spring for the subwoofer (acoustic suspension). Ported
enclosures are a little different as they utilize a tuned port to emphasize
certain frequency bands (bass reflex) and this port has the effect of
realigning the sound coming out of the port so they are in-phase with what
is being produced by the front of the sub. Ported enclosures can produce
more SOL (they are a little louder) because they are able to utilize some of
the sound energy that is always lost in a sealed enclosure.

This can be confusing. A port will let the bass out, so to speak. The
actuall efficiency is determined solely by the driver. There
are two classes of drivers, those for sealed boxes, and those for ported,
and of course some inbetween. The port increases the bandwidth
but does not increase efficiency. However a bandpass box can
increase the apparent efficiency by doing it over a narrow range of
frequencies. In other words its response can look like a mountain top
if desired.

greg

In article pKSmg.79978$Mn5.32293@pd7tw3no, Matt Ion wrote:
GregS wrote:
In article QyKmg.76925$iF6.35576@pd7tw2no, Matt Ion
wrote:

Mike G wrote:


I made the box with the internal volume that the speaker manufacturer
recommended for a sealed cabinet.
Had some 20mm multiply wood knocking around so I used that.

See, that's just asking for problems... plywood flexes too much and can
cause all kinds of nasty issues for a sub box, including weak and/or
boomy bass. The whole idea of enclosing the speaker in a box is so the
sound waves from the back don't cancel out those from the front, and if
the box is going to flex and produce sound waves itself, it sort of
negates the whole purpose.


There is a factor in the formula for calculating boxes, specifically for
loss. However in sealed boxes, losses can often improve
things. Think if it as a very tiny port.

Except a port directs a single wavefront in a single direction... a
flexing box radiates in all directions.


Flexing of the box is not usually wanted, especially if
the panels resonate, which is a big problem.

There was a article in Speaker Builder mag, about 20 years ago.
A guy was going over a AR3 speaker which is a sealed box. After
modifying the cone with various treatments, tests were run
after installing the drivers. For a final tune, he started drilling small
holes in the box to reduce the frequency of resonance.

Some of the treatments of the cone, were, installing foam inside
the dust cover. Varnishing the inner area of the cone. Placing foam strips
radially around the cone. These basic steps I have done many times.


Medium-density fiberboard (aka MDF or Medite) is the recommended
material. Glue well... don't use nails, use pre-drilled, counter-sunk
screws to put it together, but don't go too nuts with the screws:
they're really only there to hold everything together until the glue
sets up. A good wood glue should produce joints that are stronger than
the wood itself.


I have been building speakers for a long time, and never have yet used MDF.
I'm not saying MDF is not good, its just that there are many considerations
when selecting materials including availability.

There's been a lot of debate over MDF vs. other materials for speaker
boxes in general; however, we're talking about sub boxes specifically
here. Resonant acoustics of the box itself aren't as much a
consideration as its raw rigidity.

Rigidity is basically wanted for all enclosures. Where MDF shines is
in the midrange where panel resonances color the sound. Drivers exciting the 300-500 Hz
range have the most influence on vibrating the cabinet.

There is another effect of course, a very important one. In that stuffed
enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important,
FOAM.

greg

OK, this might be a gap in my knowledge, but I have ALWAYS been confused by
the assertion that in a box "stuffing acts to increase that volume" to use
your words. To me, that defies the laws of physics and I flat out refuse to
use that term. I have ALWAYS believed that this was just a shorthand way of
describing the effects stuffing can have (reduced acoustical interchange
that causes problems like standing waves) which I DID address in my
explanation. By reducing sound waves bouncing around in a box, THAT IS like
having a larger box. So in a sense, I did cover that in my explanation.

Is there something else I'm missing?

MOSFET

"MOSFET" wrote in message
m...
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the
term "wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows).

http://snipurl.com/s6zd

Mike.

Sure enough, there's the word "wadding", but I noticed the prices were all
in British Pounds. I think the reason I have never heard of it is because
it is a British term.

MOSFET

"Mike G" wrote in message
reenews.net...

"MOSFET" wrote in message
m...
What you are calling "acoustic wadding" I think is the same as adding
padding to the walls of a subwoofer enclosure. I have never heard the
term "wadding" before, hmmm. Another common technique is to fill the sub
enclosure with polyfil (the same stuff as in pillows).

http://snipurl.com/s6zd

Mike.

"MOSFET" wrote in message
news
Sure enough, there's the word "wadding", but I noticed the prices were all
in British Pounds. I think the reason I have never heard of it is because
it is a British term.

There you go. I've added something to your international audio terminology
vocabulary. :-)
I thaught you'd guess I was british from my address.
Anyway, my thanks to you and all the others who replied with helpful
information. Whatever their nationality. :-)
Mike.

Adding loosely packed materials like fiberglass or long fiber wool to
the interior of a box changes the the effective air mass which affects
box resonance. It also absorbs somewhat the higher frequency standing
waves (although in car sub boxes that is rarely an issue) but that is
not the reason for it making the box act acoustically larger, its the
change to resonant mass. That is why materials like the wool or
fiberglass work better than polyfill which has lower mass per given volume.

To the prevous poster, high-quality plywood can make an excellent
enclosure. Generations of DIY home speaker builders have known this, and
in fact a lot of older hifi enclosures are made with plywood. 13-ply
Baltic birch is a lot tougher lb. for lb. than high-density or
medium-density fiberboard. It's mostly the kids raised on car audio in
the 90's and subsequently that think MDF is the god's choice of box
material. It takes more experience and skill to craft a box well with
plywood but it will also probably outlast the MDF box by many years if
you take the time to do it right.

JD

MOSFET wrote:
There is another effect of course, a very important one. In that stuffed
enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important,
FOAM.

greg


OK, this might be a gap in my knowledge, but I have ALWAYS been confused by
the assertion that in a box "stuffing acts to increase that volume" to use
your words. To me, that defies the laws of physics and I flat out refuse to
use that term. I have ALWAYS believed that this was just a shorthand way of
describing the effects stuffing can have (reduced acoustical interchange
that causes problems like standing waves) which I DID address in my
explanation. By reducing sound waves bouncing around in a box, THAT IS like
having a larger box. So in a sense, I did cover that in my explanation.

Is there something else I'm missing?

MOSFET

MOSFET wrote:
There is another effect of course, a very important one. In that stuffed
enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important,
FOAM.

greg


OK, this might be a gap in my knowledge, but I have ALWAYS been confused by
the assertion that in a box "stuffing acts to increase that volume" to use
your words. To me, that defies the laws of physics and I flat out refuse to
use that term. I have ALWAYS believed that this was just a shorthand way of
describing the effects stuffing can have (reduced acoustical interchange
that causes problems like standing waves) which I DID address in my
explanation. By reducing sound waves bouncing around in a box, THAT IS like
having a larger box. So in a sense, I did cover that in my explanation.

Is there something else I'm missing?

Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear"
larger to the driver (internal waves take longer to reflect back).

"coughbull****cough"

Guys, all this hokum-smokum is making me go TWFER on you... I had to
bust out the textbooks. Here's some facts:

Quote: "Chipboard is the densest of all the wood materials and as it
comes in reasonably priced, uniform sheets which resist warping [sic] it
is not surprising that the great majority of speaker cabinets today are
constructed from this material."

Please note emphasis on cost.

Quote: "high quality birch plywood is also frequently encountered as an
alternative to chipboard, although both its 'Q' and more particularly
its cost are greater."

Again, emphasis on cost.

The density of chipboard (MDF is one form of chipboard, and stands for
Medium Density Fiberboard, not High Density)) is given as 0.81 x 10^3,
where plywood is slightly lower at 0.67 x 10^3. Solid oak is between the
two, solid pine well below plywood. Aluminum is rated at 2.6 x 10^3 and
steel at 7.7 x 10^3 yet you do not run into many enclosures made from
those, at least not in car audio. Aluminum is used a lot in small
bookshelf speakers where it provides denser enclosures in small cabinets
than you can build in wood. Concrete, brick, and sand all have better
densities than chipboard but again not used a lot in car audio, although
I did have the privilege once of hearing a Caddy hearse with an
enclosure stuffed full of 15's that was built from two layers of 1" MDF
with sand poured between them. That was one dead enclosure as far as
resonance.

Quote: "Speaker enclosures [sic] may employ self supporting volume
fillers such as wool-felt, resin-bonded fiberglass, or long-haired wool,
these also providing a degree of damping at the fundamental resonance."

This is due to the increased resonant mass which includes box air mass
plus stuffing mass, not because the stuffing "reduces sound waves
bouncing around in a box".

Standing waves are essentially a non-issue in subwoofer enclosures for
cars anyway; they tend to be at higher frequencies than you are sending
the box in the first place, assuming a reasonable LP filter in the
systme ahead of the box. Using damping pads or other means to reduce
coloration caused by box panel vibration is really only meaningful in
full-range systems.

Stuffing the box just lets you push the envelope by a little on box
size, just as using passive radiators lets you tune small boxes to lower
frequencies than a comparable vented box could achieve without extremely
long ports or excessive windage (port noise).

JD
thus endeth the lecture

Matt Ion wrote:

MOSFET wrote:

There is another effect of course, a very important one. In that
stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very
important, FOAM.

greg



OK, this might be a gap in my knowledge, but I have ALWAYS been
confused by the assertion that in a box "stuffing acts to increase
that volume" to use your words. To me, that defies the laws of
physics and I flat out refuse to use that term. I have ALWAYS
believed that this was just a shorthand way of describing the effects
stuffing can have (reduced acoustical interchange that causes problems
like standing waves) which I DID address in my explanation. By
reducing sound waves bouncing around in a box, THAT IS like having a
larger box. So in a sense, I did cover that in my explanation.

Is there something else I'm missing?


Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear"
larger to the driver (internal waves take longer to reflect back).

Adding loosely packed materials like fiberglass or long fiber wool to the
interior of a box changes the the effective air mass which affects box
resonance.

Box resonance? You DON'T WANT the box to resonate!

It also absorbs somewhat the higher frequency standing
waves

I DID address this already.

(although in car sub boxes that is rarely an issue) but that is
not the reason for it making the box act acoustically larger, its the
change to resonant mass. That is why materials like the wool or fiberglass
work better than polyfill which has lower mass per given volume.

Hmmmm. I really don't think changing the resonant mass has a lick to do
with ANYTHING. The ideal speaker enclosure has ABSOLUTELY NO RESONANCE to
it. Have you ever rapped your knuckles against a REALLY EXPENSIVE set of
high-end speakers? It's like knocking on concrete. I mean, THINK ABOUT IT,
if your enclosure is resonating in any way, this represents energy that is
NOT being turned into sound. This is why we use sound dampening material in
our cars, to reduce resonance as this will increase SPL's. Have you ever
been to an SPL competition? You will see these guys leaning against their
cars to try and reduce the body panels from flexing, body panels flexing
wastes energy that SHOULD be sound waves, by leaning against their cars they
can stop the panels from resonating and gain a few more decibels. The same
goes for speakers. I think your explanation has some holes.

MOSFET

Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear" larger
to the driver (internal waves take longer to reflect back).

Thanks Matt. That has always been my suspicion, but I appreciate you
validating my theory.

MOSFET

WHAT THE HELL DOES RESONANCE HAVE TO DO WITH THE INSIDE OF A SUBWOOFER?

Sure, the subwoofer itself has a natural resonant frequency that one needs
to know when calculating T/S parameters. But resonance is a BAD THING when
it comes to enclosures. IT IS WASTED ENERGY!!!! THINK ABOUT IT!

MOSFET

"John Durbin" wrote in message
...
"coughbull****cough"

Guys, all this hokum-smokum is making me go TWFER on you... I had to bust
out the textbooks. Here's some facts:

Quote: "Chipboard is the densest of all the wood materials and as it comes
in reasonably priced, uniform sheets which resist warping [sic] it is not
surprising that the great majority of speaker cabinets today are
constructed from this material."

Please note emphasis on cost.

Quote: "high quality birch plywood is also frequently encountered as an
alternative to chipboard, although both its 'Q' and more particularly its
cost are greater."

Again, emphasis on cost.

The density of chipboard (MDF is one form of chipboard, and stands for
Medium Density Fiberboard, not High Density)) is given as 0.81 x 10^3,
where plywood is slightly lower at 0.67 x 10^3. Solid oak is between the
two, solid pine well below plywood. Aluminum is rated at 2.6 x 10^3 and
steel at 7.7 x 10^3 yet you do not run into many enclosures made from
those, at least not in car audio. Aluminum is used a lot in small
bookshelf speakers where it provides denser enclosures in small cabinets
than you can build in wood. Concrete, brick, and sand all have better
densities than chipboard but again not used a lot in car audio, although I
did have the privilege once of hearing a Caddy hearse with an enclosure
stuffed full of 15's that was built from two layers of 1" MDF with sand
poured between them. That was one dead enclosure as far as resonance.

Quote: "Speaker enclosures [sic] may employ self supporting volume fillers
such as wool-felt, resin-bonded fiberglass, or long-haired wool, these
also providing a degree of damping at the fundamental resonance."

This is due to the increased resonant mass which includes box air mass
plus stuffing mass, not because the stuffing "reduces sound waves bouncing
around in a box".

Standing waves are essentially a non-issue in subwoofer enclosures for
cars anyway; they tend to be at higher frequencies than you are sending
the box in the first place, assuming a reasonable LP filter in the systme
ahead of the box. Using damping pads or other means to reduce coloration
caused by box panel vibration is really only meaningful in full-range
systems.

Stuffing the box just lets you push the envelope by a little on box size,
just as using passive radiators lets you tune small boxes to lower
frequencies than a comparable vented box could achieve without extremely
long ports or excessive windage (port noise).

JD
thus endeth the lecture

Matt Ion wrote:

MOSFET wrote:

There is another effect of course, a very important one. In that
stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important,
FOAM.

greg



OK, this might be a gap in my knowledge, but I have ALWAYS been confused
by the assertion that in a box "stuffing acts to increase that volume"
to use your words. To me, that defies the laws of physics and I flat
out refuse to use that term. I have ALWAYS believed that this was just
a shorthand way of describing the effects stuffing can have (reduced
acoustical interchange that causes problems like standing waves) which I
DID address in my explanation. By reducing sound waves bouncing around
in a box, THAT IS like having a larger box. So in a sense, I did cover
that in my explanation.

Is there something else I'm missing?


Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear" larger
to the driver (internal waves take longer to reflect back).

In article ,
"MOSFET" wrote:

WHAT THE HELL DOES RESONANCE HAVE TO DO WITH THE INSIDE OF A SUBWOOFER?

Sure, the subwoofer itself has a natural resonant frequency that one needs
to know when calculating T/S parameters. But resonance is a BAD THING when
it comes to enclosures. IT IS WASTED ENERGY!!!! THINK ABOUT IT!

MOSFET


Drivers resonate, boxed or not.

Panels of an enclosure resonating are another matter.

--
-Cyrus

*coughcasaucedoprodigynetcough*

Drivers resonate, boxed or not.

Panels of an enclosure resonating are another matter.

Exactly right, well said.

MOSFET

It may be your suspicion, but it is still wrong and is far from being
"validated". Mr. Durbin's explanation is correct. The loose stuffing inside
a box does not make the box appear larger by reducing so-called standing
waves. The concept of how it works is not new and has been studied by
speaker builders for years. Do some research and stop trying to change the
subject by arguing whether resonance is good or bad. That was not what
Durbin was saying.

- RG


"MOSFET" wrote in message
...
Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear" larger
to the driver (internal waves take longer to reflect back).

Thanks Matt. That has always been my suspicion, but I appreciate you
validating my theory.

MOSFET

Not the box, dude, the air mass. When you lower the resonant point of
the air mass by adding stuffing to it, you lower the Fb or tuning point
of the box at the same time. Has the same effect as increasing the box
size assuming the box starts out sized below nominal flat response,
which is typically the case in car enclosures. If it's already sized
above that, increasing the box volume will have the opposite effect, and
make it sound more anemic at low frequencies.

You should forget all this crap about the box panels resonating, as you
have to build a pretty flimsy enclosure for a subwoofer before panel
resonance comes into play. It's an issue for full-range enclosures where
the panel resonance causes coloration at higher frequencies but that's
not going to happen in the sub-100 Hz range where car sub boxes are
being tuned.

Pretty nice rant though, given how wrong you are. I recommend picking up
a copy of Vance Dickason's Loudspeaker Design Cookbook & giving it a
read. I was quoting from another good read on speakers and enclosures,
Collums' High Performance Loudspeaker, but the LDC has a lot more car
audio-specific content.

http://www.amazon.com/gp/product/188...lance&n=283155

JD

MOSFET wrote:
Adding loosely packed materials like fiberglass or long fiber wool to the
interior of a box changes the the effective air mass which affects box
resonance.


Box resonance? You DON'T WANT the box to resonate!

It also absorbs somewhat the higher frequency standing

waves


I DID address this already.

(although in car sub boxes that is rarely an issue) but that is

not the reason for it making the box act acoustically larger, its the
change to resonant mass. That is why materials like the wool or fiberglass
work better than polyfill which has lower mass per given volume.


Hmmmm. I really don't think changing the resonant mass has a lick to do
with ANYTHING. The ideal speaker enclosure has ABSOLUTELY NO RESONANCE to
it. Have you ever rapped your knuckles against a REALLY EXPENSIVE set of
high-end speakers? It's like knocking on concrete. I mean, THINK ABOUT IT,
if your enclosure is resonating in any way, this represents energy that is
NOT being turned into sound. This is why we use sound dampening material in
our cars, to reduce resonance as this will increase SPL's. Have you ever
been to an SPL competition? You will see these guys leaning against their
cars to try and reduce the body panels from flexing, body panels flexing
wastes energy that SHOULD be sound waves, by leaning against their cars they
can stop the panels from resonating and gain a few more decibels. The same
goes for speakers. I think your explanation has some holes.

MOSFET

Resonance is wasted energy?

Jeez, I better dump my JBL L150A's with passive radiators & L112's with
vents, cause they rely on WASTED ENERGY to extend the usable LF response
a good half-octave and that's apparently a BAD THING.

Again, just forget everything you ever heard about box resonance that
somehow manifested itself into a concern about the enclosure panels
vibrating, at least as regards car audio subwoofer applications. It's a
non-issue at these frequency ranges.

You need to crack a book and learn about enclosure physics. What did you
think that abbreviation Fb means? It's the box resonant frequency, and
the mass of air in the box (or in a port for that matter) is what
determines the frequency. Adding stuffing changes that mass, lowering Fb.

I don't understand how any of this is confusing... as RG points out, all
of these issues are well understood in the speaker community for years
now. Any decent text on enclosure design would tell you the same thing I
am.

JD

MOSFET wrote:

WHAT THE HELL DOES RESONANCE HAVE TO DO WITH THE INSIDE OF A SUBWOOFER?

Sure, the subwoofer itself has a natural resonant frequency that one needs
to know when calculating T/S parameters. But resonance is a BAD THING when
it comes to enclosures. IT IS WASTED ENERGY!!!! THINK ABOUT IT!

MOSFET

"John Durbin" wrote in message
...

"coughbull****cough"

Guys, all this hokum-smokum is making me go TWFER on you... I had to bust
out the textbooks. Here's some facts:

Quote: "Chipboard is the densest of all the wood materials and as it comes
in reasonably priced, uniform sheets which resist warping [sic] it is not
surprising that the great majority of speaker cabinets today are
constructed from this material."

Please note emphasis on cost.

Quote: "high quality birch plywood is also frequently encountered as an
alternative to chipboard, although both its 'Q' and more particularly its
cost are greater."

Again, emphasis on cost.

The density of chipboard (MDF is one form of chipboard, and stands for
Medium Density Fiberboard, not High Density)) is given as 0.81 x 10^3,
where plywood is slightly lower at 0.67 x 10^3. Solid oak is between the
two, solid pine well below plywood. Aluminum is rated at 2.6 x 10^3 and
steel at 7.7 x 10^3 yet you do not run into many enclosures made from
those, at least not in car audio. Aluminum is used a lot in small
bookshelf speakers where it provides denser enclosures in small cabinets
than you can build in wood. Concrete, brick, and sand all have better
densities than chipboard but again not used a lot in car audio, although I
did have the privilege once of hearing a Caddy hearse with an enclosure
stuffed full of 15's that was built from two layers of 1" MDF with sand
poured between them. That was one dead enclosure as far as resonance.

Quote: "Speaker enclosures [sic] may employ self supporting volume fillers
such as wool-felt, resin-bonded fiberglass, or long-haired wool, these
also providing a degree of damping at the fundamental resonance."

This is due to the increased resonant mass which includes box air mass
plus stuffing mass, not because the stuffing "reduces sound waves bouncing
around in a box".

Standing waves are essentially a non-issue in subwoofer enclosures for
cars anyway; they tend to be at higher frequencies than you are sending
the box in the first place, assuming a reasonable LP filter in the systme
ahead of the box. Using damping pads or other means to reduce coloration
caused by box panel vibration is really only meaningful in full-range
systems.

Stuffing the box just lets you push the envelope by a little on box size,
just as using passive radiators lets you tune small boxes to lower
frequencies than a comparable vented box could achieve without extremely
long ports or excessive windage (port noise).

JD
thus endeth the lecture

Matt Ion wrote:


MOSFET wrote:


There is another effect of course, a very important one. In that
stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very important,
FOAM.

greg



OK, this might be a gap in my knowledge, but I have ALWAYS been confused
by the assertion that in a box "stuffing acts to increase that volume"
to use your words. To me, that defies the laws of physics and I flat
out refuse to use that term. I have ALWAYS believed that this was just
a shorthand way of describing the effects stuffing can have (reduced
acoustical interchange that causes problems like standing waves) which I
DID address in my explanation. By reducing sound waves bouncing around
in a box, THAT IS like having a larger box. So in a sense, I did cover
that in my explanation.

Is there something else I'm missing?


Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear" larger
to the driver (internal waves take longer to reflect back).

Wow. I just got done reading this entire thread. I can see how it would be
VERY confusing for a newbie!

My general understanding over the years regarding this topic has been this:
If you properly construct a box for your subwoofer, there should be
absolutely zero need for stuffing it. If you've made a box with an internal
volume of .75 cu ft, as recommended by the manufacturer of the subwoofer
you're using (let's assume that the basket volume is a non-issue here), then
adding polyfill stuffing would essentially increase the intermal volume of
the box - lowering the desired tuned frequency. How much this lowers the
frequency, if I remember correctly, is very small....even if one were to
stuff the box almost entirely with loosely-packed polyfill. I wish I could
remember where, but I read about an experiment where they measured output
for boxes with and without stuffing and the audible differences were barely
negligible. Similar results were found to be true over and over with
several different boxes, subs, etc. Anyone remember this?

Anyway, bottom line is this: No one really "needs" to stuff a box. If you
think it sounds better with it, then by all means go for it! I myself have
stuffed my boxes all my life until recently, and the last several I've made
have been completely empty inside and they sound the same, if not better,
than the previous ones. I say put more emphasis on box construction and
less on whether to stuff or not to stuff.

Tony


--
2001 Nissan Maxima SE Anniversary Edition
Clarion DRZ9255 Head Unit, Phoenix Gold ZX475ti, ZX450 and Xenon X1200.1
Amplifiers, Dynaudio System 360 Tri-Amped In Front and Focal 130HCs For Rear
Fill, Image Dynamics IDMAX10 D4 v.3 Sub

2001 Chevy S10 ZR2
Pioneer DEH-P9600MP Head Unit, Phoenix Gold Ti500.4 Amp, Focal 165HC
Speakers & Image Dynamics ID8 D4 v.3 Sub

2006 Mustang GT Coupe
Alpine IVA-D310 DVD Head Unit, Alpine MRA-550 Digital 5.1 Amp, Boston
Acoustics Z-Series Speakers, Alpine SBS-05DC Center Channel Speaker,
Amplified MTX Thunderform Sub

Tony F wrote:
Wow. I just got done reading this entire thread. I can see how it would be
VERY confusing for a newbie!

My general understanding over the years regarding this topic has been this:
If you properly construct a box for your subwoofer, there should be
absolutely zero need for stuffing it. If you've made a box with an internal
volume of .75 cu ft, as recommended by the manufacturer of the subwoofer
you're using (let's assume that the basket volume is a non-issue here), then
adding polyfill stuffing would essentially increase the intermal volume of
the box - lowering the desired tuned frequency. How much this lowers the
frequency, if I remember correctly, is very small....even if one were to
stuff the box almost entirely with loosely-packed polyfill. I wish I could
remember where, but I read about an experiment where they measured output
for boxes with and without stuffing and the audible differences were barely
negligible. Similar results were found to be true over and over with
several different boxes, subs, etc. Anyone remember this?

Anyway, bottom line is this: No one really "needs" to stuff a box. If you
think it sounds better with it, then by all means go for it! I myself have
stuffed my boxes all my life until recently, and the last several I've made
have been completely empty inside and they sound the same, if not better,
than the previous ones. I say put more emphasis on box construction and
less on whether to stuff or not to stuff.

The fact is, you can do all the math, but there's still an element of
voodoo magic to it all. As much care as you put into the design and
construction of the box, the interior of the car is still a major part
of the "SYSTEM" and will have its own effect on the overall bass
production. To some degree, even the positioning and aiming of the sub
and box affects the final outcome. Measuring and quantifying the
acoustics of the SPECIFIC car isn't impossible, but it's damn close to
it, and is certainly far beyond impractical in most cases.

You may build a box exactly to manufacturer specs and stil find it's not
quite right... adding some stuffing may change the resonant frequency
just enough to make it match the car's acoustics better. Then again,
simply turning the whole unit around may make the difference. In the
end a certain degree of hit-and-miss experimentation may be needed to
find the "sweet spot" of the whole setup.

I know in my '87 Accord hatchback, my little 10" JL sub in a 1.2cu.ft.
box doesn't really rattle much on its own - place it right behind the
driver's seat and you barely hear it, let it alone feel it. Stick it in
the back of the hatch, though, with the seats up and the cover panels in
place, and the shape of the car nicely boosts and amplifies the mid-sub
range (80-100Hz) and shakes things quite handily inside the car, yet
without setting off seismographs outside the car.

It may be your suspicion, but it is still wrong and is far from being
"validated". Mr. Durbin's explanation is correct. The loose stuffing
inside a box does not make the box appear larger by reducing so-called
standing waves. The concept of how it works is not new and has been
studied by speaker builders for years. Do some research and stop trying to
change the subject by arguing whether resonance is good or bad. That was
not what Durbin was saying.

Yes, but if I keep the subject narrowly framed around box resonance then I'm
right. You need to do some research regarding debating (the trick is to
answer the question you WISH had been asked, politicians do it ALL THE
TIME). I mean, who wants to be wrong?

MOSFET

OK, OK.

So you're saying adding stuffing reduces the resonance of the volume of air
inside the box (not the box itself). Is that right? And this simulates a
larger box? Is this correct?

MOSFET

"John Durbin" wrote in message
...
Resonance is wasted energy?

Jeez, I better dump my JBL L150A's with passive radiators & L112's with
vents, cause they rely on WASTED ENERGY to extend the usable LF response a
good half-octave and that's apparently a BAD THING.

Again, just forget everything you ever heard about box resonance that
somehow manifested itself into a concern about the enclosure panels
vibrating, at least as regards car audio subwoofer applications. It's a
non-issue at these frequency ranges.

You need to crack a book and learn about enclosure physics. What did you
think that abbreviation Fb means? It's the box resonant frequency, and the
mass of air in the box (or in a port for that matter) is what determines
the frequency. Adding stuffing changes that mass, lowering Fb.

I don't understand how any of this is confusing... as RG points out, all
of these issues are well understood in the speaker community for years
now. Any decent text on enclosure design would tell you the same thing I
am.

JD

MOSFET wrote:

WHAT THE HELL DOES RESONANCE HAVE TO DO WITH THE INSIDE OF A SUBWOOFER?

Sure, the subwoofer itself has a natural resonant frequency that one
needs to know when calculating T/S parameters. But resonance is a BAD
THING when it comes to enclosures. IT IS WASTED ENERGY!!!! THINK ABOUT
IT!

MOSFET

"John Durbin" wrote in message
...

"coughbull****cough"

Guys, all this hokum-smokum is making me go TWFER on you... I had to bust
out the textbooks. Here's some facts:

Quote: "Chipboard is the densest of all the wood materials and as it
comes in reasonably priced, uniform sheets which resist warping [sic] it
is not surprising that the great majority of speaker cabinets today are
constructed from this material."

Please note emphasis on cost.

Quote: "high quality birch plywood is also frequently encountered as an
alternative to chipboard, although both its 'Q' and more particularly its
cost are greater."

Again, emphasis on cost.

The density of chipboard (MDF is one form of chipboard, and stands for
Medium Density Fiberboard, not High Density)) is given as 0.81 x 10^3,
where plywood is slightly lower at 0.67 x 10^3. Solid oak is between the
two, solid pine well below plywood. Aluminum is rated at 2.6 x 10^3 and
steel at 7.7 x 10^3 yet you do not run into many enclosures made from
those, at least not in car audio. Aluminum is used a lot in small
bookshelf speakers where it provides denser enclosures in small cabinets
than you can build in wood. Concrete, brick, and sand all have better
densities than chipboard but again not used a lot in car audio, although
I did have the privilege once of hearing a Caddy hearse with an enclosure
stuffed full of 15's that was built from two layers of 1" MDF with sand
poured between them. That was one dead enclosure as far as resonance.

Quote: "Speaker enclosures [sic] may employ self supporting volume
fillers such as wool-felt, resin-bonded fiberglass, or long-haired wool,
these also providing a degree of damping at the fundamental resonance."

This is due to the increased resonant mass which includes box air mass
plus stuffing mass, not because the stuffing "reduces sound waves
bouncing around in a box".

Standing waves are essentially a non-issue in subwoofer enclosures for
cars anyway; they tend to be at higher frequencies than you are sending
the box in the first place, assuming a reasonable LP filter in the systme
ahead of the box. Using damping pads or other means to reduce coloration
caused by box panel vibration is really only meaningful in full-range
systems.

Stuffing the box just lets you push the envelope by a little on box size,
just as using passive radiators lets you tune small boxes to lower
frequencies than a comparable vented box could achieve without extremely
long ports or excessive windage (port noise).

JD
thus endeth the lecture

Matt Ion wrote:


MOSFET wrote:


There is another effect of course, a very important one. In that
stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very
important, FOAM.

greg



OK, this might be a gap in my knowledge, but I have ALWAYS been
confused by the assertion that in a box "stuffing acts to increase that
volume" to use your words. To me, that defies the laws of physics and
I flat out refuse to use that term. I have ALWAYS believed that this
was just a shorthand way of describing the effects stuffing can have
(reduced acoustical interchange that causes problems like standing
waves) which I DID address in my explanation. By reducing sound waves
bouncing around in a box, THAT IS like having a larger box. So in a
sense, I did cover that in my explanation.

Is there something else I'm missing?


Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear"
larger to the driver (internal waves take longer to reflect back).

If you've made a box with an internal
volume of .75 cu ft, as recommended by the manufacturer of the subwoofer
you're using (let's assume that the basket volume is a non-issue here),
then adding polyfill stuffing would essentially increase the intermal
volume of the box - lowering the desired tuned frequency.

Yes, Tony, but the tuned frequency of what? The volume of air inside the
enclosure? In a sealed enclosure, what effect does the tuning frequency of
the volume of air inside the enclosure make any difference to anything?
That has been my entire point this whole thread. My understanding has
always been that in a sealed enclosure, the volume of air inside a box acts
as a spring to the woofer. That's it. I would think that in a well
constructed enclosure the volume of air inside a box would have the same air
pressure as the outside air. How would the resonant frequency of this
volume of air have any bearing on anything! I'm sorry, I just don't
understand. I'm so confused!

Nick

Yes, but if I keep the subject narrowly framed around box resonance then
I'm right.

MOSFET, you need to do to some research .... not me. Answering the question
you wished had been asked is called a "straw man argument" in debating
circles. Not a good tactic as you automatically lose :-)

BTW, adding loose filling changes the operation of the box from adiabatic to
isothermal. Nothing to do with standing waves as far as changing the
effective cubic volume of the box.

- RG


"MOSFET" wrote in message
...
It may be your suspicion, but it is still wrong and is far from being
"validated". Mr. Durbin's explanation is correct. The loose stuffing
inside a box does not make the box appear larger by reducing so-called
standing waves. The concept of how it works is not new and has been
studied by speaker builders for years. Do some research and stop trying
to change the subject by arguing whether resonance is good or bad. That
was not what Durbin was saying.

Yes, but if I keep the subject narrowly framed around box resonance then
I'm right. You need to do some research regarding debating (the trick is
to answer the question you WISH had been asked, politicians do it ALL THE
TIME). I mean, who wants to be wrong?

MOSFET

MOSFET, you need to do to some research .... not me. Answering the
question you wished had been asked is called a "straw man argument" in
debating circles. Not a good tactic as you automatically lose :-)

I know, I was joking. Jeeez, lighten up.

Smile.

MOSFET

RG wrote:

MOSFET, you need to do to some research .... not me. Answering the question
you wished had been asked is called a "straw man argument" in debating
circles. Not a good tactic as you automatically lose :-)

Yeah, but we're not stuffing the box with straw...

running away...

LOL ... OK, I missed that.

- RG


"MOSFET" wrote in message
m...
MOSFET, you need to do to some research .... not me. Answering the
question you wished had been asked is called a "straw man argument" in
debating circles. Not a good tactic as you automatically lose :-)

I know, I was joking. Jeeez, lighten up.

Smile.

MOSFET

Now there's an idea... who knows, eh ?

- RG


"Matt Ion" wrote in message
news:42kng.90290$Mn5.72320@pd7tw3no...
RG wrote:

MOSFET, you need to do to some research .... not me. Answering the
question you wished had been asked is called a "straw man argument" in
debating circles. Not a good tactic as you automatically lose :-)

Yeah, but we're not stuffing the box with straw...

running away...

It lowers the resonant frequency of the air mass, similar to putting the
sub in a larger box. I don't recall whether the amplitude of the
resonance is altered in the process but the frequency is.

It's not a matter of absorption as I think you may have been thinking,
it's simply changing the behavior of the air mass.

JD

MOSFET wrote:

OK, OK.

So you're saying adding stuffing reduces the resonance of the volume of air
inside the box (not the box itself). Is that right? And this simulates a
larger box? Is this correct?

MOSFET

"John Durbin" wrote in message
...

Resonance is wasted energy?

Jeez, I better dump my JBL L150A's with passive radiators & L112's with
vents, cause they rely on WASTED ENERGY to extend the usable LF response a
good half-octave and that's apparently a BAD THING.

Again, just forget everything you ever heard about box resonance that
somehow manifested itself into a concern about the enclosure panels
vibrating, at least as regards car audio subwoofer applications. It's a
non-issue at these frequency ranges.

You need to crack a book and learn about enclosure physics. What did you
think that abbreviation Fb means? It's the box resonant frequency, and the
mass of air in the box (or in a port for that matter) is what determines
the frequency. Adding stuffing changes that mass, lowering Fb.

I don't understand how any of this is confusing... as RG points out, all
of these issues are well understood in the speaker community for years
now. Any decent text on enclosure design would tell you the same thing I
am.

JD

MOSFET wrote:


WHAT THE HELL DOES RESONANCE HAVE TO DO WITH THE INSIDE OF A SUBWOOFER?

Sure, the subwoofer itself has a natural resonant frequency that one
needs to know when calculating T/S parameters. But resonance is a BAD
THING when it comes to enclosures. IT IS WASTED ENERGY!!!! THINK ABOUT
IT!

MOSFET

"John Durbin" wrote in message
. ..


"coughbull****cough"

Guys, all this hokum-smokum is making me go TWFER on you... I had to bust
out the textbooks. Here's some facts:

Quote: "Chipboard is the densest of all the wood materials and as it
comes in reasonably priced, uniform sheets which resist warping [sic] it
is not surprising that the great majority of speaker cabinets today are
constructed from this material."

Please note emphasis on cost.

Quote: "high quality birch plywood is also frequently encountered as an
alternative to chipboard, although both its 'Q' and more particularly its
cost are greater."

Again, emphasis on cost.

The density of chipboard (MDF is one form of chipboard, and stands for
Medium Density Fiberboard, not High Density)) is given as 0.81 x 10^3,
where plywood is slightly lower at 0.67 x 10^3. Solid oak is between the
two, solid pine well below plywood. Aluminum is rated at 2.6 x 10^3 and
steel at 7.7 x 10^3 yet you do not run into many enclosures made from
those, at least not in car audio. Aluminum is used a lot in small
bookshelf speakers where it provides denser enclosures in small cabinets
than you can build in wood. Concrete, brick, and sand all have better
densities than chipboard but again not used a lot in car audio, although
I did have the privilege once of hearing a Caddy hearse with an enclosure
stuffed full of 15's that was built from two layers of 1" MDF with sand
poured between them. That was one dead enclosure as far as resonance.

Quote: "Speaker enclosures [sic] may employ self supporting volume
fillers such as wool-felt, resin-bonded fiberglass, or long-haired wool,
these also providing a degree of damping at the fundamental resonance."

This is due to the increased resonant mass which includes box air mass
plus stuffing mass, not because the stuffing "reduces sound waves
bouncing around in a box".

Standing waves are essentially a non-issue in subwoofer enclosures for
cars anyway; they tend to be at higher frequencies than you are sending
the box in the first place, assuming a reasonable LP filter in the systme
ahead of the box. Using damping pads or other means to reduce coloration
caused by box panel vibration is really only meaningful in full-range
systems.

Stuffing the box just lets you push the envelope by a little on box size,
just as using passive radiators lets you tune small boxes to lower
frequencies than a comparable vented box could achieve without extremely
long ports or excessive windage (port noise).

JD
thus endeth the lecture

Matt Ion wrote:



MOSFET wrote:



There is another effect of course, a very important one. In that
stuffed enclosure
the manufacture may have specified a volume, and the stuffing acts to
increase that
volume.If you don't stuff that enclosed box, it may be too small.
Stuffing is all very different and has different effects at different
frequencies.
I make use of cotton, wool, fiberglass, and Dacron, and very
important, FOAM.

greg



OK, this might be a gap in my knowledge, but I have ALWAYS been
confused by the assertion that in a box "stuffing acts to increase that
volume" to use your words. To me, that defies the laws of physics and
I flat out refuse to use that term. I have ALWAYS believed that this
was just a shorthand way of describing the effects stuffing can have
(reduced acoustical interchange that causes problems like standing
waves) which I DID address in my explanation. By reducing sound waves
bouncing around in a box, THAT IS like having a larger box. So in a
sense, I did cover that in my explanation.

Is there something else I'm missing?


Nope, you pretty much nailed it. The stuffing DOES have the effect of
slowing down the sound waves as well, which makes the box "appear"
larger to the driver (internal waves take longer to reflect back).

Resonant frequency of the box changes the output of the system at that
frequency, also affects the driver's impedance as it appears to the amp
driving the system, etc. If you sweep the driver impedance curve in free
air & then again in the box and compare the two, you will see a large
change. Think about it this way: in open air the driver compliance is a
combination of factors that includes the relative stiffness of the
spider and the surround. When you put it in a box, the effect of the air
mass (air spring if you will) changes that compliance and your system
tuning changes with it.

This happens in a vented box too but is more complicated because the air
mass behaves differently at port resonance than it does above it.

JD

MOSFET wrote:

If you've made a box with an internal

volume of .75 cu ft, as recommended by the manufacturer of the subwoofer
you're using (let's assume that the basket volume is a non-issue here),
then adding polyfill stuffing would essentially increase the intermal
volume of the box - lowering the desired tuned frequency.


Yes, Tony, but the tuned frequency of what? The volume of air inside the
enclosure? In a sealed enclosure, what effect does the tuning frequency of
the volume of air inside the enclosure make any difference to anything?
That has been my entire point this whole thread. My understanding has
always been that in a sealed enclosure, the volume of air inside a box acts
as a spring to the woofer. That's it. I would think that in a well
constructed enclosure the volume of air inside a box would have the same air
pressure as the outside air. How would the resonant frequency of this
volume of air have any bearing on anything! I'm sorry, I just don't
understand. I'm so confused!

Nick