Exodus Audio Maelstrom-X Pre-Order Thread - Page 4 - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #91 of 480 Old 04-21-2008, 02:13 PM
Advanced Member
 
Krawdad's Avatar
 
Join Date: Aug 2004
Location: Vancouver,Wa
Posts: 526
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
If heat is the real issue addressed by stuffing. Then why is no one suggesting putting chillers, or coolers, in their subwoofers? or some enterprising company creating the Subzero Subwoofer cooler?

Just a thought.
Krawdad is offline  
Sponsored Links
Advertisement
 
post #92 of 480 Old 04-21-2008, 05:14 PM
AVS Special Member
 
Join Date: Mar 2003
Posts: 4,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 606
[quote=noah katz;13693586]
Quote:


bosso,

I don't mean to be a monkey on your back, but...

No problem at all. I've enjoyed your posts for a long time in various forums.

"As the driver heats the air inside the sealed box due to prolonged high SPL operation, when using the types of driver/amp combinations we typically use, the benefits of stuffing to apparent box size decrease."

Quote:


Air temp inside the box isn't relevant to the effective volume increase.

I have to disagree. Heated air expands, so it is relevant to the apparent volume of a trapped volume of air.

"But, this effect will be seen regardless of stuffing and box size."

That I agree with

Quote:


"In a sealed system 1/2 of the total output of the driver is radiated into the trapped air in the box and momentarily stored. Some of that stored energy will be released through the vibration of the box panels. Some of it will be released through the drivers cone, which is the weakest link in the sealed box. Some of it is absorbed and dissipated as heat by stuffing."

The first sentence is correct as fas as acoustic output, but that's about 1% of the energy the driver is putting into the box air.

The other 99% is the going into compressing/rarefacting the air spring, and on every half cycle it's dissipated as heat in the voice coil (mostly) and amp output transistors.

The electrical energy that's lost to heat in the coil is the irrelevant part to this point, as it's never converted into acoustic output before it's converted to heat.

The heat dissipated in the coil, as it raises the temperature of the trapped air is relevant in that it causes the air spring to offer more resistance by expanding the air, or increasing the pressure inside.

Quote:


"In both cases, reduction of the temperature of the trapped air and conversion of stored energy to heat, stuffing is an effective solution to varying degrees."

Again, I don't think these have anything to do with stuffing, other than the stuffing is good insulation and will impede heat xfer to the outside.

Then you'll have to explain exactly how stuffing raises apparent box volume, or what Nousaine means in his original article:

Quote:


The particulars of fiber stuffing are pretty interesting: The air inside your enclosure actually heats up as your woofer moves, making the air stiffer. When the enclosure is stuffed with fiber, the fibers wiggle, dissipating some of the heat and making the system work as though the box were larger. Theoretically, your woofer/box bass system can act like a system that's a maximum of 40 percent larger when you've latched onto the right stuffing recipe - in other words, if you have an enclosure that offers 1 cubic foot (1 ft³ ) of internal volume, in a perfect world a good stuffing job will make it perform like an enclosure that offers 1.4 cubic feet of internal
volume.

Bosso
bossobass is offline  
post #93 of 480 Old 04-21-2008, 06:06 PM
AVS Special Member
 
Looneybomber's Avatar
 
Join Date: Sep 2006
Location: Lawrence, KS
Posts: 4,666
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 23
Quote:
Originally Posted by krawdad View Post

If heat is the real issue addressed by stuffing. Then why is no one suggesting putting chillers, or coolers, in their subwoofers? or some enterprising company creating the Subzero Subwoofer cooler?

I've been pondering ways to cool a voicecoil and motor assembly. Bosso's done a lot more work on that matter though.

Quote:
Originally Posted by bossobass View Post

I have to disagree. Heated air expands, so it is relevant to the apparent volume of a trapped volume of air....The heat dissipated in the coil, as it raises the temperature of the trapped air is relevant in that it causes the air spring to offer more resistance by expanding the air, or increasing the pressure inside.

But our sealed enclosures are not 100% sealed and small amounts of air seep out/in to equalize out the pressure from inside to outside due to temperature changes (expanding the air inside), or barometric pressure changes. If it was 100% sealed, the woofer cone would protrude out or recess into the box...

YID DIY
Looneybomber is offline  
post #94 of 480 Old 04-21-2008, 06:37 PM
Advanced Member
 
04FLHRCI's Avatar
 
Join Date: Dec 2005
Posts: 777
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Bosso,

Thanks for the friendly exchange; I reached out to Phil today, he said XLR I/O and rack ears are no problem - nominal upcharge for each. I'll likely head this direction; hmm, the kit sure seems like a lot of fun too!

Regards,

Larry

[quote=bossobass;13697170]
Quote:
Originally Posted by noah katz View Post


No problem at all. I've enjoyed your posts for a long time in various forums.

"As the driver heats the air inside the sealed box due to prolonged high SPL operation, when using the types of driver/amp combinations we typically use, the benefits of stuffing to apparent box size decrease."



I have to disagree. Heated air expands, so it is relevant to the apparent volume of a trapped volume of air.

"But, this effect will be seen regardless of stuffing and box size."

That I agree with



The electrical energy that's lost to heat in the coil is the irrelevant part to this point, as it's never converted into acoustic output before it's converted to heat.

The heat dissipated in the coil, as it raises the temperature of the trapped air is relevant in that it causes the air spring to offer more resistance by expanding the air, or increasing the pressure inside.



Then you'll have to explain exactly how stuffing raises apparent box volume, or what Nousaine means in his original article:



Bosso

04FLHRCI is offline  
post #95 of 480 Old 04-22-2008, 12:45 AM
AVS Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 20,339
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Liked: 133
"No problem at all. I've enjoyed your posts for a long time in various forums."

I appreciate you being a good sport, and thanks for the kind words.

"I have to disagree. Heated air expands, so it is relevant to the apparent volume of a trapped volume of air."

It's not the apparent volume of the air that matters but the volume of the box.

If the box is perfectly sealed it will push the driver outward until equilibrium is reached.

Even if it didn't, it's not the absolute pressure that determines the effective box volume, it's the ratio pressure change to excursion.

"The electrical energy that's lost to heat in the coil is the irrelevant part to this point, as it's never converted into acoustic output before it's converted to heat."

Fair enough.

"The heat dissipated in the coil, as it raises the temperature of the trapped air is relevant in that it causes the air spring to offer more resistance by expanding the air, or increasing the pressure inside."

That's a preload, not a change in spring stiffness.

Nousaine may know a lot about speakers, but he's obviously not well versed in thermodynamics.

How would "wiggling fibers" increase apparent volume?

They wouldn't; in fact that would be a dissipative loss as was discussed earlier and would reduce output.

"Then you'll have to explain exactly how stuffing raises apparent box volume"

I did in post #79, but here it is again:

"Stuffing for low freq is to increase the effective box volume, the mechanism being absorption of heat from the air during compression, which would otherwise allow a greater heating of the air and consequent pressure rise that resists motion of the driver trying to move inward, and returning it to the air during rarefaction, where otherwise the cooling air would lower the pressure, again fighting the driver which is now moving outward.

Noah
noah katz is offline  
post #96 of 480 Old 04-22-2008, 02:48 AM
Advanced Member
 
Vinculum's Avatar
 
Join Date: Dec 2001
Location: York, Pa
Posts: 942
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
XLR & rack ears for a Bassis... I may now be interested!

Linkwitz suggests a TINY hole drilled into the cabinet of a sealed monopole subwoofer to keep ambient air pressure equalized...
Vinculum is offline  
post #97 of 480 Old 04-22-2008, 03:07 AM
AVS Special Member
 
armystud0911's Avatar
 
Join Date: Jul 2006
Location: Cincinnati
Posts: 4,423
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
lol, just how tiny? Has he tried this? I have, my smallest drill bit was far too big, so I actually pounded a nail in and pulled it out, the hole is so small that I can barely see it, yet, it produces very audible noise, I got rid of it.
armystud0911 is offline  
post #98 of 480 Old 04-22-2008, 03:36 AM
Advanced Member
 
Vinculum's Avatar
 
Join Date: Dec 2001
Location: York, Pa
Posts: 942
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
? 1mm diameter is the size he uses for his 12" Peerless sealed box, "Thor". I recall Darin using some aquarium tubing for the equlization hole in his dual 12" Rythmik box. Maybe this is no longer acceptable when we get to larger, higher displacement drivers? Something must be done to deal with the pressure induced offset of the cone. Are we relying on leaks?
Vinculum is offline  
post #99 of 480 Old 04-22-2008, 03:48 AM
AVS Special Member
 
armystud0911's Avatar
 
Join Date: Jul 2006
Location: Cincinnati
Posts: 4,423
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
There will always be some leaks in the box, you can't construct it to be completely airtight of course, I just rely on imperfection, I haven't had an issue with it yet. I did a dual TC OEM 10 build in a 0.7 cubic foot box and even after several hours of use, the drivers never suffered any sort of blowout. I know a lot of people who never use holes in their car audio subs, furthermore, people with PR subs don't use holes (at least to my knowledge) I am wondering how necessary they actually are, can anyone recall seeing holes in their commercial subs?
armystud0911 is offline  
post #100 of 480 Old 04-22-2008, 04:04 AM
Advanced Member
 
04FLHRCI's Avatar
 
Join Date: Dec 2005
Posts: 777
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Good Morning Dr. V,

Yes, Phil confirmed this for me yesterday; I believe Dave has me convinced here. I'm leaning towards the kit as I really enjoy these types of projects.

Larry

[quote=Vinculum;13699489]XLR & rack ears for a Bassis... I may now be interested!
04FLHRCI is offline  
post #101 of 480 Old 04-22-2008, 04:48 AM
Advanced Member
 
Vinculum's Avatar
 
Join Date: Dec 2001
Location: York, Pa
Posts: 942
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Army, I meant to say < or = to 1mm. The symbol didnt come out when I replied via PDA.

Good deal Larry, I hope the nominal fee isn't too high. Do u plan on a mono or dual unit?
Vinculum is offline  
post #102 of 480 Old 04-22-2008, 05:36 AM
AVS Special Member
 
armystud0911's Avatar
 
Join Date: Jul 2006
Location: Cincinnati
Posts: 4,423
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
I know folks love linkwitz, and he's a bright guy, but come on, a 10" sealed sub with 8mm xmax??? Perhaps he thinks he needs it due to how small the box is (0.5cubic feet). I don't recommend that anyone bother with subs that will do 90dB at 30Hz max output.

BTW, the hole I drilled was .75mm, pretty small, but it was still able to really whistle at high outputs, I initially just stuffed it, but that got sucked back into the sub, then I plugged it entirely. Keep in mind, that sub had two 10" drivers powered with over 3,000watts in an 18l box if ever your gonna have a blowout, it'd be then. I have heard someone who sealed his sub up ridiculously well tell me about his cone sticking out after heavy use, but thats it, one instance.

Darin decided to do his hole after reading the linkwitz link, he took the "better safe than sorry" road. No problem, but the question remains, is it necessary? From all the sealed subs I have seen built, owned or checked out, I have never before seen one with a hole to equalize pressure.
armystud0911 is offline  
post #103 of 480 Old 04-22-2008, 05:41 AM
Advanced Member
 
04FLHRCI's Avatar
 
Join Date: Dec 2005
Posts: 777
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
The XLR upgrade is a little more than I expected; however, when considering the overall package it's not to bad (picking up the kit would offset the upcharge). I would likely go with the dual unit; not initially necessary, but provides me options down the road.

Larry

[quote=Vinculum;Good deal Larry, I hope the nominal fee isn't too high. Do u plan on a mono or dual unit?[/QUOTE]
04FLHRCI is offline  
post #104 of 480 Old 04-22-2008, 07:44 AM
AVS Special Member
 
Looneybomber's Avatar
 
Join Date: Sep 2006
Location: Lawrence, KS
Posts: 4,666
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 23
Quote:
Originally Posted by armystud0911 View Post

From all the sealed subs I have seen built, owned or checked out, I have never before seen one with a hole to equalize pressure.

There's really no need to. Enough air seeps out through the mounting hardware and other places that our "leakage" quota is met without a pinhole.

There was that one sub you're refering to that had that problem. I remember he chamfered around his mounting hardware and used rubber seals, then put teflon on the threads. I think he caulked the seems too. Crazy stuff like that.
http://www.htguide.com/forum/showthr...ghlight=sealed

YID DIY
Looneybomber is offline  
post #105 of 480 Old 04-22-2008, 11:01 AM
AVS Special Member
 
Join Date: Mar 2003
Posts: 4,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 606
Quote:


"Stuffing for low freq is to increase the effective box volume, the mechanism being absorption of heat from the air during compression, which would otherwise allow a greater heating of the air and consequent pressure rise that resists motion of the driver trying to move inward, and returning it to the air during rarefaction, where otherwise the cooling air would lower the pressure, again fighting the driver which is now moving outward.
__________________

Quote:


If the box is perfectly sealed it [heat from the VC] will push the driver outward until equilibrium is reached.

Different cause (heat from cone movement inward vs radiated heat from VC), same result (pressure rise).

Both causes have similar enough results as to be insufficient to push the cone outward when at rest. More accurately, both have similar enough results as to be sufficient to push the cone outward when at rest, it's just not and obvious phenomenon.

IOW, it's the rise in the temperature of the trapped air. How that temperature is increased is irrelevant.

You could also say: It's the rise in psi. The cause of the increase is irrelevant. (Because the same result occurs from a change in barometric pressure, stuffing be damned).

Quote:


Nousaine may know a lot about speakers, but he's obviously not well versed in thermodynamics.

How would "wiggling fibers" increase apparent volume?



Bosso
bossobass is offline  
post #106 of 480 Old 04-22-2008, 11:24 AM
AVS Special Member
 
Join Date: Mar 2003
Posts: 4,509
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 606
Quote:
Originally Posted by 04FLHRCI View Post

Bosso,

Thanks for the friendly exchange; I reached out to Phil today, he said XLR I/O and rack ears are no problem - nominal upcharge for each. I'll likely head this direction; hmm, the kit sure seems like a lot of fun too!

Regards,

Larry

Always a pleasure to talk with you.

I talked to Phil last night (the guy is always there. He loves what he does) and ordered another Bassis for a client's system. He's a riot. I asked him what kind of music he likes, and he told me: "I don't listen to music, I just build the hardware".

Looking forward to your build. I think the Maelstrom-X will make a great system. The 2 channel Bassis should rack mount nicely and balanced I/O (or RCA ins and XLR outs) works great with pro amps.

Bosso
bossobass is offline  
post #107 of 480 Old 04-22-2008, 12:05 PM
Member
 
cluelessngr's Avatar
 
Join Date: Feb 2008
Posts: 81
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:


"Stuffing for low freq is to increase the effective box volume, the mechanism being absorption of heat from the air during compression, which would otherwise allow a greater heating of the air and consequent pressure rise that resists motion of the driver trying to move inward, and returning it to the air during rarefaction, where otherwise the cooling air would lower the pressure, again fighting the driver which is now moving outward.

I keep hearing over and over how the stuffing "absorbs heat".....HUH? If heat absorbtion/dissipation was what we wanted, we would be using heat sinks and peltiers, not fiberglass batting. Fiberglass is an insulator, quite frankly it sucks for absorbing heat, its designed to keep heat in, after all that is what makes it an insulator. Then I hear about the "fibers" and alledged effect that they take sound energy and through movement transfer some of this accoustical energy into heat. What about the non-fibrous batting materials? I'm sorry but this just doesn't make any sense. If we wanted to help dissipate heat from within the enclosure the LAST thing we would want to do is add fiberglass batting. What minimal (ie: extremly minimal) heat that would be dissipated by the fibers would be greatly overcome by the increased heat of the voicecoil and its inability to dissipate heat in an insulated enclosure.

What I think is actually happening here is that a semi-porous material (such as fiberglass or polyfill) is effectively creating more surface area, causing alot more defractions in a multitude of directions and this is what is making the enclosure appear larger.
cluelessngr is offline  
post #108 of 480 Old 04-22-2008, 12:12 PM
AVS Special Member
 
TheEAR's Avatar
 
Join Date: Nov 2006
Location: Montreal,CANADA
Posts: 3,464
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
Stuffing absorbs heat!

Even if fiberglass is an insulator

Stuffing is made of material(say fiberglass),obviously this material will absorb some heat(even as minute as it may be).

One solution would be to run a type of heatpipe from the motor to the outside of the box.Could be forced air in the pipe passing in a coil around the motor.Lets say the heat absorption by stuffing is too low to benefit much when a driver is pushed for extended periods of time.

The simple and effective method is a alu cone ,just like the ones used by TC Sounds and a few others. Somple and effective way to dissipate heat to the outside.

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
TheEAR is offline  
post #109 of 480 Old 04-22-2008, 12:23 PM
AVS Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 20,339
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 75 Post(s)
Liked: 133
"the hole is so small that I can barely see it, yet, it produces very audible noise, I got rid of it."

I'd stuff it w/foam, if I wasn't a poor enough craftsman to not have to worry about perfect sealing.

bosso,

"IOW, it's the rise in the temperature of the trapped air. How that temperature is increased is irrelevant.

You could also say: It's the rise in psi. The cause of the increase is irrelevant."

But what's your point? It still has no bearing on the effective volume increase.

cluelessngr,

You missed the point (did you read my explanation?).

The point is not to get rid of heat in the long term, it's to absorb and return it to the air so to reduce the instantaneous temperature changes due to instaneous pressure changes.

Noah
noah katz is offline  
post #110 of 480 Old 04-22-2008, 12:52 PM
AVS Special Member
 
Looneybomber's Avatar
 
Join Date: Sep 2006
Location: Lawrence, KS
Posts: 4,666
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 23
Quote:
Originally Posted by cluelessngr View Post

I keep hearing over and over how the stuffing "absorbs heat".....HUH? If heat absorbtion/dissipation was what we wanted, we would be using heat sinks and peltiers, not fiberglass batting. Fiberglass is an insulator, quite frankly it sucks for absorbing heat.

This is the perfect time for you to do some experimentation. Fiberglass vs. polyester vs. steel wool. The steel wool should absorb and release more heat than any of the other two options right?

Here's another thing to ponder, SF6 gas (Sulfur Hexafluoride) effectively increases enclosure volumes by 2700% over regular air.

YID DIY
Looneybomber is offline  
post #111 of 480 Old 04-22-2008, 01:00 PM
Member
 
cluelessngr's Avatar
 
Join Date: Feb 2008
Posts: 81
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I understand...this is what you said and my understanding of what you are saying. (perhaps it is my interpretation of what you are saying is wrong).

Quote:


"Stuffing for low freq is to increase the effective box volume, the mechanism being absorption of heat from the air during compression, which would otherwise allow a greater heating of the air and consequent pressure rise that resists motion of the driver trying to move inward, and returning it to the air during rarefaction, where otherwise the cooling air would lower the pressure, again fighting the driver which is now moving outward.

Ok now
1) "the mechanism being absorption of heat from the air during compression"
As I understand this as the driver moves inward air is compressed, this compression cause heat. This I agree with. This is however not to be confused with acoustical energy being transfed into heat. Addtionally you are saying that this heat is not dissipated, but in fact stored within the batting material.

2)which would otherwise allow a greater heating of the air and consequent pressure rise that resists motion of the driver trying to move inward.
The concept of heated air increases pressure I can understand. However, without significant dissipation i don't understand how it prevents "greater heating"

3)and returning it to the air during rarefaction, where otherwise the cooling air would lower the pressure, again fighting the driver which is now moving outward.
Again, if it hasn't been disipated and returns to the air during rarefaction it has undergone an increase in temperature from its original state (before compression). Thus with each full cycle of the speaker cone we get a net result of an increase in temperature every cycle unless the heat is dissipated within the batting.

And once again I still say, if it is heat we are fighting within the enclosure, all this would be mute as the fiberglass acting as in insulator is effectively not allowing disspation of heat created from the voice coil itself.
cluelessngr is offline  
post #112 of 480 Old 04-22-2008, 01:10 PM
Member
 
cluelessngr's Avatar
 
Join Date: Feb 2008
Posts: 81
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:


This is the perfect time for you to do some experimentation. Fiberglass vs. polyester vs. steel wool. The steel wool should absorb and release more heat than any of the other two options right?

In order to "absorb" heat you have to transfer it somewhere else (dissipate it) otherwise the material that you are using to absorb it quickly becomes saturated and of little use. Maybe I should just design a box with my GF's cold feet within the enclosure that way I could get good sound and some sleep at night! ;P
cluelessngr is offline  
post #113 of 480 Old 04-22-2008, 01:15 PM
AVS Special Member
 
TheEAR's Avatar
 
Join Date: Nov 2006
Location: Montreal,CANADA
Posts: 3,464
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
From Maelstrom-X preorder thread to some stuffing debate.

This train is off the tracks and falling off the cliff...

Leave the box empty or stuff the box with acoustic absorbing material the end result will be close.Heat has to be evacuated at one point as the material will be saturated quickly.

Some people like splitting a hair in eight and see how much they gain.

Ask yourself mortal , do you have as much displacement as me ? The answer is no unless you have a Windmere fan sub.
TheEAR is offline  
post #114 of 480 Old 04-22-2008, 01:57 PM
AVS Special Member
 
Mark Seaton's Avatar
 
Join Date: Jul 2000
Location: Chicago, IL, USA
Posts: 5,972
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 187
Hmm... Sounds like a lot of hot air in here.

Noah's explanation is correct.

Quote:
Originally Posted by cluelessngr View Post

I understand...this is what you said and my understanding of what you are saying. (perhaps it is my interpretation of what you are saying is wrong).

Quote:


"Stuffing for low freq is to increase the effective box volume, the mechanism being absorption of heat from the air during compression, which would otherwise allow a greater heating of the air and consequent pressure rise that resists motion of the driver trying to move inward, and returning it to the air during rarefaction, where otherwise the cooling air would lower the pressure, again fighting the driver which is now moving outward.

Ok now
1) "the mechanism being absorption of heat from the air during compression"
As I understand this as the driver moves inward air is compressed, this compression cause heat. This I agree with. This is however not to be confused with acoustical energy being transfed into heat. Addtionally you are saying that this heat is not dissipated, but in fact stored within the batting material.

In simple terms, if a confined chamber of air is compressed (driver moving in) it raises in temperature. If this chamber of air is expanded (driver moving out) it will lower in temperature. During the pressure modulation of sound reproduction, the pressure change is not huge, and constantly oscillating, so there is no significant net change of heat, just a modulation of it. Fiberglass and other matierals will store and release some of this heat on each 1/2 cycle, thereby reducing the peak to peak modulation of heat and therefore pressure. You would similarly observe less pressure modulation in a larger, unstuffed enclosure. How much larger the box appears depends on how effective the volume of stuffing is in this function.

Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." Daniel H. Burnham
Mark Seaton is offline  
post #115 of 480 Old 04-22-2008, 02:16 PM
AVS Special Member
 
Looneybomber's Avatar
 
Join Date: Sep 2006
Location: Lawrence, KS
Posts: 4,666
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 23
Quote:
Originally Posted by cluelessngr View Post

In order to "absorb" heat you have to transfer it somewhere else (dissipate it) otherwise the material that you are using to absorb it quickly becomes saturated and of little use.

When the woofer moves in, the air compresses, warms, and the material absorbs the heat, which makes the compression less (just like a bigger box). When the woofer cone moves out, the air decompresses, cools, and the material releases the heat, which makes the vacuum less (just like a bigger box).

Each change (heating or cooling) happens 40 times/second when playing a 20hz note. 120/sec at 60hz. Steel wool could easily absorb that much energy. Experiment with it and let us know how it works.

YID DIY
Looneybomber is offline  
post #116 of 480 Old 04-22-2008, 02:21 PM
AVS Special Member
 
kgveteran's Avatar
 
Join Date: Apr 2004
Location: Rochester NY
Posts: 5,663
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 14 Post(s)
Liked: 38
Hey Mark,

Quote:


How much larger the box appears depends on how effective the volume of stuffing is in this function.

We have heard 1 lb per cubic foot. Anything more defined ? Would it be as simple as measuring the response ? As the response drops you are on your way.At the point where the response begins to rise you have added too much ?

Just a guess. KG
kgveteran is online now  
post #117 of 480 Old 04-22-2008, 02:23 PM
Member
 
cluelessngr's Avatar
 
Join Date: Feb 2008
Posts: 81
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:


Some people like splitting a hair in eight and see how much they gain.

Seriously not trying to split hairs, but I think this whole heat issue is being overstated. While I can see what Noah is saying can/does happen, I question its significance when compared to other factors. I have seen alot made of this accoustical energy to heat argument as the sole or most important factor in baffling adding to effective enclosure size. Let me purpose this:

Glass is a lousy thermal insulator....so what makes fiberglass a good insulator? The fact the each individual glass fiber is made up of hollow tubes of glass. Within these tubes air is stored. So in effect, each individual microscopic fiber acts like a double pained glass window. It is this stored air that gives fiberglass its excellent insulation properties. Now if we have two enclosures, one bigger than the other (each without stuffing) we can safely assume that it will take a shorter time for a sound wave to radiate from the backside of the speaker cone to the enclosure wall and back in the smaller enclosure. This difference in time will be measurable. Now, if we add a material like fiberglass to the smaller enclosure what happens? The sound wave radiates through these fibers by going through first the glass then the air, then the glass etc etc. Each time a small amount of the sound wave is defracted/reflected etc. In effect what we have acomplished is to redirect small portions of acoustical energy and re-direct them ever so slightly with a net result of slowing down the time for the reflected wave to come back to the point of origin. For obvious reasons this is more effective at higher frequencys.

On another note, while cooling a voice coil is an interesting option, I think its benefits would be more in the arena of increased power handling of the voice coil, not in stabilization of internal cabinent temperature. That is unless you somehow passively cooled the voice coil ( fans would add unexceptable noise). In order to do this and also not dissipate hear from within the enclosure you would need a heat pipe that exited the speaker enclosure with the heat sink on the outside. This in itself would also create accoustical issues.
cluelessngr is offline  
post #118 of 480 Old 04-22-2008, 02:31 PM
Member
 
cluelessngr's Avatar
 
Join Date: Feb 2008
Posts: 81
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:


Fiberglass and other matierals will store and release some of this heat on each 1/2 cycle, thereby reducing the peak to peak modulation of heat and therefore pressure

Now thats much better.....store and release....I get it. I can completly understand that, I guess others were trying to say that same thing but not wording it the same way. Ok now, this being true, what is happening to the ambient temp within the enclosure of the real heat being produced by the voice coil and the cabinent sudden inability to dissipate this heat due the the fiberglass batting? How is the stuffings ability to modulate the heat fluctuations of the pressure variations more important than its ability to limit the ability of the voice coil to dissipate heat?
cluelessngr is offline  
post #119 of 480 Old 04-22-2008, 02:41 PM
AVS Special Member
 
Mark Seaton's Avatar
 
Join Date: Jul 2000
Location: Chicago, IL, USA
Posts: 5,972
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 8 Post(s)
Liked: 187
Quote:
Originally Posted by kgveteran View Post

Hey Mark,



We have heard 1 lb per cubic foot. Anything more defined ? Would it be as simple as measuring the response ? As the response drops you are on your way.At the point where the response begins to rise you have added too much ?

Just a guess. KG

You are very close. Your best bet is to instead look at the impedance curve, but the response will work as well, as that is what we're after. If you measure the impedance curve, you see the Fb or tuning frequency of a sealed or reflex enclosure lower until too much stuffing starts shifting it back up or squashing too much output. Of course there can be other factors at play which might justify more or less stuffing than what might seem ideal. While often ignored by those not used to working on full range designs, loudspeakers will have resonances at some higher frequencies, and those can impact the performance/sound.

Mark Seaton
Seaton Sound, Inc.
"Make no little plans; they have no magic to stir men's blood..." Daniel H. Burnham
Mark Seaton is offline  
post #120 of 480 Old 04-22-2008, 03:43 PM
AVS Special Member
 
Kevin Haskins's Avatar
 
Join Date: Feb 2005
Posts: 1,008
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
I don't have much time and don't want to get drawn into a long endless debate on this.

For you guys who have some basic college physics or chemistry. Look back at Boyle's Gas Laws or the famous PV=nRT. We called it "PIVNERT" in college.

P= Pressure
V= volume
n= moles of gas
R= Gas constant (don't ask... my wife says I constantly have gas)
T= Temp.

It is based upon the kinetic theory of gases whereby the gas molecules are modeled as little billiard balls. It is a simplified theory but it holds pretty much correct for the temp/pressure you see under our normal subwoofer use.

The bottom line is that if you increase pressure, tempeture increases (is directly proportional to the pressure). The same amount of billiard balls in a smaller space means that you have more collisions on average (higher temp).

Now.... add some fiberfill. You have the billiard balls on average not just hitting other gas molecules (billiard balls), but the fiberfill also. Those additional collisions into the fiberfill translate into a net DECREASE in the average velocity of the billiard balls. The same thing happens when you increase the volume. You have a net DECREASE in number of collisions (large enclosure) in relation to the smaller volume (smaller enclosure).

As mark points out, these are quick changes in pressure. Don't get too caught up in trying to design air conditioners for your polyfill, it won't help.


Some Wikpedia reading material.

http://en.wikipedia.org/wiki/Collision_theory

http://en.wikipedia.org/wiki/Ideal_gas_law

http://en.wikipedia.org/wiki/Boyle's_law

Kevin Haskins
Exodus Audio
Kevin Haskins is offline  
Reply DIY Speakers and Subs

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off