How critical are box dimensions 2.6/1.6/1 ???

[Guiria]

I'm building some speakers to fit inside an armoir shelf and the dimensions are going to be a little odd. The available space is 7.5 in. tall, 9.5 in. wide, and up to 19.5 inches deep. The port will have to be on the front as well. I'm using the Dayton DC130BS-8 5.25 driver and the Dayton ND20FA-6 3/4 tweeter. Using WinISD for the Dayton DC130BS-8 I can build a box that is tuned to the Fs of the driver (49 hz) with dimensions of 7.5x9.5x18.42.

I realize the optimum proportion for box dimensions is 2.6/1.6/1 but since that's not possible here; is having an 18.42 in. deep box going to give me serious internal resonance issues?

How accurate is WinISD? It tells me to use a single 1.85 inch port that's 5 inches long? (seems small)

Anything thing else you might want to throw at this design please let me know. I have yet to determine specific crossover components and speaker positioning on the front baffle.

[annunaki]

Sometimes when space contraints are limited, compromises must be made. As long as the internal volume is accurate that is what matters.

You are building a three way speaker? You are using an 8" woofer, 5.25" mid woofer and a tweeter. Is that correct???

The port size sounds about right. I would just use a 2" port though. They are easier to find.

Are you using 3/4" MDF? Will you be bracing the enclosure in a fairly extensive manner?

If this is a three way design, have you modeled the mid woofer and the bass woofer independently in your volume allowances?

Your internal volume is about .411ft^3 correct???

[Guiria]

It's actually a 5.25 driver with a 3/4 soft dome tweeter - 2 way

I am using 3/4 mdf and plan on a shelf brace about 1/3 deep in the box.

internal volume is .47 ft^3

I'm glad to hear the opinion that the ratio isn't that critical.

[Guiria]

You know that you can cheat. (to a degree)
And have a driver in a smaller box, thinking that it is in a bigger box.
By using acoustic foam. (this will help with your resonance issues.)

Are there calculations to size down the box by "X" % given "N" amount of acoustic stuffing?

[avaserfi]

You know that you can cheat. (to a degree)
And have a driver in a smaller box, thinking that it is in a bigger box.
By using acoustic foam. (this will help with your resonance issues.)

Are you sure about this? From my research in the subject acoustic foam or what I am planning on using (OC705 which is far more effective) is useful if the proper thickness is used (2" should suffice for most applications in eliminating modal resonance and stop internal energy reflection). There is one caveat however, using too much can cause bass roll off this is caused by the extreme dampening effect of OC705 which can inhibit the cabinets ability to resonate the air volume properly.

I am pretty sure this in no way will trick a driver. The best advice would be compromise and don't use the specific box dimensions. Use the T/S parameters to build the best possible box for the drivers.

Also, if you want to properly combat resonance issues the best and only way a DIYer can reasonably deal with this situation is proper bracing on all axises within the given cabinet.

[Guiria]

Read about half way down, hope this helps.

http://www.speakerplans.com/forum/forum_posts.asp?TID=11786&PID=108516

Interesting read, however, I'm not convinced at this point that it's necessary given the differences between 2-way bookshelves and subwoofers.

Let's just say I'm still looking into it. Nothing is final at this point in the game.

[WmAx]

I realize the optimum proportion for box dimensions is 2.6/1.6/1 but since that's not possible here; is having an 18.42 in. deep box going to give me serious internal resonance issues?

Avaserfi's response was appropriate. Internal dimensions are irrelevant if proper internal damping is utilized. For the longest dimension in your case, I would use 3"-4" of high density mineral board or fiberglass(6-8lb/ft3 density) boards on one side(the back). 2" on all other walls. Virtually no acoustic energy will be able to resonate/reflect within the box with this material used as specified, but the ported bass should still work satisfactorily, with only some mild loss of port output.

A very critical issue here is the transmission of box vibration to the armoir. You need to use, for example, 1" cushion foam between the armoir and the speaker. Substantial resonance will originate from the armoir if you do not take this step. Use at least a medium grade foam from an upholstery shop. The garbage found at Wal-Mart, for example, will quickly flatten out and become useless. If you want very high grade foam that will last practically forever, get a high grade latex foam. But you would likely have to order this online. Few shops carry high grade foams/resilient foams.

-Chris

[avaserfi]

Oh, I don't have any claims on speaker building.
It was just a suggestion.

Although, about 20 years ago (in my teens), I did build some speakers, and played around with poly-fill.
I have no direct measurements that I could show.

However, I am on the understanding it will help even with mid-range (bookshelf) speakers.
And one of the uses (granted, this is usually for the case of subs) is to fool the driver into acting as though it were in a bigger box.

Here is some of the stuff I am refereing to.
You can read the marketing of the material, and see its claims for mid-range clarity.
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-317

I'm sure Chris (Wmax) will chime in, to help guide you.

Please re-read my original post in this thread. I explained exactly what the benefits of using a dampening material within the cabinet are.

By absorbing internal energy in the form of sound waves resonance is lowered causing a more linear response, but before worrying about dampening proper emphasis should be placed on bracing the said cabinet to remove the more pervasive cabinet resonance.

This recommendation is based on discussions with Chris as well as reading articles on loudspeaker design, mostly by Floyd Toole.


Edit: I was beaten to it. Glad to know I am learning though :D.

[annunaki]

I'm building some speakers to fit inside an armoir shelf and the dimensions are going to be a little odd. The available space is 7.5 in. tall, 9.5 in. wide, and up to 19.5 inches deep. The port will have to be on the front as well. I'm using the Dayton DC130BS-8 5.25 driver and the Dayton ND20FA-6 3/4 tweeter. Using WinISD for the Dayton DC130BS-8 I can build a box that is tuned to the Fs of the driver (49 hz) with dimensions of 7.5x9.5x18.42.

I realize the optimum proportion for box dimensions is 2.6/1.6/1 but since that's not possible here; is having an 18.42 in. deep box going to give me serious internal resonance issues?

How accurate is WinISD? It tells me to use a single 1.85 inch port that's 5 inches long? (seems small)

Anything thing else you might want to throw at this design please let me know. I have yet to determine specific crossover components and speaker positioning on the front baffle.

As long as the driver models well in that enclosure (smooth, flat response) I see no reason why it would not work pretty well. I would do what Chris (WmAx) suggested and isolate the enclosure from the amoire. A 2" port would work well, just make sure to input that into your program to get appropriate port length. Also make sure there is a minimum of 2" clearance around the port opening inside the enclosure. Ports do not have to be large with a small driver and a fairly high tuning frequency.

Internal damping is optional. I would suggest very sturdy bracing, then adding any internal damping materials. I like to use bracing that interacts with all four walls of the cabinet structure. Here are a few pic's from the first DIY speakers I did. I cheated a bit and used B&W Signature 7 SE inwalls attached to their baffles.

http://img.photobucket.com/albums/v157/annunaki_6/cabinetpic2.jpg

http://img.photobucket.com/albums/v157/annunaki_6/Sig7pic3.jpg

http://img.photobucket.com/albums/v157/annunaki_6/000_0099.jpg

[Guiria]

Very useful info indeed. Thanks WmAx for the insight on the seperation of the speaker from the armoire...I never would have thought of that;) That's going to require some design changes but I think it'll be worth it.

Annunaki, that is some serious internal bracing. When you have internal bracing do you need to account for it in your volume measurements? ie build a larger enclosure to maintain the same net volume?

The project has changed a little. I am now using a single extended range driver (Tang Band 3" bamboo) for each enclosure. Using WinISD and porting the box tuned to 71 Hz gives me pretty flat (less than +-1 db) response. The box is .25 ft^3.

This forum rules.

[WmAx]

Annunaki, that is some serious internal bracing. When you have internal bracing do you need to account for it in your volume measurements? ie build a larger enclosure to maintain the same net volume?

You must account for bracing displacement.

BTW, the bracing seen in those pictures may seem like a lot, but even this degree of bracing will likely result in substantial audible resonances that distort timbre in a full range speaker. But I expect it would have a better result as compared to the average execution.

Even the extreme bracing/constrain wall damping utilized in the following picture links, while having almost no audible resonances, still has some in particular music tracks, when compared directly with a known non-resonant reference:

http://www.linaeum.com/productinfo/other/infinity_primus160_ultra/braces_back_s.jpg

http://www.linaeum.com/productinfo/other/infinity_primus160_ultra/braces_front_close_s.jpg

-Chris

[annunaki]

Chris,

I would have to say I do not hear any "substantial" audible resonance with this enclosure. I surely cannot feel any either when doing a frequency sweep while touching the enclosure. I am not saying it is not there, as I know that it has resonance of some sort. Everything does, however, I cannot hear any.

These enclosures have been internally dampened with polyfil. At some tim ein the future I may do mineral fiber or something on the side walls.

Thanks for your input.

[annunaki]

Annunaki, that is some serious internal bracing. When you have internal bracing do you need to account for it in your volume measurements? ie build a larger enclosure to maintain the same net volume?

The project has changed a little. I am now using a single extended range driver (Tang Band 3" bamboo) for each enclosure. Using WinISD and porting the box tuned to 71 Hz gives me pretty flat (less than +-1 db) response. The box is .25 ft^3.

This forum rules.

As Chris indicated, you will have to account for bracing displacement. I like the two way option better as it plays deeper and integrates better with a subwoofer, but a single driver option may have some useful benefits.

What bandwidth is your response good through +/-1db???

[WmAx]

Chris,

I would have to say I do not hear any "substantial" audible resonance with this enclosure. I surely cannot feel any either when doing a frequency sweep while touching the enclosure. I am not saying it is not there, as I know that it has resonance of some sort. Everything does, however, I cannot hear any.

These enclosures have been internally dampened with polyfil. At some tim ein the future I may do mineral fiber or something on the side walls.

Thanks for your input.

It is no surprise that you do not notice the resonances. However, I would bet that you can easily hear the resonances, and do not realize that this is one of the things detracting from a higher level of realistic reproduction.

I assure you, I have good reason for suspicion that even the enclosures I linked/demonstrated prior have some small level of audible resonance, though at a much smaller level than in almost any other case. These enclosures take resonance control to another level, and it's still not enough to have completely inaudible cabinets.

Another issue to address: from my own observations, while far from perfectly controlled conditions(this is difficult and time consuming), as I work with controlling resonances, and comparing to a known non-resonant reference, it would appear that my resonance detection threshold has increased substantially. I would wager that you could hear resonances just as easily compared to a proper reference; and then you may never be able to tolerate such resonances again. :)

-Chris

[annunaki]

How does one achieve a true non-resonance type enclosure then? The B&W Nautilus model seems to have a near non resonant cabinet based upon it's design I would think? Where did you get a non-resonant reference speaker?

I am quite happy with the speakers, however, they are not as detailed as newer models. B&W's drivers have improved much since my speakers were in production.

[avaserfi]

How does one achieve a true non-resonance type enclosure then? The B&W Nautilus model seems to have a near non resonant cabinet based upon it's design I would think? Where did you get a non-resonant reference speaker?

The speakers I am planning on building should be fairly close to being completely inert, but not quiet. There will be a slight (hopefully non-audible) resonance in the midrange module. So see Chris's post (#12) here (http://forums.audioholics.com/forums/showthread.php?t=35730) to get an idea. An example of a non-resonant commercial speaker would be a B&W 801D.

As far as Chris's reference speakers I believe he told me he uses "modified Beyer DT880 headphones" although I am not sure of the modifications.

edit: Fixed the link. The answer is NOT magic, although that might be less work ;).

[annunaki]

I think you linked the wrong post because there are only two posts and the are about Harry Potter?? :confused::eek::D

[avaserfi]

I think you linked the wrong post because there are only two posts and the are about Harry Potter?? :confused::eek::D

I tried the magic route, didn't work to well. I edited the link it goes to the right place this time!

[Guiria]

What bandwidth is your response good through +/-1db???

WinISD only goes up to 1 kHz so my +/-1db is from 66Hz-up given a ported .25 ft^3 enclosure. It would be nice to see how the high end models but I don't think WinISD has that capability. Maybe I'm just a newb at it.

The speakers will be in a bedroom that is 12x13.5x8. I will rarely be cranking these things since my daughter's bedroom is exactly over mine.

[WmAx]

How does one achieve a true non-resonance type enclosure then?

As far as achieving vanishingly low resonance that is not likely to be audble, one can take several routes to partially or fully address the issue:

(1) Shift the resonance band of the enclosure above that of the midrange band driver.

(2) Increase stiffness/mass to a level that reduces resonance amplitude to a sufficiently low level.

(3) Dampen the resonance by converting to an alternate energy form(heat).

(4) Forcing the resonance into a high Q band of single primary resonant frequency that is not likely to be excited substantially by most source material.

(5) De-couple midrange/midbass driver(s) from the cabinet with a suspension.

(6) Combination of the above.

The B&W Nautilus model seems to have a near non resonant cabinet based upon it's design I would think?

If you mean the top units: 801D, 802D and 800D; yes. These cabinets are virtually inert for so far as the purpose of audibility is concerned.

Where did you get a non-resonant reference speaker?

My virtually non-resonant reference is an extraordinary linear headphone([I]with some modification): a Beyerdynamic DT880 (pre-2006 model). With modifications, it has but two minor resonances (in the treble band) at a very low level, and a midband cleaner than any speaker system of which I know about. Combine this with zero room influence(no reverb contributes to making resonances harder to detect; improving this aspect yet further), and it's a superb resonant-free reference for midrange.

-Chris

[annunaki]

As far as achieving vanishingly low resonance that is not likely to be audble, one can take several routes to partially or fully address the issue:

(1) Shift the resonance band of the enclosure above that of the midrange band driver.

(2) Increase stiffness/mass to a level that reduces resonance amplitude to a sufficiently low level.

(3) Dampen the resonance by converting to an alternate energy form(heat).

(4) Forcing the resonance into a high Q band of single primary resonant frequency that is not likely to be excited substantially by most source material.

(5) De-couple midrange/midbass driver(s) from the cabinet with a suspension.

(6) Combination of the above.



If you mean the top units: 801D, 802D and 800D; yes. These cabinets are virtually inert for so far as the purpose of audibility is concerned.



My virtually non-resonant reference is an extraordinary linear headphone([I]with some modification): a Beyerdynamic DT880 (pre-2006 model). With modifications, it has but two minor resonances (in the treble band) at a very low level, and a midband cleaner than any speaker system of which I know about. Combine this with zero room influence(no reverb contributes to making resonances harder to detect; improving this aspect yet further), and it's a superb resonant-free reference for midrange.

-Chris


What does a set of those headphones run?

As for the B&W's I meant the Nautilus Model. The snail shell looking speaker, the top of the line $40,000 a pair Nautilus.

Which of the above options are the best to use in combination? I am thinking that a combination of 5, 3, and 1 would work fairly well in designing a full range speaker?

[WmAx]

What does a set of those headphones run?

If you find a pair of this older model, I guess you would end up paying about $150-$200, depending on condition. I can not recommend the current version. It has, according to measurements, an elevated treble band, compared to the older unit.

Which of the above options are the best to use in combination? I am thinking that a combination of 5, 3, and 1 would work fairly well in designing a full range speaker?

It depends on the specifics of a particular application, as well as the degree to which you execute the method(s).

Take a B&W 802D as an example. It is a combination of methods. For the woofer module, it uses extensive matrix bracing every few inches internally to push the panel resonances above the bandwidth of the wooofer. For the midrange module, they use an extremely stiff, high density composite that has high damping properties. The mid-range driver is also mounted on an extensive suspension system to decouple it from the module. The entire mid-range module in turn is decoupled by way of suspension from the woofer module, to prevent the midrange module from exciting the woofer module panels.

-Chris

[annunaki]

Chris,

I am quite familiar in how the B&W system works and is put together.

Is there a certain formula for finding the enclosure resonance after bracing has been installed? Assuming one does seperate enclosures for each driver to ensure low/no resonance, how does one test to ensure they have succeded?

What materials work best for each type of driver? MDF/HDF for the woofer/bass portion? High grade marine plywood for the midrange? Vice versa? Does a tweeter need it's own enclosure?

[annunaki]

WinISD only goes up to 1 kHz so my +/-1db is from 66Hz-up given a ported .25 ft^3 enclosure. It would be nice to see how the high end models but I don't think WinISD has that capability. Maybe I'm just a newb at it.

The speakers will be in a bedroom that is 12x13.5x8. I will rarely be cranking these things since my daughter's bedroom is exactly over mine.

You will need a better program that you can use for simulation for those drivers. The response above 1kHz will be critical. I do not think that WinIsd will go to a full range signal. Do not begin your purchase or build until you can model them full range.

[Guiria]

You will need a better program that you can use for simulation for those drivers. The response above 1kHz will be critical. I do not think that WinIsd will go to a full range signal. Do not begin your purchase or build until you can model them full range.

So what do yo use or wish you were using for speaker building software? WinISDPro will allow you to model the graph full range, however, it measures it pretty much ruler flat which I find hard to believe from a 26 dollar driver.


This is the link that shows the SPL vs. Frequency graph for the driver
http://www.partsexpress.com/pdf/264-844.pdf

How it performs in the given box, however, is a good question.

[annunaki]

WinIsd Pro Alpha is a good program. You may want to look into Leap or some others. The really good ones you usually have to pay for :(

[WmAx]

Is there a certain formula for finding the enclosure resonance after bracing has been installed?

Yes, given sufficient physical parameters for the materials to be analyzed, it is possible to estimate. But it's not efficient to do manually for a cabinet system; it is complex/labor intensive math that is best suited to software analysis. You can read some about panel resonant mode analysis at this link:

http://www.audioholics.com/education/loudspeaker-basics/lowering-mechanical-noise-floor-in-speakers

Assuming one does seperate enclosures for each driver to ensure low/no resonance, how does one test to ensure they have succeded?

To measure the panel resonant frequencies one needs to attach an accelerometer to various points on the cabinet and derive the frequency response of the cabinet surface(s) by using a driver mounted in the cabinet to provide the stimulus. The resonant points will be indicated by large response peaks in the response.

I am not aware of an existing way for a DIYer to practically measure final acoustic output response of a cabinet vs. direct driver output. You need a far field, multi-axis impulse response analysis in order to derive waterfall type response charting. With a very wide bandwidth anechoic chamber, or the speaker mounted 50ft in the air on a pole, it's possible. I have an idea on how to test in a normal room, but I have not yet tested this, nor am I ready to talk about this procedure in public before I test it.

What materials work best for each type of driver? MDF/HDF for the woofer/bass portion? High grade marine plywood for the midrange? Vice versa?

Best material(s) depends on the specific application as well as other construction techniques used in the process.

If your woofer is being cut at 100Hz, standard MDF moderately braced, or a high grade hardwood plywood, somewhat less braced, will have primary resonant modes well above 100Hz. If your woofer is being cut at 500Hz, far more consideration is required in shifting the primary resonance(s) well above this band; this is where materials like HDF or very high grade hardwood ply comes into play as being easier to use for the application as compared to MDF.


Does a tweeter need it's own enclosure?

I am not aware of any benefit unless the tweeter's back is not air tight.

-Chris

[Clarence Hyder]

Are you sure about this? From my research in the subject acoustic foam or what I am planning on using (OC705 which is far more effective) is useful if the proper thickness is used (2" should suffice for most applications in eliminating modal resonance and stop internal energy reflection). There is one caveat however, using too much can cause bass roll off this is caused by the extreme dampening effect of OC705 which can inhibit the cabinets ability to resonate the air volume properly.

I am pretty sure this in no way will trick a driver. The best advice would be compromise and don't use the specific box dimensions. Use the T/S parameters to build the best possible box for the drivers.

Also, if you want to properly combat resonance issues the best and only way a DIYer can reasonably deal with this situation is proper bracing on all axises within the given cabinet.

You can definatly attenuate resonance issues with cabinet dampening materials especially Acouta stuff, simalar to fiberglass but with much better energy absorbing properties. Also you absolutely can build a box and with material such as acousta stuff or fiberglass make the driver think its in a larger box. As much as 30 to 40 per cent.

If your brace is too close to the back of the woofer a "loading" issue can occur where the air flow around the woofer is different on one side than the other causing non linear movement of the coil and cone. Distortion grows from these gardens/

Panel resonance cant be eliminated with braces as it is the entire cabinet that vibrates. Many test have been done on this subject and its found that bracing mainly just raises the frequency of the resonance not eliminate it. Damping more or less eliminates it.

The golden ratio as noted in the fist post is a formula that if followed wont allow any standing waves to couple and therefor make them grow in magnitude. Damping does the same thing. Generally 1/2 pound of acousta stuff per cubic foot is ideal less if a ported system more

[Clarence Hyder]

How does one achieve a true non-resonance type enclosure then? The B&W Nautilus model seems to have a near non resonant cabinet based upon it's design I would think? Where did you get a non-resonant reference speaker?

I am quite happy with the speakers, however, they are not as detailed as newer models. B&W's drivers have improved much since my speakers were in production.

The closest I know of non resonant cabinets is one that is a cabinet within a cabinet. build the initial cab from 1 half inch mdf and another of 1 half or 3 quarters over it with a layer of roofing felt btween them only attached at the corners. Test proved this method to reduce cabinet resonance by 97 percent. Bracing didnt eliminate it at all it just changed the frequency.

[WmAx]

You can definatly attenuate resonance issues with cabinet dampening materials especially Acouta stuff, simalar to fiberglass but with much better energy absorbing properties. Also you absolutely can build a box and with material such as acousta stuff or fiberglass make the driver think its in a larger box. As much as 30 to 40 per cent.

Low density fiberglass, wool, poly fill and other fibers at low density have been shown to increase a closed box's apparent internal volume by some small degree. But I believe the poster was talking about high density fiberglass or mineral board, in which case, an excess of this material can prevent the tuned box resonance from occuring; this material is extremely efficient at damping acoustic energy vs. thickness. Much more effective at damping as compared to standard low density fiberglass or Acousta-Stuff(Dacron fiber that has been machine crimped). As an exampe: place 4" of the high density (6-8lb/ft^3) fiberglass or mineral wool board in all walls(type A mounting) of a an enclosure, and virtually no acoustical energy could reflect(or resonate) from about 125Hz and over. However, the material does not suddenly stop working at a fixed frequency. There would still be considerable effect well under 100Hz in this case.

Panel resonance cant be eliminated with braces as it is the entire cabinet that vibrates. Many test have been done on this subject and its found that bracing mainly just raises the frequency of the resonance not eliminate it. Damping more or less eliminates it.

Bracing is a critical part, if done correctly. While bracing raises the resonant frequency, if properly distributed with enough bracing points, the resonance will also be reduced in amplitude, to a degree. Bracing alone is certainly seems to not be the answer to a midrange enclosure(as it is very difficult to push the panel resonances completely over the midrange bandwidth), though it is applicable as an only solution for woofer modules, where one can push the panel resonances substantially over the bandwidth of the driver(s).

The golden ratio as noted in the fist post is a formula that if followed wont allow any standing waves to couple and therefor make them grow in magnitude. Damping does the same thing. Generally 1/2 pound of acousta stuff per cubic foot is ideal less if a ported system more

There is no shape one can use that will completely prevent internal cavity resonances sufficiently as a single solution. But this is useful when combined with low effectiveness damping materials as are commonly used in speakers(polyfill, standard grade foam, etc.). While these materials effectively damp upper midrange and treble resonances, they do not have much effect on lower midrange/midband frequencies in normal application unless the entire space is filled, and in my experiences, it still will not be as effective at eliminating lower mid-bass range reflections/resonances as compared to the high density board type fiberglass or mineral wool in a normal enclosure.

-Chris

[WmAx]

The closest I know of non resonant cabinets is one that is a cabinet within a cabinet. build the initial cab from 1 half inch mdf and another of 1 half or 3 quarters over it with a layer of roofing felt btween them only attached at the corners. Test proved this method to reduce cabinet resonance by 97 percent. Bracing didnt eliminate it at all it just changed the frequency.

To properly build a cabinet-in-a-cabinet system, the two cabinets must be effectively decoupled mechanically(a single solid connection will dramatically reduce the attenuation effect of the isolated cabinet systems) and have air-tight connections to prevent an air breach between the two. It is no simple task to properly build a cabinet using this method. The inner cabinet system must still take precautions to prevent a high degree of resonance, as an unbraced/non-damped inner cabinet system would have a very high amplitude that may breach acoustic output through the driver. BTW, there are better materials to use as compared to roofing felt for this application. A high density, high ILD latex foam would be more reliable in this capacity. Or, alternatively, a very low durometer rated durable rubber used in block points.

-Chris

[Clarence Hyder]

To properly build a cabinet-in-a-cabinet system, the two cabinets must be effectively decoupled mechanically(a single solid connection will dramatically reduce the attenuation effect of the isolated cabinet systems) and have air-tight connections to prevent an air breach between the two. It is no simple task to properly build a cabinet using this method. The inner cabinet system must still take precautions to prevent a high degree of resonance, as an unbraced/non-damped inner cabinet system would have a very high amplitude that may breach acoustic output through the driver. BTW, there are better materials to use as compared to roofing felt for this application. A high density, high ILD latex foam would be more reliable in this capacity. Or, alternatively, a very low durometer rated durable rubber used in block points.

-Chris

#30 Roofing felt was used in the test because it was recommended by Vance Dickason in his book. Mainly because its cost at .17 cents per foot is significantly cheaper than the 2.00 per sq. foot for loaded vynyl. and performed better in several areas and as well in allmost all of them.

And I didnt say it was easy just that this was the best way to construct an affordable anti resonant cabinet. And I know it needs to be isolated with minimal mechanical coupling. Airplanes of all types use constraining layers to dampen and attenuate the noise outside the plane. They use 5mil aluminum sheets and E.A.R's ADC-124 Lightweight damping foam , but you could buy a house for what that material cost. I try to live in the real world of DIY. I know some people have lots of money to spend, but 99 percent of the people I have attempted to help were always interested in a less expensive alternative if the end result was even relativly close. I guess I need to clarify every single statement I make in massive detail unless I want to get called on every detail of every post. Im not here to claim the throne of "King of the DIY Knowledge" just to help people that ask questions.

No one is doubting your loudspeaker prowess, I am simply trying to offer another intelligent opinion. But thanks for clarifying all those points for me. (Not exactly necessary) Not everyone has as deep an understanding of the subject as we may have. So I tend to leave out alot that I feel will only confuse novice builders. I admit I did miss the fact that he was talking about a dense material on the walls of the cabinet. And I do agree with you on that. And everything else for that matter. I just didnt type in all the details for each comment I made. Thanks lets do this again soon. Jeff Hyder