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???

 

[Gasman]

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.)

 

[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.

 

[Gasman]

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

Read about half way down, hope this helps.

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

 

[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.

 

[Gasman]

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.

 

[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 .

 

[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.

 

[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 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??