results of enlosure shape research

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I finished the report for my Acoustics class that discusses the effects of enclosure shape on speaker response. I am hesitant to post it to the forum because the bibliography is not up to par. Basically, I found that in terms of diffraction, the sphere is best in terms of shape. Using felt however, is just as good or better when used on a flat baffle. So, by rounding the edges of the baffle and using felt would be the best bet (*Flush mounting drivers is very very important too*). For internal resonances, all the evidence pointed to an enclosure that did not have parallel walls. Tapering the walls seemed to be very good, whether done like the B&W Nautilus or the Sonus Faber Amatis. As far as materials go, wood is the best. MDF or hardwoods of significant thickness will prevent enough transmission through the walls of the cabinet into the listening area to keep the desired sound unaffected. I originally thought that a more rigid material like marble would be the best, but in the case of marble, almost all transmission through the walls is prevented and a buildup of energy on the inside will almost definitely make its way back out through the cone (very bad). I didn't see any designs using this technique, but a cabinet with wood on the inside and marble on the outside, might take advantage of the benefits of both materials. Of course, some internal dampening is required to achieve the best results, although the amount is drastically decreased when you use a modified shape. The paper addresses time-alignment of the drivers, which did not seem to be a big problem in loudspeakers, unless you are far from the speakers. The best results are achieved by staying relatively close to the speakers. Slanting of the front baffle didn't seem like a good solution because it pointed the speakers at the ceiling. Separate enclosures staggered the proper distances worked best for time-alignment, but could add more problems diffraction-wise. kingdaddy's SST8's look like they would do a relatively good job in taking care of both time-alignment and diffraction. Those are the only factors I took into account for the paper, I would be happy to research other factors if anyone is interested. I can email a copy of the paper to anyone who is interested also. Hope some of the information is helpful.

Austin
 
Well done, my results mirrored yours, but as you probably know everything is a compromise, my enclosures probably suffer from some form of edge diffraction and I have tried oval foam rings around the tweeters and some other porous foams of different shapes but I can't get any positive improvement so far, and since I don't dislike anything in particular about the sound I'm not inclined to try any further. I would also like a copy of your paper if you have the time.

Thanks
mkeith@ftav.com
 

CHRIS8

Disabled Account
2001-12-12 8:47 am
VA, USA
You may of course send a copy to me, and I would be grateful. :)

chris8@mail.com

"Using felt however, is just as good or better when used on a flat baffle. "

This is only taking into consideration one aspect. Certainly, you will suppress the reradiatied diffractive energy in the band that the damping material is effective, but in this you are only concerning on axis response. Power response is just as important IME, and you will reduce off axis linearity to a very small degree in the process when compared to a damped flat baffle vs. a non damped flat baffle. Their is no comparison to a sphere though, or very large radiuses, as the linear power response provided at higher mid and treble frequencies is superior and provides for a much more linear dispersion field of acoustical energy. Of course, this assumes your intent to design for ideal power response in the first place. The specific importance of power response, though, is not my point to discuss in this thread. :) I am just pointing out that it will be affected significantly with different approaches.

-Chris
 
paper posted

This is a text only version of the paper so I hope it works ok.

I didn't learn anyhting specific about speaker design in the acoustics class, but I did get some good advice from my professor who is a great acoustician. He said, you can only rely on the formulas so much, ultimately it is your ears that will tell you the truth. He gave an example of Beranek, who designed a horrible concert hall when he was young. When asked why he had failed in designing it he said, he relied on the formulas too much. Speakerbuilding requires the same subjectivity. Keep that in mind!

Enjoy the paper.

Austin
 
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