Use of sound-absorption on speaker face?

audiojerry · « **on:** 20 Feb 2003, 04:45 pm »

I've seen the practice by some designers to use felt damping around the tweeter face as well as on other parts of the cabinet face. I was thinking of using Coustasheet from GasolineAlley. It's a very dense sheet of loaded vinyl like Black Hole, but 30% denser, 1/12" thick, and has very impressive db deadening stats.

Have you tried this or a similar product on the cabinet face?
Do you think it could make a positive difference in diffraction characteristics?

Danny Richie · « **Reply #1 on:** 20 Feb 2003, 11:09 pm »

The material you are describing sounds like it would be effective in adding mass to the front baffle or assisting with resonance control.

It would likely not have a lot of effect controlling surface reflections. It could cause some changes in the response curve by reshaping the enclosure and even causing some slight horn loading.

Thick felt is very effective as is open cell foam, but both are not real pretty to look at.

Wide speakers have a tremendous amount of surface reflections while a very narrow one like the Criterion (7.5" wide) will have very little.

I once did some testing using swept baffles and shapes that completely swept the enclosure away starting at the very edge of each driver.

One note of interest was how smooth the off axis response was.

The enclosure was complex. The results were great. The road to get there was a long one, and the rest is a long story.

JohnR · « **Reply #2 on:** 21 Feb 2003, 12:49 am »

Jerry if you are interested in experimenting there is an article here about felt:

http://www.speakerdesign.net/felt/felt_ring_vs_blocks.html

Real felt can be obtained from mcmaster.com, only in grey tho I think

azryan · « **Reply #3 on:** 21 Feb 2003, 06:23 pm »

Danny, what is the effect of the Alpha's face, since it's pretty wide, but is almost totally made up of drivers having almost no cabinet exposed on the face?

Do you still even call the face 'baffle' when it's ~97% speaker drivers?

audiojerry · « **Reply #4 on:** 4 Mar 2003, 05:21 pm »

Quote from: JohnR

Jerry if you are interested in experimenting there is an article here about felt:
http://www.speakerdesign.net/felt/felt_ring_vs_blocks.html
Real felt can be obtained from mcmaster.com, only in grey tho I think

Thanks, but I have found the best source are fabric stores, which have several varieties and thicknesses of felt, including adhesive backed . You have to elbow your way past all the women, but I'm tough.

JohnR · « **Reply #5 on:** 4 Mar 2003, 07:00 pm »

Never thought of that

Is it wool felt?

nathanm · « **Reply #6 on:** 4 Mar 2003, 07:18 pm »

So if reducing the baffle size is beneficial how would it sound if you mounted the drivers onto long tubes that were just large enough to bolt the drivers onto? I suppose there are other internal cabinet issues with mounting a driver onto a cylinder, but it was a thought. Maybe just have the tubes be about 6" long and have them go into a rectangular cabinet?

Val · « **Reply #7 on:** 5 Mar 2003, 12:19 pm »

Quote

how would it sound if you mounted the drivers onto long tubes that were just large enough to bolt the drivers onto?

nathanm, were you thinking of this speaker?

Vince Christian E9

I have listened to Vince's older models and they impressed me highly, and I also remember J. Peter Moncrieff recommending them. The E6 is supposedly very good also. He should be invited to the Audio Circle.

nathanm · « **Reply #8 on:** 5 Mar 2003, 04:01 pm »

Nope, never saw that one before. But yes, that's the same concept I was thinking of. But even those have a little bit 'o baffle around the driver. That teardrop shaped midrange unit on the B&W speakers is probably the most extreme design of reducing the front to just the cone and nothing else. Kinda interesting. Would be pretty hard to DIY that kind of thing unless you had access to a CNC machine, or maybe you could do it in clay!

Quote

frequency response 65Hz to 18.5kHz -3db

Oh gee, I think I will pay $9000 for that awesome bandwidth! Sheesh! Can't ya get minimonitors with similar bass-shyness for a helluva lot less?

theranman · « **Reply #9 on:** 5 Mar 2003, 04:53 pm »

I've also wondered about that concept along time ago, but the real question for ME is why so outrageously expensive? It's only cheap PVC pipe, and yeah, the bandwidth/price ratio sucks. Time for DIY...

Val · « **Reply #10 on:** 5 Mar 2003, 09:27 pm »

Both E6 and E9 are designed to be used with a dedicated subwoofer, check the rest of the website. I agree that it would be a perfect DIY concept.

Val

audiojerry · « **Reply #11 on:** 6 Mar 2003, 04:17 pm »

I thought I read somewhere that as frequencies get lower, the standing waves inside a long tube create problems with resonance, pressure on the back of the driver, and cone excursion problems, which can cause smearing, congestion, and a tubey (not vacuum tubey) sound.

John, I don't know the answer to your qestion about felt, but felt might be a form of wool product. I noticed at the fabric store that there was more than one kind of felt and in different gauges.

Danny Richie · « **Reply #12 on:** 6 Mar 2003, 04:43 pm »

You mean I go so far as to radius the inside edge of the woofer holes to minimize the earlier edge reflections to keep them from sounding like they are playing through a pipe, and some other designer is actually loading them in a pipe?

Here is the info a posted years ago about a series verses parallel network design: http://www.angelfire.com/tx2/grresearch/seriesvs.htm

The speaker I used for testing had the edges swept back away from the drivers.

With no baffles step loss compensation look how soon the baffle step loss rolled in. At around 1kHz and down it was making the transition.

In this design I made no baffle step loss adjustments to the upper woofer but picked up that loss with the three woofers below.

Here is a pick of the box:

How about that smooth response curve? +/-.75db

audiojerry · « **Reply #13 on:** 6 Mar 2003, 08:16 pm »

Very interesting, Danny. How long ago did you do this, and whatever happened to this project? Those cabinets with great drivers and crossovers could be something to behold.

Danny Richie · « **Reply #14 on:** 7 Mar 2003, 03:39 am »

I actually started the project several years ago.

I finished up all the measuring and testing and considered offering it as a kit.

But I think the enclosure design was a little too complex for the average hobbyist.

I also never have gotten around to painting the enclosures and finishing them up.

I wanted to finish them in a high gloss White with two odd shaped gloss Black side panels kind of like a Revel Studio or something.

I just never have finished up the job. Too many other more important matters to tend to like making a living at this and trying to stay one step ahead of everyone else.

Oh, those speakers did sound very good. The imaging especially was great. A total of six 6.5" woofers playing down to a -3db of 32Hz didn't hurt either.

MaxCast · « **Reply #15 on:** 7 Mar 2003, 01:00 pm »

Does anyone have experience with metal (aluminum) enclosures? That shape seems pretty easy to cast. One problem I see with a casting would be outside finish. ??

Brandon B · « **Reply #16 on:** 7 Mar 2003, 03:25 pm »

Quote from: JohnR

Real felt can be obtained from mcmaster.com, only in grey tho I think

The felt at MCmaster is in various grades F1 on up, which have varying amounts of wool and decreasing densities. The highest grade (F1) is over 90% wool and is white. They seem to alternate grades as gray to white to gray etc. The gray is actually sort of a purply gray with flecks of other colors in it.

I have some F1 and some F7, have not used it on my cabinets yet though.

BB