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Multi-Way Conventional loudspeakers with crossovers

Cabinet Damping
Cabinet Damping
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Old 11th April 2007, 01:18 AM   #11
pjpoes is offline pjpoes  United States
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well anyway, Dampening or Damping, now I'm not even sure whats being said there, by this material takes care of both panel resonance and air. The foam and bitum layer dampen the panel.

This is, by the way, not a stuffing like batting, and it works better at stopping panel resonance than will rockwool, fiberglass, or batting. That is because of the bitum and adhesive, etc. However the out layer of foam then also helps reduce the standing waves. I don't like the sound of a cabinet stuffed full of batting, and in a ported box, that has its own issues anyway. I hadn't found a foam product I liked until this stuff.

I will mention, Acoustastuff is different from poly batting used to stuff pillows. It looks similar, but if you compare the two together, you can see that acoustastuff is a long fiber product. There is a claim that, like wool, the long fibers help do a better job with the airborne standing waves. I can't say I know that it does, I don't really find the cost of acoustastuff to be high enough to worry about it. In the scope of a project, if I spend 500 dollars or 530 dollars, I dont really care.
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Old 11th April 2007, 01:37 AM   #12
planet10 is offline planet10  Canada
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Cabinet Damping
Quote:
Originally posted by 454Casull
Dampening is really the same as damping.

http://www.m-w.com/dictionary/dampen
Last time i saw a discussion on damp vrs dampen someone pulled up a reputable dictionary without the deaen meaning...

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Old 12th April 2007, 03:24 AM   #13
EDDIEMUNSTER is offline EDDIEMUNSTER  Canada
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Default Bubble Wrap and Peanuts

Have you tried bubble wrap? The packing material stuff? Hammer Dynamics use this stuff to line their speakers and fill the bottom of the cabinet with packing peanuts. It is cost effective and evidently very good. I just lined my column cabinets with it and it works very well.

Something to try!

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Old 12th April 2007, 03:40 AM   #14
planet10 is offline planet10  Canada
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Cabinet Damping
Default Re: Bubble Wrap and Peanuts

Quote:
Originally posted by EDDIEMUNSTER
[B]Have you tried bubble wrap? The packing material stuff? Hammer Dynamics use this stuff to line their speakers and fill the bottom of the cabinet with packing peanuts. It is cost effective and evidently very good. I just lined my column cabinets with it and it works very well.
Only in a Hammer Dynamics... never could get them to work well... burned the cabinets (and the bubble wrap) last year....

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Old 13th April 2007, 12:47 AM   #15
kscharf is offline kscharf  United States
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Quote:
will mention, Acoustastuff is different from poly batting used to stuff pillows.
Well probably true but Madisound actually SUPPLIED the pillow stuffing when I ordered accoustic fill material. I didn't know any better at the time, and the stuff worked just fine for me.
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Old 13th April 2007, 02:04 PM   #16
pjpoes is offline pjpoes  United States
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Madisound very well may have supplied actuall pillow batting, they do sell it. It is over priced through them, and I'm sorry that you didn't realize the difference. I have used a lot of different ones now and think that long fiber batting works best. Wool is nice, but in anything other than a sealed enclosure, it invites bugs. I took apart an older wool lined horn speaker and found dead moths and other creepy crawlers inside the enclosure. I also have a bag of wool batting I had to throw away because I kept it in my basement and bugs got into it, well moths mostly. That's why I use the long fiber poly batting now, sold as acoustastuff. It may be available in other ways, but I can't find it.

Someone can show me how I am thinking wrong here, but I am a little confused. One of my early internships way back in the day involved measuring the resonant frequency of these electromagnetic clutches, and finding ways to dampen them so they didn't ring. Apparently if a ringing went on, they would throw off these sensors that were used. Anyway, I thought I was told that the key to the dampening working was that it physically adhered to the surface. I have noticed multiple comments here and on various websites that suggest that you simply place the material in the enclosure loosly. Now I'm sure, given my limited understanding of physics, that this will have an effect. But it does seem like an adhesive would further enhance that, and guarantee that the material has maximum contact across all surfaces. we used to test this, well they would to show me, buy placing the bitum mat on the surface, then testing, then adding pressure clips, testing, and then finaly with an adhesive backing, and test. As contact was increased, so was dampening. I also recall that pressure improved things. For instance, if you placed in a sort of constrained layer setup, so that the weight of one metal sleeve pressed the material against the outer part, it improved things further. I wonder if using the side foams to put pressure against the back foam would improve things any.
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Old 13th April 2007, 02:57 PM   #17
EC8010 is offline EC8010  United Kingdom
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pjpoes: My earlier post in this thread should clear your confusion.

Fibrous stuff is for damping airborne standing waves. It works because the fibres are light enough to be bent by the compression and rarefaction of the air. Bending a fibre expends energy, so the more cycles of bending too and fro in one second, the more energy can be expended. Ergo, fibrous materials have absorption that rises with frequency.

Constrained layer damping is very effective. Once upon a time, JBL made boxes out of a material that was 12mm MDF, 2mm goo, 12mm MDF. Very effective. Essentially, you need a means of converting the flexing of a panel into a shear force, and make that shear force act upon a material with good damping.
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Old 13th April 2007, 08:06 PM   #18
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Cabinet Damping
Quote:
Originally posted by pjpoes
Anyway, I thought I was told that the key to the dampening working was that it physically adhered to the surface. I have noticed multiple comments here and on various websites that suggest that you simply place the material in the enclosure loosly. Now I'm sure, given my limited understanding of physics, that this will have an effect. But it does seem like an adhesive would further enhance that, and guarantee that the material has maximum contact across all surfaces.
To further elaborate on what EC8010 is saying...

You are getting 2 different kinds of damping confused. The purpose of the fibrous material is to damp the air inside the cabinet. Gluing it to the panel walls would actually degrade its performance (for all the reasons you stated). The most effective place for this damping is actually in the middle of the cabinet.

The other kind of damping is panel damping. Personally i take the approach EC8010 mentioned earlier, where panel resonances are pushed up high enuff that there is little likelihood of them being excited (except maybe by the guy on the ouside of the box rapping them with his knuckles)

dave
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