Question About The Effects of Damping Materials In the Compression Chamber of a BLH - diyAudio
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Old 18th January 2010, 04:56 AM   #1
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Default Question About The Effects of Damping Materials In the Compression Chamber of a BLH

In the process of the final assembly of the Sachiko speakers. Got them up and running at the moment, but have not made final decisions on damping material.

At the moment I have two inches of Dacron batting on the top/bottom and rear wall of the compression chamber. I also inserted a think 1/2 sheet at the back end of the throat to the horn to filter out some low level vocal information that was making it out of the horn.

Trying to determine if there are any alternate damping materials that would result in better performance in this application.

Parts Express makes a product called Sonic Barrier, that looks to be of similar construction to Black Hole 5. Its only a three layer design, versus four of the BH5, but its far more reasonably priced.

The question is this. Is there any negative effects to driver performance using this kind of material in the compression chamber? I understand that it performs well in a bass reflex design, but does it change the loading on the driver at all by the compression chamber?

Curious to know what materials others may have experimented with in a back loaded horn cabinet.

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Mister Pig
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Old 18th January 2010, 08:13 AM   #2
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One of those things that's suck-it-&-see TBH. I have no idea how you would define 'better', so YMMV. There's nothing wrong with the dacron.

Incidentally, FYI, back-horns (with a tiny handful of exceptions) do not really have a compression chamber per se. The room they are sitting in is their compression chamber. They generally do possess a low-pass filter chamber though.
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Old 19th January 2010, 09:44 PM   #3
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"The room they are sitting in"

Seems to me that we could change all sorts of "passive" components; caps, transformers and so on. We could try a SE amp or a PP....and so on...el34's 300b's....and of course we can play with stuffing in the cabinets... but i have found REALLY BIG changes to the quality of the sound by opening the windows or adding some bass absorbers to the room or (something i have tried with all the speaker amp combinations i have owned) taking them outside and setting them up in the garden. The combination of the room and the speaker is so important.

Sorry...hope this comment is not entirely out of place...
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Old 20th January 2010, 01:48 AM   #4
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Damping material is a very personal matter, its best to try and keep trying differing amounts /locations until you get the sound you like, the less the better. Ensure the speakers have broken in before trying to adjust the damping otherwise its a moving target

Keep damping away from the filter chamber path.

One of the main uses of damping material in most cases (such as this) is controlling reflections and to effectively control them, damping should be fairly central. Think behind the cone. I usually make a "ball" of damping material and "hang" it in the centre of the enclosure, thats where the reflections are meeting and causing the most problems.
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Old 20th January 2010, 07:33 PM   #5
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I, as well, used damping above and below the driver. What you're suggesting is to possibly add some more directly behind the driver as well? Might work... I'm noticing some slight midbass resonances (ie specific bass guitar notes) that I would like to smooth up.
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Old 20th January 2010, 09:59 PM   #6
hm is offline hm  Europe
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Hello,
my experience shows,
softfibre is the best material for BLH
in the press chamber and the first m
of the horn to silence lamda/4 over 100 Hz.
look my horn constructions, the RDH20 is 50%
made of softfibre.
( material feedback Schalmei from andrew)
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Old 21st January 2010, 01:16 PM   #7
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Pardon my jumping in, but I believe what hm is calling softfibre is close to what in the US is called "particle board," i.e. wood as opposed to stuffing material. I recently disassembled a German horn (an imported Einstein Rigoletto imitation) and got a first-hand look at this material.
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Old 21st January 2010, 02:22 PM   #8
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soft fiberboard help.... please

see post # 13

I call particle board a totally different material, what I refer to as particle board is "large wood chips" bonded together with glue and heat and sold in the usual 4' X 8' sheet size.

Softfibre is more like MDF which has gotten wet and expanded but not broken, IOW it is very soft and can be broken by hand.

Horst, I do not think the Softfibre would work here because it would change the chamber volume too much. I think the speaker would need a total redesign to accomodate it.


Andrew
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Last edited by Andrewbee; 21st January 2010 at 02:31 PM.
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Old 21st January 2010, 03:13 PM   #9
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Hi Andrewbee,

Aha! Okay, I stand corrected. The stuff inside my German horns is definitely closer to particle board, and from hm's pictures, I incorrectly thought they were the same stuff. However, you are correct -- looking close-up, it's not particle board:

http://www.hm-moreart.de/schalmeihartgasbiker.jpg

My apologies!
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Old 21st January 2010, 03:16 PM   #10
hm is offline hm  Europe
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Hello,

andrew you wrote (Schalmei):
"The board I get here is made by a company called "cellotex" (sp). Its also known as "hushboard" and probably other names as well. It looks similar to mdf that got
wet and expanded and breaks pretty easily."

right,
here a link i hope it works in english:
Produkte Detail - PAVATEX-Standard Dämmplatten

and look at "about what" in the middle a pic, on my HP
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