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Cornwall Acoustic Damping Material?


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I picked up a pair of 1983 Cornwalls, and after opening them found that one of them had been scavenged by mice, probably for nest material. I've done a lot of searching here and on the web, and realize that the paper used is no longer available. What is the best course of action... re-line both with acoustic egg crate foam, polyfill, or is there another material I should consider?

 

TIA,

John Moore

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9 minutes ago, Dudeisms said:

Google “klipsch cornwall damping” and the threads you need will pop up.


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Thanks... I've been doing that all morning, and there are a ton of results with as many differing opinions. I'm considering Acoustical Cotton Batts (see pic).

ats.jpg

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The Acoustical Cotton Batts you show should work just fine. I don't think the material you choose is as important as making sure that you do the same thing to both speakers.

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The seller gave me some bonded acoustical cotton panels from Acoustical Surfaces called the "Echo Eliminator" which look like will do the job. I'm going to carefully remove the old from the damaged cabinet, install this new material, and then do an A/B test before I do the same to the other non-damaged panel. I'll report back later!

 

 

EchoEliminator.jpg

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42A6C5C9-1100-4730-8BB0-0F8B5F7ED82D.thumb.jpeg.d4b1bb9dfc71c57269579c4bc8f8cfa1.jpegI bought a pair of Cornwall 1s with the same issue. They were in a garage and the bottom ports were very inviting to mice. The panels in your pic should work good. I used an acoustical wool rug pad attached with staples with good results.

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I got the first speaker done (the one with the mice damage), and tested... they sound the same to my (65-year-old) ears. It looks like the thickness is the same as the old material, I just didn't use the string. I also installed 5-way speaker binding posts. Just waiting on my caps from JEM, and then they can get moved into the living room!

Cornwall1.jpg

Cornwall2.jpg

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On 8/3/2021 at 9:44 AM, capo72 said:

The Acoustical Cotton Batts you show should work just fine. I don't think the material you choose is as important as making sure that you do the same thing to both speakers.

If you try this again, or anyone else, the density and thickness is the important feature of the material. If you do a google search you can get up to speed on how to run an "impedance sweep" on the cabinet (just bottom octaves). It does not require much in the way of equipment (tone generator, a cheap resistor and an inexpensive volt meter). This will tell you where the cabinet vent is tuned and it is a quick measure. The "apparent volume" can be changed by the addition of the material. This is turn can affect the vent tuning. Sometimes the shareware programs like HolmImpulse and REW can automate this procedure (although be careful not to overdrive your sound card)

 

An interesting measure would be to measure the vent tuning under three conditions: 1) old material, 2) bare cabinet, 3) new material. The impedance measure can be diagnostic. Whereas, actually measuring the frequency response at the lowest octaves is more complicated and there are several logistical problems you will run into. 

 

Good luck,

-Tom

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In addition to all the above suggestion, a roll of R-13 will also work, it is cheap and can be found easily. An egg crate mattress pad from Joann's or similar will work well too.

 

In this particular case, the insulation is strictly to absorb standing waves, not to add volume to the enclosure. Will an enclosure with and without insulation measure different for tuning frequency? Yes, slightly, but the change is miniscule if the insulation is installed with the premise of only reducing standing waves.

 

 

 

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If the roll of R-13 (the fluffy stuff) is compressed, then it might have an effect.

 

There is little energy coming off the back of the mid-horn and tweeter, so we don't need to worry about standing waves in the cabinet at those mid and high frequencies.

 

However the woofer will have energy coming from the back certainly (at the very low frequencies it comes through the vent, obviously). But the rest of the low frequency bandwidth -- let's think about it. Below the crossover point, the frequencies have wavelengths of 20-something inches and larger. An inch of material has some effect, but I am not sure how much. Some materials are just inappropriate (closed cell foam for instance, which is sometimes sold at Joannes as mattress pad incidentally). So if you really want to reduce standing waves you would need much more material (I am not advocating this BTW). The standing waves would only occur at certain frequencies and be quite dependent on the box geometry. Is the idea that you are somehow "hearing" the standing waves that are inside the box? My brain is small, but I don't understand the thinking.

 

The JBL engineers when referring to their horn systems (ported woofer with horn load mid and highs - similar to a Cornwall) talk mostly about "increasing the apparent volume" by lining the cabinet with pressed fiberglass. Little discussion is given toward possibly eliminating "standing waves" in those systems. 

 

Good luck,

-Tom

 

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The standing waves I am referring to are more mid-bass & mid-range frequencies. I can't speak to a conversation taken out of context, but from experience, a lot of different insulating materials will work for the above application. Are they all equal? No, but they seem to work in varying degrees. I don't think anyone here was looking for the "perfect" material to accomplish the given task. 

Edited by Curious_George
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I understand your point and I am not saying that there might be an issue with standing waves ...... however,  where is the energy coming from for these mid-bass & mid range frequencies?

 

There is very little energy coming from the back of the midrange horn. The driver is somewhat sealed and the horn is structurally solid. The sound mostly goes into the room and not to the inside of the cabinets. The woofer is different story

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When you say damped, do mean the energy is absorbed?

If so, then the choice of material, its density, its thickness are all quite important. Especially, as you go down in frequency. The wavelengths are large and an inch of material may not do much. 

I am going to stop now. 

 

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Well - I have both dampened with the new material, and new caps from JEM... I've moved them into the living room, and so far they are fantastic! Probably because these are mine, I like them better than the pair of my friend's that I updated (Crites B2 boards, and new tweeter diaphragms). I'll probably sell the KG5.5s now, since there's just no place else in the house they will fit.

livingroom.jpeg

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