I don't know exactly what the correlation is between absorbtion coeficients and performance in stuffing an acoustic suspension loudspeaker.
I'd have to get my hands on some of the recycled denim material and test it as I have always done in my little AR4x to see how it impacts Fc, Qtc and Re.
Well I don't know that either, but it would seem to me that there is more to box stuffing than just the effect of those variables, especially since simply adjusting the actual box volume can optimize those parameters yet still not sound good without some stuffing to attenuate the back wave.
Here is a link posting attenuation coeficients for various materials, including Bonded Logic Ultratouch:
http://www.bobgolds.com/AbsorptionCoefficients.htm
I is not clear how the tests are performed, but it's the only thing I've seen that appears to tests various materials in a similar fashion.
Ultratouch also shows their results, albeit marketing, of their material vs. fiberglass here:
Bonded Logic - Acoustical Products - UltraTouch+
The Ultratouch is at least as good, if not better than, FG above 125Hz, then falls off in comparison below that. So if your favorability parameters are simply to increase box volume at box resonance frequencies likely to be below 125Hz, then perhaps FG will do a better job at that. However, a properly sized box will, too. But then, there has been plenty of albeit subjective preferences for Ultratouch reported.
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I can only guess that "Bubble Wrap" must mean something different in the US, I can't believe that what we in the UK know as Bubble Wrap would work at all.
I found this on Bonded Logic's web site. The results here seem at odds with earlier 125 hz performance quoted in a post. Don't know why except to say conditions for the test were not made completely clear (re. batt thickness, etc..). I can only assume conditions were the same for both materials.
The chart shows UT on par with FG up to the 300 hz level and beyond that, about 5-10 dB better trans. loss than FG.
The chart shows UT on par with FG up to the 300 hz level and beyond that, about 5-10 dB better trans. loss than FG.
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Very typical response. But those who actually measured and listened to different damping materials know better. I don't have the measurement data any longer, but if you're inspired and are capable of measuring, go ahead and do it. I've had this same discussion on numerous forums in the past ten years and it's always the same old tune, doubts, insults, and then someone does actual measurements and everyone is left surprised.
There's nothing that works better than bubble wrap. Myself and other internet forum members (some famous ones) have measured everything we could think of and nothing even came close to the effectiveness of bubble wrap in stopping reflections as well as standing waves.
I may have hijacked this thread a bit by touting FG as the best performer in improving A.S. Fc, Qtc and Re as opposed to the OP's original question regarding back wave attenuation.
So, ridikas, what magic can bubble do regarding Fc, Qtc and Re in an A.S. Speaker? Those 3 properties are as vital, if not more so, than attenuation in an A.S. speaker.
Bubble wrap is very similar to fiberfill in regards to Fc, Qtc, increasing virtual enclosure size, etc. Most people make the false assumption that it decreases the volume and that's not the case at all. It actually increases the volume, just like any other damping materials. But bubble wrap is magnitudes better than anything else in stopping standing waves for example.
How much to stuff? I usually use a crumpled sheet of 25"X50" to stuff a 15 liter box of the medium sized bubbles (10mm).
If you have the ability to measure and don't mind taking the time for set up, go ahead. It's an eye opener.
In post #19, you said:
"And completely ineffective in just about every way:
Self adhesive grey foam
Fiberfill
Acoustastuf "
Do you wish to change your statement?
No I don't. All three of those materials are very ineffective in stopping reflections and standing waves, unless the layers are very thick for foam (over 4") and the stuffing is tightly packed, over a pound for a 15 liter volume. These are unrealistic scenarios. As for increasing Vb and effecting Qtc, just about anything will. A roll of toilet paper will.
Your curve is for Sound Transmission Loss which is usually given as a property of a wall construction. I am guessing that they built a stud and drywall wall and used FG and the other material within it and these are the curves of transmission.
The .95 reference was to measurements of mean alpha (absorption) as tested in a reverb room. This is the standard test for acoustical absorption of any sample material. A bunch of pieces of a known square footage are put into a reverb room and the before and after reverb time are used to calculate the absorption percentage vs. and open window.
An alpha of 1 means total absorption but don't freak out that you will see legitimate measurements of 1.1 or so (i.e. more than 100% absorption) This is a known anomaly of the measurement approach.
This is the right measure if the question is: how much of the back radiation will the stuffing absorb? At the same time it relates to reduction of standing waves as sound absorbed will not be reflected!
As to bubble wrap, I think it is great stuff because when I drop my cheap a$$ speakers and the magnets fall off, it catches them without damage.😀
David
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Shame on Bonded Logic for using that data in their UT+ 'Sound Control System' area of the site
Someone is going to have to explain how any damping material changes Re in any way shape or form. That is a function solely of the coil of wire, and is affected only by heat.
Ya got me lemans. My bad. The T/S property I meant to reference was Zmax, not Re. Darn diyaudio, after 1/2 hour, you can't go back and make corrections. Your words are locked in cyberspace forever! :-(
Zmax does vary with stuffing type and amount.
Here is an example of how the box resonance freq. shifts both to the left and downward as stuffing density is optimized. There is a limit however to that movement.
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