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Old 3rd December 2012, 02:29 PM   #51
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Quote:
Originally Posted by speaker dave View Post
This article has good graphs of the difference with/without various layers of felt.

Diffraction Doesn't Have to be a Problem
I was wondering if it's just diffraction effects that can be seen in these measurements or if there's also a certain amount of absorption. One would need to look at off-axis data too.
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Old 3rd December 2012, 02:35 PM   #52
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Originally Posted by markus76 View Post
I was wondering if it's just diffraction effects that can be seen in these measurements or if there's also a certain amount of absorption. One would need to look at off-axis data too.
Check out the link in post #3. The far right spreadsheet column has clickable off-axis data for 'no felt' and for 'felt'.

IMHO, absorbtion plays a large role when 1/2 inch or so thick wool felt is utilized. It's tangled mass of coarse fibers provides an ideal absorber. This felt could also be used to dampen internal cabinet reflections. After all, thick felt's absorbtion properties are exactly what the car builder use this stuff for.
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Old 3rd December 2012, 02:45 PM   #53
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IMHO, absorbtion plays a large role when 1/2 inch or so thick wool felt is utilized. It's tangled mass of coarse fibers provides an ideal absorber.
Is the flow resistivity of such felt available?
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Old 3rd December 2012, 03:15 PM   #54
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From what I've been able to research, felts run in the 0.5 to 0.7 absorbtion coeficient range. That doesn't seem as efficient an absorber as FG 700 series sheets. But effective none-the less.


Here is a link to a little bit of info.
SAE & Sheet Felt
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Old 3rd December 2012, 03:54 PM   #55
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Originally Posted by markus76 View Post
Why not use a lot more porous absorption around the speaker and control directivity? While it is a massive waste of energy it doesn't have the problems associated with waveguides.
I've done some experimentation with this and it can be quite effective (though tends to be UGLY).

I regularly use acoustic absorbtion as part of my speaker designs, it's just another tool in the loudspeaker design kit. Around the edges of horns for example, it's a lossy way of damping the mouth termination without having to make a large mouth. It doesn't preserve energy the same way, but if the passband's above the horn cutoff anyway...

I liken it to an egg. Drop an egg, it breaks. Roll it down a ramp, it keeps rolling and is like a fullsize horn. Drop it onto a pad and it doesn't keep rolling but you still have your egg.

My first recommendation to many people complaining of bright sound is to felt the baffle, it suppresses the power response peak above the XO of typical cone 'n domes.

One thing I've been meaning to try is the use of acoustic absorbtion to damp the modal character of OB cancellation. Haven't tried it out yet though.
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Last edited by badman; 3rd December 2012 at 04:20 PM.
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Old 4th December 2012, 08:11 AM   #56
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I've done some experimentation with this and it can be quite effective (though tends to be UGLY).
Like this?

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Old 4th December 2012, 03:10 PM   #57
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That's a heck of a stack of stuff- My work tends to be closer to the drivers and more structured.
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Old 4th December 2012, 03:25 PM   #58
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That's a heck of a stack of stuff- My work tends to be closer to the drivers and more structured.
Was just testing reflection patterns.
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Old 5th December 2012, 02:17 PM   #59
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Default Interesting "wool" application.

I stumbled upon this thread and thought I would offer up a recent discovery of some speakers I obtained some 20 years ago, but had in storage in their original boxes for perhaps the past 15. I recently put them into service connected to a Sony STR-6065 and Pioneer SX-780 to see how they would sound. I have now played them for the best part of a week for 8 to 10 hours a day listening to everything from NPR classical on some very clean local stations, to jazz on some fine Denon CDs I've had for many years. I had forgotten how surprisingly good and well balanced these speakers sound given their humble heritage. Indeed, I expect that already more than a few readers have started with the guffaws and scoffs to themselves. But no matter. I have other speakers that were several times costlier than these and are not as pleasing.

What I though may be of some interest to the readers of this thread is the application of the design and wool felt. The speakers are twin ported bass reflex with 8" twin mid and full bass woofers and a center miunted1 1/2" soft dome tweeter. The tweeter also has a large area of felt applied around the tweeter and the grill frame has what the makers refers to as an "acoustic lens" built into it. The twin ports can also be plugged with some supplied hard foam plugs, which I find seems to work well depending where I place the speakers and in what sized room.

With that, here are a few pictures of what I find to be a very nice and well balanced speaker especially given it;s humble heritage from American Acoustics which purportedly was an MTX brand. Perhaps they made some good product for a short period of time?

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Last edited by Phase700B; 5th December 2012 at 02:35 PM.
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Old 5th December 2012, 04:25 PM   #60
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Yes, looks cheap but effective.

I like that grille design. It is similar to one that Polk did that brought the grille in close to the tweeter (with a very variable distance around it). Works quite well and I copied it for the Snell QBX models.

David S.
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