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Old 2nd December 2012, 07:39 PM   #41
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I'm not floundering. This ain't rocket science. I gave a link to some experiments I ran that clearly show needled wool is very effective. The thicker the better.
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Old 2nd December 2012, 08:16 PM   #42
system7 is offline system7  United Kingdom
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Well, I think it IS ROCKET SCIENCE or at least COMPUTERS which is the same thing to my simple mind...it says so here:
Quote:
The compact speaker is the result of exhaustive research and the latest technology in computer assisted optimization.
Click the image to open in full size.

That's sure a dumb looking speaker. (Just my opinion....)

Now I found some confusing and unreadable stuff by some guy called Carl, which I have knocked into shape on one page so that at least we get the idea. Curve 2 is with the thick felt, Curve 4 is without and you can ignore the rest:

Click the image to open in full size.

So what's going on here?
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Old 2nd December 2012, 08:27 PM   #43
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Steve, check out McMaster Carr. They sell thick needled felt. It's a b*tch to cut.
Don't ignore those other curves. They show those other commercial products aren't nearly as effective.
You may not like the looks of the Spica, but you would like the imaging. They still are a very sought after speaker on the bay and elsewhere.
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Old 2nd December 2012, 09:24 PM   #44
system7 is offline system7  United Kingdom
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Commendable job of not rising to the bait, Mr. SpeakerDoctor! That Spica has some nice features.

I'm starting to form a notion that the felt makes the tweeter behave as if there is no baffle at all. More of a point source, and less beaming. The 6db fall in output makes sense. Why square cutout, and not round or elliptical? Dunno...will sleep on it.
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Old 2nd December 2012, 09:54 PM   #45
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Quote:
Originally Posted by system7 View Post
Commendable job of not rising to the bait, Mr. SpeakerDoctor! That Spica has some nice features.

I'm starting to form a notion that the felt makes the tweeter behave as if there is no baffle at all. More of a point source, and less beaming. The 6db fall in output makes sense. Why square cutout, and not round or elliptical? Dunno...will sleep on it.
You can ask John Bau about the cut out. He's still around. He does respond at the yahoo groups spica web site.
I forgot to mention that the SPica imaging rivals that of electrostatic panel speakers.
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Old 3rd December 2012, 10:13 AM   #46
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This article has good graphs of the difference with/without various layers of felt.

Diffraction Doesn't Have to be a Problem

Note that he finds that even natural wool felt has some reflective properties and that it shouldn't be too thick or too close to the tweeter. His best results have the thickness building up (1/4" then 1/2") around the tweeter. For the same reason, the cutout shouldn't be circular and centered on the tweeter.

David S.

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Old 3rd December 2012, 11:32 AM   #47
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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.
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Old 3rd December 2012, 11:34 AM   #48
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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

Note that he finds that even natural wool felt has some reflective properties and that it shouldn't be too thick or too close to the tweeter. His best results have the thickness building up (1/4" then 1/2") around the tweeter. For the same reason, the cutout shouldn't be circular and centered on the tweeter.

David S.
David R's study was referenced back in post #3. It's a very good study as well. I suspect system7's feeling of floundering may have to do with the empirical nature of managing diffraction with felt; as opposed to having a computer model that predicts the outcome.
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Old 3rd December 2012, 02:08 PM   #49
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Originally Posted by speakerdoctor View Post
David R's study was referenced back in post #3. It's a very good study as well. I suspect system7's feeling of floundering may have to do with the empirical nature of managing diffraction with felt; as opposed to having a computer model that predicts the outcome.
Hi Carl. Sorry, I missed that but did look through your good measurements.

As to the computer model, we can at least model the other way around and see the effects of diffraction and edges. I dabble with "the Edge" when I want to see what the potential effects are. The optimum result with surface damping or heavily radiused edges would be to revert to the 2 pi response (and a smooth 4 pi transition) and have none of the residual diffraction effects.

By the way, at PSB I had the latest LEAP software and his diffraction modeling is quite sophisticated. I remember doing a simulation of response of a driver on the box. When I moved past 90 degrees all response dissapeared. It turned out I had "turned off" diffraction modeling and without diffraction there is no response beyond the 90 degrees of the baffle.

We wouldn't have dreamed of these tools 30 years ago. We knew very well the principles involved but the thought of a PC program to give a fairly accurate response curve including diffraction effects.....

David S.
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Old 3rd December 2012, 02:18 PM   #50
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In my little study I was simply tryng to show the ineffectiveness of some commercial products on the market vs relatively thicker, needled wool felt. OTOH, David R did a much more comprehensive empirical study of felt's effects.
BTW, the felt I used in my study was exactly the same as David R. used. I believe mine was the SAE F11 type which, I imagine, is still available from McMaster-Carr.
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