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Old 29th November 2012, 10:44 PM   #1
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Default wool on the baffle?

I want to see if I can get an agreement from the experts here about this. I was having a dispute with a professor of physics about the use of wool to control reflections from the tweeter. He tells me there is no reflection since there is no wave with angle of incidence at pi/2 radians.

I can clearly hear the positive effects of wool on the baffle. Its also intuitively clear that it must be soaking up some of those nasty waves which are sliding along the baffle that should not really be there.

What do you guys think?

If there are no reflections whats the point of applying wool? Why does it work?
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Old 30th November 2012, 12:12 AM   #2
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Are there sheeps around the barn?

Ok just jookin'
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Old 30th November 2012, 12:31 AM   #3
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David Ralph's Speaker Pages - Felt Effects on Baffle Diffraction
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Old 30th November 2012, 01:01 AM   #4
system7 is offline system7  United Kingdom
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Felt on the baffle and around a tweeter has a rather strong following in the BBC tradition.

Morgan Jones did it in his Arpeggio speaker, and he's no fool:
Arpeggio Loudspeaker

The BBC did it on the LS3/5A small broadcast monitor:
The Unofficial LS3/5A Support Site

Putting damping on the outside of a baffle is actually the same thing as putting it on the inside, but I haven't tried it. Tweak away!
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File Type: jpg Felt_On_Baffle_Arpeggio_Loudspeaker.JPG (35.6 KB, 378 views)
File Type: jpg BBC_LS3-5A_Jeff_Bagby_Files.JPG (38.6 KB, 371 views)
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Old 30th November 2012, 01:15 AM   #5
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Quote:
Originally Posted by system7 View Post
Felt on the baffle and around a tweeter has a rather strong following in the BBC tradition.

Morgan Jones did it in his Arpeggio speaker, and he's no fool:
Arpeggio Loudspeaker

The BBC did it on the LS3/5A small broadcast monitor:
The Unofficial LS3/5A Support Site

Putting damping on the outside of a baffle is actually the same thing as putting it on the inside, but I haven't tried it. Tweak away!
So what are you saying? That since morgan was no fool, putting wool over a tweeter is a good thing?

And how does the LS3 from BBC fare with todays speakers? Clearly inferior would you say?
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Old 30th November 2012, 01:30 AM   #6
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There is not reflection, just diffraction at edges. It's easy to measure if it's happening, not necessarily easy to hear. The math for it is given by SL here Frequently Asked Questions.
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Old 30th November 2012, 01:33 AM   #7
system7 is offline system7  United Kingdom
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Why should the "ancients" at the BBC be wrong about diffraction effects? A mathematical principle once proved is true forever! Pythagoras' Theorem will still be as true in a million years as it was 2000 years ago!

I don't lose much sleep over tweeter diffraction, but it is more of an issue with narrow baffles. And there are things you can do about it. It's up to you if you are interested. Curved baffles, felt and offset drivers are the main solutions. I make no claim to be an expert, though I like Physics as much as you.

Here modelled on a 20 cm. wide baffle:
Attached Images
File Type: jpg Tweeter_Diffraction_20cm_Baffle.JPG (65.2 KB, 374 views)
File Type: jpg Tweeter_No_Diffraction_20cm_Baffle.JPG (66.7 KB, 365 views)
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Old 30th November 2012, 02:40 AM   #8
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Spica used a large 3/4 inch thick wool felt piece on the baffle board. It's visible under the grille in the picture at this link

Spica TC-50 / TC-50i Datasheet, The Spica Speaker Enthustiast

I've also conducted my own tweeter supression experiments comparing thick felt to some commercial products.

SPICA TC-50 Restoration and Measurements - Other Speakers and Electronics - The Classic Speaker Pages Discussion Forums

The thick, felted wool is very effective in damping diffraction.
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Old 30th November 2012, 02:59 AM   #9
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If Sonus Faber did it on certain models (leather surrounding tweeter) I guess there was a reason but you know it's nice too

And if it works for horns at their lips...

Last edited by sergeloc; 30th November 2012 at 03:03 AM.
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Old 1st December 2012, 05:40 AM   #10
system7 is offline system7  United Kingdom
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That's a very dramatic change to tweeter response with felt, speakerdoctor. Hmm...

I would have you know that Morgan Jones was a VERY GOOD BBC engineer in the days before computers when people did maths in their heads, though he has moved away from plastic cones and matching transformers these days. IMO, his Arpeggio Fostex speaker article is a MASTERCLASS...so educational.

Arpeggio Loudspeaker

Diffraction is a tricky business. SEAS with their DXT Tweeter and Steen Duelund take exactly opposite approaches! I merely follow with interest...
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File Type: jpg SEAS_27TBCD-GB-DXT_Tweeter.JPG (18.7 KB, 311 views)
File Type: jpg Steen_Duelund_Tweeter_Plate.JPG (57.9 KB, 109 views)
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Last edited by system7; 1st December 2012 at 05:56 AM.
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