View Full Version : Diffraction Control for Polk SDA Tweeters
I have been using Jim Goulding's "diffrationbegone (http://www.diffractionbegone.com/)" wool felt surrounds on my SDA 1C tweeters for a while with excellent results. I came across the following review in Stereo Mojo (http://www.stereomojo.com/Diffraction%20Be%20Gone%20Review/DIFFRACTIONBEGONEREVIEW.htm) of Jim's anti-diffraction surrounds (albeit the review is not Polk-centric). However, the review eruditely states what the surrounds do to speaker systems, and shows some photos including those of some measurements. Thus, this is my lazy way of getting around writing my own review of what the surrounds similarly do for my SDA 1Cs.
I add that the custom work Jim did for me (so that I could use the felts and still use my speaker grills) was excellent; I simply needed to provide Jim with the exact measurements. I would not recommend trying to cut the surrounds yourself, since the material is somewhat thick and I feel you'd need probably a machine, and certainly more than regular scissors, to match the exactitude of Jim's professional cuts. Furthermore, I note I needed two sets of surrounds for each 1C, since each speaker has one pair of tweeters.
Happy listening!
Looks like $5 worth of materials from a craft store. I'm not saying they don't work, but you could make something yourself easily.
Tannoy does something similar on their Dimension line. They use velvet instead of felt though.
george daniel
02-02-2008, 01:17 PM
Got a pic of the 1C's with em'?
Looks like $5 worth of materials from a craft store. I'm not saying they don't work, but you could make something yourself easily.I don't know if you could make it yourself, and I have no agenda to discourage anyone so inclined. I do know the wool felts are fairly thick (3/8" - 1/2"), and I don't have the means to make them.
My point is that they do work extremely well, in my application.
Got a pic of the 1C's with em'?I don't have a digital camera. However, my daughter is coming in from college for a visit today, and if she's got her camera, I'll see if she can snap a couple pics. If that doesn't work, my GF is coming over to watch the SuperBowl (GO PATS!!!!) this Sunday, and I could ask her to bring her camera over. Good question / request, George. I'll see if I can get some photos up in the next week or so.
george daniel
02-02-2008, 01:44 PM
Great,, I had the opportunity to speak with Jim about a year ago,on an unrelated subject,,but he seems to be a honest and well experienced audio guy.
Gaara
02-02-2008, 02:01 PM
I don't know if you could make it yourself, and I have no agenda to discourage anyone so inclined. I do know the wool felts are fairly thick (3/8" - 1/2"), and I don't have the means to make them.
My point is that they do work extremely well, in my application.
Why not? I have felted a few pairs of speakers, the felt is usually <$2 and glue is <$2. These look much nicer but at 10x the price...
F1nut
02-02-2008, 03:09 PM
MadMax and I played around with similar devices some years ago with questionable results. I threw mine away, not sure what Chuck did with his.
WilliamM2
02-02-2008, 03:13 PM
I have access to dies of all sizes at work, both round and rectangular. It would be a snap to make these in less than a minute.
I would prefer to make my own, just so I can have black. Is this one piece with a hole for both tweeters? Pics on the SDA's would be great.
Have finally got the hardware / software to take a couple pics, per earlier requests. Please see the attached files.
jakelm
02-07-2008, 07:11 PM
Would that localize the sound? Raising the area around the dome, give more of a tunnel like effect, with a more narrow sweet spot?
Would that localize the sound? Raising the area around the dome, give more of a tunnel like effect, with a more narrow sweet spot?I haven't found that to be true. I have found that my speakers seem to disappear.
WilliamM2
02-08-2008, 01:40 AM
Thanks for the pics. How large are the holes for the tweeters?
If I do try this I will probably do it as a single piece.
Thanks for the pics. How large are the holes for the tweeters?
If I do try this I will probably do it as a single piece.
I haven't measured the hole; however, there's a tape ruler in each of the photos that should give you a pretty good idea of the dimensions.
RuSsMaN
02-08-2008, 09:33 AM
I don't know if you could make it yourself, and I have no agenda to discourage anyone so inclined. I do know the wool felts are fairly thick (3/8" - 1/2"), and I don't have the means to make them.
My point is that they do work extremely well, in my application.
Great post! Sounds like a winner. I don't know why the 'acoustic blanket' rarely appears anymore, if it all. AR was successful with it, so was Infinity. From big floor standing full range speakers, to little British monitors - it just seems to WORK.
jakelm
02-08-2008, 10:35 AM
I would like to see if this will work around my Peerless on my 7's. I might use some .5" acoustic foam, I used from Parts Express (http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-520).
steveinaz
02-08-2008, 10:36 AM
William, looks like 2.5"
I would like to see if this will work around my Peerless on my 7's. I might use some .5" acoustic foam, I used from Parts Express (http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-520).
Jake, I don't believe that was made for around a tweeter. It appears to be made for mid and low range frequencies. You can pick up felt at your typical fabric store, or you can get fancy and use velvet like Tannoy uses.
jakelm
02-08-2008, 10:43 AM
Jake, I don't believe that was made for around a tweeter. It appears to be made for mid and low range frequencies.
Your probably right.
You can pick up felt at your typical fabric store, or you can get fancy and use velvet like Tannoy uses.
Red velvet cake....mmmmmmmm
The fabrick I have seen is only about 1/8" thick, do you layer it?
The fabrick I have seen is only about 1/8" thick, do you layer it?
No, no need to for HF.
http://www.polkaudio.com/images/showcase/448_5_big.jpg
Taken from our own gallery.
I want to clarify that my use of the term "felt" in my original post may be unintentionally misleading. Jim Goulding of diffractionbegone uses a thick, compressed high grade wool - the surrounds I have contain absolutely no synthetic (i.e., hard, refractive) materials.
I don't want to do a disservice to Jim or anyone else following this thread; thus, I hope this clarification helps. Happy listening!
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