Acoustic Felt...

[rogoll]

I just read Roman's article on the effects of grills in which he mentions "acoustic felt". My question is, where can I obtain acoustic felt and how does it differ from "regular" felt?

[romanbednarek]

Re: Acoustic Felt...

I got mine from McMaster-Carr but I don't recall the exact type (I bought two rolls, one that was 1"x1" and another that was 1/2"x1").

Dave Ralph (dlr) is the expert in this are and he could offer better advice than I. You can check out his website here... http://www.speakerdesign.net/

... I noticed that he has a few links regarding acoustic felt.

[dbe]

Re: Acoustic Felt...

I just read Roman's article on the effects of grills in which he mentions "acoustic felt". My question is, where can I obtain acoustic felt and how does it differ from "regular" felt?

The guy that has probably done more testing of the acoustical felts around here is dlr. I'm sure he will chime in here, but here is alink to his page on this:

http://www.speakerdesign.net/felt/felt_ring_vs_blocks.html

Like that Dave, this Dave prefers wool felt for acoustical use because it is a hollow organic fiber. The interstices in the fiber are what give it the characteristics desireable for acoustic (adiabatic) applications.

I get mine from here:

http://www.mcmaster.com/#felt/=46t2bo

Just don't forget to moth proof it

Dave

[edlafontaine]

Re: Acoustic Felt...

F-13 has favorable properties and is available in several thicknesses

[dlr]

Re: Acoustic Felt...

F-13 has favorable properties and is available in several thicknesses

Yes, that's what I used to use most often, it's the best bang-for-the-buck. F11 works marginally better, but at quite a bit more cost.

dlr

[marlboro]

Re: Acoustic Felt...

There was an article in one of those newstand stereo mags that never take advertising awhile back(5 years) on the use of the felt. They experimented using several thicknesses and several widths. They found that you needed at least 1/2 inch thick and you needed to extend it to cover the whole baffle. In addition, you had to curve it around the baffle at the edge and the radius of the curve had to be a minimum of 1.5 inch, prefer at least 2. It had to be a very gradual curve.

I almost did it with my arrays, but I had put too much energy into the oak baffle by that time.

Marlboro

[brianpowers27]

Re: Acoustic Felt...

I believe that I used 3/4" f-13 from mcmaster-carr. The difference was measurable. I no longer use it because I don't do grills and I think it is generally ugly.

It's worth mentioning that getting the felt to close to the tweeter causes loading.

P.S. THere is a site that does custom felt cutouts specifically for speakers.

[dlr]

Re: Acoustic Felt...

There was an article in one of those newstand stereo mags that never take advertising awhile back(5 years) on the use of the felt. They experimented using several thicknesses and several widths. They found that you needed at least 1/2 inch thick and you needed to extend it to cover the whole baffle. In addition, you had to curve it around the baffle at the edge and the radius of the curve had to be a minimum of 1.5 inch, prefer at least 2. It had to be a very gradual curve.

I almost did it with my arrays, but I had put too much energy into the oak baffle by that time.

Marlboro

I agree partially. It should be at 1/2" thick, yes, but it the coverage is very case dependent. I've found situations where full coverage was useful and those where a small amount of the correct thickness and geometry was sufficient. Recently I've found good response with just a triangle.

The most important piece, however, is one between drivers. The diffraction from a nearby driver often is far more influential. It is almost useless to the sides and below a midwoofer and definitely not for a woofer.

If you have a good roundover, I've never, ever found use in having felt. Small roundovers, yes, but even then you need to experiment. There is no "one size fits all" approach.

I've not put up on my site, maybe this winter I will, an article published in June 2005 audioXpress on diffraction control with felt.

dlr

[marlboro]

Re: Acoustic Felt...

DLR,

That might have been the article from AudioXpress, since its certainly in the time period and I remember pictures of diamond shaped felt. It would be interesting to see how much(if it is the same) I remembered accurately from the article.

Marlboro

[PunkSweeper]

Re: Acoustic Felt...

*runs around house yanking grills off speakers*

[billfitzmaurice]

Re: Acoustic Felt...

They experimented using several thicknesses and several widths. They found that you needed at least 1/2 inch thick and you needed to extend it to cover the whole baffle.

That depends on how low in frequency you need the felt to work. Just as is the case with damping the inner surfaces of woofer and mid enclosures the lower you go the thicker/wider it needs to be. It's hard to imagine needing to go 1/2 inch thick and covering the entire baffle to work with the short wavelengths of an average tweeter, but that doesn't mean there's no benefit in doing so. It does mean that the improvement heard is as much from the lower frequency drivers as from the tweeter.

[JRT]

Re: Acoustic Felt...

I agree partially. It should be at 1/2" thick, yes, but it the coverage is very case dependent. I've found situations where full coverage was useful and those where a small amount of the correct thickness and geometry was sufficient. Recently I've found good response with just a triangle.

The most important piece, however, is one between drivers. The diffraction from a nearby driver often is far more influential. It is almost useless to the sides and below a midwoofer and definitely not for a woofer.

If you have a good roundover, I've never, ever found use in having felt. Small roundovers, yes, but even then you need to experiment. There is no "one size fits all" approach.

I've not put up on my site, maybe this winter I will, an article published in June 2005 audioXpress on diffraction control with felt.

dlr

I saw this and thought you might find it interesting:
(follow link to see the rest of the whitepaper)

[dlr]

Re: Acoustic Felt...

I saw this and thought you might find it interesting:
(follow link to see the rest of the whitepaper)

Thanks for the link, I've never seen that one. I wonder if they ever received their patent? I know that Dunlavy got one, it was unenforceable due to prior art, but I didn't think that it was an AR patent.

dlr

[DDF]

Re: Acoustic Felt...

Here are some measurements with felt, with pictures. On axis there is very little to no impact. The biggest impact of a full baffle treatment was to greatly reduce the off axis energy of the tweeter. This calls for a redesign of the xover vs no felt.

The second effect, less pronounced, is reduction in the diffraction peak.

FWIW I didn't like the balance that this obtained, it dulled the speaker, and it couldn't be corrected with on axis tweaks. The tweeter just didn't energize the room enough for me when I tried it.

This was taken with F13 1/2" McMaster Carr felt, great stuff.

I agree with DLR, the best use of felt is between the woofer and the tweeter. See the second picture with the cylindrical enclosure. This greatly cleaned up the tweeter's response without sucking the life out of it. In this application, it also allowed the decorative wood caps. The felt was effective enough that there was no measured difference with the cap on or off.

Dave

[---k---]

Re: Acoustic Felt...

Just FYI, some measurements CJD took while developing my Khanspires. I don't remember the exact felt size, but I believe it was 1/4" thick, 4" wide, by like 6" long. It was just a quick and dirty test with strips of felt.
From: http://htguide.com/forum/showpost.ph...&postcount=315

* Black is straight response
* Blue is synthetic felt strips placed vertically on either side of the tweeter grille (so about an inch and a quarter apart)
* Red is wool felt strips placed vertically on either side of the tweeter grille