felt application

[KJP]

Just looking for an opinion on my felt application

Is good?



This will get covered by grill cloth yet to be ordered.

[ThomasW]

That's fine.... :T

[dlr]

Two comments

Just looking for an opinion on my felt application

Is good?



This will get covered by grill cloth yet to be ordered.

The piece on the angled baffle section at the top is most likely not needed. I never found much improvement when I tested that.

I'd open up the area around the tweeter a bit more. It is possible to overdo it and restrict the output and add reflections. Increasing the distance between opposing sides by 1" to get 1/2" extra distance from the dome on each of the four sides is probably closer to optimal.

[KJP]

Thanks for the input guys.

The piece on top was done with felt only because I found it easier to cut all the angles in that rather than wood.

I can always go bigger. Im glad you dont think I went too big. As it is I have clear view of the entire tweeter dome out to about 55 degrees to the side. Another half inch on each side would bump that to about 65 degrees. My focus was on dispersion and not reflection. How bad can this stuff reflect?

[wkhanna]

My Signets came with this when I bought them back in '94.
I have seen very few other speakers with this treatment to the tweeters.
The pattern used is interesting, I thought.

[Landroval]

I think having that thick felt so close to the tweeter would make it sound dull and muffled. Some of this can be compensated in the crossover, but I think you should first make a few test felt pieces for the tweeter with different sizes of openings and see which one sounds the best.

[dlr]

You'd be surprised

I can always go bigger. Im glad you dont think I went too big. As it is I have clear view of the entire tweeter dome out to about 55 degrees to the side. Another half inch on each side would bump that to about 65 degrees. My focus was on dispersion and not reflection. How bad can this stuff reflect?

Covering the front entirely can get to a point of diminishing returens, but it won't hurt. The one issue is having it too thick/too close, the latter being most problematic.

Felt is not 100 absorptive. It varies with the frequency, as do all types of damping materials. The specifics of the reason for reflections is beyond me, one would have to know the physics. I measured signficant peaks/dips in off-axis measurements at higher frequencies. The peaks can only be due to reflections at thes points.

However, the lower frequencies, below 10K, are significantly impacted by felt that is too close/too thick. I suspect that it's because at lower frequencies the impact is due to teh proximity not allowing the wave to fully establish. I don't know the wave mechanics involved specifically, but the wave has to reach some distance, probably related to the wavelength, before it is fully established such that it won't be altered by the damping material. This is on-axis, of course. Off-axis the effect is the same, but since the distances from all points that face the dome are different, the altered pattern is also different.

This is a bit of a lengthy, incomplete answer, but I don't know how else to convey my thoughts without them seeming to be simplistic.

[KJP]

Well I did some searching and found a couple of absorption coefficient lists for felt. here and here
In both, the absorption seems to be indicating increasing reflectivity with increasing frequency. :huh:

I also came across this pdf from Avalonacoustics where they speak of beveled cutouts in their grills felt.

I think I shall do as Avalon does. :T

[KJP]

I like it.



This stuff machines pretty nicely with electric pet clippers.

edit: This opened it up to 65degrees

[dlr]

Good info

I like it.



This stuff machines pretty nicely with electric pet clippers.

edit: This opened it up to 65degrees

I've been looking for easier ways to cut felt, primarily a straight cut. Slow work with an X-Acto knife is the best I've found so far.

I haven't tried trimming much as it seemed frustrating, but this looks like a good idea. It would never have occurred to me use pet clippers.

[KJP]

I did all my straight cuts with a razor blade. Once cut shaving angles with the clippers was the way to go. :T

Shaving my speakers came across as pretty funny to my wife for some reason. :huh:

[RandyMidd]

Does the use of felt help minimize diffraction?

I've yet to power up a 3-way that uses an OW1 tweeter...it reportedly has a wide dispersion, but Dennis Murphy found it to make a completely different FR in cabs with and without rounded edges...it had a diffraction peak and dip without the roundovers.

I can't roundover my cabs because they're finished...would felt likely help?

How thick and where to buy?

[ThomasW]

http://home.comcast.net/~audio-worx/page90DIY-FeltPads.html

[RandyMidd]

Cool..I'm going to McMaster Carr soon anyways...I'll pick up some felt and experiment.

[dlr]

Try this link

Cool..I'm going to McMaster Carr soon anyways...I'll pick up some felt and experiment.

The link at that page is to my site before I updated to a paid site. I've got a couple of articles on felt. There's a more thorough article in the June 2005 issue of audioXpress.

These should help you decide the approach to take (amount, type, thickness).

Dave's Speaker Pages

[ThomasW]

The link to Dave's site has been updated on my webpage