felt vs foam around tweeter

[dsrviola]

I've got a tweeter set back 3/4" back from the two midrange drivers. I'm wondering if anyone's played with both wool felt and foam. Seems like the felt would be to dense to be completely absorptive at high frequencies. (The tweeter is crossed over around 5kHz @ 9db/octave: 1st order series).

I can play with the amount of baffle to the sides of the tweeter, but as you can see I'm stuck with 3/4" in the verticle plane.

[dsrviola]

Another shot of the baffle without the sides next to the tweeter:

[dave_gerecke]

Hello dsrviola, I can't comment on the merits of your two choices. I do know that a lot of mfgs. use felt around the dome of the tweeter for this purpose. The suggestion I would make would be to perhaps using some velcro, or other removable adhesive, to temporarily attach each type of material and see which one works better.

Peace,

Dave

[dlr]

Originally posted by dsrviola
I've got a tweeter set back 3/4" back from the two midrange drivers. I'm wondering if anyone's played with both wool felt and foam. Seems like the felt would be to dense to be completely absorptive at high frequencies. (The tweeter is crossed over around 5kHz @ 9db/octave: 1st order series).

I can play with the amount of baffle to the sides of the tweeter, but as you can see I'm stuck with 3/4" in the verticle plane.

I have some foam to test, haven't done it yet, but my impression is that it is not nearly good enough for this purpose. I would suggest 3/4" F-11 or F-13 wool felt. Fill in the area around the tweeter, use a square opening cutout, not round, ensuring that the inner edge is not too close to the tweeter dome.

I have a couple of pages on felt at my site that may interest you.

Dave

[sq225917]

I've just had a set of the difractionbegone.com tweeter surrounds, 3/4 felt, very thick, and very effective on my Epos es14's.

curiously though a quick check lsitening to the tweeter and the mid rnage seperately, their effect is more on the mid range is more pronounced than on the tweeter. The felt pads were in the same position around the tweeter in both tests.

good enough for me to buy a set, he does custom options, at a price.

[Few]

I've had good luck using adhesive backed gray felt from McMaster-Carr. Look at the their catalog page 3405 online , for example. You can just type 3405 into the search field.

I found that by creating a star shaped cutout for the tweeter so that sound leaving the tweeter was never reflected directly back toward it, and beveling all the edges of the star, I could dramatically improve the measured response of the tweeter: smoother frequency response and cleaner impulse response. I had less luck with round cutouts or with acoustic foam, but I can't claim my studies were exhaustive. When I found out how well this approach worked I stopped my search.

I've modified the speaker that used the felt, though, because I found I could do even better by incorporating a waveguide. You might be able to include one that sets the tweeter back a convenient amount, eliminates the abrupt edges in the enclosure, and even buys you some low end dynamic range and looks nice, all as part of the bargain.


Few

[dsrviola]

...and the felt was definitely a LOT better sounding. Much clearer and cleaner. The difference was so dramatic that I'm thinking of trying a layer inside the enclosure. <writing this down on the mile long "to do" list>

BTW, this is how the project looks at the moment (cabinets complete): http://tinyurl.com/yl3ll33

[skeptic43]

Check out post #5 at this link: SPICA TC-50 Restoration and Measurements - The Classic Speaker Pages Discussion Forums

[dlr]

Originally Posted by skeptic43

Check out post #5 at this link: SPICA TC-50 Restoration and Measurements - The Classic Speaker Pages Discussion Forums

I tested those in 2001 with results at my site here, though I didn't link to Madisound where the rings were purchased. The ring was measurably worse than nothing. And I covered the aspect of thickness of felt as well as a bit about geometry.

One thing about geometry. I've made literally hundreds of measurements of felt in a myriad of shapes and felt combinations, including thickness. One over-riding result is that complex shapes, such as a star, are not necessary and can be less effective in some cases. The best shape is either a rectangle that is offset in one or both dimensions, a triangle or possibly an oval (too hard to cut cleanly enough). Likely why so many newer, cheaper systems use ovals for the faceplate whey they are surface mounted. The key is that these provide the least amount of points with equal distance than complicated shapes. A start just looks more impressive.

The only other common result I found was that for optimal results, the felt should not overlap much of the tweeter faceplate with the exception of nearby felt that is 1/4". 1/2" or more thickness is needed for the primary felt, but extra benefit results from thinner pieces placed inside of the thick felt, closer to the tweeter diaphragm. The improvement with this piece is usually small, however, and higher in frequency.

Dave

[dlr]

Originally Posted by dsrviola

I've got a tweeter set back 3/4" back from the two midrange drivers. I'm wondering if anyone's played with both wool felt and foam. Seems like the felt would be to dense to be completely absorptive at high frequencies. (The tweeter is crossed over around 5kHz @ 9db/octave: 1st order series).

I can play with the amount of baffle to the sides of the tweeter, but as you can see I'm stuck with 3/4" in the verticle plane.

Looking back at your baffle, I'd suggest F-11 or even F-10 (very expensive and white), not F-13. Use 3/4" thickness, cut the outside to fit the full recess, then cut a rectangle (not a square) width maybe 1" more than height. The sections above/below the tweeter should be at least 1/2", maybe 1". Start with 1" and test it if you can, you can always cut off more.

It won't be as bad as you think. I've got an article in audioXpress, June 2005, with an offset midrange on an M/T with a lot of accompanying pictures and measurements of added felt. A recessed tweeter has baffle edges that, though nearby, are highly reflective. The reflections for yours will tend to be back towards the floor from the upper edge and the ceiling from the lower edge, all spread out left-to-right based on angle of incidence. Essentially, with a relatively small amount of felt, the on-axis response will be much better than you'd expect. The reflected signals become room effects and small at that in comparison to the rest.

Dave