Felt around the tweeter

[kgveteran]

Is this for standing waves, and can there be a benefit to all tweeters ? Is there a typical frequency effected ?

I know the early Spica TC-50 used .75" wool over the whole baffle ! Is there any chance this would cause a problem instead of a fix ?

[JonMarsh]

It's for diffraction control, and is probably best optimized in a specific application with testing. Problems most often show up in the 4-12 kHz area. Audibility is a question, in more extreme cases, I think it's quite audible. More sublte examples maybe not so much.

Diffraction can also be caused by nearby drivers, producing effects lower in frequency than the above region.

Tweeter plate design can be a big problem, for example, Accuton's.

Look at this stock plot of an Accuton C13-6



Which was mounted flush for testing




Vs. a modified one with in place diffraction control with felt.






This is not the most extreme example I've seen, but the quickest one I coudl grab to post. Note that the scales are somewhat different, but still....

[Dennis H]

Ahhhh..... Jon, I see the grills are gone too. How hard were they to get off? How about the mids - going to remove those grills as well?

[JonMarsh]

Tweeter grille isn't all that hard to get off- a small awl or screw driver is all you need to pry them off. Since I'll be going with a waveguide for this set, the grille had to go anyway- I wanted to get an initial idea of how good the driver was under more ideal conditions.

For the big mids, if I was using the C88/89, Id put some damping on the grilles radially- it's got a big of a resonance. The C90-T6 grille is a different shape and contruction, sort of pre-stressed, and doesn't seem to mess anything up; very dead. That's staying on... $400 drivers, you know!

[Brandon B]

Of the 2, felt and grill removal, which do you think is a bigger factor? (I am looking at the C2-12's I am finally about to put to use). Am I mis-prioritizing by using felt around an accuton without removing the grill?

BB

[JonMarsh]

The first plot above is for the C13-6 with felt surrounding the base of the tweeter. The problem about not removing the grille is that the grille sits off the front plate, and it's the edge where the grille sits in that causes a lot of the problems. I don't think it's possible to "fix" that without removing the grille. Maybe I'm being to anal about the whole thing, maybe most folks (me included) can't hear the comb filtering above 10 kHz, but I figure the cleaner things are, the cleaner they'll sound.

Just my 0.02.

Oddly, the C30N's I have dont' measure as squirrellyl under the same conditions.

[kgveteran]

Devil's in the details :evil:

[Marc Heijligers]

The problem about not removing the grille is that the grille sits off the front plate, and it's the edge where the grille sits in that causes a lot of the problems.

Only adding felt is improving the performance already significantly (e.g., see http://www.hifivoice.com/audio/miles...ffraction.html. But the grill is a significant problem indeed, as I found out in some music, from some waterfall diagrams and an accelerometer (see the section "metal grills" on http://www.hifivoice.com/audio/miles...dampening.html. I've attached a measurement with an accelerometer on the gril (which is a mechanical measurement, not an acoustical measurement!).

Marc

[Dennis H]

Interesting stuff, Marc! Those woofer grills really do ring. I'd be tempted to remove them and protect the drivers from small hands with a fabric grill, using thick felt to stop/reduce diffraction from the grill frame. Grill cloth itself has a minimal effect on the sound; it's the frames that are nasty.

PS - you might want to edit your links. I had to copy/paste them and remove the parenthesis from the end.

[TurboFC3S]

Only adding felt is improving the performance already significantly (e.g., see http://www.hifivoice.com/audio/miles...ffraction.html. But the grill is a significant problem indeed, as I found out in some music, from some waterfall diagrams and an accelerometer (see the section "metal grills" on http://www.hifivoice.com/audio/miles...dampening.html. I've attached a measurement with an accelerometer on the gril (which is a mechanical measurement, not an acoustical measurement!).

Marc

Awesome site! I bookmarked it twice :T