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Baffle Resonance on a Three Way
Baffle Resonance on a Three Way
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Old 23rd September 2013, 01:41 AM   #1
Wavewhipper is offline Wavewhipper  United States
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Default Baffle Resonance on a Three Way

I am doing some fine adjustments to a three way conversion to an Optimus 10 1.7cf box that originally had an 8" driver, 10" passive, and the world's worst excuse of a tweeter. Doing well with the best cheapo stuff, GRS PF10-8 woofer, Goldwood GM85/8 midrange, and Goldwood GT510 silk dome.

I had some major baffle resonance problems in the low vocal and especially bongos. It's down to a minor one now. I had to make an 8" to 4" adapter because the midrange goes where the 8" driver was. Since it is hard plywood and it's size, it causes what I call bongo baffle.

Is there some way to carve out the rear of the adapter plate and maybe fill it with some putty like stuff the cure the bonk sound it resonates at ? Any tips for the pattern ? It is a luan plywood ring, 8" outside diameter and a 4" center hole.

I'm guessing offsetting the center hole could have reduced resonance.

Thanx for any advice.
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Old 23rd September 2013, 09:06 AM   #2
zmyrna is offline zmyrna  United Kingdom
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Deadening the adapter plate can be achieved with bitumen sheet (sound dampening material used in car audio) or non-drying clay/putty material.
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However doing so may make the speaker sound dull / overdamped.
My gut feeling tells me you would be better off with a solid internal brace supporting the baffle adapter piece.
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Old 24th September 2013, 03:31 AM   #3
Wavewhipper is offline Wavewhipper  United States
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Good wrk zmyrna. From the beginning I thought it needed a horizontal brace across the middle of the cabinet. If I could connect my body to my brain, I would lay the speaker baffle side up, get some beach sand, then run my sweep generator through it as I sprinkle the sand on it. That as you may know makes Chladni patterns, these show the vibration modes of the cabinet.

Putting the horizontal brace across at the middle removed most all of the coffee can notes, the right one, done, is nearly clean across the spectrum, and the left, not done yet still has the obvious coffee can sounding peaks. It was sickening to me but I got a real treat in solving the problem.

You may like this, Vibrations of a circular membrane - Wikipedia, the free encyclopedia

And there are lots of videos on Youtube showing Chladni patterns in action. Worthwhile.

Thanks for the response.
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Old 24th September 2013, 03:36 AM   #4
Wavewhipper is offline Wavewhipper  United States
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BTW, I thought the brace would be needed for bass notes, not midrange. When I thunk on the adapter plate, the waves are fooling me and behaving in a way I do not understand, yet.
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Old 24th September 2013, 05:34 AM   #5
AllenB is offline AllenB  Australia
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Baffle Resonance on a Three Way
Bracing will reduce the lower frequency issues. They cause the greatest movement in the panels and affect the transient response.

Resonances higher in frequency are harder to deal with using bracing and this is where the damping comes in handy.
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Old 24th September 2013, 10:01 AM   #6
danny_66 is offline danny_66  Belgium
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Yep,
bracing for the woofer cabinets and irregular shaped cabinets for the mids.
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Danny
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Old 24th September 2013, 06:48 PM   #7
Wavewhipper is offline Wavewhipper  United States
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The thing that got me was how the waves travel bounce back and get ya where ya least expect it. This GM85/8 did not give me such problems in a different cabinet.
From my studies, midrange can be very sassy, they make relatively low amplitude waves, but they are in a hearing band that most of the fundamental sounds are in, and it doesn't take much wave amplitude to get loud radiation.
These are made by a similarly stiff driver that is extremely tricky to simply tune out. I think I may try a magnet brace that prevents the whole mid driver assembly from possibly being the culprit by vibrating back and forth on the motor axis.

Probably another reason commercial speaker mfgrs avoid three way's. The two way's bass driver eats up most of the baffle space and doesn't leave much open area to resonate.
I'm down to only a few pulsed honks now. Maybe even the cheapo stamped woofer frame with no anti-resonance stamping architecture.

Nice looking speaker danny, I wish I could afford such a project.

Last edited by Wavewhipper; 24th September 2013 at 06:51 PM.
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Old 24th September 2013, 08:11 PM   #8
danny_66 is offline danny_66  Belgium
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Quote:
Nice looking speaker danny
Thanks.
For damping of the mid cabinet I used Twaron Angel Hair, about 5 gram/liter,
it's very effective, much better than sheep wool.
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Last edited by danny_66; 24th September 2013 at 08:17 PM.
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Old 25th September 2013, 01:43 AM   #9
Wavewhipper is offline Wavewhipper  United States
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I'll consider a build like that, the idea of separate resonators has tempted me for years. I always seem to build things as cubes. That RefSpeaker design , in addition to acoustical function, discourages stacking anything on top that might fall and puncture a driver.

It will be much easier to take a separate cavity and modify it.

Last edited by Wavewhipper; 25th September 2013 at 01:47 AM.
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Old 25th September 2013, 01:59 AM   #10
Wavewhipper is offline Wavewhipper  United States
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There are some CD's I have that really test a speaker's quality. Mostly female lead singers in clean mastered and mixed productions.

The Best of Sade # EK85287. Her voice carries a strong midrange and can bring on some nasty resonances on a bad build. The percussion is a good test for transient response. And the deep bass can really trash a sloppy woofer. There are lots of nice clean cymbal taps to test for that. Thanks to her and her band, I have tweeked for some really natural sounding cymbals and chimes.

Nora Jones can really thrash a midrange driver, and about the worst is Linda Ronstadt on Phillip Glass's 1000 Airplanes CD. I think she can break a glass, her Therimen-Like vocals were really torturing the woofer, mid, and tweeter.

Now I almost make it all through the above mentioned.
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