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Old 16th September 2012, 10:02 PM   #1
tvrgeek is offline tvrgeek  United States
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Default A tale of four speakers

As I got my "missing" package, I got 4 generic raw paper, foam surround 3 1/2 inch speakers. I went all out, they were $1.69 each.

The following plots are: Raw as supplied, Ductcap cut out and a phase plug added, a few dots in a pattern made of craft glue, and a wiped on, wiped off coat of jesso.

Measurements were one inch above the plane, gated 2 ms.
Attached Images
File Type: jpg raw.jpg (169.6 KB, 276 views)
File Type: jpg plug.jpg (169.6 KB, 267 views)
File Type: jpg dots.jpg (168.1 KB, 256 views)
File Type: jpg onecoat.jpg (175.9 KB, 252 views)
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Old 16th September 2012, 10:09 PM   #2
tvrgeek is offline tvrgeek  United States
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Before anyone asks, pictures:
Yes, it is a wire nut.
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Old 17th September 2012, 08:12 AM   #3
ODougbo is offline ODougbo  United States
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a tale of four speakers

The dots look good.

Plug: Used foam plugs many a time here, cut tiny plugs with typical hole saw. Use scrap wood with hole, then move back the 1/4" drill bit. Can make 10 in about a min. Trim with scissors.

E.g. have a 1" VC, order a 15/16" hole saw:


Amazon.com: MK Morse AV15 Hole Saw, 15/16-Inch Bi-Metal Boxed: Home Improvement
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Old 17th September 2012, 09:08 AM   #4
tvrgeek is offline tvrgeek  United States
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A foam plug would not be a phase plug as it is not reflective, but it is an idea to look at. These have a 1/2 inch vc.
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Old 18th September 2012, 09:34 PM   #5
tvrgeek is offline tvrgeek  United States
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OK, some analysis.
Phase plug reduced the depth of the dips in the 5 to 10K range by about 4 dB. It added a big spike at 18K.

One coat shifted everything down just a bit, and smoothed things by a dB or so. It has considerably more top end, but I suspect that is breakup.

Dots were considerably smoother in the 1500 to 5K range but a few dips were deeper.

No magic formula yet. Each change was, well different. Time to combine changes. I will do a thin wipe in the dotted driver and add a backside coat to the one-coat along with a bit of a thick bead around the surround.
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Old 18th September 2012, 10:38 PM   #6
ODougbo is offline ODougbo  United States
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As a top coat, water base poly may be good. It would dry fast and last forever:

Amazon.com: Exterior 450 Finish, Satin - Quart: Home Improvement
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Old 18th September 2012, 10:59 PM   #7
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Quote:
Originally Posted by tvrgeek View Post
A foam plug would not be a phase plug as it is not reflective, but it is an idea to look at. These have a 1/2 inch vc.
I have used foam ear plugs with success.

dave
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Old 18th September 2012, 11:27 PM   #8
tvrgeek is offline tvrgeek  United States
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Plugs, now why did I not think of that.

I ran impedance tests. The thin coat and the dots only shifted Fs about 3 Hz. The two sided heavy coated, which happens to also be the phase plug, shifted 24 Hz. Significant mass. I think the manufacturing tolerance is so wide I can't correlate the shift in Q.

Quick playing them just sitting on the bench. Dots sound better.
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Old 19th September 2012, 10:24 PM   #9
tvrgeek is offline tvrgeek  United States
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I figure my $7 was well spent. Time to move on. I was quite surprised how well the dots work over even very heavy damping. Sure wish we could see some inferometry pictures. Where are the college kids when you need them? I am really looking forward to hearing Dave's Fostex compared with stock and the hack job I did.

Conclusion:
Yes, the pattern treatment works quite well. No BS about it.
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Old 19th September 2012, 10:38 PM   #10
ODougbo is offline ODougbo  United States
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I was waiting for the tale about the other two speakers
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