A tale of four speakers

tvrgeek · 16th September 2012, 10:02 PM

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.

tvrgeek · 16th September 2012, 10:09 PM

Before anyone asks, pictures:
Yes, it is a wire nut.

ODougbo · 17th September 2012, 08:12 AM

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

tvrgeek · 17th September 2012, 09:08 AM

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.

tvrgeek · 18th September 2012, 09:34 PM

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.

ODougbo · 18th September 2012, 10:38 PM

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

planet10 · 18th September 2012, 10:59 PM

Quote:

Originally Posted by tvrgeek

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

tvrgeek · 18th September 2012, 11:27 PM

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.

tvrgeek · 19th September 2012, 10:24 PM

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.

ODougbo · 19th September 2012, 10:38 PM

I was waiting for the tale about the other two speakers

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17th September 2012, 08:12 AM	#3
ODougbo diyAudio Member Join Date: Aug 2011 Location: Maryland USA	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

17th September 2012, 09:08 AM	#4
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

18th September 2012, 09:34 PM	#5
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

18th September 2012, 10:38 PM	#6
ODougbo diyAudio Member Join Date: Aug 2011 Location: Maryland USA	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

18th September 2012, 11:27 PM	#8
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

19th September 2012, 10:24 PM	#9
tvrgeek diyAudio Member Join Date: Dec 2009 Location: Md	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.

19th September 2012, 10:38 PM	#10
ODougbo diyAudio Member Join Date: Aug 2011 Location: Maryland USA	I was waiting for the tale about the other two speakers