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Old 26th January 2008, 08:06 PM   #1
jay1st is offline jay1st  France
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Question Standing waves, anyone willing to experiment ?

I was looking over a couple of patents, when I found this one:

A bass reflex speaker system with a ducted port which can be made without coloration in the mid frequency band of the speaker caused by standing wave resonances in the duct. The system includes one or more openings in the wall of the duct between the ends of the duct, and covering the openings with a deflectable membrane, such as a film of latex-like material, or a rigid membrane with a flexible surround.

I'ts here.

Is there anyone willing to experiment this thing and give us the results ?
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Old 27th January 2008, 02:39 AM   #2
Tenson is offline Tenson  United Kingdom
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I have heard of a similar idea using small Helmholtz absorbers along the length of the duct or TL to absorb harmonic resonances.

Usually a careful application of light weight stuffing can cure higher harmonics without killing the fundamental though, I find.
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Old 7th February 2008, 11:03 PM   #3
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Judging by the number of commercial speakers of all price ranges tested w/o comment of any port resonance problems, it's not a problem.

I know this because thinking about it, I thought there was no way it couldn't be a problem, but then I scoured Stereophile speaker reviews and never found a mention of it.
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Old 10th February 2008, 02:14 AM   #4
Ron E is offline Ron E  United States
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It once occurred to me to use glasspack muffler type tubes as ports to reduce resonance problems. This was ~10 years ago, but I never did it.

The audibility of port resonances is very subtle. Sometimes longer ports can have real problems, though. The Infinity Overtures had a long port with a bottom exit, and when D.B Keele measured them in audio he found a ~300Hz blip and discovered the port was causing it. He ran sine burst through the system, IIRC, and could really hear the overhang around the resonant frequency with test signals. IIRC, He couldn't hear it with music.
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Old 10th February 2008, 02:33 AM   #5
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Of interest to those of interest in standing waves:

http://youtube.com/watch?v=FvJXCG8IVcA & http://youtube.com/watch?v=m6H1tLAkyjQ & http://youtube.com/watch?v=OM2dNr7EVyk ...

http://youtube.com/watch?v=ic73oZoqr70

http://youtube.com/watch?v=1e4ZmiaSZ-0 ... Physics Prof. Muller @ Berkeley does a great standing wave classroom experiment as well.

http://youtube.com/watch?v=zFjXbxcf7z0

http://youtube.com/watch?v=lNg_woUaPgM

http://youtube.com/watch?v=vrJl_8S3_rw ... I want one of these to go with my crystal wine glasses ...

http://youtube.com/watch?v=KzvKwxvd0qI

http://youtube.com/watch?v=ByxfL0qG8kg

http://youtube.com/watch?v=Tid-Gbdw9jU ... ??

http://youtube.com/watch?v=aDpmjA5IBxU ... corn starch I believe

http://youtube.com/watch?v=8feevDNEL8E
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