Dredging up more of Nelson's past. I pulled the following quote from someone on the DIY list (old Bass list):
"Have you heard of active absorbers? Not me, but my colleagues seems to be familiar with this concept, and apparently the idea is 15 years old. It seems like the only logical solution to me.
Nelson Pass seems to have designed the "Shadow" by Phantom Acoustics. (anybody heard these?). Located in Auburn, California."
I searched around a little on the web but didn't turn up anything.
What's the scoop?
Thanks,
Russ in Tucson
"Have you heard of active absorbers? Not me, but my colleagues seems to be familiar with this concept, and apparently the idea is 15 years old. It seems like the only logical solution to me.
Nelson Pass seems to have designed the "Shadow" by Phantom Acoustics. (anybody heard these?). Located in Auburn, California."
I searched around a little on the web but didn't turn up anything.
What's the scoop?
Thanks,
Russ in Tucson
Yikes!! Did a new search and found some info.
I'll read some of the reviews but would still like to hear from Nelson on this.
Thanks,
Russ
I'll read some of the reviews but would still like to hear from Nelson on this.
Thanks,
Russ
Yea, I recently looked at the patent for it on the patent web site....at least I think this is the one that has to do with that....
Try this link.....
Mark
http://patft.uspto.gov/netacgi/nph-...rch-bool.html&r=4&f=G&l=50&co1=AND&d=ptxt&s1='Pass,+Nelson'&OS="Pass,+Nelson"&RS="Pass,+Nelson"
Doesn't appear to work but go here to the quick and type in Pass, Nelson and you can grab it off the list that comes up.
http://patft.uspto.gov/netahtml/search-bool.html
Try this link.....
Mark
http://patft.uspto.gov/netacgi/nph-...rch-bool.html&r=4&f=G&l=50&co1=AND&d=ptxt&s1='Pass,+Nelson'&OS="Pass,+Nelson"&RS="Pass,+Nelson"
Doesn't appear to work but go here to the quick and type in Pass, Nelson and you can grab it off the list that comes up.
http://patft.uspto.gov/netahtml/search-bool.html
OK, I got my ftp mojo working again.
Go over to www.passlabs.com/temp to see everything I've stuck up there, and look for the files starting with "Shadow" to see a paper and a review. Some of these
are JPEG, some TIFF, some both.
Go over to www.passlabs.com/temp to see everything I've stuck up there, and look for the files starting with "Shadow" to see a paper and a review. Some of these
are JPEG, some TIFF, some both.
I think we have the same mojo, but he looks to have
more hair, and it's not gray, either.
Welcome back Fred.
more hair, and it's not gray, either.
Welcome back Fred.
A few years ago I worked on an 8 screen theatre design in Johnson Creek, WI....2 screens were THX and the HVAC contractor screwed up big time. He guaranteed that the systems would meet NC25, NC30 is required to pass crertification, but they came out more like NC38 or there abouts. The HVAC contractor was faced with the dillemma of making them quiet, fortunately I was not.....I was only the sound system and projection equipment supplier/installer. What he ended up doing was to have two active acoustical noise camncellation systems installed inside the duct work. These active systems, when turned on and calibrated, actually got the systems down to NC28!! THX was skeptical as this had never been done before......not the normal fix for this sort of problem, but they ultimately, after re-testing the NC level, accepted them as part of the system. Everyone lived happily, ever after, the theatre got its THX certification and the HVAC contractor got stuck with the bill, and installation for the devices!
Yes indeed these things work very well!!!
Mark
P.S. The company that made the noise control devices was Digisonics in Middleton, WI.
Yes indeed these things work very well!!!
Mark
P.S. The company that made the noise control devices was Digisonics in Middleton, WI.
Those used a 100W amp with an EV 8" speaker.
The mic was placed at a remote location and was DSP processed.
The mic was placed at a remote location and was DSP processed.
DIY Shadow
Well, the logical question is, can this be DIYed? We know that the system used a pair of 8" woofers in each column, which measured about 10" in diameter and 7' high. They used 25 watt amps (use an LM3886?) in inverting mode. What I'm picturing is a couple of woofers, a Panasonic capsule (is this suitable, what's a "pressure" mic?), an inverting opamp buffer with lowpass at 200Hz, and a chip amp. Now, how critical is the servo part of the amp, as this is not so easy to do for a diyer. Anything I've missed? Should be possible to do this for a couple hundred bucks each I think. I've got a particularly bad room 12x14' with problems at 50 and 100Hz using a small 2 way ported speaker. I've been designing an open baffle dipole speaker like Linkwitz does, but this might do the trick for me.
RonS
Well, the logical question is, can this be DIYed? We know that the system used a pair of 8" woofers in each column, which measured about 10" in diameter and 7' high. They used 25 watt amps (use an LM3886?) in inverting mode. What I'm picturing is a couple of woofers, a Panasonic capsule (is this suitable, what's a "pressure" mic?), an inverting opamp buffer with lowpass at 200Hz, and a chip amp. Now, how critical is the servo part of the amp, as this is not so easy to do for a diyer. Anything I've missed? Should be possible to do this for a couple hundred bucks each I think. I've got a particularly bad room 12x14' with problems at 50 and 100Hz using a small 2 way ported speaker. I've been designing an open baffle dipole speaker like Linkwitz does, but this might do the trick for me.
RonS
This thing is neat!
I would like to build one of these!
I particularly like unique gizmos that can make a substantial change in the performance of the system without years and years of experience tweaking circuits and understanding the real nuances of circuit behavior. It seems that one could make a version that produces a positive result without too much difficulty.
On the other hand, It may be just that the patent does a good job of explaining the basics of the idea, which is what one would wish to patent. Perhaps the devil is in the details. Most likely Nelson didn't just whip this up one evening after work.
The problem is the length of my list. Let's see. X-BOSOZ, Aleph 2, Aleph-X, TL speaker sys, El-Pipo, active X-over,....I should be getting to this about 2010 (if I don't dawdle).
/Vince- technophobe who likes gizmos
I would like to build one of these!
I particularly like unique gizmos that can make a substantial change in the performance of the system without years and years of experience tweaking circuits and understanding the real nuances of circuit behavior. It seems that one could make a version that produces a positive result without too much difficulty.
On the other hand, It may be just that the patent does a good job of explaining the basics of the idea, which is what one would wish to patent. Perhaps the devil is in the details. Most likely Nelson didn't just whip this up one evening after work.
The problem is the length of my list. Let's see. X-BOSOZ, Aleph 2, Aleph-X, TL speaker sys, El-Pipo, active X-over,....I should be getting to this about 2010 (if I don't dawdle).
/Vince- technophobe who likes gizmos
The patent has pretty much all the information you might
want. These are very DIY-able.
The Digisonics product is not the same thing - the DSP based
stuff removes repetitive noise from rotating parts and such.
The Shadow is an analog item, and does not differentiate
between transients and repetitive signal.
want. These are very DIY-able.
The Digisonics product is not the same thing - the DSP based
stuff removes repetitive noise from rotating parts and such.
The Shadow is an analog item, and does not differentiate
between transients and repetitive signal.
That's good news, Mr. P!
Maybe I can elevate this to a position of higher priority on my list.
Thanks for the encouragement.
Maybe I can elevate this to a position of higher priority on my list.
Thanks for the encouragement.
Nelson,
This is pretty much what I had in mind. Panasonic mic capsule into an inverting opamp gain/lowpass filter stage at 200Hz or so, followed by an LM3886 (because I have them), using either an 8 or 12" woofer that I have lying around.
I have some concerns though. Assuming that the mic capsule is flat (it is up to about 1kHz, I use them in speaker testing. Beyond that I have them calibrated against a B&K), and that the woofer is pretty flat down to whatever (I can measure, but pushing an 8" woofer to 20Hz is asking for trouble I think), what are the chances of this thing oscillating? I mean, the mic is not only measuring the pressure buildup from the source speaker, but also measuring the pressure from the "shadow" woofer. We've all heard mics getting too close to speakers on stage and the howling sound that that makes
What prevents it from happening here? Also, how does one determine the absolute volume to set this thing at? Obviously it has to be calibrated so that 1dB of spl rise creates 1dB of negative pressure, otherwise the thing starts to make it's own music. Or am I mistaken?
Cheers,
RonS
This is pretty much what I had in mind. Panasonic mic capsule into an inverting opamp gain/lowpass filter stage at 200Hz or so, followed by an LM3886 (because I have them), using either an 8 or 12" woofer that I have lying around.
I have some concerns though. Assuming that the mic capsule is flat (it is up to about 1kHz, I use them in speaker testing. Beyond that I have them calibrated against a B&K), and that the woofer is pretty flat down to whatever (I can measure, but pushing an 8" woofer to 20Hz is asking for trouble I think), what are the chances of this thing oscillating? I mean, the mic is not only measuring the pressure buildup from the source speaker, but also measuring the pressure from the "shadow" woofer. We've all heard mics getting too close to speakers on stage and the howling sound that that makes
What prevents it from happening here? Also, how does one determine the absolute volume to set this thing at? Obviously it has to be calibrated so that 1dB of spl rise creates 1dB of negative pressure, otherwise the thing starts to make it's own music. Or am I mistaken?Cheers,
RonS
The response curve of the Shadow is necessarily a bandpass with limited open loop gain to ensure stability.
The production piece had a single pole rolloff above about 100 Hz and below about 70 Hz, but these were 8 inch drivers. With bigger woofers you can think in terms of lower frequency.
You can adjust the open loop gain of the system until the woofer starts oscillating, and then back off about 3 to 6 dB.
The production piece had a single pole rolloff above about 100 Hz and below about 70 Hz, but these were 8 inch drivers. With bigger woofers you can think in terms of lower frequency.
You can adjust the open loop gain of the system until the woofer starts oscillating, and then back off about 3 to 6 dB.