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In Reply to: Time and Phase of multiple driver loudspeakers posted by audiographic on August 05, 2003 at 10:36:55:
Given the way some inmates treat minimum phase as a religion, your words can be taken as an attempt to disprove the existence of god.Thanks for the interesting posting.
Follow Ups:
Yah I read that thread with the Green Mountain audio stuff from last week and laughed! Beliefs and facts often don't mix. Guess the knowledgeable person who read all the papers forgot the basic from engineering physics 102. I did not. I'm sure the burning will commence though. Also does not seem to know the difference between acoustic and electrical curves for a transducer. Of course only the electrical curves would ever be published because if the acoustic output curves for phase were published engineering would get a whole lot more obvious. This assumes that any of these companies even COULD measure their transducer phase response, which is dubious at best. Look at frequency response curves and one sees a whole lot of integration to "smooth" the results. One company with an expensive ceramic midrange "smoothed" a 14dB peak at 2485Hz right out of their graph. The old Grapics loudspeaker company used a 30 band EQ between their noise source and test to "smooth" the frequency response for better look. Anybody who has actually tested a transducer knows that if it is +-2dB then it is darned good. As far as time/phase analysis- you cannot map impulse response into time or frequency directly. The most accurate way is to use a two tone system- the same way us antiques used to match the azimuth of the record head to the play head in the days of magnetic tape. I use a special 8 harmonic generator which has all harmonics locked to the fundimental and can measure their phase shift independantly. Tunable over the audio spectrum. TEF machine don't work either for phase. Nor does Malisa or LMS. The very early Audio control Iasys used to work but any later version of the software does not. To many complaints and to much confusion about the coherence results I suppose so the software "smoothes" the results now. Like a lot of things- if you want it right- do it right yourself- if you have the skill.
Remember this? Allow me to refresh your memory, Russ.
"Yah I read that thread with the Green Mountain audio stuff from last week and laughed! Beliefs and facts often don't mix. Guess the knowledgeable person who read all the papers forgot the basic from engineering physics 102"
Still laughing, Russ?
I am........at you dude.
HiI read both your posts and would agree with most all your points.
I had posted about called “an exception” to the same fellow’s statements, which has elements of your points as well although including horn loading
I do have a question about one of your statements though.
You said TEF does not measure acoustic phase, which is my question.
For sure MLS does not, but are you saying the TDS process is incorrect along with Heyser’s design or that the current TEF-20 does not measure phase with TDS or do you mean TEF using MLSSA doesn’t?.
I am curious as I have used all of them since the beginning and used TDS to derive the design in patent 6,411,718 which does use multiple driver s and radiates as if there were one source (according to the polar plots etc). With the drivers all being less than ¼ wl apart at xover, there would be obvious problems in the results if the phases were not “correct”.
It is possible with this approach to produce a speakers who’s acoustic phase hovers around zero degrees for much of its band width . Within this range, a square wave in makes a square wave (not perfect but not at all bad) as a mic signal, anywhere in front.
If the phases weren’t “right” it couldn’t do that and the active noise cancellation systems I worked on wouldn’t have so that’s why I question the statement.
Here is a link to one system.
Kind of a humorous application I thought when the fellow told me what he was doing with our stuff.
http://www.prosoundweb.com/install/spotlight/jets.shtmlCheers,
Tom Danley
So Tom,Looked at your patent and you get many points for being clever. Maybe even smart but that takes time to know. To say the least I was impressed. Are you spectra physics person?
Heyser uses the Hilbert transform in the TEF. See this link for details on how one can go wrong.
http://216.239.39.104/search?q=cache:vl_-_mv3A3MJ:www.mers.byu.edu/docs/reports/MERS9505.pdf+hilbert+transform&hl=en&ie=UTF-8
I searched google for hilbert transform and this pdf was the tenth link from Brigum Young. Pretty well covers what I was saying. Here is the direct PDF link:
http://www.mers.byu.edu/docs/reports/MERS9505.pdf
So short and to the point think I will save it.
regards
R
HiYes, the TEF machine used a Hilbert transform, but importantly, it was not (unlike MLS etc) used to define acoustic phase.
It was an analogue circuit (similar to that used for producing SSB in radio communications) and its job was to take the test signal and produce it in quadrature ( an identical signal but 90 degrees out of phase).
At that point both signals were used as references to the input signal to provide unambiguous phase measurement.
In the TEF 10, 12 and 12+ this was a full size computer plug in circuit board full of L’s and C’s with lots of adjustments so it had a tendency to drift off a tad after a while.
In the TEF 20, it is done in software.
A nice description of the process and loudspeaker arrival times is in in the AES loudspeaker anthology fwiw.Thanks for your comments, I am pleased with the design.
My background is more in industrial / scientific acoustics while my hobby has always been “HiFi”. Most of my time was spent at a company called Intersonics which built flight hardware for NASA, I designed and built large sections of several experiments in the Containerless manufacturing area. This involved using sound to support / position samples of molten material without contact.
Here are a couple links to the company that is using the transducer I developed for this.http://focus.aps.org/story/v2/st4
http://spaceresearch.hamptonu.edu/spring2000/groundresearch.html
I am currently the head of R&D for Sound Physics Labs and Servodrive, two loudspeaker companies, in this area I have developed several other transducers, the Servodrive woofer, the Cyclone (which is a full rotary transducer that was licensed to Phoenix Gold for the car market) and a couple others.
While our web site is lame (although being updated as we speak) some of the stuff can be seen at
WWW.servodrive.comAS you may have guessed, my current area of interest in horn loaded systems and have recently done a DIY project which is catching on.
This is at the Live-audio board, look for the Subwoofer project at
http://Live-audio.com/Cheers,
Tom Danley
Tom,Did a company (the name Infrasonics comes to mind for some reason) make subwoofers using the beltdriven servodrive system several years ago??? I ask becuase I have a good friend with a pair of these in his HiFi set-up (its a fairly large space). They are pretty amazing.
Rich Brkich
HiThe company was actually called Intersonics, we were the company that was selling them, it was my invention patent# 4,564,727.
The smallest version was a 2-15” and the current smallest model is called a Contrabass
Which has 2-15 inche driven and 2-18inch passive radiators.
This product was one of the “science” applications and was originally developed for Joyce Poole at Cornell U for her work on Elephant communication using low frequency sound. See the Aug 1989 issue of National Geographic for here results.
Unfortunately for the speaker division, the company had a policy about not marketing to the home audience.
Now days, we do sell contra's to large home theater instalations etc.
Cheers,Tom
I can't recall how my friend got them, but he has had them for several (or longer) years and they are the big version you mention (I've seen the drivers through the grills! and I recall reading the little documenation he had on them). He has (a pair of) them powered by a large Crown Macro Ref amp with a Bryston crossover for the low pass set around 40 to 50 Hz. They are mated to a Joule-Electra VZN-100 OTL amp Merlin VSM-M set-up in a strictly music only system. I've got to say they are pretty amazing and (after a little diddling around with the Bryston active xover buy yours truly) the integration between them and the mains is very good.I know this will sound pretty audio-geeky, but you haven't heard the 1812 overture until you heard it through my friends system! Keep up the good work!
Happy listening,
Rich Brkich
That link is a novel approach and will look into that sub very curious! Will also look at that patent. As far as the TEF and Hyser- He said that the TEF system can be used to make both valid and invalid measurments. I am no TEF expert but I do know what Hyser said. It may be possible to set the TEF up to make time measurments but no one I have spoken with knows how, not that you do not. If one uses the standard setups the results may or may not be valid. This depends on the mapping of sweep into the time domain being valid. I do not recall the transform name but the transform has two terms- one which maps correctly and one which does not. I would need to dig some to relocate the exact reference but this is the short answer. The problem is as a standard TEF user it is difficult to determine when the mapping is valid. Under the condition of minimum phase, as I recall, results can be accurate, however non-minimum phase conditions can produce results that are incorrect. The same problem exist with this latest Audio Control Iasys software. Sometimes it worrks- sometimes it doesn't. One never knows when. With your approach of sorting out phase with each driver and then moving on to modeling and phase with the system, this would cause me to believe that you are working with a dominant term which maps correctly. This is because you start close to the right answer and move closer. If you start far away is for certain when you get into trouble, as most transducers and speaker designers do.Good job on that speaker. Would love to listen someday. That B&O S-45 did not make a bad square wave either.
Good luck,
R
The old TEF 10 and 12 systems used the Hilbert transform, and lied about the actual phase response if it was more than a single driver, or the single driver went incoherent (break-up).The newer TEF 20 system uses a two-port measurement technique (a sort of transfer function measurement), that does provide correct acoustic phase data, as long as the time delay from the speaker acoustic source to the mic is set properly.
As a long time user of these systems, and having found the earlier TEF systems wanting in this regard, I was very careful to verify that the TEF 20 did indeed provide the correct phase data.
Jon Risch
I had been tortured by subs in rooms for years- then one day I quit using resonance peaked designs (like ports, passives, or seal box with Q over 0.57) and things got a whole lot better. Then throwing in a little DSP and at least 3 subs was able to actually make it work in a room, in spite of room size. Traded max output level for frequency response to end up pretty flat.Always wanted to do a electro-hydraulic sub transducer with about 5HP worth of motor running high pressure hydraulics. I know what to do but have never had the chance. Feel pretty good about it working fine also.
Thanks for your post and the info on you work. Have enjoyed the new stuff you bring. Maybe even you learn something from me.
Regards,
Russ
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