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Re: Tom Danley at AES Chicago

“Ok, my simulator doesn't, and I don't think it should :-) . The effect that you describe is not real. You might have seen square wave responses that are not perfect, but how do you conclude that the cause is the sloping radiation resistance? Without proper theory you cannot. It is your theory that I have opinions on, not the imperfect square wave responses.”

Funny (as in odd) an educator would describe something that is easy to measure and described by some for many years as “not real”.

“As I understand it you make a case of that the flat response of a driver comes about by the fact that the frequency dependance of the radiation resistance is balanced by the increasing mass reactance of the cone. This balance is, according to you, only perfect for the amplitude; there will be a residual phase shift due to the fact that the mass reactance introduces a shift of 90 degrees but the radiation resistance is at 0 degrees. Right?”

More or less, the crux being that the radiation resistance is mostly a changing R not a reactance which would be perfectly canceled in mag AND phase by the R-C filter (Richard Small) in the woofer mid band.
http://www.akabak.de/Texte/aes102.pdf
http://www.silcom.com/~aludwig/Sysdes/Thiele_equiv_circuit.gif

“Ok, so I take that as a "no" for most cases then. This is strange, I just hooked up a small 4" midwoofer and mounted it on a piece of cardboard to reduce the diffraction effects, and the square wave response was actually quite good. The flat parts were sloping a bit, but that can be explained by the rolloff of lower frequencies in the driver.”

Ok, carefully re-read what I said, now try what I described, take a woofer in a sealed box with flat response down low, go outside and check in its mid band. It is normal to be able to find a place in room and some frequency where you get a square wave, this is not the same as the driver radiating that over a band.

“Please give my thoughts a shot before rejecting them . loudspeaker nerd with his own "revolutionary" theory, I really do think I have this right after 18 years of teaching the subject. And this IS a theory discussion. It is NOT a discussion on measured data, but on your theory that the effects of mass reactance and frequency dependent radiation resistance do not cancel (with regard to phase). At least it is to me.”
Ok, now you really have my curiosity, you say several things which really make red flags pop up.

“Please give my thoughts a shot before rejecting them. I am not just another silly loudspeaker nerd with his own "revolutionary" theory. I really do think I have this right after 18 years of teaching the subject.”

I am not sure how you could teach this at a serious level and not be aware of Heyser’s work and his discussions of loudspeaker acoustic phase as well as the work of others on the subject. Not only that, you should be superficially familiar with active cancellation of random noise as a popular academic issue where loudspeaker acoustic phase is one primary hang up.
Also, you should know, the Hilbert transform as used in audio processing is a delay mechanism at –90 degrees.

“And this IS a theory discussion. It is NOT a discussion on measured data”
I also find it highly odd an educator would dismiss a large difference between theory and measured reality so easily. One does not have that expedient in designing something that has to produce a specific waveshape signal, even something goofy like this.

http://pdf.aiaa.org/preview/1993/PV1993_4430.pdf

Where exactly do you teach anyway?
I have to ask, are you really V in disguise?

Tom


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