I have disassembled a few.
Not really doppler. A rotating horn changes the direction the sound is firing. The speed of the rotation can be changed.
Typically used witha Hammond B3 on stage, Both heavy MF, the organ in poarticular.
dave
The spectral responses are obvious simulations: https://web.archive.org/web/20020204033734/http://www.geocities.com/kreskovs/Doppler2.html
Personal measurements were made to investigate this behaviour using a 12" Tannoy Gold coax. The woofer was driven to ~ +-1/2" excursion at fundamental free-air resonance. The horn was driven to ~ 90 dB at its sensitivity peak, from memory around 2500 Hz. The horn's output was monitored with a real time spectrum analyser with sufficient resolution to show multiple harmonic orders. Turning the woofer drive on and off made absolutely no visible difference to the tweeter's harmonic profile. At least with this driver if the effect exists it appears to be orders of magnitude below it's native distortion.
Last edited:
Agreed. Even at unpleasant-to-be-near spl, the 10" mids on my PA appear to be stationary...
Here is what the author has to say about that: "Doppler spectral lines, which are non-harmonic to the fundamental frequencies and are therefore very disturbing for a good listening experience..."
I agree that intermodulation (IM) distortion, which he alternately refers to as "Bessel" or "Doppler" spectral lines" may be more annoying than the second through twentieth harmonic distortion (HD) that his "Active Doppler Compensation" device adds.
20th harmonic increased more than 10dB, as can be seen in his charts in post #3.
His "Active Doppler Compensation" device adds a considerable amount of HD to a simple 30Hz sine wave, no telling what it does to a musical passage.
If I find IM distortion disturbing, my preference is to reduce it by adding a subwoofer, and not require the main speakers to do the "heavy lifting" below 100Hz that causes IM.
That reduces IM to lower levels than his device can, without adding the additional harmonic distortion it does.
Art
He claims what he claims, but who knows how it sounds depending on how its implemented. He has additional claims for further distortion reduction in a subsequent issue of the magazine but which depend on knowing exact diaphragm position, thus requiring drivers with position transducers.
The Leslie high frequency rotating horn does provide a real Doppler effect, that of vibrato, pitch change, frequency modulation (FM).
The slower low frequency rotor does not provide near as much pitch change, it is primarily modulating the amplitude (volume) of the woofer, amplitude modulation (AM).
Art
I did and already said it was hokum. The guy is selling a box to get rid of a kind of distortion that doesn't exist. It's pure snakeoil.
If Doppler distortion is a physical attribute of cone or membrane motion and therefore appears in loudspeakers, then it should be able to be heard in every low distortion loudspeaker ever made. It should be very clear in every wideband or fullrange loudspeaker ever made. How could one fullrange have less Doppler distortion than another?
This is what I think is happening, it's not Doppler. The woofers excursion is limited and when you add a signal to one that is already at the maximum there is going to be distortion.
Those must have been early models. The Leslie I know had a tweeter with two horn exits. The woofer stayed still and used a spinning baffle. I loved messing with my grandfathers B-3. That organ was probably the only thing he had when he died that was worth anything.
There were two effects created by spinning the baffle at two different speeds, tremolo and chorus. All of these kind of effects have names that overlap, tremolo (loud/soft), vibrato (pitch shift), chorus (phase shift, and/or frequency shift, often with multiple copies added). Manufacturers use and abuse the names for their products. The Leslie has a purity that pedals can't match.
There were two effects created by spinning the baffle at two different speeds, tremolo and chorus. All of these kind of effects have names that overlap, tremolo (loud/soft), vibrato (pitch shift), chorus (phase shift, and/or frequency shift, often with multiple copies added). Manufacturers use and abuse the names for their products. The Leslie has a purity that pedals can't match.
That’s how it’s done, no hokus-pokus box needed just common sense professional practice.
Perversely, I've taken this route one step further to remove the 'heavy lifting' from my 18" subs by adding 21s for the lowest octave and a bit!
What do you mean it doesn't exist? Its a nonlinear distortion by definition; new frequencies are created and they can be measured.
Incorrect. Its more of a problem with small diameter cone speakers playing at higher volume levels. In that case the cone needs to move increasingly like a piston. Higher frequencies being played by the same cone speaker at the same time become increasingly frequency modulated as volume levels go up.
My electrostatic speakers are at the other extreme; no doppler distortion because the diaphragm membrane hardly needs to move at all to reproduce the sound pressure levels of live music. That property is related to the large physical size of the membrane and its very low mass.
"Higher frequencies being played by the same cone speaker at the same time become increasingly frequency modulated as volume levels go up."
No, it's simply not possible to modulate the frequency by adding amplitude because there is one wave being produced by the loudspeaker not two. Also, if Doppler distortion is there then it is produced at all volume levels because it is a physical attribute of playing two frequencies on one loudspeaker driver. The fact that it couldn't be measured in the provided example except when the loudspeaker was overdriven is proof that it doesn't exist. The distortion measured is clearly IM distortion not Doppler distortion.
Your electrostatic speakers, since they are wide band drivers, should be a great demonstration of the Doppler effect. It might be exaggerated by smaller driver but it should exist in all loudspeaker drivers.
Is there Doppler distortion on a phonograph record? Is it in FM radio when the sender and receiver are stationary?
No, it's simply not possible to modulate the frequency by adding amplitude because there is one wave being produced by the loudspeaker not two. Also, if Doppler distortion is there then it is produced at all volume levels because it is a physical attribute of playing two frequencies on one loudspeaker driver. The fact that it couldn't be measured in the provided example except when the loudspeaker was overdriven is proof that it doesn't exist. The distortion measured is clearly IM distortion not Doppler distortion.
Your electrostatic speakers, since they are wide band drivers, should be a great demonstration of the Doppler effect. It might be exaggerated by smaller driver but it should exist in all loudspeaker drivers.
Is there Doppler distortion on a phonograph record? Is it in FM radio when the sender and receiver are stationary?
The effect can definitely be measured. Why do you claim it can't be measured?
It is true that it occurs at all volume levels, it just gets worse at higher volume levels.
Regarding my particular electrostatic speakers (Sound Lab), they have about as much doppler distortion as a condenser mic (which is very little), so if a recording is made with a condenser mic and played back on electrostatic speakers the doppler distortion tends to cancel.
Anyway, you need to think about this more carefully. There is a good explanation with detailed measurements by Rod Elliot at: https://sound-au.com/doppler.htm
It is true that it occurs at all volume levels, it just gets worse at higher volume levels.
Regarding my particular electrostatic speakers (Sound Lab), they have about as much doppler distortion as a condenser mic (which is very little), so if a recording is made with a condenser mic and played back on electrostatic speakers the doppler distortion tends to cancel.
Anyway, you need to think about this more carefully. There is a good explanation with detailed measurements by Rod Elliot at: https://sound-au.com/doppler.htm
Last edited: