All drivers, because they move forward and backwards will have doppler shifts associated with the movement. The shifts become potentially more of an issue where the driver covers a wide range of frequencies, for example, a wide range driver acting as a woofer which has large low frequency excursions while also carrying high frequencies that are doppler shifted by that movement.
With a concentric driver, the tweeter in the center is decoupled from the woofer so it itself is not moving because the woofer is moving so there is no particular problems with doppler shift. But, you have raised an interesting issue because the woofer cone may be acting as a waveguide for the tweeter output, and that waveguide is moving in and out thus contributing to a doppler shift.
The bigger issue is the audibility of any such doppler shift. One would expect it to be greatest with smaller cone fullrange drivers, yet I have never encountered anyone attributing characteristics of the sound of such drivers to doppler shift. This is an interesting issue.
In all my 50 years of involvement with audio, I've never heard anyone mention Doppler shift before. I've been using Tannoys for most of those years, I've yet to notice any Doppler shift.
I suggest you may be looking for a problem that doesn't exist.
I cannot recall who was the manufacturer, but I believe it was a builder of large panel speakers who extolled the virtues of law Doppler effect speakers (because of their large radiating surface, panels have quite small excursion, which reduces Doppler effect0. The same would be true of compression drivers and horn loaded drivers.
Who cares? Listen to the speakers with your music at different volume levels, and if you still like sound what difference does it make if there’s a Doppler effect or not? There are ALWAYS trade offs between different speaker designs, which is why your ears need to be the final arbiter. I’ll also add that I think concentric drivers are time/phase coherent (or maybe one or the other) that may outweigh any Doppler effect. Let your ears be your guide. Personally, I think there are much more important speaker issues (cabinet, crossover design/parts, driver quality, etc.) than worrying about the Doppler effect. Just my $0.02 FWIW.
@islandmandan, doppler distortion is very real. Most of us have had the experience of a driver leaning on the horn as the car passes us. Right as the car shifts from coming at us to going away from us the horn changes pitch. This is very noticeable. The same thing happens with drivers that are handling the lowest frequencies. To produce low bass drivers have to take long excursions, coming at you then going away. This will cause a change in pitch of the higher frequencies the driver is handling as the driver changes direction. If you can see the cone or diaphragm move this is happening. Woofers that cross over at lower frequencies cause much less trouble than full range drivers. Better yet you can protect the entire speaker by using sub woofers to handle the longer more problematic excursions isolating the speaker from this effect. It is also true that larger drivers do not have to move as far to produce the same volume of bass causing less distortion. I use full range electrostatic speakers and the difference between subs and no subs is not arguable. Even lewm would hear it:-)
As for concentric drivers, they are actually separate drivers with a crossover so the movement of the woofer will not affect the tweeter only the other frequencies it carries.
I have a pair of Thiel CS6 speakers which have first order crossovers plus a concentric mid/tweeter. This crossover design makes each driver cover a much broader frequency range. Theoretically this would worsen any doppler effect. Other Thiel models have the same characteristic - they use first order crossovers and several models have concentric drivers. Vandersteen is another example of using first order crossovers.
I’ve read dozens of Thiel speaker reviews over the years and I’ve never seen a reviewer mention anything about the doppler effect altering the sound. In fact I’ve probably read over a thousand speaker reviews in my life and I don’t recall anyone ever mentioning doppler. You would think that golden eared reviewers would race to tell you about how their exceptional hearing detected that they were hearing the doppler effects of a particular speaker.
I’m going to stick my neck out and say that the doppler effect for speakers isn’t a thing. I wouldn’t be surprised if some company cited this as a reason why their speakers are better but I suspect that not all marketing hype is real. Except when it comes to cables where you should believe everything the manufacturer says.
I mean if you setup a big speaker on a trampoline and crank up the volume real high, maybe there could be some measurable doppler effect. But there's really not much specifically about a concentric driver to be concerned about.
The woofer does act as a horn extension for a Tannoy's tweeter, but it's never been a topic of discussion or concern, to my knowledge.
I agree with Mulveling, (whose system I would love to hear), Tannoys have been recognized as one of the best-sounding speaker systems on the planet for almost all the years I've been alive.
I don't care if there is some Doppler effect happening, I love their sound, and that's what matters to me.
The Ohm acoustics speakers should not have doppler affect since all frequencies from the driver are coherent from one source and align in parallel as they leave the driver due to the driver alignment and method of transmission from back of the speaker
The most recent Thiel concentric drivers use a rippled cone area to offer additional strength that allows for flat profile to mitigate the doppler affect that would otherwise be introduced.
Doppler (intermodulation) distortion must be an issue for speaker designers or why would a company like JBL talk about it back in the 1980’s. See the link below page 3 last paragraph B460 bass system.
I they can measure and fix it they will market it as being better, but I wonder how much can be measured that we actually are distracted by? I agree with SOIX on this point.
Is there a confusion between Doppler effects and phase alignment / distortion here?
Doppler effects occur when there's movement between the source of the sound and the listener, as noted with the car horn example.
Phase distortion occurs with multiple drivers having the voice coil/cone intersections not physically aligned, which is what JBLs' L250 addresses with the sloped cabinet faces (and judicious driver 'tweaks' I suspect). That, with toying with the crossovers design, ought to have minimized phase issues.
The original Ohm speakers were single driver affairs, so no phase problems. The current Ohm speakers with their tweeters mounted directly over the inverted drivers 'average out' phase issues. Since the voice coils are at a right angle in relation to each other, one could say they're aligned.....kinda... *G*
Concentric drivers can't have the coils aligned, ever. Perhaps the tweeters' backside structure is acting upon the wavefront from the woofer behind it, but the physics involved goes off into the deep end of the pool imho.... ;)
Concentric drivers can’t have the coils aligned, ever. Perhaps the tweeters’ backside structure is acting upon the wavefront from the woofer behind it, but the physics involved goes off into the deep end of the pool imho.... ;)
The alnico/pepperpot Tannoys are supposedly configured so that the tweeter and woofer’s acoustic center are at a distance equal to a half wavelength at their crossover point (1.1 kHz). So guess what, they flip the +/- wires to one of these drivers and voila, phase coherence (at the crossover point) lol. I don’t know if the more modern ferrous/tulip models are configured in this manner.
We always called it intermodulated distortion. I always thought adding a sub and cutting off the two bottom octaves helped. I have no measurements to back that up. Do most single driver speakers usually get set up with a sub. I would lump the Tannoys in there(concentric driver). Now, when I hear Tannoy speakers they sound real good! It would be fun to experiment with them.
For most speakers today, doppler is not a real problem. It does exist and can be measured. It would most accurately be described as FREQUENCY Intermodulation distortion. When drivers are used and ran over a very large frequency the drivers move at very different rates and that causes the doppler effect. As drivers have improved, natural crossover points in 2 way designs has lowered overall and most 3 way plus designs have never had real issues. Of course, there are always exceptions, but overall, Frequency intermodulation distortion is not an issue in todays speakers.
That is interesting. I have heard electronic music where I swear they actually create new sounds, maybe not intended, by way of distortion interaction created between instruments. Maybe is frequency intermodulation distortion.
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