Doppler distortion doesn't make sense (Edit: It actually does!)

[Julf]

Maybe you should study up on beaming

I am totally familar with beaming. It affects directivity, not ability to reproduce a signal.

 

[gene_stl]

Does not change the fact that you are mis interpreting what I said. Ignored!

 

[Julf]

Maybe you should study up on beaming. It was my post and I said NOTHING about resonance. Put your words in your own mouth. Don't mis-interpret what I say, thank you.

Ah, you edited your posting after I responded. Indeed, you said nothing about resonance. I simply pointed out that every single item you mentioned in your example relied on resonance to produce/amplify sound, and that was why they had different sizes depending on the frequency (or frequency range) they were producing.

By the way, your way of responding is dangerously close to ad hominem / personal attack.

 

[MC_RME]

Ok forget about what I said before. I just tried it again. This time with the Focal Clear, which has a smaller and stiffer 40 mm driver, compared to the 80 mm of the lcd2c (which means more excursion for the same spl, I suppose). this time I tried a combination of 80 hz (because the clear doesn't like frequencies well below 50 hz), and 6k. I played the 6k tone, and as soon as I added the 80 hz I could hear a lot of very clear sidebands to the higher frequency. I also tried combination of other very low and very high frequencies and they also were clearly audible. The same combination of tones on the lcd2c results in a much cleaner upper frequency.

I don't know if this is in fact Doppler distortion, or some other kind of IMD that's unrelated (I made sure I'm not crossing 0 Dbfs with the combining waves, obviously).

Wowza, you had been too quick for me to reply

The LCDs (most planars) have much lower distortion as conventional dynamic driver headphones, especially in such tests. Main reason is the large size of the membranes (10 cm) - it can move air much more efficiently than smaller drivers (4 cm), therefore needs to perform less excursion for the same bass SPL. And it is forced to move over the whole surface, not only in a single center point.

I just had a quick listen to my old test files. Amplitude modulation was most noticeable with the combination 10 Hz and 2500 Hz (Tremolo effect), while 40 Hz with 900 Hz caused a slight frequency shift when turning the bass control up and down. I never measured the audible result, though.

 

[Biblob]

A (multiway) speaker would be less affected by Doppler than a headphone, it would seem to me. As it has been noted earlier, if a woofer plays <80-2k Hz, than the Doppler distortion would occur only in this band right? Because the woofer and tweeter would seperately play a tone, separated by the crossover frequency. (Not taking in account for the frequency slope due to the crossover).

 

[March Audio]

Intermod shows as bands at f1-f2, f1+f2, and combinations of nf1+/-mf2, where n and m are integers.

Doppler will show frequency shift that's velocity dependent. So if the the bands don't broaden and the broadening isn't a function of the lower frequency amplitude, it's not Doppler.

OK, Had a late night and I'm rather tired and probably being completely dumb, but what is the difference to FM where you would get sidebands?

 

[solderdude]

FM must be demodulated and is not the audible result ?

 

[Julf]

FM must be demodulated and is not the audible result ?

Depends on the frequency ratios. The Yamaha FM synthesizers (remember the DX7?) are a great example of audible FM sidebands.

 

[solderdude]

That's just a deliberate effect of a musical instrument (like a Leslie)
Here is another question.

When one would record a stereo signal with just 2 mics (or dummy head) and one reproduces that would there not be any doppler effect ?
There would be IM due to non-linearties but the reproduced signal is what the mic produced and not multiple electrically summed signals.

 

[Julf]

When one would record a stereo signal with just 2 mics (or dummy head) and one reproduces that would there not be any doppler effect ?
There would be IM due to non-linearties but the reproduced signal is what the mic produced and not multiple electrically summed signals.

It doesn't matter if the signals were summed electrically or acoustically (before entering the mic). The result is exactly the same.

 

[restorer-john]

but what is the difference to FM where you would get sidebands?

Think of the voice coil. The fastest rate of change and physical displacement is at the steepest part of the waveform. Doppler distortion would be greatest when a higher frequency is attempting to be reproduced over a lower one as opposed to the peaks of the waveform where rate of change (and physical movement) is less.

When one would record a stereo signal with just 2 mics (or dummy head) and one reproduces that would there not be any doppler effect ?

Doppler requires movement of either the source or the mic or both. (Or in this case the dummy head with respect to the source). No movement- no Doppler.

 

[March Audio]

FM must be demodulated and is not the audible result ?

Im not specifically referring to audibility, but no it doesnt have to be demodulated, well it does if the carrier is a radio wave, but you can FM modulate an audio signal.

 

[restorer-john]

OK, Had a late night

I'm having a few wines myself. Still helping my mate move in to their new house. Assembling furniture today. Awesome.

 

[March Audio]

Think of the voice coil. The fastest rate of change and physical displacement is at the steepest part of the waveform. Doppler distortion would be greatest when a higher frequency is attempting to be reproduced over a lower one as opposed to the peaks of the waveform where rate of change (and physical movement) is less.



Doppler requires movement of either the source or the mic or both. (Or in this case the dummy head with respect to the source). No movement- no Doppler.

and think of any signal being frequency modulated by a sine wave. does it not do the same thing? Sorry I am probably having a dumb day

so with the speaker the higher frequency wave is being compressed and rarefied by the lower frequency signal. Its frequency is going up and down.

 

[restorer-john]

but you can FM modulated an audio signal.

3/3.15KHz wow and flutter test is a classic example.

 

[Julf]

Im not specifically referring to audibility, but no it doesnt have to be demodulated, well it does if the carrier is a radio wave, but you can FM modulate an audio signal.

That is exactly how the Yamaha FM-based music synthesizers worked. Audio signals modulating audio signals, producing sidebands in the audible spectrum without any demodulation going on.

 

[Julf]

so with the speaker the higher frequency wave is being compressed and rarefied by the lower frequency signal. Its frequency is going up and down.

Exactly.

 

[Julf]

Doppler requires movement of either the source or the mic or both. (Or in this case the dummy head with respect to the source). No movement- no Doppler.

Or movement of the transducer reproducing the music...

 

[solderdude]

with the speaker the higher frequency wave is being compressed and rarefied by the lower frequency signal. Its frequency is going up and down.

Not in a multidriver system though. There we would have acoustical mixing and no FM but 2 pure tones.
How big would the amplitude difference need to be before it becomes audible (assuming linear transducer)

 

[restorer-john]

and think of any signal being frequency modulated by a sine wave. does it not do the same thing?

One is totally in the electrical domain.

This example is half electrical domain, modulating the physical domain with respect to the actual position of the sound emanating source (the vc and its acceleration characteristics) in real time.