The headphones only have one driver, so yes.
Ah, ok.
As you can't measure the response I suggest you try to do a blind test.
The headphones only have one driver, so yes.
I think I didn't really get the idea behind IMD. Can you explain how IMD would result in the sidebands I'm seeing?
Ok but why tough? What causes this?
How does it differ from harmonic distortion? Or to phrase it differently – can there be a case where harmonic distortion and intermodulation distortion aren't correlated?
It's a result of the same causes as harmonic distortion (nonlinearities in the DUT), so when you see HD, there will always be IMD if you run a two tone test.
You can set up a fictitious mathematical model that might have one and not the other, but every real system I'm aware of that has nonlinearities shows both types.
Isn't HD actually a single tone IMD?
WHat I mean is this: Distortion always have a tones harmonic components and inter-tone components. Following that logic single tone test doesn't have inter-tone components but only harmonic component of that single tone.
I have trouble thinking about an "inter" where there aren't two distinct things.
Organs have tiny little pipes that are whistles that are a few inches long and small in diameter. They also have pipes that are 64 feet long and almost a foot in diameter. One for the high frequencies and one for the low frequencies. For the same reason that there are ContraBasses Basses Cellos Violas and Violins.
Wouldn't you need a single driver speaker to perform this test? Is there even a driver you can get that plays 60hz and 6khz simultaneously?Proposal for Doppler Distortion measurement, using REW:
- Sample-synchrounous record-while-playback of the test signal, so that "no window" (==rectangular) can be used for FFT, having no frequency leakage.
- Large FFT size, 1M points, low sample rates (44.1/48khz) for high frequency resolution.
- Play twin-tone test signal of choice (like 4:1 60Hz/6kHz) and adjust levels until IMD starts to sky-rocket, back off a little.
- Mic in the "near field" but at least some 10x the observed excursion away, if possible.
- Record spectrum (averaged).
- Play high test-tone alone, record spectrum (averaged).
- Look at the number of bins occupied by the high test-tone's fundamental, compare.
- If the single-tone is exactly 1 bin wide but starts to widen in the two-tone spectrum to several bins, then this widening should be the effect of Doppler distortion. IMD frequencies might also show the widening.
Blind testing is in fact difficult. It's feasible when you already have a DSP model for correction and it parameters have been dialed in so the measured response actually betters (and does no degrade performance anywhere else, of course). Then simple switch-off of the correction will assure nothing else is changed to make testing more robust.
It is relevant due to wavelengths. The point being that a single driver for the full range of audio frequencies really hasn't been built because different sizes are needed according to wavelength. Resonance has nothing whatever to do with my point.Not really relevant. Organs (as well as cellos etc.) produce (or amplify) sound by resonance. Resonance depends on the physical measurements of the instrument. With speakers, we try to avoid resonances.
If the Doppler distortion only happens (supposedly) when the lower tone is present, I can't not know when it's on and when it's not.
It is relevant due to wavelengths. The point being that a single driver for the full range of audio frequencies really hasn't been built because different sizes are needed according to wavelength. Resonance has nothing whatever to do with my point.