# I want to propose a new type of test for headphones.

Discussion in 'Sound Science' started by razvitm, Oct 27, 2018.
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1. To someone who has headphone testing equipment, i ask you this:
Would it be possible to plot a graph of a headphone's max power handling versus frequency (before heavy distortions occur ) ?
Now what would that show us?
I think it would show how easy it is for the said headphones to produce some frequencies compared to others, for example, a headphone can be fed 1khz at 2V rms and have absolutely no problem with that, but if you feed it 30Hz at 2Vrms it will make popping noises because of the coil hitting the bottom, or the membrane deforming...
How would such a test be done?
Would such a test be useful in comparing headphones?

2. Normally for a max power test you would use a 1KHz tone, and increase the level until the THD exceeds 1%. For a max power vs frequency plot you could just repeat that at multiple frequencies.

The innerfidelity headphone measurements include a plot of THD+N vs frequency. It's not exactly what you're describing but it's somewhat related and might interest you anyway.

https://www.innerfidelity.com/conte...d-total-harmonic-distortion-plus-noise-part-1
https://www.innerfidelity.com/conte...d-total-harmonic-distortion-plus-noise-part-2

Max power vs frequency would look sort of like the inverse of THD+N vs frequency. Higher THD = lower max power, and vice versa.

3. Contributor
first the obvious issue, the actual max power is where the headphone might break/melt after a few seconds of signal. it would be better not to destroy headphones just for the sake of getting some unusable number.
so we could decide instead on some arbitrary THD value. 1% is a pretty common limit so maybe we could go for that. but then depending on headphones, we're back to square one because some headphones will have that much at all outputs at least in the low freqs. and some headphones will again come close to their physical limit before you'll have the output that results in 1% THD at all frequencies.
so we could settle on a maximum loudness, like maybe 110dB SLP that almost all headphones will handle without risk, but then we're back to mostly just showing some weird graph with information only where the headphone reaches 1% THD before hitting whatever max loudness we have picked. for most intent and purposes, just a THD graph per frequency like a lot of people measure, and the max output provided by the headphone manufacturer would already give clues.

and a practical issue, at least with cheap mics like mine, I can't measure all frequencies accurately at 110 or 120dB SPL. on mine I start getting distortions in the upper frequencies from the mic itself starting around 95dB maybe, and at something like 110dB half the time my graph would show the mic instead of the headphone in the upper range.
so personally if I wished to get some clue about how a headphone behaves when we increase the volume level, I think I would measure THD+N at 2 or 3 more reasonable different outputs, and hopefully my mic wouldn't show itself too much in the results. that might give a clue about how fast the distortions are increasing(although I tend to have similar issues as Tyll had on his THD+N graphs, N tends to be very close to the levels of distortions I measure in my room, so quieter measurements will often be polluted by noise, especially in the low end.
and of course we would miss what you first asked for, the actual moment when the driver goes banana at each freqs.

as for the usefulness of the data even if we had all settled down with proper gears and method(so not me ^_^), what would be the purpose? to know which headphone can play the loudest? is it something we care about? would you go and EQ your headphone just so that it could go 5 or 10dB louder without any frequency hitting a given distortion value? not sure about the purpose of doing that, as you might not always enjoy the resulting signature.