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What can be fixed with DSP?

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#1
Something has occured to me. We have smartphones, smart cars, smart fridges and what do I know, perhaps even smart toilets. But why don't we have smart headphones? Couldn't it be possible to have a smart headphone which would eliminate distortion by playing an inverted signal, a principle similar to the one noise cancelling headphones use? Of course, this would create distortion of its own, but of much lower level, which could then be again eliminated by the same method. You could go on and on until the distortion would be inaudible.

Or take CSD waterfall plots for instance. These measure the speed of sound decay. Couldn't the trick described above be used for increasing decay speed? If you are a reproducing a certain frequency, once you stop and the driver is resetting to its stationary position naturally, wouldn't it be possible to speed this up a bit by playing an inverted signal of a specifically calculated amplitude? Like quite literally taking the driver which is slowly finding its way back to its resting position and forcefully snapping it back in there quickly?

The algorithm could even look forward in the music track being played and evaluate to which extent to the incoming signals help reduce the decay time, and add its own little magic whenever necessary.

Am I completely crazy or do such ideas have some merit?
 

thewas

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#2
Such DSP based driver distortion is actually implemented in some current Samsung soundbars to help their very small drivers, am sure such could be implemented for headphones too, but distortion is not really a big problem on most decent headphones being quite lower compared to usual loudspeakers.
 

ernestcarl

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#3
Some resonances inherent in horn designs using abrupt, sharp bends can be eliminated with FIR-based DSP correction -- e.g. Fulcrum Acoustic's coaxial horn designs.


You can't totally eliminate distortion, though.

*But I don't buy Dave's explanation for the built-in "house sound" in the cheaper Sceptre series line of studio monitors he's designed for Presonus -- it could have been EQ'd better out of the box! But what do I know, I'm no speaker designer... so I don't really know all the reasons behind the decisions.
 
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thewas

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#4
You can't totally eliminate distortion, though.
But reduce it, its a similar principle that sensor based drivers use, i.e. compare and correct the actual driver position vs. the optimal one. Of course works only under the modal region of the driver where a driver shouldn't be optimally used anyway.
 

ernestcarl

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#5
But reduce it, its a similar principle that sensor based drivers use, i.e. compare and correct the actual driver position vs. the optimal one. Of course works only under the modal region of the driver where a driver shouldn't be optimally used anyway.
Reduce to low enough levels to be benign for a given range, I totally agree with. My thoughts are there are always absolute limits to what can be "fixed" after the case.
 

amirm

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#7
But why don't we have smart headphones?
The AKG 700NC has such equalization. Measuring with or without it being on shows the stark difference.

For any equalization to be in a headphone it must be "active." Noise cancelling ones are so EQ can be implemented in them. With regular headphones with no source of power this is obviously not possible.
 

tvrgeek

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#8
What you are talking about is basically just negative feedback. Fine, but you need a sensor accurate enough. I see no reason it is not possible in the analog domain, yet the failure of servo subs has shown this to be difficult.

DSP requires sampling, processing, and integrating. These take time. By definition, not real time. More time than you have to make a correction. Now, I suppose it is possible to characterize the driver. Send the signal to a processor, apply a reverse algorithm, integrate it and sent that signal to the cans. So you have a small delay. I suppose it is possible to make a generic processor and each pair of cans comes with downloadable correction algorithm. So, make a proposal on go-fund-me, hire some good engineers and coders and get busy.
 

thewas

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#9
DSP requires sampling, processing, and integrating. These take time. By definition, not real time. More time than you have to make a correction.
Correct, thats why the Samsung/Harman soundbar solution has no feedback, but send a pre-corrected signal to the driver since they have before measured its non-linearities. Of course this doesn't work for time-variant/drifting distortions.
 
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