A question about frequency response, particularly treble. - Page 2

I'm interested in deciphering a common phenomenological report (that is, "it sounds like _________ to me"), and more precision in the high frequency profile of various headphones could help. Maybe I was thinking of someone else, the person I'm remembering was always interested in the science of sound. I apologize if I've mistaken you for someone else.

No problem. I'm interested in music. Sound quality can get me closer to that. Science can help me figure out how to improve sound quality. It goes in that order.

If it's a big problem in the treble you're experiencing, odds are the imbalance is lower than the top octave. I'd try adjusting the 5kHz range with an equalizer and see if that helps. If not, try making small adjustments around 2.5kHz. Masking frequencies are an octave down from where they sound.
Edited by bigshot - 8/3/11 at 5:09pm

No, no problem - I've just got a decent collection of headphones, aiming for variety, and have noticed that my experiences with them seem to match the phenomenological/qualitative reports of others when it comes to "fast or slow" especially... And further that there seems to be something related to driver speed that may show up as a given sort of treble profile on a frequency response graph. See Grado graphs, Beyer graphs, Sennheiser graphs... But it's a weak hypothesis at the moment because there's just not a lot of data to go on at the moment, the plural of anecdote is not data :) I don't have the requisite free cash to buy every headphone I'd want to test, but if I had access to Headroom's testing setup I'd work out an experimental design which in order measured driver mass and impedance, then frequency response, then impulse response, then square response at 40 and an octave above, then waterfall plots of short pink noise pulses.

 

To put it straightforwardly, headphones with spikey looking treble seem to be fast, while headphones with dipped treble seem to be slow. I would like to know more about why that is. Two that interest me in particular are the AKG K701/702/Q701 and the HD-650, because they use really similar driver technology and despite substantially varying impedance (1khz, average and peak) require more or less the same power to be driven appropriately, but they don't behave very similarly in many aspects. Sennheiser's Duofoil and AKG's Varimotion both use a thicker center mass to act as a sort of tweeter for nearly-discrete high frequency reproduction, and thinner diaphragms around the center for reproduction of the sub-bass, bass, midbass, midrange and low treble frequency reproduction. They have their own names for it of course, haha, but nonetheless what it is doesn't differ dramatically. Many other factors go into the overall sound reproduction, of course, and it would be really foolish to ignore all that, but there's something about the drivers specifically which interests me and I would like to be able to explore it in more depth. So while the 10khz-20khz octave doesn't hold a tremendous amount of information per se, it's one of the few hopefully comparable data points that might offer some evidence that could eventually lead to a better answer for my question, which doesn't intercede between me and my enjoyment of headphones at all but which sure does make me curious as to what could be the cause of what I and others hear.

 

I'm not the original poster of this thread, the OP's question isn't mine, just somewhat related since it made me think of how much more useful it would be for me to have a linear graph of the interesting high frequency profiles of various cans without having to figure out a way to test them myself in person. Hope that explains it. May not be anything that interests anyone else in the least, just a pet curiosity of mine.

I'm afraid fast and slow are the kind of terms I have no idea what they mean.

In general, a peaky top octave might make extended listening uncomfortable, particularly if it's up where it's hard to hear. Sound pressure from ultra high frequencies can induce headaches, and a spike up there would cut like a knife when the volume was turned up, even if you couldn't really hear it. In closed cans that can be a problem.

Dips down would be considerably less serious. It might diminish the presence of cymbals a bit if it got too low, making them a bit less airy. But unless it was down below 12kHz or so, it probably wouldn't affect the rest of the music all that much.

Extension, square reproduction at two or three octaves and impulse response might be sufficient to make a determination whether a driver is fast or slow. Just means literally what it sounds like, a relative measure of how quickly the output sound decays from the input signal. In a musical context it could affect accuracy of transient reproduction as well as phase smearing.

It sounds to me like you're just using an overly complicated explanation for simple high frequency distortion. FR isn't able to affect decay. That would be on a whole other level of magnitude than what your theorizing. It might even be the listener's own ears distorting from a huge high frequency spike.

I think we're talking past each other. You've got the order of my thinking reversed. I think that it's the quality of the drivers that causes the inherent interestingly different high frequency profile rather than the high frequencies causing the driver behavior. It does, however, seem to show up consistently across drivers, and that's where it gets interesting to me as potentially useful data. (Anyway, that's an egg that couldn't possibly come before the chicken, could it? Hah.)

Simple to find ou. EQ the spikes out and see if the issue disappears.

As I understand it the theory is that there's a connection between fast drivers/peaky hf, and slow drivers/dipped hf - not that the FR in either case is responsible for making the driver sound fast or slow.

Is this reasoning exclusive to dynamic drivers? I think some balanced armature designs, such as the Shure 535, don't agree with your theory.

You've understood me perfectly, and yes, it's strictly to do with dynamics.
 

 

I read that typically the high frequency roll off and double hump one typically sees for headphone frequency response is primarily to keep the sound pleasant.  If the curve was entirely flat there are a bunch of problems that arise.  Spatial acuity being one of them.  The fact that I see it on so many headphones really says it is more about physical build than anything else, but I cannot imagine a headphone with a spike in the HF.  My ears would say ouch.

 

Here is a nice link explaining roll off at HF.  It explains that most amps have trouble maitainaing HF as a function of voltage.

http://www.utdallas.edu/~torlak/courses/ee3311/lectures/ch11sec12.pdf

 

 

Perhaps this may help you understand the difference between the AKG-701 and HD-650.  The 701's really have some high peaks in the Harmonic Distortion Curve.  Like you have already noticed it does not appear to have anything to do with the frequency response curves.  I checked the square wave response of both as well at 500Hz and nothing really stands out as to what you are describing.

Edited by NA Blur - 8/5/11 at 3:53pm