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All headphones being equal ?, Do headphones sound the same if well equalised
jlohl
post Jul 21 2006, 17:01
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Hi all,

I have a question about headphones sound quality :
when you equalise two different heaphones so to have a similar frequency response, do those headphones exactly sound the same ?

Some thoughts :
- quality headphones have quite low distortion levels so amplitude response is the most obvious difference
- most headphones are (?) minimun phase tranducers so correcting amplitude also corrects phase
- frequency response should not be too different to avoid gross correction (ie high peaks) that may overload your amplifier and/or transducer and bring distortion
- heaphones are not as complicated as loudspeakers. With loudspeakers you would have to correct the on-axis response and also an infinity of other out-of-axis responses (three dimensionnal frequency curves according to power response, directivity index, aso...) which is impossible. With heaphones, you have only one curve to change.
- the correction is only valid for one person because of different ear anatomies, sealing of headphones, aso

I know it is quite difficult to test because I cannot imagine an ABX test of headphones !
But has somebody tried or heard of something alike.
I can imagine that a manufacturer can do those kind of experiments but it would be a bit detrimental to high-end sales !


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Axon
post Jul 21 2006, 17:19
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You really can't tell THD unless you measure it. Speakers are notoriously bad at THD unless you want to spend $2000+ a pair, and headphones, despite their size, are not mechanically that much different from floorstanding speakers. (Ignoring balanced armatures and electrostats for a moment.)
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wylistener
post Jul 21 2006, 17:26
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QUOTE (jlohl @ Jul 21 2006, 11:01) *
I have a question about headphones sound quality :
when you equalise two different heaphones so to have a similar frequency response, do those headphones exactly sound the same ?


Absolutely not. At the most basic level, there's a difference in sound among different fundamental designs: open-back headphones sound very different than closed back headphones. And ENCLOSED-over-the-ear headphones sound different than ON-the-ear headphones. These differences cannot be compensated by EQ so that all the headphones sound the same. At this point, we haven't even gotten to the differences among manufacturer brands. And there are further differences in driver materials. Those differences can't be EQd out either.

QUOTE
Some thoughts :
- quality headphones have quite low distortion levels so amplitude response is the most obvious difference
- most headphones are (?) minimun phase tranducers so correcting amplitude also corrects phase
- frequency response should not be too different to avoid gross correction (ie high peaks) that may overload your amplifier and/or transducer and bring distortion
- heaphones are not as complicated as loudspeakers. With loudspeakers you would have to correct the on-axis response and also an infinity of other out-of-axis responses (three dimensionnal frequency curves according to power response, directivity index, aso...) which is impossible. With heaphones, you have only one curve to change.
- the correction is only valid for one person because of different ear anatomies, sealing of headphones, aso


Don't take this the wrong way... but I think these bullet points are overthinking the situation. smile.gif Water is wet. Circles are round. And headphones just sound different. Just go to a friend's house, put some cans on your ears and you'll easily hear a difference regardless of EQ settings.... you don't need esoteric golden ears kind of ABX tests to hear differences.

But another bullet point to add to your list is transient response... the "quickness" or "stiffness" of the diaphram can't be EQd either.

QUOTE
I know it is quite difficult to test because I cannot imagine an ABX test of headphones !
But has somebody tried or heard of something alike.


Grado, AKG, Sennheiser, Beyer-dynamic, Sony, etc all sound different. No EQ can make them equal to each other.
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Steve999
post Jul 21 2006, 18:42
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Very interesting question!

My headphone setup includes the AMAZING Behringer DEQ2496 digital equalizer and lots of headphones and a variety of carefully chosen (but relatively inexpensive) sources and amplification.

Just to hit a few topics addressed so far in this thread, I think the THD on most headphones is going to be of minor audible significance at best at reasonable listening levels. If someone wants to refute this with objective data, fine. I love to learn new things.

I think transient response is purely a function of frequency response. If someone wants to refute this with objective data, fine. I love to learn new things.

If two headphones with different driver materials but the same enclosures achieve the same frequency response, I would expect them to sound the same. If someone wants to refute this with objective data, fine. I love to learn new things.

I EQ all of my headphones. It's very easy to improve headphones with EQ, for the reason you set forth -- very difficult to control variables such as room response and off-axis response are minimized.

Still, I think the differences in sound between top-notch headphones vary a great deal more than those between top-notch speakers. I've noticed over the years that the ideal of what is a neutral reponse for speakers seems to have converged among manufactureres, and with ABX testing and computer modeling they seem to be striving for similar ideals. Not so for headphones, it seems. So, as a practical matter, I think it's going to be very difficult to get one model of headphones to have a very similar frequency response to another model. In my experience, it's a difficult and laborious task to get divergent frequency responses to sound the same with EQ. Also, the high frequencies, above about 4 kilohertz, tend to go a little crazy with headphones, for whatever reason (probably the curvature of the outer ear interacting with a driver so near it), and this causes headphone behavior in this area (4 khz up) to diverge radically from one model to another, in my experience. Below 4 khz, manufacturers like AKG (701), Beyer (DT880), and Sennheiser (HD595), are starting to converge in the frequency responses they achieve. To verify this you can go to headroom (headphone.com) and play with their well-done and very interesting comparative headphone frequency responses, in the technical data portion of their website. (But beware of the amp and cable snake oil there!)

Also, because of the differences in enclosures, you are going to get very different levels of ambient noise. This can make a big difference in what a headphone sounds like subjectively. With high isolation the same frequency response is going to sound different than with a very open headphone, and preferences in frequency resopnse will be different too, IMHO. An open phone, with ambient noise of the room, can be more relaxing to listeng to, for whatever reason, in my experience.

Also, I do believe that reflections between the phones and the ears play a pretty big role, and these may not always be captured by a simple frequency response graph. Just measuring frequency response of headphones is fraught with biological (ear shape) and philosophical (what's neutral with something as un-natural as headphones?) perils. If you've spent a lot of time with a lot of different headphones, you may develop an intuition that angled drivers versus drivers right on the ear versus drivers set back from the ears are going to give you a different sensation that may not be captured on a frequency response graph or in distortion measurements. Differences in ambient noise and distance/relation of drivers to the ears and the structure of the outer ear are the other side of the coin -- these are complex factors with headphones that you will not run into with speakers when trying to get them to sound the same, IMHO.

A very interesting and complex subject, IMHO. Thanks for your thoughts. It was a good read. cool.gif

Seriously, if anyone disagrees with me, have at it. I learn by people disagreeing with me. It's a very complex and interesting subject, IMHO, and an ABX test is impossible with headphones (but not impossible with amps and cables!!), so there is some room for opinion.

QUOTE (jlohl @ Jul 21 2006, 08:01) *
Hi all,

I have a question about headphones sound quality :
when you equalise two different heaphones so to have a similar frequency response, do those headphones exactly sound the same ?

Some thoughts :
- quality headphones have quite low distortion levels so amplitude response is the most obvious difference
- most headphones are (?) minimun phase tranducers so correcting amplitude also corrects phase
- frequency response should not be too different to avoid gross correction (ie high peaks) that may overload your amplifier and/or transducer and bring distortion
- heaphones are not as complicated as loudspeakers. With loudspeakers you would have to correct the on-axis response and also an infinity of other out-of-axis responses (three dimensionnal frequency curves according to power response, directivity index, aso...) which is impossible. With heaphones, you have only one curve to change.
- the correction is only valid for one person because of different ear anatomies, sealing of headphones, aso

I know it is quite difficult to test because I cannot imagine an ABX test of headphones !
But has somebody tried or heard of something alike.
I can imagine that a manufacturer can do those kind of experiments but it would be a bit detrimental to high-end sales !


This post has been edited by Steve999: Jul 21 2006, 20:31
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saratoga
post Jul 21 2006, 19:11
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The problem with EQ is that there are always going to be nonlinear effects in any mechanical transducer. As for how significant they'll be, I have no idea.
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jlohl
post Jul 21 2006, 20:56
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QUOTE
At the most basic level, there's a difference in sound among different fundamental designs: open-back headphones sound very different than closed back headphones. And ENCLOSED-over-the-ear headphones sound different than ON-the-ear headphones. These differences cannot be compensated by EQ

You're right but you can compensate this with a carefull crossfeed setup on closed headphones.

QUOTE
The problem with EQ is that there are always going to be nonlinear effects in any mechanical transducer

My question is : if you compensate all linear distortions, are non-linear distortions audible ?

QUOTE
transient response... the "quickness" or "stiffness" of the diaphram can't be EQd either.

I do agree with steve99 that transient response is just another word for frequency response, this can be equalised.

QUOTE
I do believe that reflections between the phones and the ears play a pretty big role, and these may not always be captured by a simple frequency response graph. Just measuring frequency response of headphones is fraught with biological (ear shape) and philosophical (what's neutral with something as un-natural as headphones?) perils


In AES conference on test and measurementt, Oregon 1992, Briolle and Voinier published a paper called "transfer function and subjective quality of headphones" : they tested 12 headphones on 20 listeners. They rated all headphones. After they simulated all 12 models on 3 headphones. The results of subjective quality showed a good correlation between quality of a given headphone and its simulation on another headphone. In other words, they could reproduce a headphone subjective quality on another one. Isn't it strange ?


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Madman2003
post Jul 21 2006, 21:03
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I can only talk from experience and not in the usual abx terms.

I have acces to two decent (closed) headphones, both are very different. My own are what can be described best as:

Refined, a bit bright and a (slightly) recessed midrange. The sound is thin, not in a bad way for me, but it isn't a boombox, nor does it have a very warm midrange.

Boosting it with a eq can correct for some things (i do it, because the reciever/amp and headphone are not perfectly matched), but you cannot boost things too much, because that's just plain ugly.

There is no way you can eq all headphones to sound the same, because it simply isn't there. Just like you can't turn a boombox into something more refined.
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jlohl
post Jul 21 2006, 21:37
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QUOTE
I EQ all of my headphones. It's very easy to improve headphones with EQ

steve999 : I'm interested to know how you equalise your headphones, what kind of signal do you use, how you find the best settings, aso,...


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wylistener
post Jul 21 2006, 21:38
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QUOTE (jlohl @ Jul 21 2006, 14:56) *
QUOTE
At the most basic level, there's a difference in sound among different fundamental designs: open-back headphones sound very different than closed back headphones. And ENCLOSED-over-the-ear headphones sound different than ON-the-ear headphones. These differences cannot be compensated by EQ

You're right but you can compensate this with a carefull crossfeed setup on closed headphones.


You've lost me here. Or you've changed the rules of the hypothetical discussion with your suggestion of "crossfeed setup on closed headphones". To clarify, if I have an open-back on-the-ear headphone, and I want to "EQ" it to sound like a close-back enclosed-over-ear headphone, I need to just put in a crossfeed ambience compensation? And the bass in a close-back headphones certainly feels different (pushes air around differently) than open back headphones.... I'm skeptical that EQ/modeling/whatever can reproduce that. Or maybe you meant to restrict the comparsion on closed-back headphones?

QUOTE
QUOTE
transient response... the "quickness" or "stiffness" of the diaphram can't be EQd either.

I do agree with steve99 that transient response is just another word for frequency response, this can be equalised.


Then I typed a bad description and semantics is getting in the way. I'm trying to describe the "attack" of the sound. I didn't think you could EQ the stiffness of the cone and the dampening factor. In this case, I'm thinking of the time-based artifacts (not frequency-based). I think we're just talking about two different things here. My Sennheiser HD-650 has a "faster" sound than Sony V600... the cymbals have more definition, plucked guitar strings are crispier (again because of "attack" not because "frequency response"). I use EQ on various things in the studio but I just don't see how to EQ the Sony V600 to make it sound like Sennheiser HD-650.

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greynol
post Jul 21 2006, 21:40
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Lots of discussion revolving around frequency response, not enough around phase response.


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saratoga
post Jul 21 2006, 21:43
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QUOTE (greynol @ Jul 21 2006, 13:40) *
Lots of discussion revolving around frequency response, not enough around phase response.


I don't see why you couldn't EQ that as well.
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jlohl
post Jul 21 2006, 21:54
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QUOTE
Lots of discussion revolving around frequency response, not enough around phase response.

As I already said, I think that most headphones are of a minimal phase nature, if so when you equalise the amplitude, you also equalise perfectly the phase


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jlohl
post Jul 21 2006, 22:05
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QUOTE
You've lost me here. Or you've changed the rules of the hypothetical discussion with your suggestion of "crossfeed setup on closed headphones". To clarify, if I have an open-back on-the-ear headphone, and I want to "EQ" it to sound like a close-back enclosed-over-ear headphone, I need to just put in a crossfeed ambience compensation? And the bass in a close-back headphones certainly feels different (pushes air around differently) than open back headphones.... I'm skeptical that EQ/modeling/whatever can reproduce that. Or maybe you meant to restrict the comparsion on closed-back headphones?

you are right that a crucial difference exists between closed and open heaphones.
But in the hypothesis you want a closed headphone A to sound like an open headphone B : first do a crossfeed to simulate the natural crossfeed of the open can and after do the equalisation.
For the opposite, if you try to make an open phone sound like a closed one : you have to do a transaural crosstalk attenuation, why not...


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greynol
post Jul 21 2006, 22:09
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QUOTE (jlohl @ Jul 21 2006, 13:54) *
QUOTE
Lots of discussion revolving around frequency response, not enough around phase response.

As I already said, I think that most headphones are of a minimal phase nature, if so when you equalise the amplitude, you also equalise perfectly the phase

Tweaking the frequency with an EQ affects the phase, before the signal reaches the headphones.


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Steve999
post Jul 22 2006, 01:09
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QUOTE (wylistener @ Jul 21 2006, 12:38) *
Then I typed a bad description and semantics is getting in the way. I'm trying to describe the "attack" of the sound. I didn't think you could EQ the stiffness of the cone and the dampening factor. In this case, I'm thinking of the time-based artifacts (not frequency-based). I think we're just talking about two different things here. My Sennheiser HD-650 has a "faster" sound than Sony V600... the cymbals have more definition, plucked guitar strings are crispier (again because of "attack" not because "frequency response"). I use EQ on various things in the studio but I just don't see how to EQ the Sony V600 to make it sound like Sennheiser HD-650.


I do think that what you are describing is a function of frequency response. I don't think it's time-based, or due to damping factor or stiffness of the driver. I think it has to do with the lack of resonances and/or relative emphasis in the 5 kilohertz to 10 kilohertz region. This isn't an original idea on my part -- it's a common topic of disagreement between the objectivist and subjectivist camps. I understand what you are saying -- the improvement in sound does give the impression of a more responsive or precise or more controlled driver. But I believe it's purely a function of frequency response. Now, I am a novice by any measure, so if someone has some data I'm "all ears." cool.gif

What measurable parameter of driver output do you think corresponds to this "speed" or "attack" ? That might be an interesting place to take the conversation. smile.gif



QUOTE (greynol @ Jul 21 2006, 13:09) *
QUOTE (jlohl @ Jul 21 2006, 13:54) *

QUOTE
Lots of discussion revolving around frequency response, not enough around phase response.

As I already said, I think that most headphones are of a minimal phase nature, if so when you equalise the amplitude, you also equalise perfectly the phase

Tweaking the frequency with an EQ affects the phase, before the signal reaches the headphones.


Exactly what do you mean by phase? Why wouldn't improving the frequency response in turn improve the phase response?

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greynol
post Jul 22 2006, 01:19
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QUOTE (Steve999 @ Jul 21 2006, 17:09) *
Excactly what do you mean by phase? Why wouldn't improving the frequency response in turn improve the phase response?
Phase is the delay of the signal at any given frequency.

You only have a partial picture of what goes on when looking at frequency response. It only tells you the amplitude for any given frequency. It says nothing about the relative timing between frequencies, this is where the phase response comes into play.


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Steve999
post Jul 22 2006, 01:26
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QUOTE (jlohl @ Jul 21 2006, 12:37) *
QUOTE
I EQ all of my headphones. It's very easy to improve headphones with EQ

steve999 : I'm interested to know how you equalise your headphones, what kind of signal do you use, how you find the best settings, aso,...


I use the headphone measurements at headphone.com, some measurements taken at head-fi.org (with lots of salt), and some measurements that a friend has taken with specific models of headphones. Using those as a starting point, I input the data in my Behringer DEQ2496 that should move me toward a flat response, and then I adjust to suit my taste through experimentation so that the response is very pleasing to me over a broad swath of recordings. The Behringer has both parametric and graphic EQ modes, which can be run at the same time. The graphic mode is at 1/3 octave intervals, and the parametric mode can be even more precise if you are hunting down a resonance. This usually takes two or three weeks of fine tuning to get it where I'm really satsified. I find it a pretty intense and interesting process. I use a mixer with a high-quality headphone out as a headphone amp, and this has tone controls I can use very conveniently, which I do use if a particular recording's tonal balance is highly flawed or way outside of the norm.



QUOTE (greynol @ Jul 21 2006, 16:19) *
QUOTE (Steve999 @ Jul 21 2006, 17:09) *
Excactly what do you mean by phase? Why wouldn't improving the frequency response in turn improve the phase response?
Phase is the delay of the signal at any given frequency.

You only have a partial picture of what goes on when looking at frequency response. It only tells you the amplitude for any given frequency. It says nothing about the relative timing between frequencies, this is where the phase response comes into play.


Then why would altering the frequency response with a digital equalizer alter the relative timing of the frequencies before they get to the headphone driver? This seems illogical to me.

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greynol
post Jul 22 2006, 01:36
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QUOTE (Steve999 @ Jul 21 2006, 17:26) *
Then why would altering the frequency response with a digital equalizer alter the relative timing of the frequencies before they get to the headphone driver? This seems illogical to me.

This depends on the design of the filter. If you're lucky the phase response is linear but nonetheless there will be an alteration in the phase response. Unless you want to dive into the mathematics you'll have to take this on faith. My days as an EE are long past me now but there are plenty of people here who are capable of explaining this to you in whatever detail you choose.

Edit: Please don't take this the wrong way but I'm having trouble with the placement of your responses. Most people place them underneath the quotation.

This post has been edited by greynol: Jul 22 2006, 01:43


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Steve999
post Jul 22 2006, 01:56
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QUOTE (greynol @ Jul 21 2006, 16:36) *
QUOTE (Steve999 @ Jul 21 2006, 17:26) *
Then why would altering the frequency response with a digital equalizer alter the relative timing of the frequencies before they get to the headphone driver? This seems illogical to me.

This depends on the design of the filter. If you're lucky the phase response is linear but nonetheless there will be an alteration in the phase response. Unless you want to dive into the mathematics you'll have to take this on faith. My days as an EE are long past me now but there are plenty of people here who are capable of explaining this to you in whatever detail you choose.

Edit: Please don't take this the wrong way but I'm having trouble with the placement of your responses. Most people place them underneath the quotation.


Is this better? tongue.gif Thanks for the tip. The frequency response with a digital equalizer is altered in the digital domain -- it's pure number-crunching, as I understand it. I think many of the problems presented by equalization in the analog domain have been eliminated or greatly reduced with digital equalizers, and I thought I understood that changing the phase of the signal (before it gets to the transducer) was one of the problems solved by digital EQ. Other than that, I must admit, carrying on the debate is going to take someone with a lot more expertise than I have. But thanks for your good-natured debate and for educating me. cool.gif

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greynol
post Jul 22 2006, 02:12
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QUOTE (Steve999 @ Jul 21 2006, 17:56) *
Is this better? tongue.gif Thanks for the tip. The frequency response with a digital equalizer is altered in the digital domain -- it's pure number-crunching, as I understand it. I think many of the problems presented by equalization in the analog domain have been eliminated or greatly reduced with digital equalizers, and I thought I understood that changing the phase of the signal (before it gets to the transducer) was one of the problems solved by digital EQ. Other than that, I must admit, carrying on the debate is going to take someone with a lot more expertise than I have. But thanks for your good-natured debate and for educating me. cool.gif

Phase alterations exist in the digital domain as well I'm afraid. You can't get around it.

You're quite welcome for the tip and the small amount of knowledge I have to give.


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Steve999
post Jul 22 2006, 03:19
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QUOTE (greynol @ Jul 21 2006, 17:12) *
Phase alterations exist in the digital domain as well I'm afraid. You can't get around it.

You're quite welcome for the tip and the small amount of knowledge I have to give.


I've googled this and it appears you are correct! This is a whole new area for me.

The general view seems to be, the greater the amplitude shift, the greater the phase shift, and that, generally, it's worth the EQ trade-off to get a flatter response, as long as you are not using EQ to compensate for things like large room response effects. Obviously, this wouldn't be an issue with headphones.

So I am interested to know, from anyone with an informed opinion, what would be the audible consequences of this with headphones?

Are frequency response anomalies in headphones also productive of phase shifts? Does EQ'ing them to a flatter frequency response create a compensating effect, where a phase shift due to a frequency response problem is corrected by EQ'ing the headphone frequency response itself to a flatter response? Is the apparent fact that a headphone is largely "minimum phase" relevant to the analysis?

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Steve999
post Jul 22 2006, 03:42
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QUOTE (jlohl @ Jul 21 2006, 11:56) *
In AES conference on test and measurementt, Oregon 1992, Briolle and Voinier published a paper called "transfer function and subjective quality of headphones" : they tested 12 headphones on 20 listeners. They rated all headphones. After they simulated all 12 models on 3 headphones. The results of subjective quality showed a good correlation between quality of a given headphone and its simulation on another headphone. In other words, they could reproduce a headphone subjective quality on another one. Isn't it strange ?


That is very interesting. Is there a link to the paper?

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WmAx
post Jul 22 2006, 03:50
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One would not want a linear phase DSP equalizer when correcting linear distortion(s). The standard analog circuit model(and most DSP units, such as the Behringer mentioned also use this as the model) of filter construction allows for the frequency respnose/phase to be inversed from the minimum phase anomoly(such as that inherant of a driver resonance) one in a driver(which also follows this model), net effect being a corrected phase AND frequency response. If you use a linear phase system to correct such a linear distortion, you will correct amplitude, but not phase. Although, one needs to have rather substantial phase shifts in order to become audible on music.

As for open vs. closed: their is no inherant correlation between any given aspect, excepting that of isolation. You can easily design a closed back that provides no ability for reflection(s)/resonance(s) to occur, when using proper absorbtion materials/design. Whether proper use of such materials is common, is another matter.

THD/IMD(non-linear distortions) is probably a non-issue in almost any quality headphone. The human hearing system can not detect the THD spectrum typical of most transducers, unitl is equal to single digit percents, when referring to music(pure long duraton sine wave tones make detection far easier) reproduction. I have measured a few high quality headphones for THD, and it did not even approach known audibility levels.

A very poor headphone probably has very little chance of ever sounding like a quality headphone, due to the probable severe resonances that are beyond reasonable correction(instead of a few localizable ones in a quality device) and the non-linear distortion at low frequencies at medium to high SPL.

It has been long known [1] that if you equalize two quality headphones to be the same response at the ear canal, that they will sound essentially the same.

-Chris

Footnotes
[1]On the Standardization of the Frequency Response of High-Quality Studio Headphones
Theile, Gunther
JAES, Vol. 34, No. 12, December, 1986, Pages 956-969

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saratoga
post Jul 22 2006, 04:05
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QUOTE (Steve999 @ Jul 21 2006, 19:42) *
QUOTE (jlohl @ Jul 21 2006, 11:56) *

In AES conference on test and measurementt, Oregon 1992, Briolle and Voinier published a paper called "transfer function and subjective quality of headphones" : they tested 12 headphones on 20 listeners. They rated all headphones. After they simulated all 12 models on 3 headphones. The results of subjective quality showed a good correlation between quality of a given headphone and its simulation on another headphone. In other words, they could reproduce a headphone subjective quality on another one. Isn't it strange ?


That is very interesting. Is there a link to the paper?


This is the best I can find, but I'm not about to pay $40 for it

http://www.aes.org/publications/preprints/...ints_search.cfm

Unfortunately I can't find a free copy on google, probably because of the age of the paper.
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WmAx
post Jul 22 2006, 04:08
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QUOTE (Mike Giacomelli @ Jul 21 2006, 23:05) *
This is the best I can find, but I'm not about to pay $40 for it

http://www.aes.org/publications/preprints/...ints_search.cfm

Unfortunately I can't find a free copy on google, probably because of the age of the paper.


Steve999 already has a copy of the peer-reviewed JAES article that I referenced, that refers to such experiments. However, I suppose that he never got around to reading it, or maybe he just forgot about it.... smile.gif

-Chris
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