[bigshot]

It's a coloration that sounds good to you. Nothing wrong with that, but it isn't balanced. It might not work well with acoustic music.

 

[ToTo Man]

It's a coloration that sounds good to you. Nothing wrong with that, but it isn't balanced. It might not work well with acoustic music.

Is it a colouration? Do we know for sure that headphone manufacturers voice their headphones using zero output impedance sources? Not trying to be argumentative here, just genuinely curious.

 

[bigshot]

I guess I would assume that the impedance specs are the target for a balanced response. If you're set up for it, you could try testing the response and see how it lines up. Do you have any headphones that you know have a relatively flat response to compare? When you're describing differences, it helps to describe them as specifically as possible. Generalized poetic descriptions assume a conclusion and don't really communicate anything. Better to talk about specific balances in frequency ranges. A tone sweep might reveal what is being affected.

 

[AutumnCrown]

High impedance should basically cause the diaphragm to stop moving less quickly, while damping does more or less the opposite, which is to limit sound reflections and reverberations after the signal has stopped.

I wonder if the increase in soundstage is due to the default HD6x0 tuning being overly damped, masking the spatial cues (sound reflections in recorded room) in favor of textural detail.

 

[71 dB]

I've been experimenting with the different output impedance settings offered by the AT-HA5050H headphone amp. It gives the choice of 0.1, 33, 82 and 120 ohms.

1. I'd assumed going from 0.1 ohms to 120 ohms would turn my HD600s into a loose, uncontrolled and bloomy mess but I was wrong!
2. The bass has indeed plumped out a little, but I'm more surprised by the effect it's had elsewhere. It seems to have improved the soundstage and fluidity, and has pushed the mids back a little whilst giving the top end a sweet and shimmering wetness.
3. I really like the effect, but I'm confused because I thought that output impedance mainly affected bass response, and also headphones that have large impedance swings.
4. The HD600's impedance curve between 1kHz and 10kHz is as flat as a pancake, though it does begin to rise slightly above 10kHz. Does this explain the effect I'm hearing?
5. I feel rather naughty because I am clearly violating the "less than 1/8th" rule between load and output impedance.

1. It's up to the headphone what happens when output impedance changes. Some headphones are more sensitive than others.
2. The bass boost with HD-600 caused by output impedance is: 0.0 dB (0.1 Ω), 0.4 dB (33 Ω), 0.9 dB (82 Ω) and 1.2 dB (120 Ω). So, nothing dramatic really. Higher output impedance seems to have some positive effects on the soundstage, but I don't fully understand why. Because headphones usually have their maximum impedance value around 100 Hz (resonance frequency of the driver) and also have rising impedance in the high frequency due to voice coil inductance, higher output impedance causes frequency response to change boosting 100 Hz area and also the highest octave or so. The sound becomes uncontrolled when the system damping ratio (not damping factor which is a different thing!) is less than one. For Sennheiser HD-600 the system is critically damped (damping ratio = 1) when the output impedance is 150 Ω. For 0.1 Ω, 33 Ω, 82 Ω and 120 Ω output impedances the corresponding system damping ratios are 1.184, 1.130, 1.066 and 1.027 meaning slightly overdamped systems. Again, nothing dramatic. As long as the output impedance is 150 Ω or less you have "controlled" sound from technical point of view.
3. True, but how much is a different question. For HD-600 output impedance of 120 Ω is pretty ok, but for HD-598 it would be catastrophic.
4. Yes, it rises above 10 kHz, because voice voil inductance kicks in. This probably explains partly what you hear.
5. The "less than 1/8th" rule is very general/coarse and following it ensures you don't go completely wrong with any pair of headphones. For HD-600 you need "less than half" rule. Why? Because the mechanical damping and impedance curve of the heaphones say so!

 

[ToTo Man]

1. It's up to the headphone what happens when output impedance changes. Some headphones are more sensitive than others.
2. The bass boost with HD-600 caused by output impedance is: 0.0 dB (0.1 Ω), 0.4 dB (33 Ω), 0.9 dB (82 Ω) and 1.2 dB (120 Ω). So, nothing dramatic really. Higher output impedance seems to have some positive effects on the soundstage, but I don't fully understand why. Because headphones usually have their maximum impedance value around 100 Hz (resonance frequency of the driver) and also have rising impedance in the high frequency due to voice coil inductance, higher output impedance causes frequency response to change boosting 100 Hz area and also the highest octave or so. The sound becomes uncontrolled when the system damping ratio (not damping factor which is a different thing!) is less than one. For Sennheiser HD-600 the system is critically damped (damping ratio = 1) when the output impedance is 150 Ω. For 0.1 Ω, 33 Ω, 82 Ω and 120 Ω output impedances the corresponding system damping ratios are 1.184, 1.130, 1.066 and 1.027 meaning slightly overdamped systems. Again, nothing dramatic. As long as the output impedance is 150 Ω or less you have "controlled" sound from technical point of view.
3. True, but how much is a different question. For HD-600 output impedance of 120 Ω is pretty ok, but for HD-598 it would be catastrophic.
4. Yes, it rises above 10 kHz, because voice voil inductance kicks in. This probably explains partly what you hear.
5. The "less than 1/8th" rule is very general/coarse and following it ensures you don't go completely wrong with any pair of headphones. For HD-600 you need "less than half" rule. Why? Because the mechanical damping and impedance curve of the heaphones say so!

Thank you for an awesome post! If I may ask you a few questions:

1) How do you calculate the dB bass boost of a particular headphone for different output impedances?
2) How do you calculate the output impedance at which a particular headphone is critically damped?

 

[bigshot]

High impedance should basically cause the diaphragm to stop moving less quickly, while damping does more or less the opposite, which is to limit sound reflections and reverberations after the signal has stopped. I wonder if the increase in soundstage is due to the default HD6x0 tuning being overly damped, masking the spatial cues (sound reflections in recorded room) in favor of textural detail.

I tend to doubt that. Channel separation is the main thing for reproducing soundstage in headphones, and that's generally not a problem. Flappy diaphragms would fall under the category of distortion. Speakers have way more distortion than headphones, yet they reproduce soundstage a million times better than cans. With speakers, it's the room that dictates how good the soundstage is.

 

[AutumnCrown]

I tend to doubt that. Channel separation is the main thing for reproducing soundstage in headphones, and that's generally not a problem.

But most headphones have the same amount of channel separation, right?

 

[bigshot]

Most modern audio components have inaudible levels of channel spill. That hasn't been a problem since LP records.

The problem with soundstage is that the term is so often misused in audiophile circles that the meaning has gotten lost. Soundstage is the placement of sound precisely in space. That is only possible with speakers, because headphones put sound between your ears, not ahead of you in physical space. "Headstage" is what we talk about with headphones. That is a straight line through the middle of the ears from right to left. The only way to mess that up is to mix the channels, which never happens.

There are secondary depth cues built into mixes... specifically room reflection and differences in level that indicate distance... but those are no harder to reproduce than any other part of the signal. You would have to introduce an awful lot of distortion to start messing with that, and it would make the rest of the music sound bad just as much as it would the depth cues.

 

[AutumnCrown]

Most modern audio components have inaudible levels of channel spill. That hasn't been a problem since LP records.

Right, so why would channel separation explain the differences in soundstage among different headphones if they are all the same in channel separation?

 

[bigshot]

There is no difference in soundstage in headphones, because there is no soundstage. There are differences with frequency response primarily, then distortion, and lastly dynamics. Audiophiles just don't always know how to describe different combinations of those three factors, so they make up terms that are supposed to be analogies, but they really don't apply at all. It's more accurate to speak in terms of response, distortion and dynamics. There are types of response deviations, and there are a bunch of different kinds of distortion. If you use those terms, you can point to exactly what you mean and you don't need meaningless analogies like "veiled sound" or "liquid highs".

 

[71 dB]

Thank you for an awesome post! If I may ask you a few questions:

1) How do you calculate the dB bass boost of a particular headphone for different output impedances?
2) How do you calculate the output impedance at which a particular headphone is critically damped?

Thanks, you are welcome.

1) You need output impedance Zout and the min/max impedances Zmin/Zmax of the headphone. Assuming all of these very resistive the frequency response error is Lmax - Lmin, where

Lmax = 20*log(Zmax / (Zmax + Zout))
Lmin = 20*log(Zmin / (Zmin + Zout))​

2) Zout_critical_damping = (sqrt(L / C)*(R + Rc) - 2*R*Rc) / (2*R - sqrt(L / C)), where

L = compliance of diaphragm suspension on electric side
C = diaphragm mass on electric side
R = mechanical resistance of diaphragm on electric side
Rc = voice coil resistance on electric side
​

Where do I get these parameters? I get the measured impedance curve of a headphone online and simulate it with an equivalent electric circuit. I iterate the parameters until I get a very good match with the measurements.

 

[71 dB]

Most modern audio components have inaudible levels of channel spill. That hasn't been a problem since LP records.

The problem with soundstage is that the term is so often misused in audiophile circles that the meaning has gotten lost. Soundstage is the placement of sound precisely in space. That is only possible with speakers, because headphones put sound between your ears, not ahead of you in physical space. "Headstage" is what we talk about with headphones. That is a straight line through the middle of the ears from right to left. The only way to mess that up is to mix the channels, which never happens.

There are secondary depth cues built into mixes... specifically room reflection and differences in level that indicate distance... but those are no harder to reproduce than any other part of the signal. You would have to introduce an awful lot of distortion to start messing with that, and it would make the rest of the music sound bad just as much as it would the depth cues.

Why is it so difficult for you to believe that headphones can produce out of head sounds? Even basic crossfeed manages to create miniature soundstage not to mention binaural recording which can be quite effective. I enjoy miniature out of head soundstage on my headphones daily and proper crossfeed is all I need.

 

[ToTo Man]

Thanks, you are welcome.

1) You need output impedance Zout and the min/max impedances Zmin/Zmax of the headphone. Assuming all of these very resistive the frequency response error is Lmax - Lmin, where

Lmax = 20*log(Zmax / (Zmax + Zout))
Lmin = 20*log(Zmin / (Zmin + Zout))​

2) Zout_critical_damping = (sqrt(L / C)*(R + Rc) - 2*R*Rc) / (2*R - sqrt(L / C)), where

L = compliance of diaphragm suspension on electric side
C = diaphragm mass on electric side
R = mechanical resistance of diaphragm on electric side
Rc = voice coil resistance on electric side
​

Where do I get these parameters? I get the measured impedance curve of a headphone online and simulate it with an equivalent electric circuit. I iterate the parameters until I get a very good match with the measurements.

Whoa, I think you might have lost me on the second calculation! So, most of the parameters required to calculate Zout_critical_damping are not in the public domain and can only be obtained by personally measuring the headphone, is that correct? Or do you have already have enough information to estimate it? If it's not too much trouble, would you mind walking me through one example please?

 

[bagwell359]

I guess I would assume that the impedance specs are the target for a balanced response. If you're set up for it, you could try testing the response and see how it lines up. Do you have any headphones that you know have a relatively flat response to compare? When you're describing differences, it helps to describe them as specifically as possible. Generalized poetic descriptions assume a conclusion and don't really communicate anything. Better to talk about specific balances in frequency ranges. A tone sweep might reveal what is being affected.

But what's flat? Music is dynamic. One headphone may be notably flat playing a stand up bass with sustained notes. But add in another bass signal - say short sustain drums (rototoms) and they start to modulate each other - than its not flat. The best headphone I ever heard on that test is the HD-600, but the bass under 65 Hz is lacking, and if we could assign a "Q" for the bass I'd say it was very damped (.57), and to support that I'd say the impact even in the midbass is minimized compared to other headphones and a large number of speakers I'm familiar with. The HD600 bass would be closest perhaps to panels such as the .7i, or the fairly unknown Cizek 1 w/ bass set to .57.

So in the real world "relatively" flat is subjective based on what you have heard, and what you prefer. I'd say listeners would have to be educated a good deal not to make their reference based on their preferences and/or lack of exposure.

For me the HD-600 and HD-800 would be flat frequency references. But there are things missing that makes the experience at times - astringent. My HE-500 modded with MrSpeakers Ether Flow Angled and the fuzzor mod are just about as flat as the HD-600 but seem to capture music better (classical is close outside of the missing bass heft). But things like cymbals being brushed are far more realistic then the 600. So what's that? Harmonic Distortion? or the small spike at 10k?

Ever since digital gained market share I've seen the rise of tubes to balance that, and the high buck MC vinyl thing vs digital.

I think measurements can lead you to the area you want to be in, but that subjective choice will continue to be the decider (along with budget).