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Can a headphone be "overdamped" ?
extrabigmehdi
post Jul 18 2013, 13:59
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Hello,
the output impedance of my source is 10 ohms , while the impedance of my headphone is 300 ohm,
so if I understand correctly the definition of "damping factor", the value is 300/10 i.e 30.
Often it's recommended to use a damping factor above 8 or 10.
But is there a problem , if the damping factor is too big ?

I was surprised to learn that the expensive amp HDVD800 have an output impedance of 43 ohms.
That output impedance value was measured by someone in a forum, I don't have a better source.
The hdvd800 amp, is marketed as providing the best experience for the hd800 (and other headphone sold by sennheiser).
I was expecting a lower output impedance from such expensive amp (2000$), but perhaps that 43 ohm
output impedance is intended ?

Also there's an article that use a weird analogy with pendulums, suggesting that both overdamping and underdamping problems could exist for headphone. But I'm not sure the analogy is appropriate.
http://www.innerfidelity.com/content/compa...-ohm-headphones


So can we say , if at least theoretically, it would be better to use a higher output impedance for my source ?
Can I emulate a higher output impedance, by introducing a resistance between headphone & source (such like the volume control koss vc20, that acts like an adjustable resistance) ?
What are you thoughts regarding "overdamping" & headphones ?
Thanks
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pdq
post Jul 18 2013, 14:52
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Unless the specific speaker or headphone was designed to make use of a lower damping factor (to flatten its response curve, or something similar, and that would be a very odd thing to do), damping factors higher than the minimum recommended value should be no problem.

If you are worried, placing additional resistance in series with the amp's output would be an effective way to match the other amp's damping factor.
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DVDdoug
post Jul 18 2013, 18:51
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It's very-likely that some listeners perfer some headphones with the frequency response changes you get with a higher impedance source. But the manufacturers will design, test, and "spec" the headphones with a low impedance source, because with a varying impedance sources the performance will vary.

Its even possible that some headphones improve with a higher impedance. But if that's the case, a high-quality manufacturer would add resistors inside the earcups (and they would still test & specify with a low impedance amplifier).

QUOTE
I was surprised to learn that the expensive amp HDVD800 have an output impedance of 43 ohms.
Are you sure that's the effective output impedance? (I didn't see the output impedance or output voltage spec on Sennheiser's website.) Maybe it's the recommended minimum headphone (load) impedance. For headphone & power amplifiers, it's more common to see a spec for the load impedance rather than the internal source impedance... If the spec on a headphone amp says 1 Ohm, you wouldn't want someone to think they can connect a 4 or 8 Ohm speaker. I've never seen a source impedance spec for a power amplifier... If they give you the damping factor you can calculate it.

QUOTE
Also there's an article that use a weird analogy with pendulums, suggesting that both overdamping and underdamping problems could exist for headphone. But I'm not sure the analogy is appropriate.
The analogy is OK, but the analysis is NOT!

QUOTE
Now imagine a huge motor attached to the pendulum. In this case the motor is so big that it hardly feels the pendulumís moment at all. The motor will be able to do what ever it wants regardless of whether itís near the resonant frequency or not. The large available horsepower of the motor ďdampsĒ the pendulumís natural moments.
That's true!
QUOTE
An over-damped system (orange) will be slow to respond.
NOT TRUE if the damping is coming from the "huge motor" (or low impedance). It's true if you add a damper or shock absorber, but a more powerful motor will NOT move the penduleum slower! biggrin.gif

This post has been edited by DVDdoug: Jul 18 2013, 19:09
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extrabigmehdi
post Jul 19 2013, 01:45
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QUOTE (DVDdoug @ Jul 18 2013, 18:51) *
Its even possible that some headphones improve with a higher impedance. But if that's the case, a high-quality manufacturer would add resistors inside the earcups (and they would still test & specify with a low impedance amplifier).

Well often people complain that the headphone hd800, have too much treble, and are fatiguing when run from "cheap source" ( I understand "standard transparent sources") . When I add some resistance between the source and my hd800, I notice that there's less treble, and that it's less fatiguing (usually I use an eq). Anyways the hd800, have the reputation of "being hard to drive", and I think this benefit the "audiophile market" , that Sennheiser didn't make it too trivial to run the hd800 (i.e so that it is enjoyable). You see people buying all kind of insanely expensive sources, in the hope that it would "sound better".

QUOTE
Are you sure that's the effective output impedance? (I didn't see the output impedance or output voltage spec on Sennheiser's website.)

I think someone managed to measure it, anyways the information is circulating at head-fi.
You have something similar with beyer T1 headphone (impedance of 600 ohms).
Beyer has designed an expensive amp specially designed for it , the beyer A1 with an output impedance of 100 ohms (it's specified by beyer).

So you have hd800 (300 ohm) with the amp HDVD800 (43 ohm) which imply a damping factor of roughly 7.
Then you have the beyer T1 (600 ohm) with the amp beyer A1 (100 ohm) which imply a damping factor of 6.
I think this follows a commercial logic.
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saratoga
post Jul 19 2013, 02:13
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QUOTE (extrabigmehdi @ Jul 18 2013, 20:45) *
So you have hd800 (300 ohm) with the amp HDVD800 (43 ohm) which imply a damping factor of roughly 7.
Then you have the beyer T1 (600 ohm) with the amp beyer A1 (100 ohm) which imply a damping factor of 6.
I think this follows a commercial logic.


Thats actually a pretty high ratio, similar to what most lower impedance headphones are run at on good amps.

Looking at the HDVD800, the V0p is ~25 volts. Thus the output impedance is high because the output voltage is also very high, and it would be expensive to have high voltage and low impedance. 1 ohm output @ 25V in 16 ohm IEMs would generate 17 watts of power. That's not overkill, thats a fire hazard.

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stephan_g
post Jul 19 2013, 12:33
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That being said, you can also place current limiting elsewhere, without affecting output impedance. Power supply rejection's gotta be good for something.

A HD800 on a HDVD800 would show a 0.5 dB deviation from ideal FR on a 43 ohm output. Probably audible, but minor in the grand scheme of things. I typically use a 1 dB criterion to determine whether a match is OK.

Wow, this thing has a maximum amplification of 46 dB from RCA to output. Seems a little excessive. That's an input sensitivity of 85 mV, for a 17 V output. IOW, you can make most any 600 ohm headphone go up in smoke with most any puny Euro-capped MP3 player. I would have ditched that setting (38 dB still is enough!) and started at 6 dB rather than 14 dB instead.

As far as overdamped cans go, I'd say 50 ohm HD555/595s are, most of them at least - i.e. the "bass-light" version. Not the worst move for home hifi cans, given their fairly extreme impedance swing (min/max ~50/250 ohms). They sounded somewhat anemic on low-impedances sources though.

This post has been edited by stephan_g: Jul 19 2013, 12:34
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extrabigmehdi
post Jul 19 2013, 15:10
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QUOTE (stephan_g @ Jul 19 2013, 12:33) *
A HD800 on a HDVD800 would show a 0.5 dB deviation from ideal FR on a 43 ohm output. Probably audible, but minor in the grand scheme of things. I typically use a 1 dB criterion to determine whether a match is OK.

But aren't we more sensitive to some frequencies than other ? I'd think that a change of 0.5db in the 3khz-4hz region would matter (it's where you see a peak in the equal loudness curve).

QUOTE
As far as overdamped cans go, I'd say 50 ohm HD555/595s are, most of them at least - i.e. the "bass-light" version. Not the worst move for home hifi cans, given their fairly extreme impedance swing (min/max ~50/250 ohms). They sounded somewhat anemic on low-impedances sources though.

People are consistently complaining regarding the bass of the headphones , and I'm curious if a source would make them sound less anemic.



This post has been edited by extrabigmehdi: Jul 19 2013, 15:11
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saratoga
post Jul 19 2013, 16:31
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Its really hard to hear even a 1 db difference. I doubt a fractional db change matters.
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extrabigmehdi
post Jul 19 2013, 17:36
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QUOTE (saratoga @ Jul 19 2013, 16:31) *
Its really hard to hear even a 1 db difference.

I disagree, but I guess it depends of the context (we are not abx-ing headphones).

This post has been edited by extrabigmehdi: Jul 19 2013, 17:38
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Arnold B. Kruege...
post Jul 22 2013, 15:28
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QUOTE (saratoga @ Jul 19 2013, 11:31) *
Its really hard to hear even a 1 db difference. I doubt a fractional db change matters.


You are right - the degree of audibility of the difference (how many dB height or depth, what bandwidth, what center frequency) makes a big difference. Wide bandwidth, large changes, and frequencies that are closer to the midrange are more readily heard.

There are small differences that we can reliably detect, but it generally takes a larger difference to be troublesome. The ear clearly has the ability to become accustomed to smaller audible differences and sort of adapt to them. Just about everything in the real world changes frequency response and makes some kind of difference. If small differences broke our hearing and adaptation were impossible our ability to perceive the valuable information represented by a sound (is that sound due to a tiger or a dog or a rat in the bushes?) would be diminished or lost.

The nature of the sound being affected also matters. Sounds that are brief or rapidly changing make it more difficult to hear small changes. Familiarity and repetition favor reliably hearing small changes.

Under ideal conditions 1 dB changes that are broad and/or centered towards the middle frequency ranges can be reliably heard with appropriate program material.
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