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Topic: Possible effects of headphone amp on sound quality (Read 6681 times) previous topic - next topic
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Possible effects of headphone amp on sound quality

Does anybody know possible effects of using headphone amplifier on sound quality?
(except louder sound and driving high-resistance headphones better)

Frequency response, SNR, THD, crosstalk, subjective tests etc.

/EDIT\ I don't trust the guys at HeadWize completely. I think they're biased sometimes. \EDIT/
ruxvilti'a

Possible effects of headphone amp on sound quality

Reply #1 –
At least frequency response changes are common, due to low output impedance of headphone amps (compared to sound cards etc).

Possible effects of headphone amp on sound quality

Reply #2 –
Does it rule out power amplifier headphone output, that are usually high impedance (330 Ohm resistor in serial with the speaker output) ?

Possible effects of headphone amp on sound quality

Reply #3 –
A much better forum than HeadWize is Head-Fi.  If no one here seems to be able to come up with an answer, your next best bet is there. 

Possible effects of headphone amp on sound quality

Reply #4 –
Quote
Does it rule out power amplifier headphone output, that are usually high impedance (330 Ohm resistor in serial with the speaker output) ?

It all depends on the particular phone used.
E.g. my Philips HP890 sound pretty much the same off from either low or hi Z outputs.
Quite different to my other phones, Beyer DT931, which get an awfull rise at the lower end of f-response, driven off a Z in range of 300ohms.

Possible effects of headphone amp on sound quality

Reply #5 –
I've hoped for some measurements. 
/EDIT\ Some related info: link \EDIT/

/EDIT\
Tried looping back to soundcard to see the frequency response is, well, shite
On the other hand, test vinyl recorded properly (as well as one other)
My integrated just hid deficiencies of these headphones.
Can't wait to get new ones - in next week.

Sharper bass - only with few pieces (my electronic music showed, it was muddy as hell)
Freq analysis showed a peak at 110Hz and at 250Hz. \EDIT/
ruxvilti'a

Possible effects of headphone amp on sound quality

Reply #6 –
There are a few factors why dedicated amps work better than pcdp's or reciever jacks. 
What most people seem to care about with pcdp's is battery life, price and size, and they design them with that in mind. So they more or less neuter the amps in them with cheap op-amp chips and undersized caps, which is why they have a hard time driving higher impedance cans. Hell, some have a hard time driving lower impedance cans if the part quality is really sub-par. They also seem to be more likely to color the sound, I want to hear the music, not the player.  You'd be suprised at how good some pcdp's sound if you bypass their crap amp and use the line out with a decent amp.

A lot of recievers have a resistor from the main amp to bring down the power for the headphone jack, that means it'll be able to drive high impedance cans. But it also means that it'll have a really high output impedance. That muddies up the bass for any set, I'm not sure why, but it does. Headphones like a lower output impedance than theirs.

Recievers sometimes have an op-amp based amp seperate from the main amp, but most of the time it seems like it was thrown in as an afterthought and lesser parts end up being used.

Recievers seem to have a higher noise floor and headphones bring that out. On quite a few, if you turn up the volume with nothing connected but headphones, you'll hear hiss and hum. On my Ear+ amp, if I do the same, it's silent even when maxed.

Usually if you use something designed especially for that purpose, you'll get better results than something designed with many things in mind, as more things get compromised.

Possible effects of headphone amp on sound quality

Reply #8 –
Headphone amps, same as speakers amps, are power amplifiers, intended to drive the headphone (or speaker) properly, making posible to do it without frequency response desviations or added distortion.

A good headphone amp will accomplish this same way than a good speaker amp does. A headphone amp is just like a speaker amp, but with quite lower requirements. It does not need to provide as much power as a speaker amp, since a headphone needs just some mW to be driven properly. And it does not need to have as low output impedance as a speaker amp, because headphones are much higher impedance than speakers, and because headphones are not very sensitive to electrical damping factor, because they are already very damped mechanically.

If a headphone output has too high output impedance, and the headphone has a greatly varying impedance over frequency, it will cause frequency response desviations over the sound. If the headphone output can't provide much current (=power), it will distort on loud passages when connecting low impedance headphones.

A good headphone amp will avoid these issues due to having a reasonably low output impedance and a high enough current capability. A line-out won't accomplish any of these two.

Possible effects of headphone amp on sound quality

Reply #9 –
Quote
Here's one view on this matter (not necessarily the complete truth):
http://www.headphone.com/headphonegeek/the...timpedances.php

That seems to match with a quick measurement I did this morning over my Revo headphone output.

This would mean that, despite what I wrote, in case of headphones, output impedance, in some cases, can have some influence in damping factor, that translates mostly on frequency response at the headphone resonant frequency. I'll try to investigate a little bit more over this.

Possible effects of headphone amp on sound quality

Reply #10 –
That text was exactly what I was looking for!

My experimentational (is there such an English word?) mind figured,
that my old integrated amp just isn't good for this purpose.
(Damn psychoacoustics, nearly fooled me )

/me has decided to use TerraTec built-in phone-amp,
which is of suprisingly good quality.
Not much of a difference with 48 Ohm phones though. (slightly smoother sound)
ruxvilti'a

Possible effects of headphone amp on sound quality

Reply #11 –
Quote
This would mean that, despite what I wrote, in case of headphones, output impedance, in some cases, can have some influence in damping factor, that translates mostly on frequency response at the headphone resonant frequency. I'll try to investigate a little bit more over this.

Well, I investigated, and I can say that the differences in frequency response are not due to lack of damping, but due to impedance loading at the source. So, as I said, this will happen just when there are great impedance variations across frequency at a headphone, and the output impedance of the source is high.

This great impedance variations happen usually in high impedance headphones, that is one possible reason why they are said to be more difficult to drive. It's not that they are more difficult to drive (because in fact they need not much current to be driven, due to this same high impedance), but that in some cases the bass will sound bloated if the output impedance of the source is too high. Also, high impedance headphones may require more output voltage in order not to sound too quiet, but this depends on the actual headphone sensitivity.

Possible effects of headphone amp on sound quality

Reply #12 –
Did you perform some tests yourself or is this based on measurements someone else made?
Anyways, that explanation seems plausible (about what i thought before seeing that a bit baffling headphone.com article).

Thanks!

Possible effects of headphone amp on sound quality

Reply #13 –
Quote
Did you perform some tests yourself or is this based on measurements someone else made?

Both measurements I did and also theory.

You can download an Excel spreadsheet I just worte that calulates the effect of this impedance loading. There's one example for an HD580 headphone that has a min and max impedances of 300 and 600 ohm respectively:

http://www.kikeg.arrakis.es/various/zout_zl.xls

Possible effects of headphone amp on sound quality

Reply #14 –
1. Less distortion with difficult load phones, on which sound card's internal amplifier capability is exceeded (very audible)

2. On true low Ohm output amplifiers you also get a flatter frequency response on those headphones on which the impedance curve is not linear (tested on Finnish Hi-Fi magazine, in various issues).

So yeah, in short, it pays off at least for headphones that are a difficult load or headphones that have non-linear impedance curves, if you're headphone amp is powerful enough and has a near zero ohm output.

regards,
Halcyon