[odigg]

I don't know if this is a DIY question, but there are people here with the technical background here that can answer this.

I'm going to use an analogy to regular speakers to ask this. Let's say I buy a pair of speakers capable of handling 100W rms. Then Let's say I purchase two amplifiers with identical sound, but one has a 20W rms output and the other has a 100W rms output. Both amplifiers are capable are providing that power across the whole frequency range.

Is the only difference between the sound from the two amps the potential loudness? If I listen to the 100W speakers with the 20W amp, will there be a "sound quality" difference compared to when I listen to the same volume with the 100W amp? Isn't this basically what a volume knob does, changing the power output?

So my question now follows about headphones. Will an amp that provides 100 ma equally across the frequency range sound the same at the same volume as an amp that can provide 300ma consistently across the frequency range?

My understanding of why a weak amplifier can't power power hungry headphones is that the power delivery is not equal across frequencies. Some amps distort or collapse under the load's power requirement at certain frequencies. This is why we change caps to improve bass response.

So, when we compare a weak amp (not able to provide even power across all frequencies) vs a powerful amp (able to provide even power across all frequencies), that is what causes a difference is sound quality.

Am I thinking along the right lines here?

 

[gyrodec]

I think they best way to answer this is to use an example I remember from old speaker amp reviews. The Apogee Scintillias were one of the top dog speakers in the 80s, but they were very, very hard to drive with 1.2 ohm and bad phase angles on the impedance. Most amps used to drive them were 200W plus monsters (Krell etc) but the 25W class a Mark Levinson monoblocks (sorry, I forget the number) were rated as one of the very best amps for these speakers, better even than the Krells, but they did have a lower max volume. The MLs had a power supply that was enormous and lots of output transistors, not just for a 25W amp, but even for a 200W amp, and so it had almost unlimited current delivery up to its maximum voltage swing. Most 200W amps couldn’t drive as much current as easily as the ML and so didn’t sound as good on these demanding speakers.

Now, most 200W amps would sound better than most 25W amps on these speakers, as the current drive on a 200W amp is usually much better than a 25W amp. So, if your theoretical lower current headphone amp might not sound quite as good as the higher current one, on a very current hungry set of cans. On most cans there should be little difference, but with a stressful enough load, you probably could hear a difference.

 

[holland]

Quote:

Originally Posted by odigg /img/forum/go_quote.gif My understanding of why a weak amplifier can't power power hungry headphones is that the power delivery is not equal across frequencies. Some amps distort or collapse under the load's power requirement at certain frequencies. This is why we change caps to improve bass response.

Define "power hungry", please. Define "weak amplifier", please. Define "some amps", please.

I'm not too sure about your last sentence. There are other factors in play, like effective RC and RLC circuits as well with the headphones, the ESR of the caps, the inductors used in some areas responding to the ESR of the caps, etc. Also some people like some aspects of certain caps, and it's not necessarily a change to improve bass response. That, seems to me, a common misrepresentation. There's also the metal aspects, change cap = better sound automagically.

Speaker amplifiers are rated at a given load. 4 ohms, 8 ohms, etc. Headphone amplifiers are not "standardized" in that fashion. Impedence and sensitivity also varies with frequency, as the loads are non-linear, so you're right in your approach from my perspective.

IME, the popular headphones are not that difficult a load, with a few exceptions. I've not really heard of headphones that swing in impedence from 1 ohm to 1kohms, for example. Of the data I've seen on headroom's site, it seems a much narrower range.

Perhaps some of the designers have measured their amps with a real headphone load and can better extrapolate with data points.