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Beyers + resistance

post #1 of 7
Thread Starter 
Is there an explanation on why Beyer treble is tamed with higher output impedance? The only thing I've come across was that a matched impedance maximizes power transfer, while a low impedance output should maximize voltage.

Also another thing I wondered about was that my 80 wpc amp uses 220 ohm resistors because I assume that it would fry the phones otherwise. My question is if you just add a 220 ohm resistor to a headphone amp which already has a much lower wattage compared to a speaker amp, aren't you killing the power even further?
post #2 of 7
Hello,

Please note that if you are not willing to accept the sound of Beyer you should not get Beyer. This is because you can buy other headphones which do not have this high freq problems while sounding wonderfully.

The resistance you speak of is somewhat confusing. No speaker amplifiers should be terminated by 220 ohm. Unless of course the design was not really intended to drive 8 ohm load and the designer forced it to drive 220 ohm + 8 ohm load instead. This is very poor idea in my opinion, because designing an amp to precisely be able to drive 8 ohm load is relatively trivial.

Please describe your 220W/ch amp in more details.

Also, it is not recommendable for any headphones to be driven by high power speaker amplifiers. They have higher noise levels and higher distortion levels.

The result of putting a resistor in the signal path does dissipate some power. The reason for putting resistor this way is not what you assume. It is there to meet audio equipment standard. Which is that all headphone out can be assumed to have 120 ohm output impedance. Also, the output we have on headphone amplifier is 10~20mW. So the dissipation at the resistors are also very small. Thus, the amplifiers will not be effected except for the fact that they see higher impedance load (which is good.).

Tomo
post #3 of 7
Thread Starter 
Woops sorry bout the wording...I meant it uses 220 ohm resistors at its headphone jack. The Beyers just sound better from this amp than other amps I've heard like the Creek or even my JMT portable. As for distortion values I can turn it up at volumes more than other dedicated HP amps with any of my phones including low impedance Grados, and still not hear noise cause it is pretty clean amp for speaker amp(claims to have 110 S/N, .04% THD).

As for buying other phones that are better, I've tried just about everything in the similar pricerange, and didn't care much for the HD600. The Ety's are a little better at a slightly higher price...but I already have those and wanted a full-size phone. And higher-end Grado's are pricy.

Right now out of the jack of the amp, my Beyers sound good enough to be very competitive with my Ety's so I'm pretty sure I've accepted Beyer sound. I was just wondering what makes me accept Beyer sound with higher output impedance compared to low impedance.
post #4 of 7
You get a R-L-C filter effect with interaction of cable and driver capacitance, inductance and resistivity. Adding resistor changes the cutoff frequency (lowers it) so that you get a low-pass filter which will attenuate high frequencies. If you put big enough resistor you'll get headphones that sound like AM radio.
post #5 of 7
AOS-For an average headphone driver, what is its overall reactance? are most drivers similar, or totally different? thx
btw, i've measured the dc resistance of a couple of cheap headphones (never do this with anything you want to use again) and it was exactly equal to the rated impedence @ 1khz...
post #6 of 7
Sorry, I am not really the expert on headphone reactance issues . I may sound authoritative at times but I often speak from intuition (luckily I usually get it right but not always).

There was a discussion on HeadWize about these things. When it's back up, search for "snubber", I think it was in that thread. There was also some info on how HD-600 reactance varies with frequency, that article is I believe available.
post #7 of 7
Hi Tim,

The answer to your question is quite simple.

The 220 Ohm resistance, together with the impedance of your headphone Z, makes a voltage divider that lowers the voltage seen by the headphone.
Roughly the lowering factor is

Z/(Z+220)

The impedance of the headphone is frequency dependent and normally has higher values for lower frequencies. For instance HD600 has a 300 Ohm impedance at frequencies above 1 kHz but a 550 Ohm at frequencies below 150 Hz.

Simple mathematics shows that the attenuation of the higher frequencies is stronger than that of the lower frequencies.

I'm glad you like your DT931 :-)

Cheers,

Jan
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