Adding impedance to headphones

I have just a few questions about adding impedance to a couple of my headphones.

KSC75
Since selling my pair of KSC75s to another head-fier (you know who you are), I have decided to retake a pair that I have been letting a co-worker use for the past several months (he's now using a pair of EX51s, better isolation), and they are the rat shack model with the volume controller. I am going to ditch the vol pot, as it tends to pull on my ears while I am jogging. Since I am doing that much to them, I figured I might take the time to experiment. I remember hearing something about adding impedance improving the sound of them, but I cannot find the thread stating so. Anybody know if this is true or not? Also, how does it affect the sound?

Westone UM2
The main reason I want to add impedance to these is to hopefully get rid of the hiss I hear when using them out of the HP out on my X5L (minor, but it's there). For this phone, I have heard that adding impedance actually kills the SQ of these, but I can't seem to find that thread either. Any ideas?

ultimate ears iem come with one, you can buy a kit separately that has them in it. I came across a site they other day, might be worth emailing the guy to get a price on them http://apuresound.com/products.html

I do not have any experience with iem so i can not say what it will do to the sound quality

Adding impedance can change the sound, but the changes will vary from setup to setup. Usually headphones with high impedance seem to be more readily affected by such impedance adapters. In general, I think the bass is emphasized.

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Since the volume control is variable impedance, you can try that to see at what position you like the sound the best. Then if you want to put a fixed resistor in the place of the volume pot, cut out the pot and measure its impedance at your favorite position.

With digital players, higher digital volume may result in better resolution. So the overall sound may be better with digital volume turned up, then external analog volume turned down (on the headphones), or with a fixed resistor.

Correct me if I am wrong, but I am pretty sure that impedance and resistance are two different things. Impedance is pretty costly to measure. The volume control changes the resistance. Some headphones do not benefit from such adapters, but most people swear that the KSC-75s do. I am going to listen to mine for a while, and then I am going to put some resistance on them and see what happens.

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The impedance of R is its resistance, at any fequency. The impedance of L and C changes as frequency changes.

The context is talking about put in a resistor in serial with the headphone driver. If L and C are put in, the frequecy response will be changed.

Wow, somebody brought this thread back from the dead! I guess as a bit of an update, I sold the UM2 and I removed the volume pot from the KSC75 and just wired them straight back together. Soldering resistors directly to the cables can be a bit of a PITA (what does that mean anyways).

Thanks for the advice guys, even if I don't have a clue what you're talking about.

And looking back, I should have titled this thread "Adding resistance to headphones". That probably would have been a little clearer.

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Since when do people start using words/abbreviations they don't know. Some people are just a Pain In The Azz...

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Well... here's the impedance graph for the KSC55/75. . . . can somebody help me calculate how much should be added in series?? Or should I just randomly throw on 75ohm or 100ohm or what???

what do you want to acheive?

commonly headphone amps have very low output R and the frequency response is measured with Voltage drive ( 0 output R )

If you used a pure Current source driver you could expect the magnitude of the impedance hump to be added to the V drive frequency response plot

A voltage output type amp with higher series R looks more like a Current source as the R increases, and attenuates the average signal more

very approximately you could expect a R 10% of the nominal headphone resistance to limit the added bass hump to <1 dB

http://www.provide.net/~djcarlst/abx_crit.htm

shows the frequency response changes that are expected to be detectable

for this impedance graph I would guess <30 Ohms series R would not be detectable after drive level matching for the average attenuation ( from nominal -3.5 dB atten vs -1.6 dB at 150 Ohm impedance peak with 30 Ohm series R for ~ 2 dB difference for 1 octave near 80 Hz )

EQ in the signal path should be able to give equivalent results in terms of changing the frequency resoponse

What I think could make sense looking at the graph is to make power delivered to the headphones equal for both 60 (flat response) and 150 ohms (peak impedance). You get it using the equation R = sqrt(Z1*Z2) = sqrt (60*150) = sqrt(9000) = 94,4 ohms. Such resistors don't exist but you can find 91 or 100 ohms. Use metal film resistors of 1% or lower tolerance (carbon film resistors of lower grade deteriorate sound sometimes) for each channel in series, the bass will rise for sure, but resulting impedance might be to high for a mp3 player to play loud enough. The best experiment is to use the volume control, measure the resistance of the headphone transducer alone, then with the volume control connected, and finally subtract these two resistances to find the resistance set on the volume control.

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Thank you SOOO MUCH!!! I think everyone learns better thru examples.

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Soo... resistors in series will add up, right? So a 45ohm adapter would make most sense, since KSC75 is stock 60ohms??

If I can't buy a 45ohm adapter, I'm assuming the 75ohm adapters will work BEST with the KSCs and an amp??

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I don't have the volume control... I don't even have wires on this one pair of KSCs I'm about to recable and such -- my friends destroyed them, but it was just more motivation for me.

http://www.head-fi.org/forums/showthread.php?t=201098

For a volume control type of setup. That is if you want to attenuate the volume without affecting the sound.

fwiw: A volume pot does not change the impedance of the headphones as you change the volume. The presence of the volume control will change the overall impedance of the headphones, but it doesn't change dynamically with different volume levels. You'd have to use a variable resistor (varistor) to do that, and a volume control is not a varistor, it's a potentiometer.

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He's saying that because KSC75 is 60ohms min, and 150ohms max, the "best" resistor to add is 94.4ohms, to get a total of 154ohms min, and 244ohms max.

There is absolutely no 'logic' to that logic. There is nothing to say that the distribution of impedance across the frequency bandwidth is uniform, so adding the enough so that the "middle" between impedance between 60 and 150 ohms is silly. It would make more sense to either work with the minimum impedance so that you know at least you always have X impedance, or work with the nominal impedance.