DIY impedance adapter

Adding resistors to change the impedence of the headphone does NOT change the voicing and frequency response of the headphone. The 250 ohm version sounds different than the 80 ohm version because of different windings in the voice coil, magnets used, and other system wide changes - not just a resistor in the system. 

basic point that adding 170 Ohm series R won't make a 80 Ohm Beyer into a 250 Ohm is correct

everything else is wrong

adding series R does change frequency response of headphones with bumpy impedance vs frequency curves - typically boosting bass at the mass-spring resonance frequency of the driver - you need to look at the impedance vs frequency curve

keeping the same model number and offering different Z cans implies to me that everything except the voice coil is identical - why else keep the model number the same

if the voice coil has the same mass, dimensions with only the wire gage, number of turns changed then the headphone should have the same electro-acoustic properties - just as if an ideal transformer had been inserted to give the impedance change

if you really want to tailor response with series Z then you might look at http://www.linkwitzlab.com/reference_earphones.htm - the principle could be applied to any dynamic headphone

How on earth would it not just be a linear bump in impedance (shifting the whole imp/fq graph up)? The additional R is a static quantity, no? 

Honestly curious here. What you are presenting above doesn't make sense to me if you are simply adding linear resistance to an existing system. 

dynamic drivers aren't pure R, they have complex impedance and usually a bass resonance (single driver)

HeadRoom graph (likely mislabled the 250 - looks like 80 Ohm nominal Z to me)

the attenuation is less with series R at the peak of the impedance curve than at the nominal ~ 1kHz impedance - giving some bass boost

I get that, but since the added resistor is linear and pre-driver, that should just shift the whole load and curve up, not affect it's shape since there is no change to the driver itself, in indeed, even the signal hitting it (the resistor is soaking the extra). 

At best, I can see the added resistor eliminating any low level hiss or noise in the system... but that is all that makes sense. 

The series resistor forms a voltage divider with the load (headphones). 

The load impedance varies with frequency and because of this the voltage across the load varies with frequency. 

Because the voltage varies with frequency we get peaks and dips at various frequencies. 

Depending on the headphone these changes may be significant or not, and may be pleasant or not although more often than not they are on the nicer side of things with simple single-driver headphones anyways.

Ok, I think that makes sense. So you end up with a variable fraction of the original V, depending on frequency (using the headphone as one of the resistors in series). Not a linear jump (e.g. 2 resistors alone). 

Thanks for the correction, and patience, both of you. 

So with all that said - my basic point that this mod will not replicate the 250Ohm version of the Beyer DT250 is correct - but it will likely have some change to the FQR (probably bass resonance boost according to jcx). Yes?

Quote:

Originally Posted by liamstrain 

So with all that said - my basic point that this mod will not replicate the 250Ohm version of the Beyer DT250 is correct - but it will likely have some change to the FQR (probably bass resonance boost according to jcx). Yes?

Exactly. 

I would wait for a set of DT250/250 to come around second hand. Buy them & sell the DT250/80. It saves you the trouble of figuring out what to do with a set of 80 ohm drivers & all the markings on the headphones are right. 

Quote:

Originally Posted by markanini 

So with the DT250-80, PX100 and KSC75 adding inline resistance would be a bass-boost mod of sorts? Non-linear characteristics of impedance vs frequency will be accentuated?

Yes, you would get a mild bass boost AND poorer damping factor (which would sound like looser, bloomier bass) AND poorer efficiency in the amplifier/headphone interface. 

If you like more bass use an EQ.

I have some PX 100-ii, nice cans.