DT880 600ohm BS - Page 2  

One possibility is that many amps have too much gain, so when you use them with lower impedance cans, the volume pot is always turned down low. Half the signal gets dumped back into the ground, etc. etc. But with 600Ω you get to crank the pot up higher, and less of the signal gets wasted. Also, some amps also only sound good when used past a minimum gain level.

 

Disclaimer: I own a DT880/250Ω, and have never heard the 600Ω version. Would be nice if the only difference is the volume, then all I'd need to do is lower the gain on my amp to hear what all the fuss is about.

I own the 250 ohm version. Someone send me a set of 600 ohm-ers and I'll measure both side-by-side. You'll see they have different frequency response curves.

It doesn't necessarily mean it sounded "faster".  Just that the diaphragm will move faster from the same amount of power, because it weighs less.  What that may actually sound like depends on a lot of other factors.

 

AFIK the drivers in each series/revision (except for the 770, which FR graphs suggest something else) are exactly the same except for the gauge of the wire in the voice coil.  You can't really compare a completely different driver design.  The magnets could be larger, smaller, weaker, or stronger.  The same for the diaphragm.  It can also have softer or stiffer suspension as well.  The important thing is that these comparisons need to hold all else equal.

 

Ignoring your aggressive language for now, which I find distracting in an objective discussion, I don't understand your point here.

 

With regards to output impedence, doesn't the higher dampening factor on the 600ohm version make it more immune to coloration due to the headphone's non-flat impedence? That said, most amplifers don't have higher than ~120ohm out impedence (even the OTL tubes) so in this sense the 250ohm version seems good enough.

 

In addition, I am confused by your goals. Do you just want to prove there's a difference, or do you want to see an improvement? An improvement in what sense? A flatter FR?

With higher impedance, you get less current requirements, higher damping factor, higher signal-to-noise ratio, less crosstalk, and probably some other things I am forgetting.  Amps aren't quite perfectly linear, so I wouldn't be surprised to see different responses to different loads.  In many applications (I mean not audio in general), impedance in the low hundreds and especially in the tens is often considered unusual and difficult to deal with.  Some of the highest-fidelity line-driver op amps aren't spec'd for impedances below 600 ohms, so a more "typical" load might be better driven.  As mentioned earlier, many volume potentiometers have issues with channel balance in low settings, which a high impedance headphone would not need to be operated at.  Non-class A amplifiers have more trouble at around zero output, which happens more at a lower gain setting required by lower impedances.

 

Of course, these differences are most likely very marginal between 250/600 versions, though the 32 ohm version could be somewhat different because of these things.  Just take these as possible factors.

Edited by mikeaj - 8/12/10 at 8:42pm

I agree - should not be a factor in 250ohm vs 600ohm, but quite possibly in a 32ohm.

if voice coil conductor mass is kept constant with the number of turns being the only variable changed then the effect is identical to using an ideal transformer to change the terminal impedance

 

the electro-acoustic response should be identical, when referenced to drive power

 

Keeping coil mass the same, the 600 ohm coil will have more turns due to the smaller wire. More turns means more inductance. More inductance means less high frequency SPL.

I can't find my measurements but remember the 600 ohm version having less SPL in the 10-20kHz region than the 250 ohm version. If someone would send me a 600 ohm set I can repeat the test and end the speculation.

not when normalized properly - you have more wire resistance in the same porportion and the L/R time constant stays the same, the Z rise starts at the same frequency, at the same rate so the driver behaves the same as one with a fewer turn, lower Z voice coil and an ideal transformer

 

there is a difference if you have external fixed Z in the amplifier - but keeping amplifier output Z constant and changing driver Z changes the system, not the electoacoustic parameters of the headphone - which are measured in terms of the driver's terminal voltage and current vs frequency

With real world, round wire coils, keeping the coil mass constant, the finer wire, higher resistance coil will have disproportionately more turns and more inductance because of greater packing efficiency, causing a reduction in high frequency SPL. Using rectangular wire will more closely approach your theory, but there's still the insulation thickness needed in real-world coils.

Edited by Donald North - 8/12/10 at 11:37pm

I was trying to give a idealized rule to help simplify the analysis - second order effects like practical packing factor/insulation thickness, mag circuit gap dimensions, assembly tolerances may be become important but require more detailed knowledge of the actual product's engineering - as a dynamic transducer 1st order design principle the idealized transformer view is useful and will be presented earlier in a electroacoustic design book than the issues you bring up 

Edited by jcx - 8/12/10 at 11:55pm

I understand what you're saying, but I'm bringing up these issues because I suspect they're contributing to the difference in frequency response between the 2 versions.