DT880 600ohm BS - Page 8  

Hi chiniesekiwi, I have always agreed with the evidence you put forward.  I was referring more to tube distortion (or amplifying colourations from an amp). While I have no evidence to support this hypothesis at the moment, when I owned my LDMKIII, I tried to use the lowest gain setting possible, as higher gain settings seemed to fatten and warm the sound.  Other head-fiers found the same thing with their LDMKIIIs.  It is possible that the need to use more gain on a higher impedance headphone (e.g.600ohms), adds more of the amplifiers unique colourations to the sound (though personally, a good amp should be transparent).

Anyone care to chime in on this?
 

Quote:

Originally Posted by chinesekiwi 

Counter point one:

 

Higher gain settings might introduce more distortion when driving 600ohm version though this is a reflection of the amp and not the headphone and is likely achieved with amplifiers with Zout >0ohm.

 

RMAA M3 amp stats:

 

 

The THD was actually higher at 8 ohms than it was for the others .0011 to .0009 but this is a null point as it's inaudible and within margin or error.

 

Anyone measured the sensitivity of both the DT880/250 and DT880/600 in dB/mW or dB/V? 

Though this is hardly "evidence", some posts over at the Little Dot forum suggest that different gain settings seem to measure / sound different, and a 600ohm phone might require a gain adjustment on some amps, which could add colourations to the sound that could account for some percieved differences in sound quality.  When I owned a LDMKIII, my impressions were the same; I spent hours adjusting gain settings and found that higher gain settings correlated with increases in bass, and decreases in treble.  Soundstage seemed to increase in high gain settings as well, though by what mechanism I cannot tell.

Let the record show that it is the amplifier, and not the headphone that is the cause of a change in sound.

http://www.littledot.net/forum/viewtopic.php?f=3&t=587&p=2900

That would be a valid hypothesis, though according to my calculations (and calculations that other head-fi members have done), the zout would have to be significantly higher than 0 before differences can be heard.  I'd have to run some calculations, but when the zout is ~120ohm, the 250ohm DT880 will have a boost of about 0.5-1dB @100hz, whereas the 600ohm would likely remain flat.  Of course this phenomena of different load impedance to zout ratios would hold true for all headphones that I've ever seen.  When using the DT880s from integrated amplifiers with zouts of ~220ohm, the differences would start becoming more obvious.  Thanks for the valid hypothesis maverickronin.
 

Quote:

Originally Posted by maverickronin 

Add this one.

 

Hypothesis #3 – Beyerdynamic DT880 250ohm and 600ohm are audibly identical when connected to a source/amp with a Z out of zero and are audibly different when connected to a source/amp with a non zero Z out.

In my experience, and based on comments from professionals, headphones are resistance controlled, and not mass controlled, and therefore are not as susceptible to the effects of damping factor (Loudspeaker and Headphone Handbook 1998)

Headphone transducers are resistance-controlled, not mass-controlled like loudspeaker drivers above the main resonance. In any case 'damping factor' is largely nonsense - most of the resistance in the circuit is the voice-coil resistance and reducing the amplifier source impedance to infinitesimal proportions has an exactly corresponding effect on damping - infinitesimal.

However, the source impedance affects the *frequency response* of a loudspeaker because the motional impedance varies with frequency, and thus so does the voltage drop across the source impedance. This means that the source impedance (including the cable) should be less than about one-twentieth (not one two-hundredth or less!) of the rated impedance of the loudspeaker, to give a *worst-possible change* in frequency response from true voltage-drive of 0.5 dB.

Personally, most professionals don't use the term "damping factor" as it is a non-quantifiable term.  From all the measurements I've seen, damping factor is a colloquial term used as a rule of thumb when contrasting the Zout of an amp, to the impedance curve of a loudspeaker or headphone.  The Zout acts as a voltage divider, and for loudspeakers which have a huge impedance curve, high Zouts can lead to huge changes in FQ response.  Headphones have very flat impedance curves, and it seems that only Zouts that are higher than the load impedance (damping factor <1), can have audible changes in FQ response.  Likewise, impulse response doesn't really change until the Zout equals or exceed the load impedance.  So for all intents and purposes, damping factors of even 1 for headphones just "start" to potentially create audible differences. 

I've calculated the FQ response with several of my headphones (which range from 32ohms to 250ohm) with my Presonus HP4 which has a Zout of 51ohms.  We're looking at damping factors that are worse than 1, and as high as 5.  At worst (less than 1 damping factor) there is a 1.15db boost @100hz which is audible, but everything with a damping factor of 1.5 to 5 has a change of less than 0.5db at the resonant frequency, which is essentially inaudible unless you're REALLY trying to spot the difference.  Of course, each headphone has it's unique impedance curve, and some headphones might be less immune to damping factors than others.  With a zout of 120ohm, a 250ohm DT880 would have less than a 0.5db increase at the resonant frequency of 100hz, which is just bordering on the threshold of audibility (PM me if you want the calculations).  Indeed, this is a damping factor of 2, and yet there is virtually no change to how it will measure (unlike a loudspeaker which would severely suffer)

I would imagine some tube amps with a high Zout (greater than 200ohm) might produce very slight changes in FQ response compared to the 600ohm version but the differences would likely be subtle enough that they couldn't possible account for the "amazing improvement in the 600ohm version" that so many head-fiers claim to hear (while others don't find any difference)
 

Quote:

Originally Posted by maverickronin 

Do those calculations include damping factor, or is it just based on power transfer?  I was thinking that the change in damping factor would account for more of the audible differences.  I don't know how important damping factor is to the much lighter diaphragms of headphones as compared to loudspeakers though.  I had this idea because most of the people who recommend the 600s over the 250s pair them OTL tube amps.  If those differences in the distortion graphs are too low to hear, then this is the last physical reason I can think of for them to be different.

 

The load/Z out ratio does hold true for all other headphones, but no other manufacturer AFIK makes such near identical models that only seem to vary in impedance which creates the problem we are trying to solve.  These choices would seem to give you a chance to better match your amp.

 

My hypothesis is based on the 600s having a higher damping factor than the 250s when used with OTL tube amps.  I'm going to guess that most OTL tube amps have a Z out in the 120 ohm range.  That's what the Z out on my Crak that I'm going to build this weekend is, so I'm over generalizing a lot here.  Tell me if I'm wrong.  Back to damping factor.  I've read that for speakers a damping factor of about 20 is all you need, since anything higher won't be audible.  I'm guessing that the reduced mass and excursion of a headphone diaphragm would require a smaller damping factor than a loudspeaker.

 

If the damping factor of just over 2 (for Z out = 120 and 250 ohm drivers) is already past the threshold of audibility the a damping factor of 5 for the 600s won't make a difference.  I don't thing the power transfer differences account for differences reported by some, but I don't know enough about it to say with much certainty.  Since many SS amps have very low output impedance and damping factor improvement is inaudible after a point it makes sense that the 250s and 600s should measure very closely on such gear.  Assuming a 1 ohm Z out, a damping factor of 600 shouldn't be audibly different than one of 250.

And it's necessary to know the impedance curve of any headphone being measured.  For my calculations, I have resorted to headroom impedance curve graphs, and my calculations are only as good as the data available.  Typically, most headphones have a resonant peak at around 100hz which is where the Zout will have the most effect.  Like the meier page suggests, higher zouts will darken the sound / increase the bass, whereas low zouts will flatten the FQ response (typically a good thing). 

But of course, there is that pesky 120ohm IEC standard that may or may not have been intended by the manufacturers. 

Wow!  Rumour has it that Beyerdynamic is working on an amazing 10,000ohm version of their DT770/880/990 headphones!  According to the latest head-fi mythology, these new models should sound unbelievable with excellent transient response.

In addition to microscropically thin voice coils, they also come with 15km of microscopically thin cable and come with a state of the art cord winder!

Now I'm just being silly - that's ridiculous.

I heard that 120V won't be enough, and that you'll need at least a $10,000 amp in order to drive them to their full potential.  I heard tubes are best.