Originally Posted by xnor
I don't know any serious engineer that listens with headphones connected to a tube amp in the studio.
You misinterpreted me, I never said that tube specifically improves/gives an accurate sound, in fact I said the reverse. I just said that many fellow Head-Fier's or Hi-Fiers tend to go for the 'live' sound. But ultimately, what was the music recorded by? Yes, a mic. Will the recording ever take into account human hearing? Probably, but even so, the acoustics of the studio is heck different from a live and even in live recordings, mics tend to pick up the resonances that will feel out of place. Thus some go for Tube amps as it is EASIER to compensate with distortion than EQing/DSP with SS amps with high end audio. Alternatively they are just trying to enjoy the music the way they feel best. Will it be accurate, neutral? Sure as hell no. But compared to the SS system, will it sound more 'live'? Most probably. That being said, as someone who helps do mixing sometimes, I do appreciate solid states a lot more for their accuracy. Everyone plays with audio in different ways and there are no specific or 1 way to enjoy music.
Actually if you read the diyaudio newsletter, it will summarise everything I said since I do quote parts from it.
Anyways time to answer more questions, I may be wrong feel free to correct me. Most of it is a summary of previously written material.
On headphone impedance- The impedance(Z) rating on a headphone that determines electrical damping which in turn can correlate to mechanical resonances and power. Low Z typically means more current flow needed rather than voltage while High Z means higher output voltage is needed. Its more of a energy delivery mode
Output impedance of a amp- its the Z of a amp, typically tube amps have higher Z than SS. SS amps are best 0 ohm or near 0 but some manufacturers amps have large Z as a crude form of stabilising the amp.
Sensitivity- Amount of power needed for a given sound pressure level(SPL)
Why is impedance and sensitivity such a big deal?
Basically they determine a few things the most important is of course, volume levels. This article and its source material provides the picture. Of course I'm going to summarise it. Note that with SS amps of high Z and tube amps, these numbers are usually almost worthless, which will be explained.
P = (Vmax * Vmax) / Headphone Impedance
Gives the peak power at a given headphone impedance for the voltage
dBSPL = Sensitivity(of headphone) in dB/mW + 10 * LOG ( Pmax of amp in mW)
this gives the peak SPL of a certain headphone that can be reached given the maximum power of an amp.
Of course why else knowing these are important? Its also because they will also determine what TYPE of amp to but. With high impedance phones with high sensitivity ala Beyerdynamic headphones, any mid range amp will do as they are easier to drive. Then the question arrives, which amps more difficult to find/pair with?
There are 2 types,
Those built for low impedance, very high sensitivity/Balanced Armature headphones/IEMs because one they typical require a very low noise floor(SNR) and require 0 ohm output impedance to sound good. These do not require much power though. Examples are the Sony XBA-4, Denon headphones and many other BA driver IEMs rated 16- 32 ohm. If of interest the ER-4s does not fall into the category despite being a BA due to its high impedance.
Built for low impedance, low sensitivity, which not only means that it is ridiculously hard to drive, also that typical tube amps with their low current reserves just don't stand a chance. Examples of such are Hifiman orthos especially HE-6, AKG K/Q70X.
So what do the more expensive amps have in common? Usually lower impedance values, higher current values and much lower noise floors. For those types mentioned SS is preferred though there are some tube amps which do the job(very expensive).
But why lower impedance headphones are harder to pair? It's because of electrical damping factor, to reduce amp distortion and increase linearity, reduce mechanical resonance of the headphone driver, lower amp output impedances are needed to pair with low impedance amps. This Benchmark article explains it all. An example of such an amp is also the highly acclaimed Violectric V200 amp which has a output impedance of a fantastic 0.06ohms.
Violectric also explains it in detail so I don't have to,
Why is a high damping factor essential ?
When actuated, electro-dynamic systems respond with a counterforce. When the voice coil of a headphone has been displaced by the signal, an (error)-current will be induced when it swings back to its initial position. This current must be suppressed as far as possible, which is effected best if the amplifier's output impedance is the lowest possible. The damping factor describes nothing but the ratio between output impedance of an amplifier and a given load. Since there is no known technical specifications, we define the load (voice coil impedance) as 50 ohms. This results in an output impedance of <0.06 ohms in case of the HPA V200.
Damping factor is basically: Zin/Zout Note that 50ohms is also a typical value of an Ortho driver. According to nwavguy, a damping factor of at least 8 is desirable.
Edited by firev1 - 2/10/12 at 9:00pm