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Damping factor/ impedance response: Can any amp drive a headphone with flat impedance response?

post #1 of 17
Thread Starter 

There has been a lot of talk about damping factor and impedance response around here lately.  Such things as "sensitive headphone drivers do not need damping factors as speaker drivers do" and such.  I am wondering if a headphone such as the Denon D2000 (which has an impedance of 25ohms across the board) if at all susceptible to the problems associated with low damping factor.  After all, if the output impedance of the amp is high enough to distort the frequency response, won't it equally distort it and, thus, not really distort it at all?

 

For example, my Fiio E9 has an output impedance of 10.  This is "too high" according to a lot of people.  It is a damping factor of 2.5, well below the damping factor of 8 commonly pointed to as the minimum damping factor one wants.  But does it really make a difference?  

 

For headphones with flat impedance response, does the damping factor make much a difference, if any difference at all?  

post #2 of 17

The AH-D2000 does not have flat impedance. But it is close to being flat, so the E9 will only add a frequency response variation of about 0.5 dB.

Electrical damping also affects distortion, that is, the current flowing through a headphone driver is not a perfect linear function of the voltage. Unfortunately, none of the sites that publish headphone graphs (Inner Fidelity, etc.) include information on this effect. However, if a headphone has a very flat impedance/phase graph, and it does not produce significant distortion on the output of a high impedance source either, then I think low or high output impedance indeed does not make much difference. This is most likely to happen with orthodynamic/planar magnetic drivers.

 

post #3 of 17
Thread Starter 
But is electrical damping really so important for tiny headphones drivers? And couldn't we basically consider a variation of half a decibel to be inaudible?
post #4 of 17
Quote:
Originally Posted by scannon18 View Post

But is electrical damping really so important for tiny headphones drivers?

 

For some (e.g. the Sennheiser HD5xx series), it makes a difference, for others, not so much.

 

Quote:
Originally Posted by scannon18 View Post

And couldn't we basically consider a variation of half a decibel to be inaudible?


I was able to hear the 0.5 dB bass boost caused by driving a 250 Ohm DT770 from a 100 Ohm source in an ABX test. But you are right that it is not quite a significant difference. If I replaced the DT770 with an HD598, then the variation would have been more like 6 dB.

 

post #5 of 17
Thread Starter 
Well 6 DB is certainly large enough. And. 5 is detectable. I guess I'm just wondering if I am missing out on something because I only have a damping factor of 2.5
post #6 of 17
Quote:
Originally Posted by scannon18 View Post

I guess I'm just wondering if I am missing out on something because I only have a damping factor of 2.5


It is not perfect, but increasing it would not be that much of an improvement. If you have the FiiO E7 with the E9, you can easily try it by using the E7 instead of the E9.

 

post #7 of 17
Thread Starter 
Quote:
Originally Posted by stv014 View Post



It is not perfect, but increasing it would not be that much of an improvement. If you have the FiiO E7 with the E9, you can easily try it by using the E7 instead of the E9.

I do own the E7. The E9 sounds much better. In fact that is what prompted me to start this thread. Damping factor from the e9 is 2.5 compared to roughly 125 from the e7 but the e9 sounds much cleaner, just an improvement in every way from the e7.


Edit : spelling
post #8 of 17
Quote:
Originally Posted by scannon18 View Post

There has been a lot of talk about damping factor and impedance response around here lately.  Such things as "sensitive headphone drivers do not need damping factors as speaker drivers do" and such.  I am wondering if a headphone such as the Denon D2000 (which has an impedance of 25ohms across the board) if at all susceptible to the problems associated with low damping factor.  After all, if the output impedance of the amp is high enough to distort the frequency response, won't it equally distort it and, thus, not really distort it at all?

 

For example, my Fiio E9 has an output impedance of 10.  This is "too high" according to a lot of people.  It is a damping factor of 2.5, well below the damping factor of 8 commonly pointed to as the minimum damping factor one wants.  But does it really make a difference?  

 

For headphones with flat impedance response, does the damping factor make much a difference, if any difference at all?  



 

 

This is an insanely complicated question. To try and attempt to answer your question: It depends on how much inductance and capacitance your headphones have. You would need to look at an impedance plot of your 'phones, the impedance plot would have to show magnitude and phase angle of the impedance WRT to frequency. If your phones had a fair amount of inductive reactance at some frequencies then they would store some enrgy and you would need a low output impedance to control your headphones properly. That is a very, very simplified answer to a very complex question. Sorry I can't translate it into English. :) But if you like your E9 then don't worry, be happy. They seem to be compatible with your phones. Occasionally I use my 62 ohm Q701s with a high output impedance tube amp, it should sound too good, but for SOME kinds of music it sounds great. For other stuff (like Aerosmith) it sounds like mush.
post #9 of 17

its not that complicated

 

single driver headphones are "simple enough" to be characterized as "minimum phase" linear systems - the impedance phase and magnitude are totally co-determinant - given one curve you can accurately predict the other

 

Orthodynmaics generally have nearly flat impedance vs frequency plots == pure resistive impedance

 

single driver headphones that do show impedance variation usually show a mass-spring bass bump resonance, sometimes a slight inductive rise towards highest audio frequencies

 

 

most amps have essentially flat output Z over audio - with a few DAP and OTL tube amps having a output coupling C that can give a little roll off in the lowest octaves with low Z headphones

 

output xfmr in higher end tube amps can limit bandwidth at both audio frequency extremes - really good output transformers cost >$50 each OEM qty - won't be found in sub $1k cost commercial amps

 

cheap xfmr output tube amps have cheap iron - will have restricted audio bandwidth, low frequency distortion

post #10 of 17
Thread Starter 

I appreciate the above replies, however things have gotten a bit complicated.  What is phase, phase angle, magnitude, etc.?  What is "output coupling C?"

 

Haha every time I think I understand amps it they turn out to be far more complicated than I had imagined.

post #11 of 17
Quote:
Originally Posted by scannon18 View Post

Damping factor from the e9 is 2.5 compared to roughly 125 from the e7 but the e9 sounds much cleaner, just an improvement in every way from the e7.


Well, the E9 does have lower distortion, but it is also difficult to compare amplifiers without accurately matching levels; slightly louder sound is perceived as better quality.

 

post #12 of 17
Quote:
Originally Posted by scannon18 View Post

I appreciate the above replies, however things have gotten a bit complicated.  What is phase, phase angle, magnitude, etc.?  What is "output coupling C?"

 

Haha every time I think I understand amps it they turn out to be far more complicated than I had imagined.


I am referring to the impedance of the headphone.
Basically phase, phase angle and magnitude are a mathematical way of expressing how much resistance, inductance and capacitance your headphones have with respect to frequency.

In other words, if you see variations in impedance magnitude and phase on an impedance curve then your headphone would have some inductance and capacitance.

 

To answer the original question:   (assuming we are comparing two headphones with a 50 ohm average impedance and the same sensitivity)  a headphone with flat impedance curve is easier to drive than a headphone with a "non-flat" (or complex) impedance curve.  It doesn't mean that most decent headphone amps won't drive a "non-flat" impedance.   One of the many reasons why a solid state headphone amp may have an output impedance of 10 or 20 or more ohms is it is an easy way to make the amp "OK" for driving a complex impedance.

 

Yes, amps are very complicated creatures.

Lucky for us, headphones are easier to drive than 2, 3 or 4 way loudspeakers or electrostatic loudspeakers, etc.

 

Impedance:    this may drive you to drink, LOL!    http://en.wikipedia.org/wiki/Electrical_impedance

something co-written by second year Electrical Engineering student, will require a bit less drinking, LOL!    http://www.head-fi.org/a/headphone-impedance

 

An Output Coupling C is an Output Coupling Capacitor.   In an Output Transformerless (OTL) Tube amp it is used to block the DC voltage in the amp from damaging your headphones.

 

Have you seen the Glossary of terms?  http://en.wikipedia.org/wiki/Electrical_impedance    written by numerous Head Fi members, more than you really want to know about 'phones and electricity, etc.

 

post #13 of 17
Quote:
Originally Posted by scannon18 View Post

  What is phase, phase angle, magnitude, etc.?  



An analog electrical signal is uniquely described by three parameters: frequency, amplitude and phase.

 

Amplitude:  The amplitude refers to the magnitude of the signal.  Think of it as the parameter that determines the volume level.

 

Phase:  Phase refers to the relative time delay or time difference between two signals.  Phase is always a phase difference and relative.  There's no such thing as absolute phase..  Think of it as the shearing of the signal in time.  Example, feed a component with a signal consisting of just two frequencies.  One tone is 50Hz and the other tone is 15,000Hz.  Depending on the equipment, the two signals will not appear at the ouput at precisely the same time.  If the signals are delayed relative to one another, the output signal will be phase incoherent. The delay might be miniscule, but a delay it is nevertheless.  This delay of the 50Hz signal relative to the 15,000Hz signal at the output is the phase difference.  The phase angle is just a mathematical way of describing this relationship of a lag in time.

 

This delay of frequencies relative to each other is often called group delay.  Another importance characteristic is the phase between voltage and current.  The phase difference between voltage and current has implications for power delivery.


Edited by Mauricio - 4/7/12 at 10:25pm
post #14 of 17
Quote:
Originally Posted by Mauricio View Post



An analog electrical signal is uniquely described by three parameters: frequency, amplitude and phase.

 

Amplitude:  The amplitude refers to the magnitude of the signal.  Think of it as the parameter that determines the volume level.

 

Phase:  Phase refers to the relative time delay or time difference between two signals.  Phase is always a phase difference and relative.  There's no such thing as absolute phase..  Think of it as the shearing of the signal in time.  Example, feed a component with a signal consisting of just two frequencies.  One tone is 50Hz and the other tone is 15,000Hz.  Depending on the equipment, the two signals will not appear at the ouput at precisely the same time.  If the signals are delayed relative to one another, the output signal will be phase incoherent. The delay might be miniscule, but a delay it is nevertheless.  This delay of the 50Hz signal relative to the 15,000Hz signal at the output is the phase difference.  The phase angle is just a mathematical way of describing this relationship of a lag in time.


This is all well and true and basically accurate.  Magnitude and phase can be used to characterize an analog signal or headphone impedance.

But,

I'm not too sure if Scannon's question was referring to magnitude and phase WRT to impedance or WRT to analog signals?

 

Scannon, are we answering your questions or just confusing the hell out of you and getting WAAAY off topic with a pile of electrical BS?

 

Flat impedance curve:   damping factor and output impedance not too important. Fairly easy to drive.

 

Impedance varying with frequency?   Best accuracy is found with a headphone amp with low output impedance, which leads to higher damping factor.

 

 


 

 

post #15 of 17

For low impedance loads, it is important that the amp not only have a low output impedance, but also that it have high current capability.  Insufficient current capability can drive the amp into audible distortion.

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