[Head-Fi PSA] The impedance of a headphone is not how hard it is to drive.

Good point. Good warning. To be fair, given how most people talk about it, its easy to see how one would come to the original false conclusion. I know I certainly believed that when I first started getting into the headphone world.

I've been fighting this rumor for a while. Maybe you'll get somewhere 

BTW, an amp will need over 10 times the power to drive the K701 to the same volume as the V6, going by the specs in your post. 10 dB = 10x power. Specifically it would need around 25x as much power and 5x as much voltage.

Wow this is great stuff! I actually didnt know the stuff about about dB/mW.

So if sensitivity rating takes precedence over impedance (if im getting that right), then what does impedance really do..? 

Thanks for the important info. Needless to say, I was of the opinion that lower the impedance of the headphones, easier it is to drive. I did not even know about the sensitivity ratings.

I also find this myth to be very annoying. What is even worse, is that even considering the sensitivity, the suggestion that any high impedance headphone could be easy to drive is usually countered with the argument that "yes, it will be loud but not driven to its full potential in terms of sound quality", citing unmeasurable and unquantifiable aspects like "control", "sound stage", "dynamics", and others. According to the myth, there is some magical property of high impedance that will always make it "hard to drive" no matter what, and require some very expensive (usually tube) amplifier. These suggestions discourage many people from buying headphones that would in reality work fine with their setup.

However, just as harmful is the belief that low impedance is always easy to drive. For example, the Sennheiser HD5xx series is frequently recommended to newbies on the ground that the ~50 Ohm impedance must be "easy to drive", yet in fact these have an impedance peak of nearly 300 Ohm at about 90 Hz, making them more sensitive to the output impedance of the source and require a higher damping factor than most other headphones. Low impedance is also often recommended for sources that have known high output impedance (that includes many sound cards that do not have a dedicated headphone amplifier); in reality, from a 120 Ohm output impedance source a 250 Ohm headphone will get more power than a 32 Ohm one, not to mention the really poor electrical damping with the latter. The source may also feed the output through a capacitor (to remove DC), this again works in the favor of high impedance loads (the lower the impedance of the load, the worse the bass extension gets). For a given output voltage, amplifiers usually also perform worse with lower impedance loads in terms of distortion.

Even a combination of high impedance and low sensitivity can have its advantages, as long as sufficient volume can be achieved without clipping or noticeable distortion, as it will make any volume independent noise or hum from the source quieter. With an analog volume control that is implemented using a simple stereo potentiometer, there may also be some channel imbalance when the volume has to be turned down very low because of the sensitive headphone (this affects the FiiO E9, for example).

Very good write up!  I have to admit, being new to this pursuit, I wasn't really aware of the relationship between resistance and sensitivity.

Quote:

Originally Posted by stv014 

I also find this myth to be very annoying. What is even worse, is that even considering the sensitivity, the suggestion that any high impedance headphone could be easy to drive is usually countered with the argument that "yes, it will be loud but not driven to its full potential in terms of sound quality", citing unmeasurable and unquantifiable aspects like "control", "sound stage", "dynamics", and others. According to the myth, there is some magical property of high impedance that will always make it "hard to drive" no matter what, and require some very expensive (usually tube) amplifier. These suggestions discourage many people from buying headphones that would in reality work fine with their setup.

 

However, just as harmful is the belief that low impedance is always easy to drive. For example, the Sennheiser HD5xx series is frequently recommended to newbies on the ground that the ~50 Ohm impedance must be "easy to drive", yet in fact these have an impedance peak of nearly 300 Ohm at about 90 Hz, making them more sensitive to the output impedance of the source and require a higher damping factor than most other headphones. Low impedance is also often recommended for sources that have known high output impedance (that includes many sound cards that do not have a dedicated headphone amplifier); in reality, from a 120 Ohm output impedance source a 250 Ohm headphone will get more power than a 32 Ohm one, not to mention the really poor electrical damping with the latter. The source may also feed the output through a capacitor (to remove DC), this again works in the favor of high impedance loads (the lower the impedance of the load, the worse the bass extension gets). For a given output voltage, amplifiers usually also perform worse with lower impedance loads in terms of distortion.

 

Even a combination of high impedance and low sensitivity can have its advantages, as long as sufficient volume can be achieved without clipping or noticeable distortion, as it will make any volume independent noise or hum from the source quieter. With an analog volume control that is implemented using a simple stereo potentiometer, there may also be some channel imbalance when the volume has to be turned down very low because of the sensitive headphone (this affects the FiiO E9, for example).

 

Please be patient and help me out here.

I have Grados, 32 ohm and efficient as you no doubt know, and I want to buy an all tube headphone amp.  What output impedance figure should I be looking for?  TIA.
 

Quote:

Originally Posted by bbophead 

Please be patient and help me out here.

 

I have Grados, 32 ohm and efficient as you no doubt know, and I want to buy an all tube headphone amp.  What output impedance figure should I be looking for?  TIA.

Close to 0 ohms if you want neutrality (though the amp itself may be colored), whatever else if you want coloration (mid-bass at 100 Hz in particular).

The effects of up to 10 ohms will be subtle, even inaudible.

Quote:

Originally Posted by Head Injury 

Close to 0 ohms if you want neutrality (though the amp itself may be colored), whatever else if you want coloration (mid-bass at 100 Hz in particular).

 

The effects of up to 10 ohms will be subtle, even inaudible.

Hey, if I wanted neutrality I wouldn't have Grados, now would I?

But, seriously, thanks for the info.
 

It's not so much a myth as a misconception borne of lack of understanding.  And even for people who do understand, there's something to be said for simplicity.  We could have started with the sensitivity rating and argued the same thing re: impedance.

New people coming to the hobby generally want answers to specific questions (see above) and many not be interested in having to calculate dB SPL = Sensitivity in dB/mW + 10 * LOG ( ( Voltage * Voltage ) / Impedance).

ahh thankyou for correcting my misconceptions ... ive been one of those that took on the impedance = usually harder to drive idea, i did realise that it wasnt always the case but i didnt know what the casue was -thankyou OP/.