Way to tell how easily driven a set of cans are ?

[Fink Ployd]

I have a set of sennheiser 201`s which are 24ohm, they sound very nice , but with my mp3 player, they are a bit insensitive and have to driven hard to get a bit of volume.

Im looking for another pair of cans, what is the technical figure which illustrates how easy or difficult it is to drive a given set and what sort of figure is representative of an easily driven pair ?

 

[LingLing1337]

I'm not sure... On my TC7520, my HD485 has to be set at around 11:00 on the pot, my SR225 at just under 9:00. Both are 32 Ohm. So obviously it's not all to do with the Ohms.

 

[logwed]

Sensitivity and Impedance are the figures that you are looking for.

 

[Zombie_X]

The lower the impedance/sensitivity = easier to drive
The higher the impedance/sensitivity = harder to drive

This is not always entirely true though, though I don't know of any headphones that this applies to. I've just hears stories. And I may be talking out of my butt about this stuff though this is what I've been told.

 

[LingLing1337]

^Is there a way to measure sensitivity?

 

[Zombie_X]

Not sure.... I'm not entirely sure. I don't know much about this technical HP stuff.

 

[aristos_achaion]

AKG's site, for one, seems to think so. Here's the specs for the k701, including "sensitivity":

 

[MaloS]

Sensitivity + impedance combined will let you figure out how much volume you can get out of your equipment, but not necessarily how well driven the headphone is as a result. Some particular Sony's are sensitive and low impedance, but still sound like convoluted garbage without sufficient headroom and control coming from the equipment pushing them.

Quote:

^Is there a way to measure sensitivity?

Easy, define what sensitivity is, then just measure it as per definition. I think the current standard is 'sound intensity resulting from given input power'. Usually done in dB per miliwatt, using 1000 hz wave as input.

 

[Ishcabible]

Magic!!!



Actually, it all depends on the impedance and sensitivity. High impedance and/or low sensitivity make it hard to drive.

 

[boomana]

Quote:

Originally Posted by Zombie_X /img/forum/go_quote.gif The lower the impedance/sensitivity = easier to drive The higher the impedance/sensitivity = harder to drive

Not quite. Low sensitivity headphones are harder to drive than high sensitivity headphones. Sensitivity is the sound pressure level produced when a certain voltage is applied (dB/mV). If you have a high sensitivity headphone, it can draw more current from an amp than a low sensitivity headphone, even if they're equally efficient, at the same volume position. Low sensitivity headphones (i.e, K701s) should not, ideally, be paired with amps that have low voltage swing (i.e., portables).

That's the problem when folks look just at impedance. They see low, and think "easy to drive." That's only part of the story.

 

[boomana]

Quote:

Originally Posted by MaloS /img/forum/go_quote.gif I think the current standard is 'sound intensity resulting from given input power'. Usually done in dB per miliwatt, using 1000 hz wave as input.

Though I'm in the early learning stages myself, I think (please, o' knowledgeable ones, correct me if I'm wrong) that's the definition of efficiency: sound pressure level produced when a certain power is applied (dB/mW). Sensitivity is the sound pressure level produced when a certain voltage is applied (dB/mV),

 

[Uncle Erik]

You guys only have half of the equation. The output impedance of your amp plays a big part, as does the power output of the amp.

If your headphones have an impedance of 32 Ohms, they will be driven very, very differently from a solid state amp with an output impedance of 2 Ohms and a tube OTL amp with an output impedance of 150 Ohms. Unless you know the output impedance of the amp you're using (even soundcards and iPods have amps) then headphone impedance is almost meaningless.

Once you figure out the impedance relationship between the amp and the headphones, then you can calculate how much power gets through to the headphones. For that, the power output of the amp figures along with the sensitivity of the headphones.

If you want to get slightly more complex, the ratio of the headphone impedance to the output impedance is referred to as the Damping Factor. The lower the output impedance is to the headphone impedance, the higher the damping factor and the more control the amp has over the headphones.

Also, keep in mind that both the headphone impedance and output impedance are not static numbers. Both vary depending on frequency and are plotted on a curve. It gets complicated, but this means that power delivered to the headphones will vary depending on frequency. This is where a lot of the sound signature of an amp comes from and it determines synergy with particular headphones.

So, to the OP, the real answer is it depends. How easy something is to drive depends on what you're driving it with. This is why I recommend picking the headphones you want, then finding a proper amp for them. Not all headphones and amps sound good together, but it's more important to have the headphones you want than it is to get the amp you want and not have it match your headphones.

 

[Zombie_X]

Quote:

Originally Posted by boomana /img/forum/go_quote.gif Not quite. Low sensitivity headphones are harder to drive than high sensitivity headphones. Sensitivity is the sound pressure level produced when a certain voltage is applied (dB/mV). If you have a high sensitivity headphone, it can draw more current from an amp than a low sensitivity headphone, even if they're equally efficient, at the same volume position. Low sensitivity headphones (i.e, K701s) should not, ideally, be paired with amps that have low voltage swing (i.e., portables). That's the problem when folks look just at impedance. They see low, and think "easy to drive." That's only part of the story.

Yeah, that's why I said I may be talking out of my butt. That's one part of HP I'm not entirely familiar with.. Thanks for thoroughly explaining it to me.

 

[boomana]

Zombie X, I'm learning all this right along with you

 

[Ericular]

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif Once you figure out the impedance relationship between the amp and the headphones, then you can calculate how much power gets through to the headphones. For that, the power output of the amp figures along with the sensitivity of the headphones.

Thanks for this info... I am intrigued by it. I read somewhere that the output impedance of the iPod Touch is 32 ohms. With this knowledge, is there a formula or calculator that would help me predict how much volume I'd get from a certain headphone if I knew the headphone's (average) impedance and sensitivity?