[blipblop]

Why are some phones low impedance, and some high? At first I thought it correlated with quality but then we see Grado headphones at 32 ohms or so AND my new ATH A900s at a 40 ohms, and they both sound fantastic.
Add to this confusing mix, the notion of efficiency, where a high impedance can may listenable unamped than a lower impedence, but inefficient can.

What the hell is going on? I did a search and couldn't find the answer.

 

[Chefguru]

Impedance is the amount of power the headphone needs. Most headphones follow the rule that the lower the impedance is, the better it does with out an amp. But there are a lot of exceptions ( k1000 is one of the biggest).
Impedance has no relationship to quality, it just that every headphone are designed differently and requires a different amount of power .

 

[markl]

There is no correlation between impedence rating and sound quality. Knowing a headphone's impedence/efficiency will tell you nothing about how it sounds. It will tell you which amps are likely to make better partners, though. Some amps have trouble delivering sufficient current to drive low-impedence cans (some tube amps have this problem), some amps don't have the voltage swing to power high-impedence headphones (many cheap jacks in receivers, CDPs and portable devices).

 

[rodbac]

Bump for a subject that I've been trying to draw a bead on for a while now...

 

[Chefguru]

Quote:

Originally posted by rodbac Bump for a subject that I've been trying to draw a bead on for a while now...

Your bumping a thread that just got two post in the last couple mins ?

 

[Canman]

Quote:

Originally posted by Chefguru Impedance is the amount of power the headphone needs...

This is not true.

Impedance is the total opposition to the flow of electric current seen at the output of the amplifier.

Like Markl said, impedance and efficiency have no correlation to sound quality, except in component matching.

 

[blipblop]

Okay, I see. But, does a low impedence can mean that the effect of an amp upon performance improvement is much less? That is, will my a900s not improve that much from being pumped through a PIMETA or PPA because it has a 40 ohm impedance?

 

[Canman]

The following is as I understand it. Please correct me if I am wrong.

A lower impedance headphone tells you that its opposition to current to the amplifier is lower.

This means that an amplifier will output more current at a given voltage. (remember Power = Voltage * Current)

However here is where efficiency comes into play because a headphone with higher efficiency will be able to produce sound at X dB with less current applied than a lower efficiency headphone at the same decibel level.

Don't confuse quantity and quality. Just because a headphone is of low impedance it does not mean that A) it doesn't require a large amount of current to operate optimally or B) It does not benefit from a higher quality amplifier.

Take for example, the Grado HP-1000, with an impedance of 40 ohms. It requires a decent amount of current to get it sounding optimal and will easily show any change in quality of amplification.

Although electrostatic transducers operate under different principals it is interesting to note that the Stax Omega II has an impedance of 170,000 ohms. This means that the voltage at the output of the amplifier has to be extremely high, around 580 volts.

It is also important to note that impedance is a nominal measurement, meaning it is an average. Since impedance is frequency dependent, the actual impedance at any given frequency can be very different from the impedance at another frequency. It is easier for amplifiers to drive loads that have flatter impedance curves, meaning, that the variance of impedance is low over the frequency range.

 

[lindrone]

Quote:

Okay, I see. But, does a low impedence can mean that the effect of an amp upon performance improvement is much less? That is, will my a900s not improve that much from being pumped through a PIMETA or PPA because it has a 40 ohm impedance?

That's more about perception of sound, I think.

For example, let's say there's a measureable, acceptible level at which a HD600 is supposed to sound like. Since it doesn't mate well to your typical headphone jack, you can't even reach the volume level that it's supposed to be at. Thus the addition of an amp gives you both an acceptible volume level plus a qualitative improvement in the sound.

Perceptually that's a huge, tremendous benefit. Thereotically though, if you had a headphone jack that mated well with the HD600 to begin with, the addition of an amp would've only been the qualitative difference still, not the volume.

With a headphone like the A900, the low impedance allows it to reach an acceptible volume level out of just any device. Which means the addition of an amp is making qualitative improvement only, not volume improvements.

So perceptually you're getting a less improvements. Also, taken in context, most of the cheap, low-level amps does more to increase volume than quality... thus a lower-level amp (Mint Meta, Airhead...) really doesn't do much for a headphone that only needs qualitative improvements.

With that said, I thought the PPA mated very well with the A900... smooth, clear delivery of sound... everything sounds very smooth.

 

[markl]

Quote:

But, does a low impedence can mean that the effect of an amp upon performance improvement is much less?

IMO, the answer is an emphatic "no". All headphones by definition need an "amp". Every component with a headphone jack is by definition a "headphone amp", but most jacks/amps on most consumer audio gear is a total afterthought, a cheap $0.25 OEM little circuit. Obviously, you need an amp that can output sufficient power (current and voltage) to drive your headphones to their maximum and keep them happy. But merely providing adequate power in terms of paper specs is not sufficient by itself to guarantee good sound, far from it. As much as it's about providing adequate power, it's also equally about the *quality* of that power. Better quality components make a better amp, and those upgrades are equally audible through low-impedence headphones as they are through high. You can have the worlds most powerful amp in terms of its specs, but if it's a poor circuit design made with the cheapest available parts, it will still sound like crap.

We like to say that low-impedence cans are "easy" to drive and don't need an amp. I don't fully agree with this generalization. There are a number of headamps that can't really drive low-impedence headphones very well at all (EMP, RKV without impedencer come to mind off the top of my head). Low-impedence simply means that they require more current as opposed to higher voltage. Not all headamps are equipped to deliver all the current they need. Speakers are typically rated between 4-8 ohms, but i wouldn't try to run them off a typical headphone jack!

Conversely, not all amps are equipped to provide proper voltage that high-impedence cans need to sound their best. Typically, cheap headphone jacks on portable gear and home CD players can't cut it in this area, and for these types of "headamps", high-impedence cans are hard for them to drive properly. This is why people like to say the Senn HD600 is "hard to drive", because *typical* jacks on *typical* gear won't be able to drive them at their fullest.

Long story short, to get the best sound from your cans, you need good quality amplification, all headphones will benefit equally from improved amplification.

Mark

 

[wallijonn]

Quote:

Why are some phones low impedance, and some high?

Because headphones have been matched to current technology.

First it was tubes and 600 ohms. (Actually I think it originally was about 1200 ohms for airplanes, then 600 ohms for radio).
Then it was transistors and 300 ohms.
They tried to set a headphone standard at 120 ohms. Seems no one listened.
Now it is op amps and 32 ohms.

If you are using an amp - forget about efifecency. there are at least two methods to measure effeciency. And it is not over the whole frequency range, usually at 1 KHz. That will not tell you how it will sound. Just worry that you can push enough voltage and/or current to drive the headphone without distortion. The less distortion produced or inherent in the transistors (or tubes or opamps), the better it will sound. It will sound cleaner and without distortion.

lower impedance headphones are more sensitive to changes in voltage, they therefore may not have a low noise floor (or high noise floor depending on how you rationalise it). Higher imedance headphones have less sensitivity to voltage changes (the volume control) so you can adjust it more minutely. Which is why one has to sometimes change their volume control - to give better control.

Basically, if you have sound cards and portable equipment, you want lower impedance headphones. Batteries store current. If how ever you are using them from a receiver, preamp outputs, tape decks, CD players, etc., you want high impedance headphones.

just do a search for impedance. you should see some very long dissertations and discussions.

 

[aerius]

Quote:

Originally posted by markl Long story short, to get the best sound from your cans, you need good quality amplification, all headphones will benefit equally from improved amplification.

Yup, even a lowly Senn 495 which has a 32 Ohm impedance benefits a fair bit from being driven by a good amp instead of my receiver jack. I'm burning in another mini-Gilmore amp right now, and I plugged the crappy throwaway set of headphones that came with my Walkman into it. Even those complete pieces of crap sound a bit better with the amp. However, no amp is gonna make them sound better than my Senn 580s, just like there's no speaker amp in existence that'll make my boombox sound better than a B&W 800 series speaker.

 

[blipblop]

This should be a sticky - I haven't seen so many depthful explanations in one thread ever. Thanks!

 

[rodbac]

Quote:

Your bumping a thread that just got two post in the last couple mins ?

Force of habit, bumpcop...

(it's a way of expressing my interest in the subject, thereby hopefully encouraging, however minutely, participation- is that OK, or shall I clear my bumps with someone first in the future?)

 

[halcyon]

Please remember that for many (if not most) headphones, impedance varies as a function of frequency. This variation can be bigger or smaller depending on the output impedance of the headphone amplifier that drives the headphones.

In almost all cases (sans some Beyerdynamics) a near zero impedance yeilds the best results (in terms of flatness of intended frequency response compared to an idealized curve).

However, many phones have a non-flat impedance-frequency curve even when connected to a near zero impedance output.