The effect of impedance

One noticable thing: volume. Higher-impedance cans tend to require a higher volume knob to achieve the same volume level as lower-impedance ones.

Of course, that is moot point if your amp is anything like the GS Solo and delivers the same volume level at a given knob position, regardless of impedance.

Cheers!

Mainly amp synnergy. High impedence cans are (generally) voltage hungry and need an amp circuit capable of delivering a large +V/-V swing. A low impedance can (generally) needs an amp circuit with large current reserve capacity. Common oppinion is that low impedance cans do not need robust amplification, I (for one) disagree with this belief. I can very easily hear the difference between all my low impedence cans when they are under-amped.

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I think so as well. Seemed to be the case with my HD 201's

Yes, V=IR.

However, that only shows the relation between the variables. It still says nothing about the driver, nothing about how it will sound, nothing about how much amperage is needed, absolutely nothing.

The advantage a low impedence driver has is that your amp can more easily output its wattage. A high impedence driver would require higher voltage levels to get the same level of output. Depending on the amp, you might be limited in available wattage before clipping.

It's just like car audio. You have an amp rated for 100w rms @ 4ohms. However, it can also output 200w rms @ 2ohms and 400w rms @ 1ohm. If you hooked up an 8ohm home audio woofer, you're looking at something more towards 50w rms. These are max values as above this point, you get excess distortion and clipping. The same would apply for whatever source you're running for your headphone. Now realize I said absolutely nothing about the actual headphone.

Just like in car audio and home audio, impedence means nothing. An 8ohm driver versus a 4ohm driver of the same design will behave the same. It's just that the 4ohm driver lets the amp more easily output more amps.

Now you might be saying that impedence controls how loud the driver will get. Sort of, but only in the reference to the amp and source volume position. However, the driver itself will have a given sensitivity. Back to home and car audio again, you have an 8ohm home audio driver and a 4ohm car audio driver. You obviosly have different effects on the amp. However, let's say the home audio driver has a sensitivity of 92dB and the car audio driver has a sensitivity of 86dB. Well, the car audio driver can certainly get more amps run through it, but its sensitivity adversely counteracts that by having much smaller volume gains per watt of power. The much higher sensitivity of the home audio woofer actually makes it capable of getting louder, not only per watt but even when considering max available wattage(half) to it versus the car audio woofer.

Even now, this says absolutely nothing about how the driver will sound. This has no impact on tonality, level of detail, or anything for that matter. That comes down to speaker design.

x2. Each and every headphone is designed around a particular impedance. A headphone that operates with a 300-Ohm impedance can sound just like one that operates with a 30-Ohm impedance.

To the OP, the only sure answer to your question is that, for a given voltage gain, a low-impedance headphone will play louder than a high-impedance headphone.

A more interesting question is, what is the influence of an amplifier's output impedance on headphone sound? Especially compared to the input impedance of a headphone?

???Huh???

Seriously?! That's cool! Any idea how it works?

Impedance is Z, resistance, capacitance, and inductance all contribute to impedance

So, how does all of the above comments fit into the subject of etymotic ER4P & ER4S ? They sound different correct? Why/how does the impedance difference effect their sound?

I only own the ER4P but use a portable amp which converts them into "S". Unless I'm losing my mind, it sounds different(better).

The following may not be what was intended by the OP but it is an interesting slant on headphone impedance.

It is unusual to have a can that has a flat impedance curve.

So for the effect on a single can where you have a peak in its curve, at that peak you will have sound level change from the rest of the frequency range. There is one web site that shows and discusses this issue on individual can basis.

Surprisingly the Ultrasone Edition series has a remarkable flat impedance curves from 20 hz to 20 khz.

There are a couple of Sony cans that I am unfamiliar with that are also flat.

Spot on!

That was one of the reasons Kevin Gilmore developed the Dynalo seen in the following link
http://headwize.com/projects/showfil...lmore3_prj.htm
(The Gilmore Lite amp is the commercial version of this design)

On a more personal note, I've seen vast improvements in amped Grado's vs non-amped. This includes a simple CMOY amp.

Never mind; I answered my own question with a little research.

I am pretty sure, from reading his project announcement, that his goal was to properly drive low impedance cans. Now, how they drive high impedance cans, I am not sure. Any member with a DIY dynalo, or a Headamp Gilmore lite could help you out on that. I've only heard it with Grado's, and it is quite nice.

Back to the OP,
In terms of sound, it's really hard to gauge whether impedance has an effect on the same headphone because manufacturers typically don't make multiple variations of the same models. Beyerdynamic and Etymotic are the only ones that come to mind. Various post comments have been made indicating that there is an audible difference in the impedance of the phones in terms of the sound signature. Overall, it seems as if people prefer higher impedance versions when driving them isn't a concern. This may have very much to do with the properties the amp driving them has when loaded with a high impedance load.