[Dragonmilenario]

hello i want to buy the Senn´s HD650 but i discovered that ti have 300 ohm, and the HD595 only 50. ¿what is the meaning of the impedance in the headphones? ¿is related by the signal volume?

thanks, i´m a newie in the headphone world.

 

[dag655321]

I wont go into the technical explanation of what impedance is (cause I am not sure I have it exactly right, and there aren't any EEs here right now), but it is roughly "the resistance to the flow of electicity". Practically speaking, a higher impedance headphone will take more power to drive than a lower imedance headphone at equivalent volumes. A 50 Ohm pair of headphone can be easliy driven by a portable player without an amp. a 300 Ohm pair can be driven by a protable player, but you will get a lower maximum volume. You will want to use an amp with a 300 Ohm pair whenever possible.

For example, my iPod can drive my Senn HD-590's (120 ohm) to reasonable levels, but not really loud. I never listen that loud, so it doesn't bother me. On the other hand, my HeadRoom Airhead, can drive the HD-590's to very high levels, and sounds better than the direct iPod at reasonable levels.

The short answer is 50 Ohms will work fine directly from a portable player, and 300 Ohms will require an amp for peak performance, but can be used without. Most of the headphones that come with portable players are around 32 Ohms, and the players are designed for that.

 

[Funkstar]

^^^ truth.

Put very simply its more or less how much power the phones need to operate.

What you need to watch for is that when you turn up an unamped source too loud (to power the higher ohms) you may get distortion which could negate any benefits of having the better headphones in the first place. If its a good source and/or its amped i wouldnt worry too much and just get the better phones.

That said, Ohms arent a measure of quality as some people think. The top phones from Grado (RS series) for example are only 32 Ohm where as HD-580's are 300, but the are Grados still better (both in quality and sound*).

Just treat it as how much you need to turn the volume knob around, not a measure of quality

[size=xx-small]*IMO[/size]

 

[dag655321]

I forgot to mention that aside from the impedance, the HD650's annd 595's are very different headphones. Yes they are both from Sennheiser, but there are designed differently. The general opinion is that the 650's are a little laid back, but very detailed, like sitting in the middle of a concert hall. The 595's are usually considered more bright and "aggresive", more like sitting in the front row of a rock concert.

I suggest reading the many forum posts around here realting either or both of them. Also check out the detailed descriptions provided by HeadRoom (www.headphone.com) on thier repsective product pages. You might want to let your musical tastes determine which pair you want.

 

[Alick]

Whilst the effect of the explanations above is a reasonable guide, they are not entirely accurate. Impedance is the quantity that determines the amplitude of current for a given voltage in an AC circuit, nothing more, nothing less. It is not a measure of quality and whilst providing a guide to how much power will be needed to drive a pair of phones, efficiency also plays a large part in that determination so it is no more than a guide.

Impedance is the product of the resistance and the reactance (the impeding effect of purely capacitive and inductive elements in a circuit) and varies with frequency. Resistance does not vary with frequency. Strictly speaking, the impedance of headphones should be quoted at a specified frequency as it is not a fixed value at all audio frequencies.

HTH

 

[sgrossklass]

Generally, given the same sensitivity (which may vary, of course), cans with high impedance want to see more output voltage while ones with low impedance can live with less voltage but need more current for the same volume. Thus high-impedance cans will be better suited for home use where sufficiently high voltages are not a problem (generally +/-12V tends to be present) and opamps may be used for amplification, while low-impedance cans will suit portable devices with their lower output voltages and power amp chips (i.e. generally sufficiently high currents).
Critical cases are insensitive high-impedance cans (typically described as "hard to drive") and very low-impedance cans that require insane amounts of current, which at the power buffering possible in small portable devices will lead to higher battery drain. Low-impedance cans also get harder to drive for devices with non-negligible output impedances (typically, home speaker amps and receivers, but also radios that have a speaker of their own) as the voltage drop across the internal resistance rises. The sweet spot is at load impedance = output impedance. (If output impedance --> 0, then only the maximum current will limit the possible output power.) That's why I can wring higher volume out of my HD590 (120 ohm) than either a DT231 (32 ohm) or a HD424 (2k ohm) on an amp with a Z_out of ~140 ohm. (Given a source with very limited output current, however, like a SB AWE64 line out, the HD424 is at an advantage since you can get undistorted playback when the HD590 already is too much for the opamps used. At the same time, it isn't going to be much fun out of a pocket radio running off a single 1.5 V cell - a HD650 wouldn't either -, where the DT231 would be best suited.)

Related issues are the influence of output impedance on frequency response (the impedance of headphones frequently varies considerably with frequency while the output impedance tends to be fairly constant, thus frequency response will be altered as you go to higher output impedances) and the bass roll-off encountered when there are coupling caps in the output and you connect low-impedance cans (the output+load impedances together with the coupling caps form a nice highpass which scales with 1/(R*C) frequency wise, i.e. you'd need to compensate lower impedances with fatter coupling caps), as frequently to be observed with onboard sound and such.