Impedence (Ohms)... what is it, exactly?

Discussion in 'OT Technology' started by coronet, Jan 23, 2005.

  1. coronet

    coronet Do Andriods Dream of Electric Sheep?

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    What's the diffrence between low and high impedence headphones, and which is better for which situations and why?
     
  2. 04

    04 Guest

    Not quite. impedence is alternating current resistance (more or less). It is the real resistance (which measures the opposition of current flow for direct current) plus the imaginary component (which measures the phase relationship between current and voltage in an alternating current frequency). When added together you get impedence.

    For a given voltage, then yes, a lower impedence headphone would be louder. But that assumes that the amplification device can increase current in a linear fashion as the impedence drops.

    Here's a good article for more in depth information: http://en.wikipedia.org/wiki/Impedance
     
  3. 04

    04 Guest

    Basically, the only difference (all other factors equal) is that the low impedence headphones require less voltage applied in order to get a certain amount of power. To give a high impedence headphone the same power as the low impedence ones, you will have to increase the voltage, which can sometimes be an issue for lower powered devices such as portable media players. Many of them are not able to create a high enough voltage on the headphone outputs.

    So, generally, the low impedence headphones are better for portable devices. If you have say a home receiver with a robust headphone output, the impedence might not be an issue, however.

    That means that headphones like the Sennheiser HD-600 series (with a nominal impedence of 300 ohms) might not get loud enough for your tastes with a portable cd player, but a headphone like any of the Grado line (with a nominal impedence of 32 ohms) will. Even if the HD-600's played as loud as the Grado's with the same amount of power, with a low voltage headphone output, the Grado's could be close to 10 decibels louder. That can make a big difference, especially if you want to listen loud with a portable player and dont want to buy an amplifier.
     
  4. coronet

    coronet Do Andriods Dream of Electric Sheep?

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    Oh, OK. I mainly wondered because my Etymotic ER-4P has an impedence of 27 Ohms, whereas the ER-4S has 100 Ohms; wondered what it meant (And the AKG K1000 had a 10000 Ohm impedence and the Sony MDR-R10 had a 40... so you can see where I really got lost!). Thanks. So why doesn't everyone aim for a low impedence value? Can it affect sound quality or frequency responce or something? Also, if I were to use, say, a cMoy Pocket Tin Amp (which I still haven't completed :o ), should I buy the ER-4P --> ER-4S conversion cable (which I guess replaces the impedence values)?
     
  5. P07r0457

    P07r0457 New Member

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    high impedence units require more power to get the same level of sound when compared to a low-impedence unit. The benefit, however, is high-ohm units usually sound better.
     
  6. 04

    04 Guest

    :confused:

    The Grado RS series of phones is very well regarded, yet has a rather low nominal impedence. If your source had a very high output impedence (which isnt very good), then I could see the higher impedence headphones being better, but otherwise, the impedence wont affect sound quality.

    They work the same way as car speakers. A 2 ohm speaker isnt necessarily going to sound worse than an 8 ohm one and vise versa.
     
  7. 04

    04 Guest

    To be honest, I dont know why manufacturers vary impedence in such a large range. If your source has a very high output impedence, it would affect the frequency response of low impedence phones moreso than the high impedence ones. That may be one reason. However, this should rarely even be an issue.

    The CMOY should do a great job driving low or high impedence phones in most cases. An interesting thing about the CMOY though, is that it will have MORE power output for higher impedence phones! If you want more information about this let me know :o

    The Etymotic power version has a lower impedence because its designed to be better suited for use with portable devices. So the Stereo version would probably be better suited for use with the CMOY, but either should work.
     
  8. coronet

    coronet Do Andriods Dream of Electric Sheep?

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    Thanks very much. I understand now. :cool:

    But enlighten me on the cMoy... :o
     
  9. 04

    04 Guest

    Well the opamp can only output a certain amount of current before distortion sets in. Since a higher impedence headphone needs more voltage and less current than a lower impedence headphone, that means that the power output will probably be higher with the high impedence headphones.

    It shouldnt be too much of an issue unless you like to listen REALLY loud with low impedence phones.
     

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