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OT question for you amp/electronics experts...

Discussion in 'Off Topic [BG]' started by secretdonkey, Jul 7, 2004.

  1. secretdonkey


    Oct 9, 2002
    Austin, TX
    So, I finally convinced myself to buy an iPod a couple of weeks ago. Next had to be a decent set of earphones -- my set of Etymotic Research ER-4P arrived yesterday.

    Etymotic makes several versions of this earphone. Among these, the ER-4S version is more of a audiophile home-use version, and the ER-4P model which features lower impedence, so as to get more volume out of smaller, portable device amplifiers such as that in the iPod.

    They may have lower impedence, but I still found myself listening to my iPod at about the same volume setting (85% or so) as with the stock phones... but I did seem to notice one big difference outside of the much-improved sound: the battery seemed to drain much quicker.

    I know next to nothing about the electronics behind this, but my experience tells me that at lower impedences my bass amp runs hotter - so it would make sense that it is using more power than with a higher impedence cab setup.

    I know that my bass amp is much louder sounding running at 4 ohms than 8, but I can imagine and guess that while the new phones have a lower impedence, other factors (e.g., a cleaner, distortion-free sound) conspire to make their *apparent* loudness pretty close to that of the higher-impedence stock phones. If my thinking is correct, at the same volume/EQ settings, lower impedence phones will use more battery power than high impedence phones.

    So, is my little theory on target, or is it off base?
  2. Well, my knowledge is more related to home theater/amplifier setups, rather than portable devices/headphones, but I hope I can explain this is Amplifier terms that might help you understand your theory a little more, and yes, you are right on the money. In this example, the amplifier would be the iPod, and the speaker being the headphones.

    A well designed amplifier with a strong power supply will double the amount of power in watts that it sends to a speaker with each halving of impedance. For instance, an amplifier might send 100 watts to a speaker with an 8-ohm impedance. When the impedance is halved to 4 ohms that amplifier would send out 200 watts of power. In the real world, few amplifiers are actually able to double their power output as impedance halves due to limitations on their power supply and design. Additionally, few amplifiers are able to put out power for any significant length of time with impedances of 3 ohms or less (the amplifier must be able to supply huge amounts of power as the impedance decreases below 4 ohms - in fact, many receivers cannot operate below 6 or even 8 ohms).

    If you need any more info or advice on this, you can PM me.