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All about headphone levels - answers to the variation on level with different gear

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  • All about headphone levels - answers to the variation on level with different gear

    I posted the following in another thread recently and figured it could probably do with it's own thread. Hopefully this will shed some light on the often asked question about why headphones and equipment combinations vary so much in level. OK, here's the info I posted earlier.....


    Here's a few tech notes on headphones and impedance. I'll try to word it in an easy to understand manner but that isn't always easy.

    In the world of headphones, there are four main factors that typically determine what headphones will suit what outputs.
    These factors are current, voltage, wattage and impedance.

    * Impedance is the amount of 'resistance' or 'load' presented (in this case by the headphones). The higher the number, the less the load (but not necessarily louder as explained below).
    * Voltage is, in this case, the amplitude of the signal, measured in Volts.
    * Current is the strength of that signal and how capable it is, measured in Amps.
    * Wattage is the total power if the signal and is obtained by multiplying Volts and Amps together.

    As you can see, it is the wattage that will determine the overall capability of the headphone amplifier. A high wattage amplifier (ie lots of volts AND amps) will be able to drive any headphones to a loud level.

    OK then, why the variation? Why not just make an amplifier that can drive all headphones to a loud enough level?
    Cost! It is easier and cheaper to make a lower wattage amplifier.

    It is also easier to make an amplifier with a high voltage swing but low current capacity which is fine for driving high impedance headphones. Such headphones require less effort (current) to drive them and will present less of a load to the amplifier. Perfect for a high voltage, low current amplifier. Such amplifiers are common amongst semi professional equipment driven from mains power (ie from a wall socket) because there is plenty of voltage present from their power supplies.

    Low impedance headphones were created when battery powered equipment became popular. The higher voltages found in mains powered equipment were not available from a couple of batteries so low voltage, high current amplifiers were created which can drive low impedance headphones perfectly. Remember, low impedance headphones require less voltage but more effort (or current) to drive them.

    Now we have a situation where there's both low and high impedance headphones on the market and both mains and battery powered equipment too.
    If we plug low impedance headphones (requiring low voltage and high current) into an amplifier designed for high impedance loads (high voltage, low current), these headphones will load down the amplifier reducing its voltage 'swing' and therefore reducing the output level.
    If we plug high impedance headphones (requiring high voltage and low current) into an amplifier designed for low impedance headphones (low voltage and high current), the amplifier won't have the voltage swing necessary to drive these headphones and, once again, low level.

    What can be done to fix this?
    There are two possibilities and the first is to find out the recommended impedance for the item in question and buy headphones to suit it.
    The second possibility is that the manufacturer has designed the amplifier to drive all impedance headphones. These amplifiers are typically only found in top of the line studio and professional equipment where manufacturing costs are not an issue. These devices typically have headphone amplifiers capable of both high voltage AND current (which equals higher wattage) and can drive any headphones.
    Care must be taken using such amplifiers with low impedance headphones because they will be capable of VERY loud levels and can easily damage hearing! Some of these headphone amplifiers are even capable of driving small speakers!!

    I have used both high impedance headphones (my AKG K240's) and low impedance headphones (various DJ models) with my TD20 and it is more than capable of tearing my ears off with either!!
    My AKG's are next to useless on battery powered equipment though because they are designed for professional use and these battery powered devices do not have a high enough voltage swing to drive them properly. However, I bought them for studio use so that is not a problem. I also bought a pair of AKG low impedance 'bud style' earphones for my mp3 player which are designed for portable battery powered equipment.

    I hope this rather long winded post helps to answer your questions without confusing things too much!
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