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Question on rating speakers

Discussion in 'Home Cinema Speakers' started by docjan_uk, Aug 25, 2004.

  1. docjan_uk

    docjan_uk
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    OK, Im still unclear on one particular aspect... say Im going to get an amp that can knock out around 80 watts at 8 ohms and it mentions 110 watts at 6 ohms.. does this mean that it can deal with speakers that are listed on a site as 45/80 watts with impedence from 4-8 ohms? how about speakers listed with the same impedence ratings but 60/100 watts.

    Im not sure why these two values are given in watt rating.... is the first its rating at 8 ohms and the second the rating at 6 or 4 ohms? (in which case I guess the amp would have no problem supplying power).
     
  2. Beobloke

    Beobloke
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    A brief guide to the hideously complex world of power and impedance ratings!! -

    Firstly, the speaker impedance of 4-8Ohms means that the speaker's minimum impedance at a particular frequency is 4 Ohms, but for most of the rest of the frequency range it is nearer 8. This is quite common for modern speakers and any modern amplifier will cope with this. Problems only arise when you connect more than one pair of speakers to an amp - this will mean that if the speakers are connected in parallel (which they nearly always are) then the amplifier will see a 2 Ohm load at certain frequencies and many cheaper and less powerful amplifiers will not be happy about this, as their power supplies will run out of current.

    For the amplifier power rating, the 4Ohm figure will always be higher as the power supply will deliver extra current for the same output voltage and thus give an increased power output. In theory this would keep going higher as you go down to a 2Ohm load, then a 1Ohm etc. but in reality this will be limited by the design of the amplifier's power supply and the maximum amount of current it can deliver (remembering that these are voltage amplifiers) For example, 40Watts into 8 Ohms requires 17.9Volts output at a current of 2.2A. Keeping the 17.9V output but changing the load to 4Ohms will give a power output of 80W but require a current of 4.46A.

    For the items you list, an amplifier with 80W into 8Ohms will be fine with the speakers rated at 45/80W (usually the 2 numbers refers to music and peak power - ignore the former!!). Remember that it is easier to damage a speaker by over-driving it with a low-powered amplifier than a high-powered one as a result of the distortion that arises when you crank up the volume! Also, at normal listening level, an amplifier is only pushing out a few watts per channel.

    Adam.
     
  3. docjan_uk

    docjan_uk
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    Thanks for the info ;)... I guess I'll be sticking with the CD1's at 80 watts.
     

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