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amps and watts

Discussion in 'AV Receivers & Amplifiers' started by roland, Dec 14, 2003.

  1. roland

    roland
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    Thinking of buying a Pioneer vsxc301,the advert read that it was 75 watt output not saying into what ohm speakers.On looking at Pioneers website that is into 4 ohms speakers, and only 40 watt output into 8 ohms speakers. Does it really take that much more power to drive 8 ohm speakers.The Mordaunt Short "Premier package" speakers say nominal 4-8 ohms, what does this mean.
    Also does anyone know if you can adjust the volume of each speaker yourself, with the Pioneer vsxc301 amp, as it says it sets the speakers up automatically.
    Many thanks
     
  2. rjlawson

    rjlawson
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    Not sure on the power, but you can set up individual channels yourself. You choose the size of the room (small/medium/large), size of speakers (small/large) & the listening position (front/centre/rear). But then you can alter the individual volumes as desired.
     
  3. roland

    roland
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    Thank you RJLawson for your reply,Do you mean you can alter the volumes of each speaker ie.left rear, right rear, left front,etc.
    or the rear both speakers, front both speakers, centre etc.)
    Thank you
     
  4. rjlawson

    rjlawson
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    When you turn the test-tone on, you can alter fl,c,fr,rl,rr,sub volume individually. I think you can get the full manual from the support www site, might be worth having a look through, as it covers all functions.
     
  5. roland

    roland
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    Thank you very much RJLawson, you have been most helpful.
     
  6. rjlawson

    rjlawson
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    No probs, I've only had my amp for just over a week - I'm new to all this, but the forums have been very handy. It's nice to be able to help someone else out!

    FWIW I got the VSX-C301 with Wharfedale Moviestar 60+ speakers from the local SuperFi to go with my Sky+, Philips DVDR70 & Gamecube. Spent a fair bit on cables (optical, co-ax & sub), but need to get some decent speaker cables.

    So far I'm dead chuffed with it & the missus seems pretty OK. Speakers are the same colour as the rest of the furniture, and all the hi-fi kit is silver! Haven't bothered putting the SCARTs through the amp, but I might give it a whirl & see if there's any advantage?
     
  7. Reiner

    Reiner
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    Actually it takes exactly double the power to drive 4 Ohm speakers (compared to 8 Ohm speakers).
    A good amp (and there aren't many which can do that) doubles it's power if the impedance is halved.
    Usually this limitation is caused by the power supply section.

    Take a look at some Mark Levinson amps and be impressed. Don't look at the price though! ;)

    Mark Levinson No.33: 8 Ohm - 300 Watt, 4 Ohm - 600 Watt, 2 Ohm - 1200 Watt, 1 Ohm - 2400 Watt

    It's most likely a 4 Ohm speaker. No such thing as "4-8 Ohm".
     
  8. davehk

    davehk
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    "Actually it takes exactly double the power to drive 4 Ohm speakers (compared to 8 Ohm speakers)."

    Not quite. The point is that it takes 1.414 time the CURRENT to drive a four ohm speaker to the SAME power as an 8 ohm. Which, all other aspects of the speakers being equal, will give the same volume.

    P = I^2*Z = 2(I^2)*Z/2 = (1.414*I)^2 *Z/2

    And also only 0.707 times the voltage. So the PSU's (current) rating is, as you say, the limiting factor here.

    [QUOTE
    It's most likely a 4 Ohm speaker. No such thing as "4-8 Ohm". [/B][/QUOTE]

    Actually, 4-8 Ohm is probably a lot more accurate. Loudspeaker impedance varies with frequency. An "8 Ohm" rating is a nominal value - the actual range could be anything from 2 to, say 16 or more ohms at the resonant frequency of the system. The actual 8-ohm value probably only occurs at one or two specific frequencies.

    4-8 is at least a range!

    Decent speakers may be supplied with an impedance v. frequency plot. It's also quite easy to produce one if you have a signal generator and a decent AC voltmeter.
     
  9. RobDickinson

    RobDickinson
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    Also how much actual sound you get from the speacers depends more on the speaker efficiency than the wattage delivered.
     
  10. davehk

    davehk
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    Exactly, hence the "all other aspects of the speakers being equal, will give the same volume"

    If you want to compare efficency, this will appear in the specs as something like "90dB/W at 1m" Typical ranges are 85dB/W to 105 dB/W. Generally, (not always) higher sound quality == less efficient speakers and hence bigger amps needed to get the required levels.
     

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