Question Home Audio WATTS OHMS?

Discussion in 'Hi-Fi Stereo Speakers' started by MJNGP, Apr 16, 2016.

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  1. MJNGP

    MJNGP
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    Hi,
    I have an integrated amp that offers 45w +45w at 4ohms (Denon UPA-F07).
    I have tried to understand what this means, but have sadly failed. Please could someone let me know what the max output speakers I could safely use. Currently have some pretty rubbish Sonys (SS-H771) which I think run at max 125w, but can handle less than half of the volume offered by the amp.
    I would really appreciate any practical (genuine) advice. THANKS o_O
     
  2. dogfonos

    dogfonos
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    Most folk with experience in high quality recorded music playback don't get too hung up about such figures but use them more as a (very) rough guide.

    To generalise...
    Amplifiers generate power (unit: Watt), speakers accept that power (unit: Watt). Speakers have a nominal impedance, a sort of approximated electrical resistance (unit: Ohm).

    The power an amplifier generates depends, in part, on the connected speaker's impedance. Most amplifiers are able to generate more power into low impedance speakers than into high impedance speakers (up to a point anyway). So your Denon amp can generate a maximum of 45 W of power, on each stereo channel (hence 45W + 45W), into speakers with a 4 Ohm (nominal) impedance - according to your figures.

    Connect an 8 Ohm nominal impedance speaker to the amp and the amp's maximum power output would reduce, generally speaking. Typical nominal impedances for modern hifi speakers usually lie in the range 4 to 8 Ohms but there are exceptions.

    When you see a power rating on a particular speaker, it refers to the power handling capability of the speaker and not the speaker's power output (which, acoustically, would be a mere fraction of the power entering the speaker because speakers are very inefficient at converting electrical energy into sound).

    Too much amplifier power can damage a speaker so caution needs to be exercised with the amplifier volume control if you connect speakers with a lower power handling than the amplifier's maximum output power. That said, it's not uncommon for a high power output amplifier to be used quite safely with lower power handling speakers - just be careful with the amps volume control.

    In reality, the reverse can also be true...
    A low powered amplifier can sometimes damage a speaker with a high power handling rating if the amplifier's volume control is set too high. This is due to the amplifier being overdriven and generating distortion which can damage the speakers' tweeters. And even if the amplifier's maximum output was carefully matched with the speakers power handling, it's still possible to damage the speakers with certain music/tones/sound effects.

    If I understand correctly, you're saying that the SONY speakers struggle to cope with the DENON amplifier's power even with the amp's volume control set about halfway. That doesn't surprise me much. The problem with manufacturer's figures is that they often lie - another reason why few of us pay much attention to figures though I have to say, IME, that higher end manufacturers tend to be more honest with their product specifications. Another thing - some amplifiers (often cheaper ones) output close to their maximum power when the volume control reaches about halfway.

    What is your aim here? Are you after a replacement set of speakers and wish to know what models would work with your existing Denon amp? Answer: A speaker with a 4 Ohm or higher nominal impedance and a power handling rating of around 40 W or more, i.e. just about any budget hifi speaker on the market. More upmarket speakers sometimes specify an optimum amplifier maximum power output range (e.g. 40W to 150W).
     

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