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Thread: Question on Amplifier and speaker

  1. #1
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    Default Question on Amplifier and speaker

    Hi all,

    Need to ask a question, mayb some of u can help.

    I have an amplifier with 40W 4Ohm output single channel, can I connect 2 40W 8Ohm speakers to this single channel output?

    Will there be any sound output or will it burn my amplifier or speaker?

    Thanks. Hope to hear some answers on this.

    Good day!

  2. #2

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    Are you talking about running a pair of 8ohms speakers in parallel to a single channel output of 4ohms?

    Running the pair of 8ohms speakers in parallel will give you a impedence load of 4ohms, which will match your 4ohms output of the amp. But I'll caution against pushing your amp in case the impedence load falls below 4ohms, in which case your amp will be over-driven, clip and burn.

  3. #3
    Senior Member jnet6's Avatar
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    higher the "ohm" of yr speakers, the easier yr amp goin to drive it.

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    Hope you're referring to a pair of + / - terminals on your amp.

    For this scenario, try to use only 1 pair of speakers. If your amp states 4ohms @ 40W RMS / channel .... for 8ohm speakers, it would be 80W RMS / channel.

    Always hook 1 speaker to a terminal. Never piggy back. You will still have sound, but it'll weaken the signal and put additonal stress on your amplifier when you run the amp.

  5. #5

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    Quote Originally Posted by jnet6
    higher the "ohm" of yr speakers, the easier yr amp goin to drive it.
    This is incorrect. A high ohm rating on the speaker means a high input impedence load, in this case it means that the amp is not able to work at the max power efficiency. i.e. an amp rated at 40W with an output impedence of 4ohms when coupled to a 40W speaker with an input impedence of 8ohms will only be able to deliver 20W of power to the speaker.
    Last edited by edlye; 27th May 2005 at 12:41 PM.

  6. #6

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    Quote Originally Posted by dEthANGeL
    Hope you're referring to a pair of + / - terminals on your amp.

    For this scenario, try to use only 1 pair of speakers. If your amp states 4ohms @ 40W RMS / channel .... for 8ohm speakers, it would be 80W RMS / channel.
    His amp has a single channel output rated at 40W with an output impedence of 4ohms. When coupled to one 40W speaker with an input impedence of 8ohms, the amp will only be able to deliver 20W of power to the speaker.


    Quote Originally Posted by dEthANGeL
    Always hook 1 speaker to a terminal. Never piggy back. You will still have sound, but it'll weaken the signal and put additonal stress on your amplifier when you run the amp.
    What you are referring to is running a pair of speakers to a single channel output on an amp in series. In this case, running a pair of 8ohms speakers in series will create an input impedence load of 16ohms. This just creates additional load for the amp to overcome, which explains the weakened signal hence lower speaker output volume.

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    Quote Originally Posted by edlye
    This is incorrect. A high ohm rating on the speaker means a high input impedence load, in this case it means that the amp is not able to work at the max power efficiency. i.e. an amp rated at 40W with an output impedence of 4ohms when coupled to a 40W speaker with an input impedence of 8ohms will only be able to deliver 20W of power to the speaker.

    Both of you are wrong and right.. It all depends on the amp's design..

    A current limited amp will usually deliver more power to a higher-impedance load.

    A voltage limited amp will usually deliver less power to a higher-impedance load.


    The user can simply test driving the speakers in parallel.. It'd take a fair period of clipping to cause damage to the speakers and/ or amp. Simply turn off the setup if it starts clipping at the playback volume.

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    Thanks for all the inputs. I think I get what you all says...

    Edlye and firefox are very right. Definitely the amp will be overloaded and the sound quality will be affected, but it's worth for me to experiment.

    My only worry is when will the amp give way on me?

  9. #9

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    Quote Originally Posted by Firefox
    Both of you are wrong and right.. It all depends on the amp's design..

    A current limited amp will usually deliver more power to a higher-impedance load.

    A voltage limited amp will usually deliver less power to a higher-impedance load.


    The user can simply test driving the speakers in parallel.. It'd take a fair period of clipping to cause damage to the speakers and/ or amp. Simply turn off the setup if it starts clipping at the playback volume.
    For the lay person's benefit, a current limited amp is commonly also known as a tube amp, and a voltage limited amp is commonly also known as a transistor or solid-state amp. While it is true that a current limited amp will usually deliver more power to a higher-impedance load, we will have to watch for heat and clipping because I suspect that the speakers would be spec'ed at nominal impedence load, hence might present a input impedence load of less than 4 ohms at rated specs. Like what firefox said, just test out the speakers in parallel and switch off if it starts to clip or emit excessive heat.

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    The only SS amp that's virtually impervious to the impedance load I've seen is a diy'ed unit.. With auto sensing and biasing circuits.. Delivers 800W into 8ohm loads, 1600W into 16 ohm loads and can handle loads as low as 0.5 ohms..
    Only thing is it's a pure Class A design that has a nice and toasty power consumption of 3.3kW and requires chilled water to cool it at 180 gallons/ hour..

    Parts cost alone runs up to US$7.5K..

    Then of course, there's always the Krell MRA.. 1kW into 8 ohms, 2kW into 4 ohms, 4kW into 2ohms & 16kW into 0.5ohms..

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