ohms matching speakers and receivers question from a newbie...

Discussion in 'Archived Threads 2001-2004' started by Ryan_A, Jan 2, 2002.

  1. Ryan_A

    Ryan_A Auditioning

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    I've read several suggestions to newbies (like myself) that they should match their speakers to their receivers in regards to ohms.

    This got me to thinking about my recent new setup.

    My Pioneer suggests speakers between 8-16 ohms.

    My Cerwin Vega speakers list a 4 ohm rating.

    Since my basic understanding of ohm in regards to a measure of impedence. I'm figuring that low ohm rating means low impedence... therefore my speakers should be fine.

    If I were to have speakers rated at say 18-20 ohms (if there are such things)... then I would have a problem because the receiver will only push between 8-16 ohms.

    Is this correct?

    I've looked for such questions on several FAQ and not had any luck.
     
  2. ColinM

    ColinM Cinematographer

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    Let me throw this out and then we will see what more experienced folks think -

    A speaker soaks up signal from the amp. The Ohms tell us how much signal is soaked up, higher number = more soak-up.

    No speaker = a short circuit, zero ohms. Bad!

    4 ohms give back quite a bit of current to the amp, which it dissipates as heat. OK if ze amp is rated for it.

    8 ohms give back much less than the 4, and all amps are happy with that.

    Baisically the lower you go with ohmage, the closer you get to shorting out the amp. Some amps are built for it, some are not. If yours says 8 for the min, you CAN go with 4, just keep the volume down, check to see how much heat it gives off, and keep it well ventilated or install a fan.

    Anyone else?

    HappyNewYear!
     
  3. Gordon C Jr

    Gordon C Jr Stunt Coordinator

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    Ryan,

    I believe impedance has an inverse relationship with current drawn. That is, the lower the Ohm speaker in the circuit, the higher the current demand or drain. Higher Ohm speakers than those recommended by manufacturer should not have any adverse effects on Amp/Receiver equipment. However, lower impedance than manufacturers recommended could be bad for Amp/Receiver equipment if, as Colin pointed out, the volume is turned up to a point at which the speakers draw more current from the amp than the amp is capable of providing. It’s somewhat similar to putting a 200 watt light bulb into a 100 watt maximum outlet (This could blow a fuse and present a fire hazard, since the circuit and outlet is designed for 100 watt maximum and the 200 watt light bulb is demanding more current than the outlet design). However, if the light bulb has a dimmer switch (similar to volume level on receiver), the lights could be dimmed to a level that is adequate for the outlet and will only draw current equivalent to 100 watt bulb.

    The problem here is that unless you have the proper measuring devices, it is very difficult to determine at what point you’re speakers are demanding too much current. What also complicates matters is that your speakers current demand is not constant and varies with various music and movie scenes. When thunderous bass such as a cannon or explosion or thunderstorm occurs, your speakers are being challenged and will usually demand more current.

    You could probably find more details and scenarios of mixing Ohms in the DIY section, since in order to build a speaker, you need to have a good understanding of how Ohms of each individual speaker (woofer, mid & tweeter) affect the overall Ohm of the speaker and whether to connect them in parallel or series.

    “If I were to have speakers rated at say 18-20 ohms (if there are such things)... then I would have a problem because the receiver will only push between 8-16 ohms.“

    I don’t see this senario being a problem, except you may not be able to get much volume levels out of too high of a speaker. The opposite would be a bad setup: Having a 2 ohm speaker connected to a 8-16 ohm suggested amp. It would sound load and you wouldn’t need to turn the volume too much to get a lot of sound, but the amp would overheat at well below reference level volume and more than likely clip.

    Back to your setup, if you never play extreme volumes and the amp doesn’t get too hot, you shouldn’t have any problems. If you have clipped your amp in the past by turning it up too load, you know where the threshold of clipping is. Clipping an amp is never good news, it will send out high frequency distortion and blow your tweeters easily.

    Just my 2 cents that turned into more like 4 cents
     
  4. Eric_M

    Eric_M Stunt Coordinator

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    ok in regards to switches for Ohms in the back of recievers such as the Onkyo I am getting.

    On the back there is a switch so you can swith from 4 ohms to 6 ohms.

    The monitor 7's I am getting are 8 ohms. So I can adjust the switch to either or and I should be fine then?

    Would it really matter or would the only difference be I might be able to play it louder at the 6 ohm level?
     
  5. Drew Eckhardt

    Drew Eckhardt Stunt Coordinator

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    If it has a switch, in the low impedance position the switch probably cuts the output stage rail voltage, because you have both current (voltage/impedance) and power (actually, waste heat disipitation which is a function of power and efficiency. Power is voltage squared/impedance) limits that you can't exceed without potential damage to the amp (or blowing a fuse, which could be a warranty claim that's expensive to process) and this is a cheap (an extra tap on the transformer secondaries plus a switch) way to guarantee that you can't exceed the limits.

    Cutting the voltage will make you more likely to clip (the required output would be more positive or negative than the corresponding rail voltage (there's one for +, one for -)) resulting in a square wave form.

    Clipping is bad because a square wave is a sum of sine waves including high frequencies. Tweeters don't have good power handling, and can blow from the resulting high-power high-frequency. Normally, this is OK because music has more power at lower frequencies.

    IOW, if there's a 4ohm/6ohm switch and you have 8ohm speakers you want to set it in the 8ohm position.
     
  6. Eric_M

    Eric_M Stunt Coordinator

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    Umm yeah what he said hehe.

    you mean the 6 ohm position?
     
  7. Chuck Kent

    Chuck Kent Supporting Actor

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