Ohm load

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johnnyamerika
johnnyamerika Posts: 382
edited March 2002 in Technical/Setup
Does anyone here with and Onkyo reciever and Polk speakers run with the switch set to 4ohms minimum as opposed to 6? What would this do for power output?

john
Post edited by johnnyamerika on
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  • jcaut
    jcaut Posts: 1,849
    edited March 2002
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    My guess would be that it reduces the maximum output voltage slightly, so that when supplying the greater current required by 4 Ohm speakers, the power dissipated by the output transistors stays within safe limits. That's just a guess, so if anyone knows for sure, I'm interested as well.

    I'm relatively sure that switching the switch to four Ohm position limits the maximum output somehow. Just how much it limits power depends on the individual receiver or amp. Most receivers would probably still put out more power into a 4 Ohm load than they do at 8 Ohms, (The Sony 333ES receiver I had was actually rated LESS at 4 Ohms than 8, which was one of the things that I didn't like about it), but how much more depends on the construction of the amp.

    Jason
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  • scottvamp
    scottvamp Posts: 3,277
    edited March 2002
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    John, I will be looking into this tonight. I am currently running two sets of main speakers and will be looking into this when I get home. You said something about a switch on the Onkyo? Where is this located? :confused:
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  • johnnyamerika
    johnnyamerika Posts: 382
    edited March 2002
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    On my reciever (595), it's located below the Speaker B terminals:

    txds595r.gif

    On the 700 series and up it seems to be fixed at 6 ohms minimum. I wonder why that is, as typically higher-end speakers run on lower ohms levels. Is that right?
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  • presidan
    presidan Posts: 116
    edited March 2002
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    Nice rear!

    I'm gonna have to check if my denon has this also...
    But i want to know exactly what lowering the ohm does sound quality wise ? The receiver dishes out more watts ? Sound stays the same ? What exactly happens ?
    RT2000i
    F/X1000
    CS400i
    DENON AVR-3802
    PIONEER PDP 4360-HD 43"
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  • kanicker
    kanicker Posts: 86
    edited March 2002
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    Related to this: Could a 4ohm amplifier/reciever output damage an 8ohm speaker? I want to run my 8ohm speakers in parallel, but I'm concerned that if for whatever reason, one speaker falls out of the loop, then the ohms wont match and bad things could happen.

    I do know that a 4ohm speaker with an 8ohm amp would be bad for the amp...

    help? directions to help?
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  • Steve@3dai
    Steve@3dai Posts: 983
    edited March 2002
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    Well, "in theory" a lower ohm load would be less resistance, thus greater amplification. This is certainly true in the Bel Canto amplifiers.

    Will it hurt to run 4ohm speakers on a 8ohm amp? Not if the amp is quality enough. I know a guy that is running 4ohm Martin Logans off of a Arcam AVR-100 and has no problems. I run my LSi9s off a Arcam A65 without any problems whatsoever.

    If the amp is quality enough, I don't think you'll run into any problems. But, more than likely I wouldn't recommend running multiple ohm loads on the same amp. That could give some funky resistance on the amp, dunno for sure there.

    - Steve
    LSi 9/C/FX
    Arcam AVR-200
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  • jcaut
    jcaut Posts: 1,849
    edited March 2002
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    Sound-wise, there's no difference between 4 Ohms and 8 Ohms, all else being equal. The 4 Ohms speakers will demand more current from an amp and it takes a better quality amp to supply high current.

    If you have a switch on your receiver, you're probably better off leaving it set to the higher-impedence setting, unless you're actually driving a lower impedence load. An amp should produce more power as the impedence drops, however, all amps have limits in this respect. I believe the impedence selector switch is just a means of ensuring that the limits aren't exceeded when using more than one set of speakers, or lower-than-"normal" impedence speakers.

    This may not be true in all cases, but USUALLY the LACK of an impedence selector switch says "more robust amp construction" to me.

    Jason
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  • johnnyamerika
    johnnyamerika Posts: 382
    edited March 2002
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    Yeah I see what you mean....I'm curious, even if the ohm selector is set to 4 ohm minimum, does that mean the amp will run at 4? It says minimum, not what will be output. For instance there's no 8, but this receiver averages a load of about 7 (gotta check the numbers). All I am wondering about is if the 595 and 696 have selectors to reach 4 ohms, which is harder to drive, why would the clearly better amp (700 and above) not have capabilities of reaching lower ohms?
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  • jcaut
    jcaut Posts: 1,849
    edited March 2002
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    The impedence selector switch doesn't really have anything to do with the output of the amp, other than that it probably sets an upper limit on absolute power output. Impedence is an electrical term for a "dynamic" resistance: It's the opposition to the flow of current, in an AC circuit. The amp is going to operate at whatever "load" is connected to it, regardless of the position of the switch. The switch just modifies the operation of the amp in such a way as to keep it stable when driving lower-impedence loads.

    Your question about why cheaper receivers give you the option of driving 4 Ohm loads, while some of the higher-end receivers don't, is a good one. I don't really have an answer for it, but I'm thinking.:)

    I do know that expecting a $1000 home theater receiver to be able to put out 100 or more honest, high-current watts into 5 (or 6..7..) channels, with 4 Ohm drive capability, is not reasonable. That's why, when there's a 4-or-8-Ohm switch, it's usually only effective on the front L&R channels. The better quality receivers usually compromise by allowing all channels to operate at, say, 6 Ohms. I figure most of them would probably tolerate 4 Ohm speakers on the two front channels.

    Jason
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  • johnnyamerika
    johnnyamerika Posts: 382
    edited March 2002
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    Originally posted by jcaut
    I do know that expecting a $1000 home theater receiver to be able to put out 100 or more honest, high-current watts into 5 (or 6..7..) channels, with 4 Ohm drive capability, is not reasonable.

    Right, at that point you need to look to higher-end power sources...sounds like reason enough to limit the load to 6 ohms.

    Thanks for the help!

    Looking into that further, Polks, at the least the 800 towers I have, run nominally at 8 ohms. So trying to run them lower than that could potentially damage them or your reciever, correct?
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  • jcaut
    jcaut Posts: 1,849
    edited March 2002
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    Not really. There's no way to run your 800's at a lower impedence. Not without hooking up more speakers. Impedence is a characteristic of the speakers, not the amp or receiver. Make sense?

    Jason
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  • johnnyamerika
    johnnyamerika Posts: 382
    edited March 2002
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    Yep, I got it. Just did some online research and I think I have it figured out now. THanks for the help!
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  • scottvamp
    scottvamp Posts: 3,277
    edited March 2002
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    OK I did the reseach. My Onkyo Manual says not to operate below 6 ohms. Safe operation according to Onkyo is 6 to 16 ohms. Even though it seemed to work fine I do not what to risk damaging the reciever.
    Problem---my new pair in parellel pull 4 ohms.
    Solution--wired them in series to pull 16 ohms.
    It seems that I have to crank the volume up a bit more. But I compensated buy bumping up the db + 3 on the mains. Somehow it doesn't quite seem the same though. I have to some more listening. But the reciever seems to run cooler than the 4 ohm load.:)
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