Axiom Home Page Forums General Discussion Technical Questions Ohms--matching amplifiers and speakers

Damn you're good Sushi...

Now what does all that mean in newbie english?

Jim, let me give it a try. The expression of Ohm's law which is probably most in point with Doc Jon's question is I=E/R(i.e. current equals voltage divided by resistance). This shows us that if the voltage isn't reduced, when the resistance of the speaker is 4ohms rather than 8ohms the current will be doubled.If the receiver can't handle this and is in danger of overheating its protective circuit will cause a shutdown. To prevent this many receivers have a "4 ohm" switch on the back or setting in the setup menu. This reduces the voltage which can be supplied and thereby the maximum current flow,without a shutdown. Since it also reduces the maximum power available this setting should only be used when experience has showed it to be absolutely necessary.

Then, despite knowing all the equations,sometimes mysterious shutdowns plague even powerful THX certified(which certification includes testing with low impedance speakers)receivers such as early samples of sushi's Pioneer 45TX. Apparently Pioneer has now corrected what may have been an overly-sensitive protective circuit and now just about anything goes.

Oh, well--I *thought* it made perfect sense. Now I'm back to being confused! But don't worry, Sushi, I think I've got the basic concept.

theaterdoc

Holy impedance, Batman--I can't believe the avalanche of technical dialogue started by my innocent question!

theaterdoc

Thank you very much. I crave to learn this stuff inside and out. That was newbie enough for me. So now I understand the purpose of the ohm switch on back of my 1300. The lower the ohms, the lower the output of watts per channel rating of a receiver/amp?

Yes, Jim, in restricting the voltage and current, the maximum power available is also reduced when the switch is set to 4 ohms. So, regardless of what speakers are being used, the 4 ohm position shouldn't be set unless the receiver has been shutting off because of low-impedance speakers being driven.

Although it is way too late for me to be up and i've had about 2 bottles of a truly fine wine, i am a touch confused myself nowif not incredibly idzzy.
When ohms decrease, power output usuallly increases (preferably by double from 8 to 4 ohms.)
Can you clarify your last statement?

Point of note, i actually got my Onkyo 797 up to 85 on the absolute scale this evening.
Decibels measured 110 on the ol sound meter. (approx. 2.5m from centre speakers).

In reply to:

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The lower the ohms, the lower the output of watts per channel rating of a receiver/amp?

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jbzn, I think JohnK got you correctly. But just in case... if you meant by "the lower the ohms" the ohm rating of the speakers (not the position of protection selector switch on the back of a receiver), in fact the opposite is true.

"The lower the speaker's ohm rating, the higher the max power (watt per channel) that a receiver can pump out to the speaker" -- as long as the receiver does not shut itself down.

Sorry for the confusion, but English is my SECOND language, and it's been hard enough for me. The Newbiese would be my THIRD... LOL

Chess, by now you may have had the third bottle of that wine and are on the floor, but if you can read this, we're talking about two different 4 ohm situations. You're correct that if sufficient voltage and therefore current was available more power(theoretically double) would be available into a 4 ohm speaker as compared to a 8 ohm speaker. However, I was speaking of the 4 ohm SWITCH POSITION which limits voltage and thereby current and allows for less maximum power to any given speaker than when in the 8 ohm position.

Thanks for the clarification.
Not only was i reading something again in the wee hours of the morning but add to that a copious amount of wine, port and imported beer.
I need more sleep.