6 OHM verses 8 OHM ...what are the differences?

[Tombanjo]

Well, that brings us to the age old battle btw seperates and receivers. Audiophiles claim that you can't cram all those features and switching circuts in the same box with all your power supply without creating noise. They were saying this about 2ch for years, imagine what five or seven does?

With the advent of these new "super duper" big $$$ receivers (some as high as $7000+) come the claims of overcoming this problem. I have never had the opportunity to test out a high end receiver, but I've come to this conclusion. If features like room correction, every DSP mode known to man, and whatever other do dads aren't that important to you, why take the chance on increasing your noise floor? Also inherent in those receivers is the fact that they are more prone to breakdown just by definition. Too much stuff crammed in one box.

For $4000 (retail) on up, and that's the price point where they say they're as good as seperates, you can get a pretty damn good amp and pre amp. The pre/pros these days have just about all of the features you need. A minus is the cost of cabling to connect the two, but then again, access is easier for any reconnecting you want to do back there as opposed to those heavy, giant receivers.

[sandeepnandy]

Hi,

one small query. I am buying the onkyo tx-nr906 europe model. its says 220 w/ch @ 6ohms . the specification is under:
Amplifier

[akirby]

They're fine. Notice the rating says 140 wpc @ 8 ohms. When you use speakers with a lower resistance (6 or 4 or 2 ohms) you get more usable power out of the amplifier (assuming the amplifier is designed to go that low). Looks like you can go to 6 ohm speakers and get a bit more power but 8 is fine. No idea what the different abbreviations are but I'm sure google would find them for you.

[Richard]

I dont know what is FTC, IEC and JEITA difference.

Any time you measure something the method and result is based on a reference - that's all that means. It rarely has any value to consumers but if some one were to try and reproduce those results they NEED to know the reference that was used for testing or the outcome may not match.

[museken]

I have a Pioneer vsx-919ah Receiver over the years the tolerances in the circuitry has dwindled and the 120 rms is there but you really have to crank it. So I ordered An Onkyo TX-nr709 with 110 Rms The Onkyo supports both 8 OHMS and 6 Ohms.... From what I gather 6 OHMS speakers will push 130 Rms output. My question is should I have all speakers at 6 Ohms? Could I mix it up? Should I just keep the 8 ohm rating. I know your going to say it depends on the technology of the receiver but I do not have this unit yet. The reason I ask is the receiver would have to recognize the impedance from the output to each speaker. How can it possibly do that?. You have different gauges of wires = resistance. On a receiver the amp output is usually a RCA jack with like gauge 6 wire in it to define it. It seems at least to me all speakers should be 6 ohms with lots of Rms wattage support. I mean if your increasing 110 to 130 rms that's a massive increase in power. Sorry,...My question is can I mix the 8 ohm speakers with the 6 ohms speakers rated for the power with out dissolving the tolerance of the board on the Onkyo badly.

[Dave3putt]

Without knowing how many speakers you plan to run, I would just leave everything at 8 ohms and see how you like the sound. If it's 5 or 7 speakers, I think the Onkyo will hold it's own in the power department a little better than the Pioneer. Remember that receivers are rated almost always now at 2 channels driven. 110 watts is still a lot of power. You should easily be able to go deaf using 8 ohms with decent speakers.

[dk]

[quote="museken"]
...The reason I ask is the receiver would have to recognize the impedance from the output to each speaker. How can it possibly do that?..

The receiver has an internal DC power supply. The peak power delivered to a speaker
depends on the voltage of that power supply and the impedance of the speaker.

From the Onkyo datasheet, the output power vs. speaker impedance is as follows:
3 Ohms 250 Watts
4 Ohms 220 Watts
6 Ohms 170 Watts
8 Ohms 130 Watts

From this data you can infer that the receiver is using a DC power supply around 30 Volts.
(Power equals Voltage squared divided by Ohms)
It delivers 31.9 Volts when connected into 8 Ohms. Because of internal resistance, the voltage
drops down to 27.4 Volts when connected into 3 Ohms.

The channel connected to 6 Ohms will be 1.2 dB louder than the 8 Ohm channel.
dB = 10 times LOG ( Power6 / Power8 )

http://www.eu.onkyo.com/downloads/1/4/7 ... eet_EN.pdf

[jordanm]

Reading this thread made me so glad I checked this a couple of years ago, when I bought the better Yamaha AVR, rated 140 x 7 channels at 8 Ohms, and my speakers are big enough and 8 Ohms to match.

[Roger Halstead]

From a practical approach, most amps are designed at a maximum power at some given impedance, be it 8 ohms or 6 ohms or what ever. Maximum power will be transferred into the load (speakers) when the impedance of the amp matches the impedance of the speakers. They don't match you don't get maximum power.

IF you have a 200 watt amp designed to work into an 8 ohm load going to a lower impedance load is not going to get more power out of it in the real world.

Now if and it's a big if, you have a 200 watt amp designed to work into an impedance range of 2 through 8 ohms it's still a 200 watt amp and you just tap off the matching transformer.

You don't normally have an amp that delivers 5 A into an indeterminate load. It'll deliver say 5A into an 8 Ohm load for P=I^2 *R or 25*8 = 200 watts. But that amp is unlikely to be able to deliver more than 5A into a 2 ohm load. Now if you try for a constant voltage where P = E^2/R going to the lower resistance is likely to load down the voltage to well less than what it was at 8 ohms. Besides, you have to have proper impedance matching that will not draw the amplifier section out of the linear portion of it's amplification cycle/curve.

The aforementioned math treats the different loads on an amp as if all remains equal, but it doesn't. A 200 watt amp is a 200 watt amp whether it is *matched* into a 2 ohm load of an 8 ohm load. If you could maintain the voltage across the *LOADs* entire range of impedance then you could get the extra power, BUT it doesn't come for free. You would need a 1600 watt amp to get 1600 watts into that 2 ohm load. You are not going to get it by replacing an 8 phm speaker with a 2 ohm and matching it to the amp.

How about a high quality 6 to 8 ohm transformer if you want a real match although you really don't need one.

[dk]

From a practical approach, most amps are designed at a maximum power at some given impedance, be it 8 ohms or 6 ohms or what ever. Maximum power will be transferred into the load (speakers) when the impedance of the amp matches the impedance of the speakers. They don't match you don't get maximum power.

IF you have a 200 watt amp designed to work into an 8 ohm load going to a lower impedance load is not going to get more power out of it in the real world.
.....

I'm thinking of a push-pull transistor amplifier that is DC-coupled to the speakers.
From the datasheet below, the Onkyo does just that.
From the Onkyo datasheet, the output power vs. speaker impedance is as follows:
3 Ohms 250 Watts
4 Ohms 220 Watts
6 Ohms 170 Watts
8 Ohms 130 Watts

I might be guessing wrong, but I suspect they're not using an output transformer.
I suspect it's a direct-coupled amplifier.