Ok I'm trying to get a HIGH level understanding of Ohm ratings with my receiver, speakers and wires. Heres what I got:

Receiver: Onkyo TX-NR905 (http://onkyousa.com/model.cfm?m=TX-NR905&p=f&class=Receiver)

Power (8ohms 20-20kHz 0.08%) /Ch -
Power (8ohms 20-20kHz 0.05%) /Ch 140W
Continuous 6ohms Rated
Certified 4ohms performance
Speaker Impedance 4 ohms–16 ohms or 6 ohms–16 ohms
Speakers: ProCinema 1000 Plus (http://www.definitivetech.com/loudspeakers/procinema/procinema_1000.html)

Nominal Imp.: 4 - 8 ohms.
Wire:

50 - 60 foot run.


I know nothing about ohms, so please bare with me. :)

1) The receiver has several ohms ratings as you can see. Which one is considered the "ohm load"?

2) Is the ohm output something that is configured on the receiver?

3) Is the ohm output variable or constant?

4) My speakers are rated at 4 - 8 ohms, does this mean they can handle power/ohm load of between 4 - 8 ohms only?

5) What will happen( performace wise ) with the speakers/audio if the ohm load is below or above 4 - 8 ohms?

5) I'm looking at Roger Russels chart and I'm trying to determine which wire options would be suitable for my setup. He specifies "ohm load" in his chart, but I have little understanding of ohms and my receiver has different ohm ratings. I'm a little confused. :confused:

http://www.roger-russell.com/wire/wire.htm#wiretable

Based on the information above what are wire options?.

Thanks

Christopher

1) The receiver has several ohms ratings as you can see. Which one is considered the "ohm load"?

Those specs refer to the impedance (ohms) of the speaker connected to the receiver.

2) Is the ohm output something that is configured on the receiver?

Some receivers have a switch that you can set to different positions when using lower impedance speakers. This switch does not set the ohms per se, but switches on additional circuitry inside the receiver to limit current or voltage to the output stages of the amp. That limiting is intended to keep the receiver from getting too hot when using lower impedance speaker loads.

Some, including myself, recommend to leave the switch in the 8 ohm position regardless of the speaker's impedance.

3) Is the ohm output variable or constant?

There really isn't an "ohm output" in the sense you are thinking. The receiver merely reacts to the impedance of the speakers connected to it. Lower impedance/less ohms of the speakers, the more power the receiver puts out. However, there is a point of diminishing returns for most equipment. Too low of impedance and the receiver/amp may be damaged, although most just overheat and shut down until they cool off.

4) My speakers are rated at 4 - 8 ohms, does this mean they can handle power/ohm load of between 4 - 8 ohms only?

No. That rating is the load the speakers present to the receiver. The receiver will then respond by putting out power according to it's rating for the specified impedance of the speakers. Of course, the receiver does not put out full power all the time. In a most basic sense you control that power output with the volume control somewhere between 0% and 100% of the maximum. The maximum is what the receiver spec says for the impedance of the speakers connected to it.

5) What will happen( performace wise ) with the speakers/audio if the ohm load is below or above 4 - 8 ohms?

Again, the speaker is the load. So, in that respect, nothing happens to the speaker - it is what it is for impedance. Bear in mind that virtually all speakers vary in impedance depending on the frequency of the sound. Don't worry about this right now - that's in course 102, or perhaps 201. ;)

If the speaker is lower impedance, it will present a more difficult load for the receiver. The receiver will try to put out more power at lower impedance and most will to some degree. However, as I mentioned previously, too low of an impedance may damage the receiver or at least cause it to operate hotter and possibly shut down from overheating.

If the speaker is higher impedance, it presents less load to the receiver. The drawback of using higher impedance speakers is that the receiver does not put out as much power. There really isn't any risk in using higher impedance speakers from an equipment standpoint.

5) I'm looking at Roger Russels chart and I'm trying to determine which wire options would be suitable for my setup. He specifies "ohm load" in his chart, but I have little understanding of ohms and my receiver has different ohm ratings. I'm a little confused.

Because the speaker manufacturer has put in that "universal" 4-8 ohm impedance spec, it's just a bit more confusing.

You would be fine using either the 8 ohm recommendations or the 4 ohm recommendations. Use the 4 ohms recommendations if you want to be on the conservative/"safe" side, although it's very UNlikely that you would notice a performance difference either way.

Your receiver rating just tells you whether it'll be able to drive your speakers--which in your case, it will. Your wire choice should be based on the impedance of your speakers. I agree with who: 12-gauge is the safe choice, but 14-gauge is good enough.

Some, including myself, recommend to leave the switch in the 8 ohm position regardless of the speaker's impedance.

Very interesting theory - and this is safe? I am currently using 4 6Ohm speakers on my Yamaha RX-V659, and I have it set to the 6Ohm setting.
If I buy new 8Ohm speakers for my front channels, and I want to intermix them with my old 6Ohm rear channels, I would then be advised to just set the Receiver to 8Ohm then?

I also have a pair of small Cambridge Soundworks satellite speakers, unfortunately I am unsure of their Ohmage. Is there a way to find this out what they are? It is not listed on them. I'm guessing they'd be six or four, but I'm wary to connect them together with 8 Ohm speakers. Or can I just go ahead? They are little 2" table-top thingys from a computer 2.1 system.

I know nothing about ohms, so please bare with me. :)

I think you mean bear with me, as "bare with me" means to display our naughty bits, and I'm not going to do that.

Very interesting theory - and this is safe? I am currently using 4 6Ohm speakers on my Yamaha RX-V659, and I have it set to the 6Ohm setting.
If I buy new 8Ohm speakers for my front channels, and I want to intermix them with my old 6Ohm rear channels, I would then be advised to just set the Receiver to 8Ohm then?

The conservative thing is to follow your user manual or Yamaha FAQ. However as whoaru99 said it is unlikely to cause a problem.


I also have a pair of small Cambridge Soundworks satellite speakers, unfortunately I am unsure of their Ohmage. Is there a way to find this out what they are? It is not listed on them. I'm guessing they'd be six or four, but I'm wary to connect them together with 8 Ohm speakers. Or can I just go ahead? They are little 2" table-top thingys from a computer 2.1 system.

Not a good idea. Most of those PC systems have satellites with no onboard crossover and really dinky drivers. Driven by your receiver you run a good chance of frying the little things or having poor quality sound (or both for a while). However DC resistance is usually a bit less than the nominal impedance, so if you buy or borrow a multi-meter you can measure the resistance across the speaker input terminals or connector (disconnect the speaker first). 8 Ohm speakers usually measure <8 and >6 Ohms. A 6 Ohm speaker should measure <6 but >4 Ohms.

If you were thinking about connecting two speakers to one channel don't bother- it won't sound better. If you are bound to experiment remember that impedance adds in series (8 Ohms + 6 Ohms = 14 Ohms) but in a parallel circuit the resistance decreases (1/8 + 1/6 = 1/0.29 or 3.43 Ohms)

Hello,
Thanks for the answer.

The conservative thing is to follow your user manual or Yamaha FAQ. However as whoaru99 said it is unlikely to cause a problem.
Well, the thing is the manual only says:
"If you are to use 4 or 6 ohm speakers, set "SP IMP." to "6ΩMIN" as follow BEFORE using this unit."
and then proceeds to detail on how to set it to that. Doesn't anywhere mention mixing impedances. Nor does it say anywhere DO NOT set to 6Ω when using 8 ohm speakers.
So I really can't figure it out.

Not a good idea. Most of those PC systems have satellites with no onboard crossover and really dinky drivers. Driven by your receiver you run a good chance of frying the little things or having poor quality sound (or both for a while). However DC resistance is usually a bit less than the nominal impedance, so if you buy or borrow a multi-meter you can measure the resistance across the speaker input terminals or connector (disconnect the speaker first). 8 Ohm speakers usually measure <8 and >6 Ohms. A 6 Ohm speaker should measure <6 but >4 Ohms.
OK, I will bust out the multimeter in the course of the evening.
The Speakers seem to have screwholes, but I cant quite figure out what screwdriver to stick in (they're pretty deep). They are fairly nice speakers actually, not at all like your bog standard computer speakers feel, and the sound is reasonable for a 2" driver in a 3" cube. They were originally used with a subwoofer/amp, but it busted.

If you were thinking about connecting two speakers to one channel don't bother- it won't sound better. If you are bound to experiment remember that impedance adds in series (8 Ohms + 6 Ohms = 14 Ohms) but in a parallel circuit the resistance decreases (1/8 + 1/6 = 1/0.29 or 3.43 Ohms)
No, actually what I was thinking of was attaching the little speakers to the "Zone 2" or "Front Speakers B" output of the receiver, and then placing them on my desk, so I can do some light music listening while working - and since they are so small, they would not take much room.

Well, the thing is the manual only says:
"If you are to use 4 or 6 ohm speakers, set "SP IMP." to "6ΩMIN" as follow BEFORE using this unit."
... Doesn't anywhere mention mixing impedances. Nor does it say anywhere DO NOT set to 6Ω when using 8 ohm speakers.

While each channel has a separate power amplifier circuit, the impedance setting on your receiver appears to be global. In any HT system the mains and center carry most of the water. The demands on the surround channels are relatively brief and light. So a global setting makes sense.

In my system I run 8 Ohm mains and 4 Ohm surrounds and a 6 Ohm center. The US version of my receiver does not have an impedance switch. The full bandwidth, all channels driven power is given for 8 Ohms only. Power into 6 Ohms is at 1 kHz only and only "dynamic" power is given for 3 and 4 Ohms. It has a fairly tight power supply and cannot deliver double the Watts into 4 Ohms.

In actual use even with a 6 Ohm center channel speaker and 4 Ohms surrounds, I've never tripped a protection circuit, nor does the receiver seem to run hotter than with all 8 Ohms loads.

There is no reason to set the switch for 6 Ohm loads when using 8 Ohm speakers. I don't know what circuits are employed but there is a potential for either limiting max output power or introducing a higher noise/distortion level.

OK, I will bust out the multimeter in the course of the evening.
The Speakers seem to have screwholes, but I cant quite figure out what screwdriver to stick in (they're pretty deep). They are fairly nice speakers actually, not at all like your bog standard computer speakers feel, and the sound is reasonable for a 2" driver in a 3" cube. They were originally used with a subwoofer/amp, but it busted.

Try using a flashlight. The screws could be Torx, Phillips, in-hex, square drive or something else. Do you need to open the case because there is not a hard wired cable or because the jack is not standard (mini-phone plug RCA plug or other Radio Shack item)? When you open the speaker if there is a capacitor wired in series with one terminal you have a simple high pass crossover. If there is nothing then you have no crossover. In either case watch the volume levels. That little 2" driver is likely to sound pretty thin. But what the heck its scrap otherwise.
QUOTE]

While each channel has a separate power amplifier circuit, the impedance setting on your receiver appears to be global. In any HT system the mains and center carry most of the water. The demands on the surround channels are relatively brief and light. So a global setting makes sense.

In my system I run 8 Ohm mains and 4 Ohm surrounds and a 6 Ohm center. The US version of my receiver does not have an impedance switch. The full bandwidth, all channels driven power is given for 8 Ohms only. Power into 6 Ohms is at 1 kHz only and only "dynamic" power is given for 3 and 4 Ohms. It has a fairly tight power supply and cannot deliver double the Watts into 4 Ohms.

In actual use even with a 6 Ohm center channel speaker and 4 Ohms surrounds, I've never tripped a protection circuit, nor does the receiver seem to run hotter than with all 8 Ohms loads.

There is no reason to set the switch for 6 Ohm loads when using 8 Ohm speakers. I don't know what circuits are employed but there is a potential for either limiting max output power or introducing a higher noise/distortion level.
So, if I use 8 ohm fronts and center, 6 ohm rears, and (probably) 4 or 6 ohm zone 2 speakers, I should just leave the rec on 8?

And so the 6 ohm speaker will just receive less voltage than but the same current as the 8 ohm, right? - thus having a lower impedance and less wattage? Or how can I picture that technically?

Try using a flashlight. The screws could be Torx, Phillips, in-hex, square drive or something else. Do you need to open the case because there is not a hard wired cable or because the jack is not standard (mini-phone plug RCA plug or other Radio Shack item)? When you open the speaker if there is a capacitor wired in series with one terminal you have a simple high pass crossover. If there is nothing then you have no crossover. In either case watch the volume levels. That little 2" driver is likely to sound pretty thin. But what the heck its scrap otherwise.

Yeah, I will take a closer look once I get my arm out of this sling.
No, the connectors are bog standard speaker wire, the reason why I want to unscrew it is to look for a crossover.

The sound is kind of thin, but for a small form factor background music / talk radio producer it is allright.

EDIT: The multimeter measures around 3 Ohms if my multimeter isn't off...
and looking into the holes on the back doesn't show a screwhead, but rather the back of the screws - the heads are behind the (non-removable) speaker-grill. doesn't look like there's anyway to open these things then.

So, if I use 8 ohm fronts and center, 6 ohm rears, and (probably) 4 or 6 ohm zone 2 speakers, I should just leave the rec on 8?
Yes I think that will be fine.

And so the 6 ohm speaker will just receive less voltage than but the same current as the 8 ohm, right? - thus having a lower impedance and less wattage? Or how can I picture that technically?

We will ignore the fact that speakers are not simple resistive loads (drivers and crossovers have present a load that varies with frequency and changes as the crossover components and speaker voice coil warm up with use). Instead we can treat a speaker with a nominal impedance of 8 Ohms as presenting a constant 8 Ohm load and a 4 Ohm speaker as presenting a 4 Ohm load.

Ohm's Law is what you are asking about. It lays out the relationship between E (electromotive force/Volts), I (current/ Amperes) and W (power/ Watts).

If the load is constant then as voltage increases, both power and current increase. If one is changed the others change. There is a hoary old chart below.

The maximum output power of an amplifier is a function of the voltage and current it can deliver into the load. The amplifier has some maximum voltage it can sustain and some maximum current it can deliver at that voltage. If an amplifier is fully capable into both 8 and 4 Ohms it must deliver twice the power into the 4 Ohms load. Most cannot do this, but that is not in and of itself the sign of a good or bad design.

If you think of a light bulb as the speaker it draws 75 Watts on a 120 Volt line with a current of .625 amps. As it heats up the resistance of the filiment rises to 192 Ohms. If it were an 8 Ohm speaker it would draw 1800 Watts and a current of 15 amps (a household lighting circuit) or lesser amount sufficient to burn out the voice coil.

So for 100 Watts into 8 Ohms we can calculate both the current and the voltage in several ways. For example
A= sq rt of (W/R)
A = sq rt (100/8)
A= sq rt (12.5)
A = 3.5 Amperes

V= A x R
V= 12.5 x 8
V= 100 Volts

For a 4 Ohm load at 100 Watts--
A= sq rt (100/4)
A= sq rt (25.0)
A= 5 Amperes

V= A x R
V= 5 x 4
V= 20 Volts

As the load resistance drops the voltage needed drops, but the current goes up. Autos have 12 volt systems able to sustain high currents and that is why 4 Ohm speakers were often used in cars, and most auto radios only developed about 3 Watts.

Generally speaking however it costs more to design and build a home amp that is fully capable at low output impedances, so most units are aimed at the nominal 6/8 Ohm speaker, but will happily drive 4 Ohm loads. Loads below 4 are difficult for many and impossible for most to drive.

http://www.the12volt.com/ssi/getimage.asp?imgFN=ohmtable.gif

Hello trekguy,

Thank you for the very elaborate answer.
Here is a little anecdote:
A friend of mine had a New Year's eve Party, and a Yamaha 2 channel amp was used to power four 8 Ohm speakers to provide music.
Due to oversight the Amp had been set to the "min 16 Ohm when using 4 speakers" setting, which was appropriate for powering two 8 Ohm speakers.
After several hours the overheat protection shutdown kicked in.

Do you think this was accelerated by powering lower Ohm speakers than the Amp was set for?

And another question.
I was thinking (does anyone else feel they can think best in the shower??) and I had the idea, would it be possible to run a 1.4:1 transformer between the amp and the 4 Ohm speakers as to make the amp see them as a 8 Ohm load? Or would this just further contribute to mismatching / messing up the sound?

Thanks