Questions about Ohms.

[ouimetnick]

Simple quick question here... well I have a few.
My receiver (Yamaha HTR-6230) has a few options. You can choose 6Ω Minimum or 8Ω Minumum? why not have it be JUST 6Ω min?

When it says 6Ω this means you can use speakers that are rated 6Ω or higher. So 8Ω, or 16Ω would be fine? If so, they why also say 8Ω minimum?

Also lets say you have a 4Ω speaker, connected to an amp that drives 6Ω or 8Ω, would that damage the speaker, or the amplifier? From what I gather, the 4Ω speaker would draw 4x more current (??wattage??) at the same volume?

What if you connected 16Ω speakers to an 8Ω amp? Would that hard the speaker, and not the amp, or would it be okay? Or more commonly, a 4Ω amp driving an 8Ω speaker?

Perhaps the most obvious question, is why so many different ohms? Car Audio has 2Ω, Subwoofer amplifiers, and some receivers use 4Ω or 6Ω, HiFi receivers use 6Ω, 8Ω or 16Ω.

Why doesn't everybody use ONLY 4Ω, or 8Ω? Why do companies decide what to do? Using one ohm rating like 4Ω would simplify everything. I'm sure there is a reason though.

Please explain and educate me on this topic.

 

[Jon_Logan]

The "6 ohm" setting will give you the best reliability. The "8 ohm" setting will give you the most output power. The ball is in you're court. Me? I'd go with the "6 ohm" setting, because, it looks like, Yamaha didn't make that one too robustly.

Either setting will drive any functioning speaker.

 

[ouimetnick]

The "6 ohm" setting will give you the best reliability. The "8 ohm" setting will give you the most output power. The ball is in you're court. Me? I'd go with the "6 ohm" setting, because, it looks like, Yamaha didn't make that one too robustly.

Either setting will drive any functioning speaker.

You mean the receiver is not robustly, or the setting on 8Ω isn't? Also, the specs say 100 Watts per channel. I checked and checked, and it seems that on 6Ω or 8Ω you still get 100W?

I thought the less Ω means less resistance, so 6Ω would give you more power?

Also, do you know the answers to driving a 8Ω speaker with a 4Ω amp? What will that hurt? The speaker or amp?

From what I gather, driving say a 4Ω speaker with a 8Ω amp, will cause the amp to run hotter as it is drawing 4x more current, and at high volumes, destroy the amp?

 

[dumptruck]

If a speaker was simple like a resistor, then it would make sense to have a standard, but they aren't. Almost all drivers (the individual speakers on their own) have an impedance that varies a great deal depending on the frequency, and that interacts in a complex way with the whole system of driver, cabinet, crossover, and amplifier to determine the overall performance characteristics. You can imagine that when you are actually designing a speaker, there are a lot of trade offs and various concerns that lead to ending up at this or that nominal impedance.

The impedance spec that you see on loudspeakers and amps functions as kind of a guideline that lets you know if your amplifier will handle it well. It is not any sort of exact figure, except in very rare cases. You can also use it in combination with your amp's specs and the speaker sensitivity rating to approximate what volume level you can reach.

As for your receiver, I actually have no idea what that setting does, except that one way or another it's limiting itself to allow speaker impedance that dips below 8 ohms.

 

[Jon_Logan]

Typically, the 4/8 ohm or whatever setting switches in a different set of transformer secondary windings. The higher voltage winding are supposed to be for when the higher impedance speakers are used.

What makes amplifiers break is high current through the output transistors and high voltage across them. If a lower impedance speaker is connected, the current demand goes up. If you keep a high voltage across the output transistors, they are that much closer to dangerous territory. So one solution is to lower the voltage across the output transistors if a lower impedance speaker is connected. Yamaha chose to do this on your unit.

Another approach would be to add more output transistors so the higher current is shared amongst more transistors. That is a more costly approach, however.

 

[ouimetnick]

Typically, the 4/8 ohm or whatever setting switches in a different set of transformer secondary windings. The higher voltage winding are supposed to be for when the higher impedance speakers are used.

What makes amplifiers break is high current through the output transistors and high voltage across them. If a lower impedance speaker is connected, the current demand goes up. If you keep a high voltage across the output transistors, they are that much closer to dangerous territory. So one solution is to lower the voltage across the output transistors if a lower impedance speaker is connected. Yamaha chose to do this on your unit.

Another approach would be to add more output transistors so the higher current is shared amongst more transistors. That is a more costly approach, however.

So if I'm driving 8Ω or higher speakers, it doesn't matter if I chose 8Ω min or 6Ω min? And thats true with all amplifiers/receivers? You can use a higher or equivalent Ω rating with an amp with out any issues?

 

[Betomon]

So if I'm driving 8Ω or higher speakers, it doesn't matter if I chose 8Ω min or 6Ω min? And thats true with all amplifiers/receivers? You can use a higher or equivalent Ω rating with an amp with out any issues?

You can chose either setting to drive 8 Ohm speakers with. And it just depends on what the amplifier/receiver is rated at. If it is rated for 4 Ohms, then it will be able to handle 4, 6, 8 etc, but not any lower than 4. So if your amp is rated at 6 Ohms minimum, then it would be detrimental to it if you drive 4 Ohm speakers with it (or lower).

 

[ouimetnick]

You can chose either setting to drive 8 Ohm speakers with. And it just depends on what the amplifier/receiver is rated at. If it is rated for 4 Ohms, then it will be able to handle 4, 6, 8 etc, but not any lower than 4. So if your amp is rated at 6 Ohms minimum, then it would be detrimental to it if you drive 4 Ohm speakers with it (or lower).

Okay. so to simplyfy, using speakers with a higher impedance (higher Ω rating) than the amp that is driving them, is fine for the receiver/amplifier. HOWEVER using a speaker that has a lower impedance than the amp that is driving it will cause strain on the amp.

 

[Betomon]

Also lets say you have a 4Ω speaker, connected to an amp that drives 6Ω or 8Ω, would that damage the speaker, or the amplifier? From what I gather, the 4Ω speaker would draw 4x more current (??wattage??) at the same volume?

What if you connected 16Ω speakers to an 8Ω amp? Would that hard the speaker, and not the amp, or would it be okay? Or more commonly, a 4Ω amp driving an 8Ω speaker?

Please explain and educate me on this topic.

The lower the resistance does mean more power gets across (because of less resistance) but not without costs: if you have lower resistance, the amp has to be able to take the added load on it. Since more power is running to the speaker, more is also coming back to the amp, and if it is not designed to handle the extra heat and stress, it will blow.

 

[Betomon]

Okay. so to simplyfy, using speakers with a higher impedance (higher Ω rating) than the amp that is driving them, is fine for the receiver/amplifier. HOWEVER using a speaker that has a lower impedance than the amp that is driving it will cause strain on the amp.

Yes. :yes:

 

[nick12345]

Using 8Ω speakers on a 4Ω amp won't do any harm at all. Using 4Ω speakers on an 8Ω amp will damage the amp at high volumes. Most have some form of protection in case this happens.

 

[ouimetnick]

Yes. :yes:

I find it odd that Yamaha even made that option then. Why not say 6Ω minimum impedance?

Now how come subwoofers typicaly use 4Ω or 6Ω, and home theater receivers use 8Ω, and cars use 2Ω? Whats wrong with a subwoofer being 8Ω and its plate amp being 8Ω?

 

[ouimetnick]

And one more thing.

Lets say

100W at 8Ω
This means MORE wattage at 4Ω
Possibly

200W at 4Ω?

Another example

100W at 4Ω would mean less wattage at 8Ω

Possibly

50W at 8Ω

However the first example comes with the risk of damaging the receiver.... even though there is more wattage. correct?

 

[woodj]

What dumptruck said + the thing that muddies the waters is that some amplifier outputs have a range of allowable outputs that represent the lowest (or somewhere nearest) impedance that the amplifier should see across those particular outputs.
The listed impedance of the speaker indicates what the nominal impedance of the speaker is.
So across 16 ohm outputs, you should have a device around 16 ohms impedance and 8 for 8 and 4 for 4.
When you get to 6 ohm devices, unless there is a 6 ohm output, it should (notice I said should, not would) be safer on the 4 ohm output, since it (theoretically) would present a slightly higher load than designated on the amp.
Thing is all amps are not created equal, and some are affected in different ways.

 

[ouimetnick]

What dumptruck said + the thing that muddies the waters is that some amplifier outputs have a range of allowable outputs that represent the lowest (or somewhere nearest) impedance that the amplifier should see across those particular outputs.
The listed impedance of the speaker indicates what the nominal impedance of the speaker is.
So across 16 ohm outputs, you should have a device around 16 ohms impedance and 8 for 8 and 4 for 4.
When you get to 6 ohm devices, unless there is a 6 ohm output, it should (notice I said should, not would) be safer on the 4 ohm output, since it (theoretically) would present a slightly higher load than designated on the amp.
Thing is all amps are not created equal, and some are affected in different ways.

? So a 6Ω amp would be safer driving a 4Ω speaker? Also, from what I understand, a 4Ω amp will not have any strain provided you have the amp drive 4Ω or greater (8Ω,16Ω etc)

But the more Ohms, the more resistance. So an 8Ω speaker has more resistance that a 4Ω one. So wouldn't a 4Ω amp be strained driving an 8Ω speaker as the 8Ω has more resistance. Like 8Ω pushing against the 4Ω?

i'm not sure.

 

[dumptruck]

You had the basic idea way up there: use speakers of equal or higher impedance rating to the amp. There is no "4-ohm amp", only amps that are rated to handle as low as a 4-ohm load, and amps that aren't. Yes you get less power as speaker impedance goes up, but less power does not equal strain - more power does. You would go into clipping at lower power on, say a 16-ohm speaker, but you will find 16-ohm speakers are usually very high efficiency, so it balances out. It's a little more complicated with tube amps, but lets skip that.

 

[ouimetnick]

You had the basic idea way up there: use speakers of equal or higher impedance rating to the amp. There is no "4-ohm amp", only amps that are rated to handle as low as a 4-ohm load, and amps that aren't. Yes you get less power as speaker impedance goes up, but less power does not equal strain - more power does. You would go into clipping at lower power on, say a 16-ohm speaker, but you will find 16-ohm speakers are usually very high efficiency, so it balances out. It's a little more complicated with tube amps, but lets skip that.t.

My powered subwoofer is rated at 4Ω.

I thought if I had lets say a 8Ω amp, it can handle 8Ω or greater (meaning 16Ω)

And the subwofer amp I have must be rated 4Ω or less (maybe 2Ω?) to handle a 4Ω speaker, correct?

 

[dumptruck]

That is the rated power output into 4-ohms at 0.15%THD. There is a rated power output into 8-ohms at 0.15%THD too, but they did not publish it, presumably because it came with a 4-ohm woofer so that's the only spec that matters.

 

[MOPAR3]

Here's my take on speakers and resistance. Low ohm speakers,4ohms and down are current driven speakers. 8 ohms and up are voltage driven speakers. In a car system they tend to use 4 and 2 ohm or less speaker systems because theres alot of current availble but with a low voltage. At home with 125 volts availible at the outlet 8 ohm and up speakers make better sense. The bottom line is the least amount of power supply components in an amp make it cheaper and easier to build. In a car you have to use a bunch of mosfets to step up voltage if you want to drive high voltage to 8 ohm speakers. At home you need a large transfomer and a bunch of caps to drive high current into low ohm speakers.

 

[ouimetnick]

That is the rated power output into 4-ohms at 0.15%THD. There is a rated power output into 8-ohms at 0.15%THD too, but they did not publish it, presumably because it came with a 4-ohm speaker so that's the only spec that matters.

What does all the0.15%THD stuff mean? THD=Total Harmonic Distortion?

So 75 watts at 4Ω at 0.15% Total Harmonic Distortion?

Whats all that about?

Sorry guys. I'm only 15. We don't learn this stuff in Engineering... well at least not yet.