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The Ohm matching game

Raphaz

Raphaz

AK Subscriber
Subscriber
I’d like to learn a bit more about the Ohm matching of amps/receivers and speakers.

Is it always better to match recommended Ohms for amplifier and speakers?
I understand that an 8 Ohm amp or receiver has to work harder to drive 6 Ohm speakers than 8 Ohm speakers — I guess that also means that the stated sensitivity values for the speakers go down.

What happens if I drive 6 Ohm speakers with a 4 Ohm receiver or amp?
 
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"What happens if I drive 6 Ohm speakers with a 4 Ohm receiver or amp?"

You hear music!, and amp runs cooler. An amp rated for lower ohms than the speakers ohm rating is fine.

My rule is to only run my 4 ohm speakers with an amp that is rated for 4 ohm speakers in the user manual i.e., it has a RMS rating in watts for 4 ohm speakers. The RMS rating is for a continuous load. Crutchfield has amps that are described as "4 ohm capable", but some do not have a 4 ohm RMS rating, so I would not use them because the amp will run hotter. And some mfg will give a 4 ohm RMS rating for their amp, but will not give the THD when driving the 4 ohm load, though they will give the THD for an 8 ohm load. The reason being is the THD "can" increase when driving lower ohm speakers.
 
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With modern transistor gear you don't have to "match" anything. The output impedance of the amplifier is practically zero, however, there's usually a lower limit to the impedance it is safe to drive. If the amplifier is claimed safe to drive 4 ohms, any impedance above 4 ohms is safe. If driving a higher impedance than 4 ohms, the amp won't be able to deliver the same power as it would into 4 ohms, but it will be safe.
Valve (tube) amplifiers with an output transformer are different beasts. They'll often have a 4 ohm output and an 8 ohm output, and you should use the output which is closest to the impedance of the speakers. Of course, the speaker impedance is just a nominal figure anyway and an "8 ohm" speaker may be as low as 4 ohms at some frequencies and as high as (maybe?) 30 ohms at others. I think there's a DIN standard as to how the nominal figure is determined, but I don't think the standard is rigorously applied.
 
Generally speaking all you need to know is the minimum impedance rating for the amp in question, It is usually marked on the back of the reciever or amp near the speaker terminals. As long as it's lower the the nominal impedance often marked on the back of the speaker your good.

This applies to Solid State amplifiers.

Tube amps often have multiple taps on their output transformers. You want to choose the tap that is closest to the speakers nominal impedance.
 
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Back in the day we always matched in put and output impedances to get the best energy transfer and fewer resonances. Be it a phone line or audio line. As amplifiers have to help control speaker drivers the idea is to have a very low generating impedance or source impedance to prevent the back EMF created by the speaker influencing the source. The back voltage if it has a shorting load from the source the driver is less likely to ring or over shoot the desired displacement. When the AR-1 and AR-3 were first introduced the designer felt amps should have a 4 ohm generating impedance which would allow the acoustic suspension woofers to be more dynamic as some consumers felt that AR speakers did not have the dynamic capability horn loaded speakers had at the time.
 
My speakers are 6Ω nominal and I'm using the 4Ω output on my tube amp. My Yamaha RX-A2080 also has an Ω selector on initial setup which I set to 4.
 
Depending on the current capability of the amp you either choose the 4 ohm tap for marginal amps or the 8 ohm tape if they have plenty of reserve. A Mcintosh MC 240 is capable of 55 watts per channel at rated distortion. The older 275's were capable of close to 95 watts meeting factory specs. The new 275's have even better capabilities and better signal to noise ratio. My favorite Mac tube amp was the MC 3500 MK I which was rated at 350 watts but could reach close to 480 watts before clipping while meeting specs. Its not only the design of the tube circuits but the great output transformers that no other tube manufacturer has been able to equal. In other words you get what you pay for. Mcintosh is a life time investment. Acuphase is, too but they are all SS.
 
Thank you all.

To clarify:
The receiver that currently gets the most playing time in my system is the R-2000. It’s not tubes, it’s an SS with a unique "X" Power Amplifier circuit and has a stated 8 Ohm matching impedance and 150 WPC. But recommended speaker impedance according to the user guide is anywhere between 4 and 16 Ohms. I like the sound (but not so much the maintenance).
It currently powers a pair of Q500 and a R-112SW sub which I believe has 300 RMS (600 peak). I can’t find its Ohm ratings (probably 8 Ohm) but since it’s active it may not matter. The sub is connected to the R-2000’s pre out.
There’s also a Wiim Pro+ connected to the receiver to power wireless, powered remotes — but that’s probably not relevant.

I’m looking to get other main speakers with better sensitivity and more room filling capabilities (long story, I started a conversation about that in another thread). That’s when the Ohm matching question came up.

Either way, according to the posters above I gather that if I keep the R-2000 (which I will for now) it’s best for me to aim for 8 Ohm (or higher, which is rare) speakers. Is that correct?

And I’m assuming Ohm matching would even be more important when more than one (passive) speaker pair was used?
 
Wanted to add: I believe there’s no Ohm switching option on the R-2000.

A MC (as mentioned above) would be great if I had the budget for a really good vintage model with low maintenance and easy repair (should it be needed at some point).
I do not trust the newer MC models and support under Bose management and I don’t want to spend that kind of money on a closed all-on-one-board kind of circuit that would need to be replaced as a whole if something fails, and the board and parts may not be available when that happens. I had a lengthy discussion with my repair guy… Also, for now, for similar reasons, I’d like to keep DAC, wireless transmitters and such separate from the receiver/amp as that technology still evolves.
Besides I like the sq of my R-2000 a lot — when it works properly up to original specs it sounds amazing. Mine needs repair again now and I want to give it one more chance, hoping that I get it to work without issues for a couple more years. If not, I’m not sure what I’d replace it with. But that would be a discussion for another, separate thread.
 
My 4 ohm speakers really came alive at lower volumes when I got a Marantz Model 50 integrated amp that is rated for 4 ohms, or with my old Proton D540 with twin power supplies and Bass EQ turned on, it was not rated for 4 ohms and ran hot, so hot I got a pancake fan for it and that kept it cool.

The current KEF Q500s are 8 ohm speakers, so you should be fine if your Yamaha R-2000 is working properly. But given it is from the early '80s, it could turn into a money pit.

As for new speakers, that sound better, yes I would stick with 8 ohm speakers if you want to stay with the R-2000.

The Q500s only have one 5-1/2" woofer, that is really small. My EPI A500s have a 10" woofer in comparison and two 12" passive bass radiators, and that definitely puts out great bass. You have an active sub which should fill in for the speakers lack of bass. I have never used a sub, never felt the need with my speakers. You may want to try speakers that have bigger woofers, without the need for a sub, and see how they sound for you.
 
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rothwellaudio said:
(...) I think there's a DIN standard as to how the nominal figure is determined, but I don't think the standard is rigorously applied.
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Yup, DIN-compliant determination of loudspeaker impedance (alias Scheinwiderstand in German) was part of the content of the DIN 45573 (of which I don't have a copy, though). Whereas the paragraph on speaker impedance in the DIN45500 only demands, that the actual impedance at any frequency within the nominal frequency range (= Übertragungsbereich) may not drop below the nominal impedance (determined according to DIN 45573) by more than 20 % - with the lower and upper limit of the Übertragungsbereich being the frequencies, at which the response drops to -8 dB relative to an average line of the response between 100 Hz and 4 kHz.

Greetings from Munich!

Manfred / lini
 
Hallo Manfred/lini,

What can I say! Hoch lebe die Welt der Deutschen Industrie Normen! (Schein)widerstand zwecklos.

Thank you.
 
Sandman1221 said:
My 4 ohm speakers really came alive at lower volumes when I got a Marantz Model 50 integrated amp that is rated for 4 ohms, or with my old Proton D540 with twin power supplies and Bass EQ turned on, it was not rated for 4 ohms and ran hot, so hot I got a pancake fan for it and that kept it cool.

The current KEF Q500s are 8 ohm speakers, so you should be fine if your Yamaha R-2000 is working properly. But given it is from the early '80s, it could turn into a money pit.

As for new speakers, that sound better, yes I would stick with 8 ohm speakers if you want to stay with the R-2000.

The Q500s only have one 5-1/2" woofer, that is really small. My EPI A500s have a 10" woofer in comparison and two 12" passive bass radiators, and that definitely puts out great bass. You have an active sub which should fill in for the speakers lack of bass. I have never used a sub, never felt the need with my speakers. You may want to try speakers that have bigger woofers, without the need for a sub, and see how they sound for you.
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8 Ohm they shall be. And yes, slightly larger woofers and maybe horns or waveguides for the tweeters; definitely better sensitivity, and then placing the speakers higher up.

You’re right, the R-2000 becomes a bit of a money pit. But go find me something that sounds equally good when it works.
Mine was just fully serviced a couple weeks ago, should be up to specs (and I think he fixed something on the relay/rail for the X power, not sure). But there’s that brown noise again. Wonder if it’s the STK IC or defective terminals. At least for this round Ernesto honors his service warranty. Fingers crossed.
 
Raphaz said:
8 Ohm they shall be. And yes, slightly larger woofers and maybe horns or waveguides for the tweeters; definitely better sensitivity, and then placing the speakers higher up.

You’re right, the R-2000 becomes a bit of a money pit. But go find me something that sounds equally good when it works.
Mine was just fully serviced a couple weeks ago, should be up to specs (and I think he fixed something on the relay/rail for the X power, not sure). But there’s that brown noise again. Wonder if it’s the STK IC or defective terminals. At least for this round Ernesto honors his service warranty. Fingers crossed.
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Marantz Model 50 will sound better!, it will easily drive 4 ohm speakers, and it has a remote. No tuner though, just an all analogue integrated amplifier. And no repair issues for 20 years or more! All electronic controls and switches, no more crackling Volume potentiometer!
 
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I have some Panasonic and SONY speakers that came with one of those plastic 'all in one' bookshelf stereos. You know....the ones that look like alien spacecraft? Anyway, I tried to measure the ohms on those, and the multimeter would not even respond. Is that because they are 2 ohms or less??
 
Raphaz said:
...What happens if I drive 6 Ohm speakers with a 4 Ohm receiver or amp?
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Nothing has changed when you asked a variation of the same question a few weeks ago in your other thread post #63

Upgrading from KEF Q500

That’s what I do already. Thank you.
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Try not to over think this, about a year or so ago there was a newer member and despite all the great explanations, info etc he was adamant that he needed to have specifically a 6ohm receiver.

My understanding is there are very few amps/receivers that were specifically designed as only a "4 Ohm" amp or "6 Ohm" receiver.

As you're already aware of per post #64 in the above mentioned thread A lot of manufacturers would note in their manuals, usually under "Power Output" what they're were rated at for say Primarily 8ohms and 4ohms
 
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Raphaz said:
8 Ohm they shall be. And yes, slightly larger woofers and maybe horns or waveguides for the tweeters; definitely better sensitivity, and then placing the speakers higher up.

You’re right, the R-2000 becomes a bit of a money pit. But go find me something that sounds equally good when it works.
Mine was just fully serviced a couple weeks ago, should be up to specs (and I think he fixed something on the relay/rail for the X power, not sure). But there’s that brown noise again. Wonder if it’s the STK IC or defective terminals. At least for this round Ernesto honors his service warranty. Fingers crossed.
Click to expand...
Get a Yamaha CR-2040. One of Yamaha's best sounding receivers
 
gizzyman47 said:
Get a Yamaha CR-2040. One of Yamaha's best sounding receivers
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I wouldn’t mind a good deal for a CR-2040 in good shape. It’s been on my radar for a while. It’s an outstanding receiver, looks great, has meters and maintenance should be easier. I’d be sacrificing power and headroom, though, it’s hard to beat that X-Processor. Also, I’m suspicious that I’d prefer the sound of the R-2000 slightly over the CR-2040 (I imagine the latter to sound a tad warmer, a bit more tube-like when compared, but I could be wrong, I haven’t heard one yet).

For now I’ll get the R-2000 repaired again and hope that it’ll hold up for a bit longer.

Doesn’t belong in this thread but since it came up: Are there some simple moves worth the investment/time to improve the reliability of the R-2000 so that it requires less repair and maintenance? Is there a substitute for the STKs? Better heatsink? Better transformers, capacitors, speaker terminals? What should I ask my repair/service guy to look into (that he hasn’t already)?
 
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