Bi/tri-amping stereo speakers with a 5.1/7.1 receiver

[anm]

Confused again!?!?
I thought receiver makers publish 4ohm ratings because that has higher power ratings.

For example 3490 has

120 Watts per channel, 20Hz – 20kHz,
@ <0.07% THD, both channels driven into 8 ohms
150 Watts per channel, 20Hz – 20kHz
@ <0.2% THD, both channels driven into 4 ohms

They could publish a 4 ohm rating and a 2 ohm rating if they wanted to. But those ratings would come with significantly lower power ratings as well since most receivers aren't designed with high current output stages. People don't buy low power ratings. They have been trained by the industry to want more and more power. In other words, because the manufacturer chooses not to publish 6 ohm specifications does not mean the product can't handle 6 ohm nominal impedances. In fact, it can do so with ease.

 

[fmw]

OK, I'll dig into that for you. lower impedance loads draw more current that higher impedance loads. What that means is that more power is required to reach a given volume level with a lower impedance load since power increases as current increases with all other things being equel. So as long as you haven't exhausted the power supply's ability to deliver current, you will see a higher power figure with lower impedances. But when you reach the power supply's limit, then it's all over. Then you get distortion, overheating, broken piston rods, snapped tree limbs and general unhappiness.

Receiver power supplies are not high current types for reasons of economy. If you want to use them with lower impedances than those for which they were designed then you need to operate them at lower power settings. Your 100 watt amp may fall apart at full output into a 4 ohm load. But at 15 or 20 watts, as an example, it may do just fine. So, even though, power would increase at a given volume level with lower impedance, you may reach the power supply's limit well before reaching full power. So you would see amplifier stress at a lower power setting than you would with a high current amplifier. So that 8 ohm 100 watt amplifier may poop out at 20 watts into 4 ohms and that, in effect, would become the real power rating in my book. And 20 watts may well be plenty to drive a home audio system.

High current designs will increase maximum power in watts as impedance drops. Lower current designs simply won't go far enough to reach maximum rated output at low impedances without becoming stressed.

I admit my initial statement was designed to be simple moreso than complete and so was this one. But perhaps this will help explain what I meant.

 

[PENG]

So that 8 ohm 100 watt amplifier may poop out at 20 watts into 4 ohms and that, in effect, would become the real power rating in my book. And 20 watts may well be plenty to drive a home audio system.

The amp won't poop out at 20W into 4 ohms. Mathematically, everything else being equal, 100W into 8 ohms will get you 50W into 4 ohms if you keep the current the same. So half the impedance, half the power. To keep power the same at 4 ohms, the amp has to output approximately 1.414 (square root of 2) times, or 41.4% higher current. If the amp can output double the current into 4 ohms (half of 8 ohms), then it can double the output to 200W, so called 'double down'.

 

[fmw]

The amp won't poop out at 20W into 4 ohms. Mathematically, everything else being equal, 100W into 8 ohms will get you 50W into 4 ohms if you keep the current the same. So half the impedance, half the power. To keep power the same at 4 ohms, the amp has to output approximately 1.414 (square root of 2) times, or 41.4% higher current. If the amp can output double the current into 4 ohms (half of 8 ohms), then it can double the output to 200W, so called 'double down'.

You are talking about amps that are stable at 4 ohms. I'm talking about amps that are not.

 

[anm]

what would you say about this particular stereo receiver/ amp - 3490 for which I posted the specs?

It does mention a 4 ohm rating, and also says has a high current design:

• High-current capability, ultrawide-bandwidth amplifier design with
low negative feedback
• All-discrete amplifier circuitry

High Instantaneous Current Capability (HCC): ±45 Amps

 

[PENG]

You are talking about amps that are stable at 4 ohms. I'm talking about amps that are not.

Yes I am talking about amps that are stable into 4 ohms, such that it will deliver the same current, but at half the voltage into half the impedance, and half the power.

I kow you know the formula but for clarity they are:

P=V^2/R, or P=I^2*R, also for clarity I use R (resistance) instead Z (impedance) to avoid the power factor confusion.

Also the famous V=I*R

So if that 100W amp is stable with an 8 ohm load,

It has to output =sqrt(100*8) or 28.28427V into the 8 ohms load and the current=V/R=28.28427/8=3.5534A.

Now if you lower the resistive load to 4 ohms, while keeping the same voltage, the current will double and most amp will become unstable, but if you turn the volume down so that the output is halved to V=28.28427/2=14.142135V, then

current=14.142135/4 or 3.5534A, same as before.

Power=I^2*R (or you can use V^2/R to get the same result)=3.5534^2*4=50W

Again, if that 100W amp is stable driving an 8 ohm load, there is no reason for it to become unstable when driving a 4 ohm load up to 50W as long as you turn the volume down to the point where the voltage is half of what it is when driving the 8 ohm load.

That being said, the simple calculations I used are for a load resistance. In the real world, the impedance of a speaker as well as the phase angle that the current lags or leads the applied voltage will fluctuate with frequency so it is possible that your example amp will in fact become unstable when driving a speaker rated 4 ohm nominal.

We may want to keep in mind that while the definitions of 'nominal impedance' are not clear, there is a IEC guideline apparently.

According to an article in this linK (http://www.epanorama.net/documents/audio/speaker_impedance.html):

"The IEC standard (IEC60268-3) allows any "increase" above the rated value, but limits the "decrease". The standard does not allow the impedance to fall below the 80 % of the nominal value at any frequency, including DC."

I think we are on the same page but I am actually trying to clarify some relevant points for anm. I know in doing so I may confuse him.

 

[PENG]

Confused again!?!?
I thought receiver makers publish 4ohm ratings because that has higher power ratings.

For example 3490 has

120 Watts per channel, 20Hz – 20kHz,
@ <0.07% THD, both channels driven into 8 ohms
150 Watts per channel, 20Hz – 20kHz
@ <0.2% THD, both channels driven into 4 ohms

It is rated for 4 ohms but I (my own subjective opinion) would not consider it a high current amp because its 150W 4 ohm rating indicates that it cannot even deliver the same current that it would into 8 ohms, let alone a higher current that a 4 ohm load would demand. If it could in fact maintain the same current (not higher), it would have been rated 170W

Again, it is rated for 4 ohms but the spec clearly tells you not to exceed the continuous rating of 150W. So keep in mind if you use it with 4 ohm speakers, everything else (e.g. when compared to 8 ohm speaker with the same sensitivity) being equal you will get lower SPL. As long as you can accept these facts, then go ahead and enjoy it.

 

[PENG]

what would you say about this particular stereo receiver/ amp - 3490 for which I posted the specs?

It does mention a 4 ohm rating, and also says has a high current design:

• High-current capability, ultrawide-bandwidth amplifier design with
low negative feedback
• All-discrete amplifier circuitry

High Instantaneous Current Capability (HCC): ±45 Amps

Please see my response to your early post but I want to add here that a high current amp should not only has a robust power supply that can deliver the current that the load demands even when the impedance of the load dip belows its so called nominal value. Such amps must also have robust amp sections that can handle high currents. If not the output transistors will melt down or the protective circuit will shut them down to save them. Based on their published specifications and many lab measurements on their older models such as the 330, 630, I have the feeling that they tend to have decent power supplies in them but their power amp sections seemed current limited relatively speaking.

 

[fmw]

Please see my response to your early post but I want to add here that a high current amp should not only has a robust power supply that can deliver the current that the load demands even when the impedance of the load dip belows its so called nominal value. Such amps must also have robust amp sections that can handle high currents. If not the output transistors will melt down or the protective circuit will shut them down to save them. Based on their published specifications and many lab measurements on their older models such as the 330, 630, I have the feeling that they tend to have decent power supplies in them but their power amp sections seemed current limited relatively speaking.

Depending, of course, on the power level used. All this stuff relates to full power measurements. We don't run our amplifiers at full power. At least 99% of us do not.

 

[fmw]

Again, it is rated for 4 ohms but the spec clearly tells you not to exceed the continuous rating of 150W. So keep in mind if you use it with 4 ohm speakers, everything else (e.g. when compared to 8 ohm speaker with the same sensitivity) being equal you will get lower SPL. As long as you can accept these facts, then go ahead and enjoy it.

That was precisely my point. And more importantly, almost nobody gets anywhere near running 150w output from a power amp in a home. Amps are overpowered for many reasons. Low impedance loads are just one of them.

And no, you won't get a lower SPL because most of us do not listen to our audio systems with full power and sit there with hearing protectors. Please, let's try to get past the audio babble and deal with real life situations and common sense.

 

[PENG]

And no, you won't get a lower SPL because most of us do not listen to our audio systems with full power and sit there with hearing protectors. Please, let's try to get past the audio babble and deal with real life situations and common sense.

You are entitled to your opinion but I assume know the difference between audio babble and science. In this hobby, what most people do may not be suitable for certain people. May be most people don't listen to anything that has more than 10 dB dynamic swings but there are people who do. Now, that's my opinion only and I certainly don't expect you to agree, or disagree.

 

[fmw]

I wasn't suggesting the audio babble was inaccurate. I was just suggesting that doesn't relate to real life home audio use. The consumer audio business is filled with truths that come from pro audio. Some of them are meaningful in home audio and some are not.

There are people who have home theaters as large as commercial theaters but not many. For the most part, we can ignore amplifier power in the vast majority of home installations. The reason is that the equipment is basically overpowered for its intended application. I'm not suggesting that overpowering is a bad thing. I'm just suggesting that consumer audio enthusiasts make way too much of amplifier performance.

I grew up in the days when a 15 watt per channel tube amp was more than adequate for home audio. Even to this day a 15 watt per channel tube amp would serve just fine in my own home theater to drive the mains. I have a powered subwoofer and that's what really needs the power. The mains don't need it in my 20X24 listening room with speakers of average efficiency. I know that because I have a recording wattmeter connected to one of my mains. So do we need 100 watts per channel? Almost every time I can say no. There are some unusual applications that would require it but not many. Not many at all. Yet audiophiles tend to assume worst case when worst case almost never occurs. It is a bit of a sore point with me and apologize if I raised your hackles.

 

[beemer_cruisin]

Hey, I've been reading through this thread and I have a somewhat related question. I just purchased an HK AVR 354 and a pair of Klipsch RF-82s. I wanted to bi-amp the speakers but I cannot find anything in the manual about bi-amping. Does anyone have any recommendations on which speaker outputs/sound setting that I should use in the 354 to hook up the speakers? Or is there a bi-amp setting in the receiver that I missed? Just wanted make sure that I don't damage the speakers by hooking them up wrong.

Thanks

 

[PHANofPHUNK]

fmw...

you are an audio nut!

 

[fmw]

Hey, I've been reading through this thread and I have a somewhat related question. I just purchased an HK AVR 354 and a pair of Klipsch RF-82s. I wanted to bi-amp the speakers but I cannot find anything in the manual about bi-amping. Does anyone have any recommendations on which speaker outputs/sound setting that I should use in the 354 to hook up the speakers? Or is there a bi-amp setting in the receiver that I missed? Just wanted make sure that I don't damage the speakers by hooking them up wrong.

Thanks

Don't waste your time or your wire. It won't make any difference. All the amps in your receiver are driven by the same power supply. You can't get any more power from the supply than it can put out no matter how many amps you use. And, obviously, more power isn't likely to make any difference if you could get it.

 

[fmw]

you are an audio nut!

I guess I am. I grew up the son of a high end audiophile and followed the high end mantra for 40 years. Then one day I started questioning some of the "truths" in high end audio and began doing bias controlled listening tests. That cured me of the high end audio bug and it also cured the bug in the dozen or so people who have helped me with the tests.

I remember when it started. I spent some time on one of the old newsgroups debating the audibility of digital cables and power cords with other audiophiles. Believing that digital cables and power cords could have some audible characteristic simply went against common sense to say nothing of the laws of physics. I started with an exhaustive bias controlled test of digital cables and power cords - none of which had audible characteristics. One thing led to another. After a while it became as much a passion for the truth as it did a hobby. I still enjoy audio, obviously, but I don't let beliefs get in my way any longer.

The audio business is rife with science that doesn't apply to the subject and beliefs that one can describe as nearly religious. I spend a lot of time and effort trying to bring truth and sanity to the whole audio business but it is a losing battle. People aren't really all that interested in the truth. They prefer their beliefs and the opinions of believers instead of the facts of the truth seekers.

Take the fellow above who wants to biamplify his speakers from the same power supply. Despite what I or others say, he will do it and may well "hear" some difference because of his expectations and biases. He will go on happily believing that what he did had a positive impact on sonics without ever doing what it takes to complete a scientifically valid test. That's how it starts and grows.

Biamplification comes from pro audio. It's purpose is to power separate drivers that have been isolated from each other with an active crossover network. The purpose isn't to add more power. Tweeters, as an example only use milliwatts of power. The purpose is isolation and control. If a pro audio guy needs more power, he uses a larger amplifier. There is no reason to biamplify two ends of a passive crossover network. That is a ficticious activity promulaged by the high end audio industry. The science from pro audio is perverted and applied to built in passive networks where it doesn't do anything. It helps them sell more products.

What the fellow above wants to do is powered biwiring. Biwiring did not come from pro audio. A pro audio guy wouldn't waste his time with it. He may never have heard of the practice. It came from consumer high end cable manufacturers. Guess why?

I just try to set the record straight when I can.

 

[anm]

I think a good way to bi-amp is use two amps, one for each front speaker.
I had same question some time back and got the same answer from fmw, and I believe him on what he says about bi-wiring.

However, there are some onkyo receivers that claim they can bridge 2 rear channels of 7.1 to be bridged with fronts. I believe that can make a difference. Don't know if HK 354 has the same feature.
In India, power supply is 220volts, so I think I can draw lot more power on a single supply compared to 110V supply.

regards

Don't waste your time or your wire. It won't make any difference. All the amps in your receiver are driven by the same power supply. You can't get any more power from the supply than it can put out no matter how many amps you use. And, obviously, more power isn't likely to make any difference if you could get it.

 

[bandphan]

it should be dependent on the crossover, or using an active crossover. If your crossover is passive little to no benefit wll be gained.

 

[anm]

Are you saying bridging capability of an amplifier is dependent on type of cross over? If bridging gives higher wattage output, even then there would be no gain with passive crossover? I doubt that.

regards

it should be dependent on the crossover, or using an active crossover. If your crossover is passive little to no benefit wll be gained.

 

[bandphan]

Are you saying bridging capability of an amplifier is dependent on type of cross over? If bridging gives higher wattage output, even then there would be no gain with passive crossover? I doubt that.

regards

ok do as you like but most speakers while containing 2 sets of binding posts, do not have a crossover designed for it, so as you wish

feel free to explain otherwise