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Topic: Passive bi-amping with AVR (Read 98765 times) previous topic - next topic
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Passive bi-amping with AVR

Reply #25 –
Quote from: Rich B on
Quote from: Arnold B. Krueger on
Quote from: Rich B on
Arnold, is it not true that the additional current reserve from a larger amp that may be needed for higher levels does make the power supply stiffer at lower levels?


All things being equal a more powerful amp will have a stiffer power supply, that goes to reason.

However each channel of a power amp has built-in power supply rejection features, and the extra stiffness does nothing for sound quality.


An audiophile friend of mine told me that extra power could improve the bass of the speaker. I thought about that and wondered how a surplus of power beyond what is needed at a given voltage could result in a difference and it doesn't appear to make much sense to me. How could a surplus of current affect the speaker at low drive voltages?


Beats me.

If you test just one channel of a stereo or multi channel amp, there is obviously a surplus of power supply available. If you test both channels, the only effect of any significance is a slight decrease in maximum power per channel which makes perfect sense.  Nothing much changes if you test at lower power levels which are where most people operate their amps most of the time.

Of course I'll bet money that your friend is basing his ideas on anything but good listening tests and correct theoretical analysis. In fact he probably knows little or nothing of either and just another audiophile who tends to take everything at face value whether  it is true or false.

Passive bi-amping with AVR

Reply #26 –
Quote from: Arnold B. Krueger on
Quote from: Rich B on
Quote from: Arnold B. Krueger on
Quote from: Rich B on
Arnold, is it not true that the additional current reserve from a larger amp that may be needed for higher levels does make the power supply stiffer at lower levels?


All things being equal a more powerful amp will have a stiffer power supply, that goes to reason.

However each channel of a power amp has built-in power supply rejection features, and the extra stiffness does nothing for sound quality.


An audiophile friend of mine told me that extra power could improve the bass of the speaker. I thought about that and wondered how a surplus of power beyond what is needed at a given voltage could result in a difference and it doesn't appear to make much sense to me. How could a surplus of current affect the speaker at low drive voltages?


Beats me.

If you test just one channel of a stereo or multi channel amp, there is obviously a surplus of power supply available. If you test both channels, the only effect of any significance is a slight decrease in maximum power per channel which makes perfect sense.  Nothing much changes if you test at lower power levels which are where most people operate their amps most of the time.

Of course I'll bet money that your friend is basing his ideas on anything but good listening tests and correct theoretical analysis. In fact he probably knows little or nothing of either and just another audiophile who tends to take everything at face value whether  it is true or false.


I thought a surplus of something was just excess, am I right? Or something in reserve? My first thought was that excess current can't affect the sound beyond what is needed because the load won't 'see' it, or react to it unless the voltage was raised high enough.

BTW, what is drive voltage? Is that just the user increasing/decreasing the volume on the amp?

Passive bi-amping with AVR

Reply #27 –
Quote from: Rich B on
I thought a surplus of something was just excess, am I right? Or something in reserve?


It is surplus until you need it. But if it will damage speakers or break your your lease or your ears, it is obviously wasted. We often find that people, in search of "ample reserves" end up with a Frankenstein Monster of an amp.

Quote
My first thought was that excess current can't affect the sound beyond what is needed because the load won't 'see' it, or react to it unless the voltage was raised high enough.



Hold that thought!


Quote
BTW, what is drive voltage?


Voltage that drives. Used in many contexts.

Quote
Is that just the user increasing/decreasing the volume on the amp?


Often

Passive bi-amping with AVR

Reply #28 –
Quote from: Rich B on
BTW, what is drive voltage?

It means that the output of the amp is a voltage that follows the input (times gain and volume control attenuation). The load draws whatever current it needs.

In other words, an output impedance ~= 0.


"I hear it when I see it."

Passive bi-amping with AVR

Reply #29 –
Quote from: xnor on
Quote from: Rich B on
BTW, what is drive voltage?

It means that the output of the amp is a voltage that follows the input (times gain and volume control attenuation). The load draws whatever current it needs.

In other words, an output impedance ~= 0.


Sorry, I'm not an EE, so I may use the terms incorrectly. Isn't drive voltage and voltage swing sort of the same thing? If I say that someone does not listen loud enough to make use of the excess current available then I mean there is insufficient drive voltage, or voltage swing from the amp to force the amp to supply the extra current, but again, if I'm using the terms incorrectly here then please correct me.

Passive bi-amping with AVR

Reply #30 –
An amplifier has a maximum output voltage and a maximum output current.

Depending on these values, as well as the impedance of the speaker that it is driving, an amplifier will reach either its maximum voltage or its maximum current when driving the speaker. When that happens, it makes no difference how much extra it has of the one that is not at its maximum. This excess capacity will be unused.

If the speaker impedance is fairly low then the current limit will be reached first, and there will be extra margin on the voltage. If the speaker impedance is fairly high then the voltage limit will be reached and there will  be extra margin on the current.

Ideally both limits will be reaches simultaneously and the speaker impedance will be optimally matched to the amplifier, giving the maximum possible wattage from this amplifier into this speaker.

Passive bi-amping with AVR

Reply #31 –
Quote from: pdq on
An amplifier has a maximum output voltage and a maximum output current.

Depending on these values, as well as the impedance of the speaker that it is driving, an amplifier will reach either its maximum voltage or its maximum current when driving the speaker. When that happens, it makes no difference how much extra it has of the one that is not at its maximum. This excess capacity will be unused.

If the speaker impedance is fairly low then the current limit will be reached first, and there will be extra margin on the voltage. If the speaker impedance is fairly high then the voltage limit will be reached and there will  be extra margin on the current.

Ideally both limits will be reaches simultaneously and the speaker impedance will be optimally matched to the amplifier, giving the maximum possible wattage from this amplifier into this speaker.


I was more concerned about the whole 'excess current' having any benefit to the sound at lower drive voltages, as is commonly claimed by audiophiles. Just increasing the total available amount is claimed to improve the ability of the amp to control the speaker or some such.

What I wanted to know is that - surely if there is insufficient voltage swing then it wouldn't matter how much excess current is available from the amp because the speaker would never see it, react to it, etc, unless the voltage levels increased.

So if you kept the drive voltage the same and just increased maximum current supply, that surplus of current won't be realised at the same drive voltages. I don't know if I'm making myself clear. English is not my first language.

Passive bi-amping with AVR

Reply #32 –
Quote from: Rich B on
Sorry, I'm not an EE, so I may use the terms incorrectly. Isn't drive voltage and voltage swing sort of the same thing?

No, not at all.

Voltage drive tells you, that the amp behaves like a voltage source. Let's say 1V at the input leads to 2V at the amp's output (due to gain and volume control position). With a voltage source it doesn't matter if you connect a 4, 8, or 1000 ohm load - it will output 2V across that load. (I=V/R, so currents in the most simple case would be 0.5A, 0.25A, 0.002A)

Output voltage swing tells you the range of voltage that the amp can produce, which is usually a bit lower than the supply voltages.

Let's say the power supply provides +/-5V and the amplifier can output up to +/-4V. So we have Vpp (voltage peak-to-peak) = 8V, Vp (voltage peak) = 4V, Vrms (root mean square) = 2.828V




Quote from: Rich B on
If I say that someone does not listen loud enough to make use of the excess current available then I mean there is insufficient drive voltage, or voltage swing from the amp to force the amp to supply the extra current, but again, if I'm using the terms incorrectly here then please correct me.


As you turn up the volume control, you turn up the output voltage. The "right amount" of current is drawn automatically by the load. Low current does not mean insufficient anything, but just a high load resistance for a given output voltage.
None of these numbers will tell you how loud the speaker will play. For that you need to include the sensitivity or efficiency.
"I hear it when I see it."

Passive bi-amping with AVR

Reply #33 –
Quote from: Rich B on
I was more concerned about the whole 'excess current' having any benefit to the sound at lower drive voltages, as is commonly claimed by audiophiles. Just increasing the total available amount is claimed to improve the ability of the amp to control the speaker or some such.

What I wanted to know is that - surely if there is insufficient voltage swing then it wouldn't matter how much excess current is available from the amp because the speaker would never see it, react to it, etc, unless the voltage levels increased.

So if you kept the drive voltage the same and just increased maximum current supply, that surplus of current won't be realised at the same drive voltages. I don't know if I'm making myself clear. English is not my first language.

Increasing the available current beyond what the speaker will draw has no benefit, other than to allow it to drive a lower impedance speaker or two speakers in parallel.

What is probably being referred to is damping factor, which is a measure of the output impedance of the amplifier. Depending on the circuit design, you could have a low power amp with a high damping factor, or a high power amp with a low damping factor, though it may be easier to achieve a high damping factor in a high power amp than a low power amp.

Passive bi-amping with AVR

Reply #34 –
Quote from: xnor on
Quote from: Rich B on
Sorry, I'm not an EE, so I may use the terms incorrectly. Isn't drive voltage and voltage swing sort of the same thing?

No, not at all.

Voltage drive tells you, that the amp behaves like a voltage source. Let's say 1V at the input leads to 2V at the amp's output (due to gain and volume control position). With a voltage source it doesn't matter if you connect a 4, 8, or 1000 ohm load - it will output 2V across that load. (I=V/R, so currents in the most simple case would be 0.5A, 0.25A, 0.002A)

Output voltage swing tells you the range of voltage that the amp can produce, which is usually a bit lower than the supply voltages.

Let's say the power supply provides +/-5V and the amplifier can output up to +/-4V. So we have Vpp (voltage peak-to-peak) = 8V, Vp (voltage peak) = 4V, Vrms (root mean square) = 2.828V


Sorry, then I was misusing the term. What I meant by drive voltage was the same thing as output voltage = how loud the volume is turned up. If the user turns the volume up more it means the output voltage increases. That's what I meant, but I think I used the wrong term to express it.

Passive bi-amping with AVR

Reply #35 –
Yeah, but the term voltage drive has nothing to do with volume controls or gain per se. All it means it that your device (audio power amplifier in this case) approximates an ideal voltage source.

As such, it tries to output whichever voltage it is "configured" to output. In the case of an audio amplifier that is typically input voltage * gain * volume control gain. The load (loudspeaker) is ignored. The amplifier that is "configured" to output 1V will try to keep up that voltage even if the load impedance drops from 8 ohm to 1 ohm.

The output impedance is close to 0. This means that if you move the cone of a connected woofer, which will generate a voltage, from the point of view of the woofer the amplifier will look like a short. This is electrical damping ... audiophiles use the umbrella term "tightness" I guess.
"I hear it when I see it."

Passive bi-amping with AVR

Reply #36 –
Quote from: xnor on
The output impedance is close to 0. This means that if you move the cone of a connected woofer, which will generate a voltage, from the point of view of the woofer the amplifier will look like a short. This is electrical damping ... audiophiles use the umbrella term "tightness" I guess.


As you probably know the voltage from the woofer voice coil is almost totally resisted by the low source impedance of the amplifier, but is hardly resisted at all by the resistance of the voice coil which is usually one or more orders of magnitude (10x each order of magnitude - for Rich) larger.

Passive bi-amping with AVR

Reply #37 –
Quote from: Arnold B. Krueger on
As you probably know the voltage from the woofer voice coil is almost totally resisted by the low source impedance of the amplifier, but is hardly resisted at all by the resistance of the voice coil which is usually one or more orders of magnitude (10x each order of magnitude - for Rich) larger.

I think it's the other way around. The amplifier looks like a short, so offers little to no resistance to the back EMF - current can flow freely. So the whole voltage will drop across the resistance of the voice coil effectively dampening itself.

Tap the cone of an unconnected woofer. Now short (either with a piece of wire or by connecting it to an amp that outputs 0V) the woofer and repeat. There should be a clear difference.
"I hear it when I see it."

Passive bi-amping with AVR

Reply #38 –
Quote from: xnor on
Quote from: Arnold B. Krueger on
As you probably know the voltage from the woofer voice coil is almost totally resisted by the low source impedance of the amplifier, but is hardly resisted at all by the resistance of the voice coil which is usually one or more orders of magnitude (10x each order of magnitude - for Rich) larger.



Didn't I say that? ;-).  What is gives more resistance to an applied voltage (so-called back EMF from the speaker) than a dead short? Hence: "Total resistance".

Quote
I think it's the other way around. The amplifier looks like a short, so offers little to no resistance to the back EMF - current can flow freely. So the whole voltage will drop across the resistance of the voice coil effectively dampening itself.

Tap the cone of an unconnected woofer. Now short (either with a piece of wire or by connecting it to an amp that outputs 0V) the woofer and repeat. There should be a clear difference.


Totally agree with all those facts, all the time!]

Passive bi-amping with AVR

Reply #39 –
Not sure, it's confusing how you phrase it.
"I hear it when I see it."

Passive bi-amping with AVR

Reply #41 –
So passive bi-amping using the AVR has no headroom benefits whatsoever? If you have to drive larger, or less efficient, or lower impedance front speakers, you saying bi-amping would make no difference at all?  Won't it make the system perform more efficiently?

Passive bi-amping with AVR

Reply #43 –
Quote from: Rich B on
So passive bi-amping using the AVR has no headroom benefits whatsoever? If you have to drive larger, or less efficient, or lower impedance front speakers, you saying bi-amping would make no difference at all?
 

There is absolutely no difference in audible performance whatsoever if you don't overdrive your amplifiers to the point of clipping, at all.

  So the next logical question is, "Yes, but can I turn up the music to a higher level before the onset of clipping by using two stereo amps (instead of just one) in passive bi-amping mode?" The answer is still effectively "NO" because the unlike active bi-amping where each amp is given a limited range of frequencies to reproduce, which is less of a burden than the full range (less of a burden at least for the amp that only has to do the easy to amplify highs), each amp in passive bi-amping is presented with the full range signal. The only difference from the amp's perspective is that the load has changed.

In the case of the "high frequency" amp [remember that's a misnomer, both it and the other amp are actually amplifying the full range signal in passive bi-amping] the load is indeed usually lighter and it could in theory play louder before the onset of clipping, but obviously you wouldn't want to dial up its output (even though it has more capability now) unless you want to EQ the signal by intentionally playing your tweeters too loudly.

In the case of the "low frequency" amp almost nothing has changed. The problem is the bass is pretty much always the part of the musical spectrum which is the power gobbling burden for any typical amp playing typical music and neither the incoming signal, nor the load the "bass" amp sees in the hard to reproduce bass range has changed. The off loaded "burden" of it not seeing the easy to reproduce tweeter's part of the sound spectrum hasn't increased its capability in the bass, not by even 1 dB. So here we see the bottle neck of what stops you from turning your system up to 11 doesn't change by using passive bi-amping. The same part of the music which distorts first still distorts at the exact same level as it does when mono-amping.

I can hear it now: "Ah, but when you do play the music loudly (using passive bi-amping) to the point of distorting the woofer amp, the first to go, it is playing into a speaker with a disconnected tweeter so that distortion will sound different and "more pleasing" than distortion playing into a full range speaker." Oy. Whatever. I know of no blind study which shows people perceive their systems as playing "more powerfully" or with "less distorted peaks" when using this "fool's bi-amping" method as many in the know call it. There's lots of anecdotal, unsubstantiated, sighted BS about how wonderful it is at any level, though.

Quote
Won't it make the system perform more efficiently?


Efficient? That wouldn't be my word for it. Here's what passive bi-amping actually costs (multichannel AVR users are slightly different than separates):

- twice as much speaker wires [plus a y-cord to send the preamp signal to two amps and an extra patch cord]

- twice as much amplifiers

- twice as much rack space taken up

- nearly twice as much electricity consumed from the wall

- nearly twice the amplifier heat generated into the room, increasing your AC bill in the summer

- nearly twice the burden placed on a single power supply in multichannel designs, like AVRs, hence lower maximum wattage capability in Sound and Visions' ACD {all channels driven simultaneously with sine waves} testing

Bi-wiring and passive bi-amping were invented by the audio retail industry so people would buy-wire and buy-amplifiers, in both cases increasing their profits to twice that of customers who don't buy-in to this silliness. Active bi-wiring (using electronic crossovers) on the other hand is legit.

Passive bi-amping with AVR

Reply #44 –
Spot on mzil, but there seems to be a confusion of the Marantz AVR with the Yamaha RichB mentioned in the "bench testing amps" thread.
"I hear it when I see it."

Passive bi-amping with AVR

Reply #45 –
Quote from: Rich B on
So passive bi-amping using the AVR has no headroom benefits whatsoever?


I would say "no significant" but I have to admit that in theory there are very slight benefits - maybe a dB or less additional power.

The amp's power supply has to provide the same amount of power either way, but two power amp circuits are involved instead one of one circuit  per speaker, and there is are very slight benefits to splitting up the speaker loads - the same 1/2 dB or so.

I did some simulations with as cheap AVR, some 2-way crosovers, and some resistive loads, and that is what evolved.

If I split the speakers up over 4 power amps in the same AVR there was a very slight benefit over splitting it up over just 2 even though the same power has to come from the power supply either way.

Quote
If you have to drive larger, or less efficient, or lower impedance front speakers, you saying bi-amping would make no difference at all?  Won't it make the system perform more efficiently?


I would say nothing that is worth the trouble, but enough for someone that we both know to make a big thing about it on AVS. ;-)

Passive bi-amping with AVR

Reply #46 –
BTW, I'm referring to AVR biamping, not using separate dedicated amps or anything like that. An engineering fellow told me that the separate amps in the AVR may run cooler, or that there may be a better and more even distribution of heat.

Passive bi-amping with AVR

Reply #47 –
Quote from: Rich B on
An engineering fellow told me that the separate amps in the AVR may run cooler, or that there may be a better and more even distribution of heat.

What would that have to do with sound?
I've already linked you to the only possible benefit, full clipping spectra or low passed clipping spectra. Key being "clipping", you would have to drive the amplifier into some form of non-linearity. Which is possible.

Quote from: Arnold B. Krueger on
I would say nothing that is worth the trouble, but enough for someone that we both know to make a big thing about it on AVS. ;-)

You referring to jj's thoughts on the subject? He would tell RichB the same thing I did. Depends.

cheers,

AJ
Loudspeaker manufacturer

Passive bi-amping with AVR

Reply #48 –
Let's pretend for the moment that the bass amplifier in a fool's bi-amp mode configuration does sound decidedly less offensive when you just barely start to clip the peaks, since there is no tweeter to reproduce the highs of that distortion from that amp and that's where it is subjectively most nasty to the ear. Well guess what? That window of "Wow, look how much louder I can [effectively] now play the music thanks to passive bi-amping" is extremely narrow* before you hit a brand new, but different road block.


When the tops of the waveforms start to flatten, the onset of clipping, not only have you reached the limit of that amp's clean sounding range you also have reached the end of its music amplification. Going any louder with the main preamp's volume knob will increase the tweeter amp's output, but all that happens with the already distorting woofer amp is an even flatter, nearing square wave shape to its waveform. It doesn't play the music more loudly like it should. Your overall system's highs are successfully increasing in level but your lows are maxed out so the spectral balance of the music will become too bright (treble heavy/bass shy).

So how much louder can you play a system before you notice the tweeters are playing at a higher level than they should be, compared to the woofers? I'm thinking 1 dB, maybe even less with the right material. [With the proper narrow band of pink noise I bet I could hear even less than half a dB.]

*[In fact instead of calling it "narrow" you might instead call the onset of this new problem instantaneous.]


Passive bi-amping with AVR

Reply #49 –
Last time I looked at listened to signals being driven further into clipping, they appeared to get louder. If you look at the spectral content, you can easily see why this is the case.

As you keep going you will reach a breaking point, however, if not literally speaking.

FWIW, I utilize a volume boost with increased distortion every time I stomp on my overdrive pedal to take a solo.