This may not be the best/only place to post this. I am building a 2-way speaker and wanted to include a bi-amp terminal cup just to cover myself for future use cases. This got me to thinking about using a multichannel AVR, in this case an old 5.1, as a source of multiple amp channels for stereo playback.
Many of the AVR that I have come across have a playback option called "Multi-Stereo" or something like that. This mode pushes stereo signals to each channel . . . meaning both Right and Surround Right play the right side of a stereo signal and left the opposite.
Does this mean that an AVR in this mode could be used to Bi-Amp passive speakers? The sole purpose of this version of Bi-Amping would be to provide greater headroom in the form of more power per channel/driver. I realize true Bi-Amping typically refers to the use of multiple amps when using an active crossover.
A possible supplemental benefit is that an AVR offers rudimentary DSP capabilities, level and tone adjustment that could be applied to each driver individually. At the very least this could function like an adjustable L-Pad for a tweeter.
If a speaker has an internal passive crossover but the terminals are connected separately to each section of a 2-way crossover, is there any reason this wouldn't work? And am I correct in thinking that this would better utilize the available power of an AVR during stereo playback?
Ultimately, an AVR can just be put in Analog Direct and run as a normal stereo, but it seems like you would be leaving power on the table.
Many of the AVR that I have come across have a playback option called "Multi-Stereo" or something like that. This mode pushes stereo signals to each channel . . . meaning both Right and Surround Right play the right side of a stereo signal and left the opposite.
Does this mean that an AVR in this mode could be used to Bi-Amp passive speakers? The sole purpose of this version of Bi-Amping would be to provide greater headroom in the form of more power per channel/driver. I realize true Bi-Amping typically refers to the use of multiple amps when using an active crossover.
A possible supplemental benefit is that an AVR offers rudimentary DSP capabilities, level and tone adjustment that could be applied to each driver individually. At the very least this could function like an adjustable L-Pad for a tweeter.
If a speaker has an internal passive crossover but the terminals are connected separately to each section of a 2-way crossover, is there any reason this wouldn't work? And am I correct in thinking that this would better utilize the available power of an AVR during stereo playback?
Ultimately, an AVR can just be put in Analog Direct and run as a normal stereo, but it seems like you would be leaving power on the table.
This is totally possible with the right AVR. First most avr are not true 5 channel amps, most are 3 channel with the rear surround channels bridged to the front. As you can see most avr are not ‘leaving watts on the table’. The easiest way to get the input your looking for to these channels is to use the ‘5.1 direct’ inputs. Also remember the avr, even if it has 5 full channels, is not meant to run like this with 4 or 5 channels run at high power your pretty likely to have heat or PS issues. Also I don’t know of a way in this configuration to use any dsp from the avr.
I have a denon avr3300 which had issues with the dsp card. I stripped all digital stuff out, connected direct input (physically, not using the existing 5.1 inputs) into all 5 channels and now it runs 2 dvc subs 4x105 in 8 ohms. The 3300 has a large transformer but a small heatsink with a fan. I have not had heat or PS issues.
I have a denon avr3300 which had issues with the dsp card. I stripped all digital stuff out, connected direct input (physically, not using the existing 5.1 inputs) into all 5 channels and now it runs 2 dvc subs 4x105 in 8 ohms. The 3300 has a large transformer but a small heatsink with a fan. I have not had heat or PS issues.
You have a perhaps common misunderstanding about power. Once upon a time, I worked for a $3B audio giant, and went to dinner (well, really lots of sake but there WAS some food at some point ha ha). He explained to me that power amplifiers do not really deliver power, it is kind of a byproduct:
(1) Almost every amplifier actually amplifies VOLTAGE. Let's say at a maximum peak, your CD player or whatever delivers 2 volts. And the amplifier has a gain of, ten, it will then try to output 2*10=20V.
(2) Electrical current will then flow out from the amp, per depending on the load it sees, according to Ohm's Law current I = voltage V divided by resistance R. (Resistors RESIST the flow of current). Let us connect the amp to perfect test resistors:
8 ohm: I=V/R=20/8=2.5 amperes
4 ohm: I=V/R=20/4=5 amperes
2 ohm: I=V/R=20/2=10 amperes
It is this CURRENT which amplifiers struggle to provide, and CURRENT which drives the cost, and CURRENT which produces waste heat*
(3) When the current flow into our perfect test resistors, power is produced according to the formula P=I^2*R. Notice the BIG dependence on current!
8 ohm: P=2.5^2*8=50 watts
4 ohm: P=5^2*4=100 watts
2 ohm: P=10^2*2=200 watts
More and more power! Well, except for that darn waste heat*
(4) Now real speakers are not like resistors at all. Not even close. So why do we see "8 ohms" etc? Well, speakers are so complicated, it is impractical to test amplifiers into something that simulates a speaker, especially since every speaker is different. So the amps are just tested into resistors. Actuall speakers have an IMPEDANCE which is kind of like resistance, but complicated by time and frequency. Into real speakers, the current drawn may well violate the operating capacity of the transistors. That means clipping, or protection circuits kicking in, or a burned smell and smoke 😱
Anyway to passive biamping: yes, you could employ unused AVR channels as you say. But you will NOT get significantly more power. Think of one channel driving your woofer/crossover: it puts out X volts, but the impedance becomes higher into the mid and high frequencies. So not "all of the power" is actually delivered. Similarly your channel driving the tweeter/crossover has a very high impedance at low frequencies, draws little current = little power.
--> You've just shifted power between channels.
"But wait, each channel is not loaded as hard, so it should be able to put out more!" Not really:
- The woofer channel is "relieved" by no high frequencies...but that represents a little bit of power only, so doesn't make much difference.
- In an AVR, everything connects to a common power supply, which limits the power. Splitting that into more channels doesn't really help.
Some proponents (especially cable companies 😉) suggest that biamping even from the same amp channel yields tremendous sound differences, because you have "separated" the low and high frequency currents. The electrical engineer part of my brain says this is crap, but the scientist part of my brain replies that I've never bothered to test it.
You don't have anything to lose with what you're proposing, so go for it, why not. But what would be instructive would be to have some people listen on different days and see if they notice anything, without telling them of the change. That is a "semi-blind" experiment 😛
*(5) the waste heat goes by the square of the current. Not strictly as there are other losses, but supposing it is so then the losses would be proportional like this:
8 ohm: 2.5^2=6.25
4 ohm: 5^2=25
2 ohm: 10^2=100
that does not mean the losses would be 100 watts for the 2 ohms! But they would be maybe 16 times as much as for 8 ohms. That is another reason why I really dislike loading amplifiers down to their maximum impedance.
I have no idea what I am looking at really, but the AVR (CHEAP Song STR-DG520 from a century ago) has 5 pairs of MN2488 & MP1620 power transistors on the heatsink. Would this imply that it is truely 5 channel, or could a couple sets still be bridged internally? No Direct inputs though.
The AVR I am using still gives level and tone control for each channel in this setting, this is all I was talking about. Just simple control, not true EQ.
Thanks head_unit for the informative reply. I get why I would still be power limited.
Is there any advantage in terms of distortion? For example, if I am using 50 watts total, wouldn't there be a difference between putting 50 watts through a single set of transistors as compared 25 watts through two sets of transistors? (This wouldn't actually be the split because the woofer/tweeter split isn't 50/50) Also, if I am not actually getting more power, then wouldn't I have better thermal performance by dividing the channels?
Obviously this question may also be an over simplification because it would depend on the performance of the transistors themselves. Having recently discovered Audio Science Review, it seems like most amps distortion decreases until about half power and then begins to increase rapidly. So if I am under utilizing two sets of transistors, I very well may experience greater distortion albeit with more headroom. (Assuming the amp actually behaves as discrete channels)
If I can summarize the advise I think I am getting, the only gain in power I might see is the difference of what a tweeter would require (on the order of a handful of watts at loud listening?). And this is barring any limitations of the power supply.
I at least like that both the answers so far have given the sense of "try it and find out," which inevitably I will. I'm not expecting much, just playing around with things I have laying around.
One other thing to watch, lower end AVR's may be only rated to drive 8 ohm speakers. They may not be able to drive a lower ohm speaker, because of the current requirements as started by head_unit.
If you use a 4 ohm speaker and the AVR overheats or shuts down, you'll know why.
If you use a 4 ohm speaker and the AVR overheats or shuts down, you'll know why.
I have used AVR's as amps using active XO in PC and feeding the multi channel signal via HDMI to the AVR: simple and cost effective active speakers!
One thing to watch out for is the channel delays, they seem to be active in 'direct mode' at least on some AVR's, so I would recommend checking delays with scope. If you have different delays on the channels it will mess up the sound, even small delays.
I have not come across an AVR with 'fake rear channels'.
One thing to watch out for is the channel delays, they seem to be active in 'direct mode' at least on some AVR's, so I would recommend checking delays with scope. If you have different delays on the channels it will mess up the sound, even small delays.
I have not come across an AVR with 'fake rear channels'.
Certainly something I am concerned about. Both drivers are rated nominally at 8 Ohms, but I am going to be measuring the impedance as well.
That sounds cool, what setup (software/hardware) are you using to augment the HDMI signal?
While I see where you're going with this, there's literally no benefit.
All of the benefit of bi-amping comes from getting rid of the passive crossover. There's zero benefit to this "passive bi-amping", no matter what the HiFi magazines might tell you.
That said, you can use the AVR as a 5-channel amplifier in a nice case, and use an external active crossover. No harm in that at all. Just get rid of the passive crossovers.
Chris
All of the benefit of bi-amping comes from getting rid of the passive crossover. There's zero benefit to this "passive bi-amping", no matter what the HiFi magazines might tell you.
That said, you can use the AVR as a 5-channel amplifier in a nice case, and use an external active crossover. No harm in that at all. Just get rid of the passive crossovers.
Chris
Passive crossovers, a bad thing? Why?
Bi-Amping is interesting to DIYers for numerous reasons. For example they can use or build amps appropriate to the band of interest. They can distribute the power and reduce distortion per output. They can begin to set themselves up for an active testing setup which they might later convert back to passive for completeness.
Bi-Amping is interesting to DIYers for numerous reasons. For example they can use or build amps appropriate to the band of interest. They can distribute the power and reduce distortion per output. They can begin to set themselves up for an active testing setup which they might later convert back to passive for completeness.
If you have a Windows PC, you can install Equalizer APO to to the DSP work. More info is here on the forum, and elsewhere.
Only other hardware you need is a HDMI-cable between the PC and AVR 🙂 Ok, you should have measuring gear to EQ the driver responses, and verify by measuring the complete system.
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