Bi-amping the Statements

[Mrpictureman]

Has anyone actually bi-amped their Statements and if so is there a noticeable difference in the sound? Was it worth it in your opinion? Please post any pictures or diagrams of your connections and equipment used.

[AdelaaR]

I'd like to add to or rephrase your question:
Does bi-amping make sense in any situation, ever?
Why would it be better than just having one powerfull enough amp to drive all drivers at once?
Isn't the added cost of multiple amps and cables and connections simply unnecessary?

[penngray]

Maybe the OP should consider a fully active version of the Statement design.

Add a couple of MiniDSPs and have fun!!

[ThomasW]

To the OP are you talking about splitting sections of the existing passive crossover and using those with separate power amps? Or replacing the entire passive crossover with an active unit?

[BigJim_inFLA]

I always thought that unless you were going to use active crossovers to split the signal before you amplify, and bypass part if not all of the passive crossover, you didn't really gain much. Is there a situation where you might want to bi-amp, yet still retain the passive crossovers?

I myself am building the Statements and have considered building them so that I could bi-amp in the future, dual sets of binding posts and split the woofer crossover from the mid/high. I am not sure which route I will take yet.

[Maklar]

Isn't the added cost of multiple amps and cables and connections simply unnecessary?

It might be the case where the OP has a receiver that has unused channels. As an example, I have an Onkyo TX-NR1007 which allows 9 channels but I only use 5 so I can use some of the other channels to biamp speakes. I've wondered similar thing about Jed's Dynamic series.

[Jed]

I've wondered similar thing about Jed's Dynamic series.

The Dynamic Series (all except the new RS150-4/RS28F 2 way) have a separate assembled woofer board and mid/tweeter board, so you can biamp if you really want to. The kit comes with a single set of binding posts though, so you'd need to order another pair, so you can wire the inputs separately.

[AdelaaR]

It might be the case where the OP has a receiver that has unused channels. As an example, I have an Onkyo TX-NR1007 which allows 9 channels but I only use 5 so I can use some of the other channels to biamp speakes. I've wondered similar thing about Jed's Dynamic series.

Okay ... I never thought about that particular situation and can certainly see the sense of it

[Cort]

When I built my mini statement I also bought all new gear (tv, reciever amp, blu-ray). I hooked up the onkyo ht-rc270 and it all sounded sweet, the decided to try the bi amp out, I just split the crossover so that the woofs were on one channel and the mid and tweet were on the other. Sounded sweeter and a little louder. Then I added a emotiva upa-5, not bi amped, and that sounds the best. The upa-5 really made a difference, especially at low and mid volume levels, more detailed and fuller.

So I would recommend that you go ahead and bi-amp since you have the extra channels.

BTW for the onkyo and music it sounds the best in pure audio mode. I've run the audessy and tried to improve the sound manually with the built in eq's and all I've tweaked only seems to degrade things to my ears, not that I think it needs improvement, it's just that experience in life says that you can almost always find a knob that will give you results beyond expectations. So I got calibrated mic to see what sounds best to my ears and compare it with standards. I havn't had a chance to play with it yet but will post the results when I do. My only complaint at this point is that bad recordings now sound really bad

[Bear]

Okay ... I never thought about that particular situation and can certainly see the sense of it

Only if there is some benefit to the receiver for using the other channels. Usually, you get more available current when you use fewer channels (PSU limitation), so there's often a benefit to not using more channels even though you have them.

[Mrpictureman]

When I built my Statements (still need to add a finish to the cabinets) I wired the crossovers seperately for bi-amping to give me added options. Given that I am realatively cluesless about the actual benifits and connections. What is needed beyond the amps? An additional active crossover, if so any suggestions on one and what happens to the speakers crossovers? As mentioned the speaher crossovers are setup for biamping so do I need an active crossover? I am currently running a Denon 3802 I did have an external powr amp hooked up to the Denon until it gave out. I am planning on doing a complete upgrade to new equipment perhaps to emotiva?

ThomasW
To the OP are you talking about splitting sections of the existing passive crossover and using those with separate power amps? Or replacing the entire passive crossover with an active unit?

That's one of the questions, is there a sound difference or does it make sense just to use the Statements crossover or go active.

[ThomasW]

or go active.

So you have access to an active crossover that's an exact match for the passive unit?

If not you're wasting your money

[Mrpictureman]

So you have access to an active crossover that's an exact match for the passive unit?

If not you're wasting your money

No I do not have an active crossover at this time I am looking for options to bi-amp and how to do the connections for the best sound preferably through the bi-amped crossovers already in the Statements.

[Jim Holtz]

No I do not have an active crossover at this time I am looking for options to bi-amp and how to do the connections for the best sound preferably through the bi-amped crossovers already in the Statements.

Just add an extra set of binding posts and connect the mid/ribbon circuit together to one and woofers to the other set. If you bi-amp, the gain of the amps needs to be matched so volume levels will be as intended.

Active crossovers are almost a religious discussion that is subjective at best. The Statements crossovers are highly optimized and voiced so, IMHO, there's nothing to be gained by going active.

Active is great and preferable for sub crossovers and can potentially be used to advantage in woofer circuits of a multi-way speaker but improved sound quality would not be one of the advantages that I'd list for a woofer section of a multi-way speaker.

Just my $.02 worth...

Jim

[Mrpictureman]

Just add an extra set of binding posts and connect the mid/ribbon circuit together to one and woofers to the other set. If you bi-amp, the gain of the amps needs to be matched so volume levels will be as intended.

Thanks Jim, I have that already set up, now how do I connect two amps for the Statements to a pre/pro, receiver...etc There is usually only one set of inputs for the amp, in bi-amping I would need 2 front input sets correct? Is there another piece of equipment that would bring it all together or am I missing something?

[BobEllis]

A couple of Y adapters to split the signal from one set of pre-outs to two amps. Most pre/pros can handle this, but if the amps are particularly low impedance you might have an issue that you will hear as distortion when trying to be loud.

Don't be surprised if you don't hear a significant/any difference. I am in the go fully active or don't go at all camp. With the Statements I would think a single decent amp is plenty. As Jim said, the crossover design is pretty optimized. Going active would be at best direct copying the transfer functions Curt developed. Anything else would be just Statement-like.

[Face]

IMO, I wouldn't bother.

You would be better served by upgrading your associated gear if you're looking for something better.

[cjd]

Agree 100% with Face.

The only time you really gain from bi-amping is if you're using an amplification stage that isn't quite up to the task - separating out the heavier swing loads of the woofer circuit can clean up the signal on the mid-tweet. Or so the only example with data (that I remember) suggested.

That said, using un-used channels on a receiver may not have the same benefit as they usually share a power supply, and that tends to be where the problems lie more often than not. So you'd end up with more wiring and not much difference at all.

C

[Mrpictureman]

Thanks for everyones help, I appreciate it

[Paul Spencer]

I'm not a big fan of passive bi-amping. I think a lot of guys try it because they have the urge to meddle! Even if you have the extra channels, I'd rather let the power supply rest easy.

Now if you actively bi-amp, the most obvious improvement is likely to be experienced at the limits of operation. When the amp runs out of steam, it will clip. Go active and you now have more effective power so you are less likely to see clipping when driving them hard. Crossing at say 300 Hz divides the power bandwidth in half. Your chances of clipping the mid top section goes way down. If the amp driving the woofers goes into clipping with some bass heavy content, it will be less objectionable as it will not affect the tweeter. The result will be a cleaner system when pushed.

At ordinary levels I wouldn't expect a difference, provided you get the active to do the same job. Where active really shines is where it does things that can't be done passively. But that's now what we are talking about here. So you stand to gain a bit more clean output. In theory you might gain some extra improvement though a higher damping factor, that's a moot point.

I prefer active for other reasons - it's ideally suited to doing all kinds of diy projects quickly. It's more about convenience than performance.

[Bear]

I'm not a big fan of passive bi-amping. I think a lot of guys try it because they have the urge to meddle! Even if you have the extra channels, I'd rather let the power supply rest easy.

Now if you actively bi-amp, the most obvious improvement is likely to be experienced at the limits of operation. When the amp runs out of steam, it will clip. Go active and you now have more effective power so you are less likely to see clipping when driving them hard. Crossing at say 300 Hz divides the power bandwidth in half. Your chances of clipping the mid top section goes way down. If the amp driving the woofers goes into clipping with some bass heavy content, it will be less objectionable as it will not affect the tweeter. The result will be a cleaner system when pushed.

At ordinary levels I wouldn't expect a difference, provided you get the active to do the same job. Where active really shines is where it does things that can't be done passively. But that's now what we are talking about here. So you stand to gain a bit more clean output. In theory you might gain some extra improvement though a higher damping factor, that's a moot point.

I prefer active for other reasons - it's ideally suited to doing all kinds of diy projects quickly. It's more about convenience than performance.

I bolded an area where someone might get confused. You still get clipping, but you are correct in that less of your frequency band will be clipped, so it might be less objectionable. That does not make clipping a good practice, though. Just potentially less bad/objectionable when you want to turn it up to 11.

[Paul Spencer]

You still get clipping, but you are correct in that less of your frequency band will be clipped, so it might be less objectionable.

Are we talking about the same thing? I'm talking about active bi-amping here.

That would only be true if the actively bi-amped version were running at a higher level.

Example.

100w > passive driven to the point of clipping

Now let's biamp actively with 2 channels of 100w with a 300 Hz crossover. The power required for each of the two sections is now 50% based on power bandwidth alone. So while the other is just starting to clip at just over 100w, now each channel only needs 50w so we have 3db of extra headroom. If we push the volume up more because the sound is still clean enough, we'll get a little more output before it clips again, but at this point it might be limited to the woofers if they are running hotter, but if crossing around 300 Hz it could also be the mid/top clipping if pushed hard enough, but at that point too much is being asked.

[AdelaaR]

I'd like to ask another question: does anyone here actually ever play their speakers at 100dB? If so ... in what circumstances and in how big a room?

[BigJim_inFLA]

I'd like to ask another question: does anyone here actually ever play their speakers at 100dB? If so ... in what circumstances and in how big a room?

Yes. Its not unusual to see peaks over 100 dB during movie nights. Also I have teenagers in the house so we have dance parties. None of them can dance, but that doesn't stop them. The music is sustained 100+ dB. This is in an open living room/kitchen area, approx. 21 x 36 with 12 ft ceilings. I'll grant you that this is not normal listening, but it does happen fairly regularly.

[AdelaaR]

None of them can dance, but that doesn't stop them.

Good one

[Bear]

Are we talking about the same thing? I'm talking about active bi-amping here.

Probably not. This is also why I tried to point out that there might be some confusion. Active crossovers generally require separate channels of amplification (I'm sure someone with enough money could make an active, high-power crossover). Bi-amping, in my lexicon, is using an existing passive crossover, but using a separate amplification channel for one or more sections of the passive XO (e.g., Tweeter and Midwoofer). Once you are discussing an active crossover, the rest of the discussion is irrelevant because you are fundamentally talking about the benefits of active vs. passive crossovers generally. The number of amplification channels used is secondary. If you have a different meaning for "actively bi-amped", then I am truly lost.

That would only be true if the actively bi-amped version were running at a higher level.

Example.

100w > passive driven to the point of clipping

Now let's biamp actively with 2 channels of 100w with a 300 Hz crossover. The power required for each of the two sections is now 50% based on power bandwidth alone. So while the other is just starting to clip at just over 100w, now each channel only needs 50w so we have 3db of extra headroom. If we push the volume up more because the sound is still clean enough, we'll get a little more output before it clips again, but at this point it might be limited to the woofers if they are running hotter, but if crossing around 300 Hz it could also be the mid/top clipping if pushed hard enough, but at that point too much is being asked.

Given that the origin of the thread was discussing the benefits of bi-amplification, and not active crossovers, the real point for bi-amplification is that you do have a minor benefit with clipping, assuming your amplifier is reasonably well-designed, because the artifacts from clipping could be limited to one channel (again, there may be some dependencies on the amplifier design -- that's beyond my experience and knowledge). However, using a passive crossover, you do not get a power savings of any sort. In fact, you may consume more power since you are doubling the output requirements from the amplifier for that speaker e.g., the midwoofer would need 100W and the tweeter would need 100W).

The bottom line (at least for me): using a passive crossover, you do not get any real benefit under normal circumstances using multiple amplifier channels to power a loudspeaker, while you pay a penalty with the increased capital and operating costs.

[Paul Spencer]

Bear,

It seems to me that bi-amping used to mean active and the exception was "passive bi-amping." Now it's the other way around, probably because people now have extra channels and want to try a way to use them. Passive bi-amping hardly seems worth it and I'd rather keep the power in reserve. I assumed the OP was talking about active bi-amping, perhaps I was mistaken.

Passive bi-amping ... it would take just minutes to try it.

[Bear]

Bear,

It seems to me that bi-amping used to mean active and the exception was "passive bi-amping." Now it's the other way around, probably because people now have extra channels and want to try a way to use them. Passive bi-amping hardly seems worth it and I'd rather keep the power in reserve. I assumed the OP was talking about active bi-amping, perhaps I was mistaken.

Passive bi-amping ... it would take just minutes to try it.

No harm, no foul. Bi-wiring and bi-amping are concepts from almost the dawn of high-end hi-fi. With good cables (low capacitance, low inductance) and good amps, there's not really a good reason to go with either of the above as many have stated. If I wanted to listen to a higher-distortion amplifier, then these do have some merits, but only within the context of what the amplifier (or cables) do to the signal.

[Davey]

It's more descriptive to think of this as either a "line-level crossover" (before the amp) or a "speaker-level crossover" (after the amp.)

"Line-level" crossovers can either be active or passive.
"Speaker-level" crossovers are passive.

"Line-level" crossovers MUST utilize separate amplifier channels and those channels are obviously bandwidth limited. (With all the advantages that entails.)

"Speaker-level" crossovers CAN utilize separate amplifier channels but those channels are not (generally) bandwidth limited. When using multiple amplifiers ("passive bi-amping") the voltage swings would be the same, but since the high-level crossover is separated into multiple sections the current requirements on each amplifier would be different.

Hope that helps.

Cheers,

Dave.

[1Michael]

I'd like to ask another question: does anyone here actually ever play their speakers at 100dB? If so ... in what circumstances and in how big a room?

Quite often. Thats why I build big speakers :B

[Cort]

We love to go to concerts and hang out in the front so 100db is coomon at my house as well, my bird can hit 110 db so he loves it. BTW the room is 18 x 38 x8-12 foot cielings and a very open stairwell to a 30x16x12 room

[wettou]

We love to go to concerts and hang out in the front so 100db is coomon at my house as well, my bird can hit 110 db so he loves it. BTW the room is 18 x 38 x8-12 foot ceilings and a very open stairwell to a 30x16x12 room

100db hey!

Exposure Time Guidelines

Accepted standards for recommended permissible exposure time for continuous time weighted average noise, according to NIOSH and CDC, 2002. For every 3 dBAs over 85dBA, the permissible exposure time before possible damage can occur is cut in half.





The Noise Navigator®: a database of over 1700 noise sources.

Developed by Elliott Berger, MS, Senior Scientist with 3M Occupational Health and Environmental Safety Division.

http://www.e-a-r.com/hearingconservation/faq_main.cfm

http://www.cdc.gov/niosh/topics/noise/pubs/lookatnoise.html

http://www.cdc.gov/niosh/blog/

And if you have Kids with iPods

http://www.listentoyourbuds.org/

[technodanvan]

^^^

A fair point, but two things:

1. OSHA is pretty conservative with most exposure limits, I wouldn't doubt noise could be included in that. Keep in mind they post these with the intent to protect both workers from hearing damage and companies from lawsuits.

2. Studies have shown that loud noise that you WANT to hear does not generally elicit the same damage as unexpected, uncomfortable sounds. This isn't necessarily due to frequency, I think it's more due to other stressors that the nervous system creates when undergoing loud, unpleasant noises.

On-topic:

I've read a lot about bi-amping in the past and have yet to really come up with a good reason to do it. Most speakers - to include DIY and otherwise - simply don't require that much power individually. I also have serious doubts that separating the signal would alter the sound in any noticeable fashion, at least to my ears.

[wettou]

^^^A fair point, but two things:

1. OSHA is pretty conservative with most exposure limits, I wouldn't doubt noise could be included in that. Keep in mind they post these with the intent to protect both workers from hearing damage and companies from lawsuits.

2. Studies have shown that loud noise that you WANT to hear does not generally elicit the same damage as unexpected, uncomfortable sounds. This isn't necessarily due to frequency, I think it's more due to other stressors that the nervous system creates when undergoing loud, unpleasant noises.

On-topic:

I've read a lot about bi-amping in the past and have yet to really come up with a good reason to do it. Most speakers - to include DIY and otherwise - simply don't require that much power individually. I also have serious doubts that separating the signal would alter the sound in any noticeable fashion, at least to my ears.

I agree forget bi-amping unless you have an active crossover

[owdi]

Wow, lots of misinformation in this thread.

However, using a passive crossover, you do not get a power savings of any sort. In fact, you may consume more power since you are doubling the output requirements from the amplifier for that speaker e.g., the midwoofer would need 100W and the tweeter would need 100W).

Nothing about biamping doubles the output requirements from the amplifier. When using a single channel, the crossover splits the signal between the drivers and wastes some power as heat. That 100W you put into your speaker could be 50 watts to the woofer, 40 watts to the tweeter and 10 watts wasted. If you were to push 100W from each channel, well that would be 200 watts and +3db.

The main benefit to biamping the statements would be independent level control over the mid/tweet and woofer, so you wouldn't need to pad down the mid/tweet to be the same sensitivity as the woofers. This would make the statements more efficient, but would require a crossover redesign, since you can't just pull the resistors in the mid and tweeter circuits.

[Johnloudb]

2. Studies have shown that loud noise that you WANT to hear does not generally elicit the same damage as unexpected, uncomfortable sounds. This isn't necessarily due to frequency, I think it's more due to other stressors that the nervous system creates when undergoing loud, unpleasant noises.

What studies are you referring to? Is there a link you could post to that?

We respond differently to sounds we like, but I've never heard that it changes the SPL at which sound can damage your hearing. Some sounds, even really quiet sounds can hurt your ears, and cause tinnitus and hyperacusis ( increased sensitivity to sounds ). But, that's not hearing damage.

[AdelaaR]

Hearing loss is definately an isue but for critical listening I do not like the music to be too loud anyway ... I try to find the "just loud enough" setting

[Bear]

Wow, lots of misinformation in this thread.

Ouch. Okay, let's get a bit more specific. I rapidly run out of knowledge in the details of amplifier design, but my source material is pretty decent (e.g., passdiy.com).

Nothing about biamping doubles the output requirements from the amplifier.

Let's tackle this in a bit.

When using a single channel, the crossover splits the signal between the drivers and wastes some power as heat.

Agree here.

That 100W you put into your speaker could be 50 watts to the woofer, 40 watts to the tweeter and 10 watts wasted.

Yes ... and no. Let's hold impedance constant for a moment and look into this.

You have two macro level issues at work here. First, you have the amplifier design/topology. If you have a pure Class A amplifier, then you basically create a load with every energized channel (current source, rather than voltage source). With Class AB, you will have a basic bias level load, and then you will see a change in load depending upon how hard you are driving it. With other topologies, you end up with similar issues, just with lower base loads and more efficient conversion of wall electricity into delivered power to the speakers. So, energizing an incremental channel (assuming you could de-energize it in your multi-channel amp, or turning on a mono block) can cost you some amount of incremental power (real power) from the wall.

We'll get to actual gain structure here in a minute when we get back to the impedance.

Second, we need to look at the passive crossover itself, ignoring line losses from multiple sets of speaker cables since those should be minimal. The HP and LP elements (capacitors and inductors, respectively) create a reactive load at frequencies outside of the passband. Thus, from a real power standpoint, you are correct that no work is being done outside the passband, so there is no "power". However, for non-DC, you care about apparent power when looking at what you draw from the wall, and from an apparent power standpoint, the reactive load does matter. The reactive load will basically cause all of the power outside the passband to be converted to heat.

Remember: you would ideally create a crossover that had a smooth transition in terms of SPL for a given amount of applied power.

Now let's turn to a practical example with the interaction of the two. This is where gain structure and impedance comes into play. If I had two identical loads (constant impedance), then it makes sense that the load would be the same assuming that I'm using identical amps to drive each side (with the same gain structure). Once we let the two halves vary in impedance, then you can get differences in the power draw with a non-class AB amplifier, but this will be additive. In other words, if one half of the speaker was at an impedance that drew 100 watts from a voltage source, then the power draw on the other side would be <= 100 watts. With a well-designed passive crossover that doesn't create a big peak or dip at Fc, the power draw is the same.

Ignoring phase angle and going with straight Ohm's law, if you had a 4 ohm woofer section married to a 6 ohm tweeter section to produce a constant SPL at 100W of power (perfectly flat frequency response), the woofer is pulling 100 watts at 20 volts ( 100 = 4 * 5^2 ), while the tweeter is pulling 100W at 24.5 volts (100 = 6 * 4.08^2 ). You can eliminate any padding differences between the two sections to change the power draw, but you would also then create a peak or a valley in your response curve if you tried to marry the two halves back together again in a passive XO. In other words, practical speakers designed to have smooth frequency responses should basically double their power draw when you add an amplifier to bi-amp the two halves of a crossover (or triple with tri-amping for a three-way, etc.).

If you were to push 100W from each channel, well that would be 200 watts and +3db.

SPL is frequency dependent. You would need to double the power available at a given frequency to get the 3dB gain.

The main benefit to biamping the statements would be independent level control over the mid/tweet and woofer, so you wouldn't need to pad down the mid/tweet to be the same sensitivity as the woofers. This would make the statements more efficient, but would require a crossover redesign, since you can't just pull the resistors in the mid and tweeter circuits.

Because of the use of padding (resistive loads), and the design practice of creating a smooth FR through the XO region, you would expect to see equal power draw (plus or minus) when you bi-amp.

At least as far as I know. Now, what did I miss, aside from the effects of several large simplifying assumptions?

[AdelaaR]

Okay bear ... you lost me there.

[Bear]

Okay bear ... you lost me there.

No worries. Let's do it with bullet points in a different order than above.

• Well-designed practical speakers are designed to have smooth frequency response through the crossover region.
• Smooth frequency response means that you don't have a big jump or dip in SPL.
• You accomplish this by using inductors, capacitors and resistors.
• As a result of all of the above, you would see a relatively constant efficiency across the audible spectrum.
• Thus, if you are going to play the woofer and the tweeter at the same volume level in a bi-amp configuration, you will need the same power driving each, which means you have the same power consumption.
• Same power consumption means that you effectively double the power usage when going to a bi-amp configuration.
• Caveat to the above: with a multi-channel amp, you may already be "paying for" the power draw on the unused channel, depending upon its design.

You can bi-amp to use different amplifiers for the woofer and the tweeter, but then you are effectively using a quasi-active/passive hybrid crossover, and not a true fully-passive crossover.

[technodanvan]

What studies are you referring to? Is there a link you could post to that?

We respond differently to sounds we like, but I've never heard that it changes the SPL at which sound can damage your hearing. Some sounds, even really quiet sounds can hurt your ears, and cause tinnitus and hyperacusis ( increased sensitivity to sounds ). But, that's not hearing damage.

Me and my online mouth again.

What I should have said was that there are some 'theories' that this is the case, however proving it is difficult considering the generally long length of time it would take to get meaningful results.

If I recall correctly the theory originated from people noticing there are quite a few musicians who are arguably exposed to ridiculous levels of noise for extended periods without noticeable adverse affects. That said, there are definitely a percentage of them who do indeed suffer some damage, whether it be tinnitus or overall degradation.

Who knows, maybe it just has to do with the drugs/alcohol/habits off the stage.

I'll see if I can find the original study/article and PM you to avoid cluttering up this thread...I want to say it was in a music-centric magazine, though I can't recall the name.

[meb46]

Ouch... well according to NIOSH... my 45 minute gym session every day with my earphones banging away should have already driven me deaf...

Interesting thread, and I would never claim to be an expert in this field. From my experience there are few advantages on Bi-Amping. Where I have had successes is Bi-Amping Monitor Audio PL200's with a Denon 4810. Using 4 channels instead of two you can essentially deliver a slightly increased level of power... taking into account load and current draw... The PL200's love a bit more power and you can notice an audiable difference in bottom end punch... not much... but you can hear an improvement. I'm sure if these were matched with a more powerful Power Amp and Separate Pre-Amp (These are used in a music environment only) there would be no need to use a Bi-Amp approach.

Again... just my 2 cents...

[owdi]

• Thus, if you are going to play the woofer and the tweeter at the same volume level in a bi-amp configuration, you will need the same power driving each, which means you have the same power consumption.
• Same power consumption means that you effectively double the power usage when going to a bi-amp configuration.

That's the part I take issue with. It's not same power, it's same voltage. The impedance load changes when you split the woofer and tweeter, so each channel requires less current after you bi-amp.

If you did really double the power usage when you bi-amp, where does the extra power go? Heat or sound?

[AdelaaR]

Another thing: amps are never 100% efficient so when driving multiple amps ... doesn't the inefficiency add up to create more inefficiency?
Same for the connections: every connection has loss of signal ... doesn't adding more cables and more connections add more loss?

I might be wrong here (I am a newbie after all) but in my job as a telephone and XDSL technician I know that having less cables and less connections is almost always better as it reduces the chance of having problems with noise or conductivity.

[Paul Spencer]

In terms of efficiency, passive biamping would be a waste. Active biamping in theory is more efficient due to the losses of a passive crossover, but just to have an extra amp running uses up some extra power as well, quite possibly more than is saved with the active crossover.