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Learn WHY passive bi-amping isn't actually more powerful:

43K views 183 replies 21 participants last post by  markrubin 
#1 · (Edited)
If you have another 2 amp channels and mean passive aka fool's bi-amping, then no as well. This has been discussed to death. Use the search function.
I'm not so sure that would help the OP because just as many if not more people, including some with electrical engineering degrees, fall for the myth that passive bi-amping improves output power. It doesn't. And I don't mean "by much", I mean the traditional FTC 5-rule power rating spec of 20-20kHz, at X% distortion or less, continuous, into an X ohm load (often 8 or 4), X number of stated channels driven, does not increase by even a fraction of a dB!
---

Please keep an open mind and examine the evidence I will present for yourselves, everyone. It's not all that hard to understand with the following graphic I have made of an actual consumer speaker impedance load with and without the tweeter to woofer jumper bars (straps) removed (to allow a bi-amp connection). Let's look at a typical bass frequency which is easy to read on both of the charts I am about to produce, 200 Hz, found in nearly all normal music.

As we all know when passive bi-amping the two amps [the "bass" amp and the "treble" amp] in truth receive the exact same incoming full range signal. So people need to dispel this notion that the bass amp is less burdened because it doesn't "see" the full frequency range. Baloney. BOTH AMPS SEE THE FULL RANGE coming in. So in determining what an amp can do and how loud it can play before the onset of clipping we need to know two simple things:

A) The incoming signal content including its frequency, duration, and level [there's no change there]

and

B) The load the amp sees when reproducing that frequency. [OK, that one does change a bit but not in a significant way for the hardest part of the audible spectrum the amp has to drive, the low bass, as I will now demonstrate.]

Here's the animated GIF I made of a fairly typical 2-way, bi-amp capable speaker [a KEF Q100 IIRC] from another poster (AJ in Florida) . This measurement was made with good, but affordable equipment and there is a little bit of measurement slop (minor inconsistencies) which should be ignored [even how tightly you screw down your speaker wire posts, reading to reading, which alters the electrical connection's contact area, can make this sort of change] plus my Photoshop skills of combining the two images into a single, perfectly overlapped one which alternates as an animation is not so great, but I think people will get the picture.

The two alternating images show the impedance load change in ohms [0-100] on the vertical axis vs. frequency [20-20kHz] on the horizontal axis, measured at the woofer section's speaker terminals with, and then without, the jumper bars to the tweeter in place [i.e. the load the amp will see when using traditional mono-amping vs. the load when passive bi-amping]:

Notice the major changes are in the high frequencies but the low bass stays pretty consistent.

OK, that's what the load appears as to the amp under the two scenarios. Now let's use an Audio Precision analyzer [thanks to Audioholics for posting this detailed graph], to measure what a typical AVR amp channel, in this case from a Denon AVR-4310CI, can do at any given frequency in terms of maximum, continuous power output, measured in watts, in this case into the 4 ohm load the speaker poses in much of the bass range:


OK, now that way have the raw data in front of us, let's do some analysis!

Question 1: When the jumper bars to the tweeter are disconnected so we are just driving the woofer section from this amp by itself, what is the maximum continuous output level in watts this amp channel can produce at 200 Hz, into the speaker's 4 ohm load found at this frequency, before it will start to clip?

The Correct Answer: about 267 watts into the 4 ohm load

Question 2:
When the jumper bars to the tweeter are connected so we are driving both the woofer section and also the tweeter section, i.e. conventional mono-amping, what is the maximum continuous output level in watts this amp channel can produce at 200 Hz, into the speaker's 4 ohm load found at this frequency, before it will start clip?

The Correct Answer: also about 267 watts into 4 ohms!

So if our music contains the exceedingly common frequency of 200Hz, how many dB louder can the bi-amped speaker play this frequency before the onset of distortion compared to the same speaker reproducing the same music content but through mono-amping?

The Correct Answer: 0 dB louder, none, i.e. the bi-amped scenario will have clipping problems at the exact same point: that is to say it can not play normal, full range music any more loudly before it will distort (clip).

For those of you who might not know, bass is the hardest part of the frequency range for systems to reproduce, not the treble, which is why using weaker amps for the tweeters in active bi-amp setups can be a useful cost cutting move that usually won't compromise performance. But suddenly having huge amounts of reserve power for the treble, by using an equally powerful tweeter amp when bi-amping, doesn't help us for normal music reproduction because our bottleneck of how loud we can play before we start to clip is pretty much always due to the bass, such as the 200Hz example I just gave.

Passive bi-amping's claim to "improve maximum power output" is baloney, folks. You can neither measure a greater output [with normal full range music] nor hear it. People who claim otherwise are suffering from expectation bias, which is common to every single human on the planet, without exception, including myself.
 

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#2 ·
You need a frequency-dependent load to demonstrate the theoretical (and measurable) differences of passive bi-amping. As you know, I am not a fan, but you can measure the differences -- I do not think anyone would hear them. Here are my thoughts (as posted many times before, and are essentially the same as those of everybody else who argues against the relevance of "passive" bi-amping AFAIK).

Here's a thought experiment: Mix a 100 Hz and 10 kHz signal at a ratio of say 10:1. That is, the 100 Hz signal is 10 times larger than the 10 kHz signal (it is probably a much larger ratio in practice). Using a single amplifier, it generates enough voltage to deliver the combined signal to the speaker, and of course the appropriate amount of current as well. Make another assumption, that the impedance of the speaker is the same at both frequencies, not terribly likely but which is higher or lower depends on other things not worth getting into for this experiment. Now switch to "passive" bi-amping as implemented by most AVRs. The two amplifier channels have exactly the same voltage output, but now the bass (woofer) amp delivers about 10x the current of the tweeter amp due to the passive crossover in the speaker. That provides a little more headroom for the amps since there is less IR drop across the output devices due to the lower current, and distortion might be a little less. The woofer amp is not supplying current to the tweeter, and the tweeter amp is not supplying current to the woofer. That is the argument in favor, but in practice the difference is almost certainly negligible.

Here's where things converge again: If the tweeter amp was putting out the same power as the woofer amp, it would limit the same, and there would be no power benefit. That means m. zillch's analysis applies, the statement below is true, and there is no gain in max power. In fact, due to bias current in the amps and losses in the power supply and other parts of the circuit, there is likely to be a little less total power available than just using a single amplifier channel. So it could actually be a little worse than m. zillch's analysis.

TRUE!
m. zillch said:
Passive bi-amping's claim to "improve maximum power output" is baloney, folks.

A few more points of interest... Note neither driver, woofer or tweeter, sees any more power than the amp can provide. If you have a 100 W amp, the most either driver can see is 100 W. Use two 100 W amplifiers, split the frequencies through the crossover, and the woofer still sees a max of 100 W, as does the tweeter. Even with active designs the goal is not to double power using two identical amplifiers; that does not happen. It takes about 3 dB increase to provide a significant increase in volume (this is not the detection threshold, but the level at which you bump volume when someone says "turn it up a notch!"). That takes twice the power. Making it sound twice as loud in the midrange requires about 10 dB increase in SPL, and takes ten times the power. If you want it louder, you need a bigger amplifier.

There are a few more arguments pro and con but I think that covers the biggest ones. In the real world it just doesn't help.

As an aside, when I first read of passive bi-amping, I took it to mean using a passive instead of active line-level crossover between preamp and power amps, which then drove the woofer and tweeter sans crossovers in the speaker. Typical pro bi-amping approach, though active crossovers are the norm. You can then choose big bass amps, smaller tweeter amps, and save power (and size, and weight) plus implement a cleaner, steeper crossover that does not deal with speaker-level signals and thus does not add more loss and such. (Note passive speaker crossovers can help reduce impedance excursions seen by the amp, correct some phase issues, and so forth so they are not the boogeyman often portrayed -- they have their benefits, too, though a good active design will generally offer better performance.) The idea of using two identical amps, with the same signal going through them, to drive the speaker with the upper and lower crossover inputs separated, had never occurred to me and I couldn't understand why one would bother. The answer for me was not any theoretical advantage that would be inaudible but a marketing feature easily implemented to exploit the typical audiophile's misunderstanding of how it worked (or not). Hey, you've got extra amplifiers, so bi-amp and you have double the power to the speakers! Misleading...
 
#3 · (Edited)
You need a frequency-dependent load to demonstrate the theoretical (and measurable) differences of passive bi-amping.
Yes, I attempted to be careful to point out that the total and complete lack of added output power when passively bi-amping was in regards to full range music, not specific cherry-picked frequencies deceptively selected by marketers, in the overlapping crossover region where both woofer and tweeter contribute equally to the speaker's total output. In that narrow range the woofer might theoretically produce a meaningful change in the load the amp sees hence a tiny bump in maximum output can occur (potentially at least), in that range only, so for people that listen exclusively to music in just that narrow frequency range and without any other lower frequencies present that will clip at the same point they always do, there may even be a perceptible boost in maximum output for that narrow frequency range of a dB or 2 when passively bi-amping.

What's truly sad is there will now be people who will conclude:"That added, let's say 1.7dB or so boost I theoretically can achieve specifically in just the 3.5kHz region (or so), when there is no other bass content present anywhere in the song that clips at the same level it always does, must be the cause of the benefit in sound output I hear in my sighted (not blind) evaluations.:(
 
#5 · (Edited)
Yah, and as you say that is a tiny increase in maximum power,
More specifically not an increase of power output capability for full range music, 20-20kHz, whatsoever, it is only for a tiny range which is not the part that typically saps amp power capabilities, whereas doing the smart thing and selling the first amp to then buying one with double the wattage of the one you sold will truly yield an increase in power by 3dB and most importantly across all frequencies, 20-20kHz.
 
#7 · (Edited)
Obviously in any discussion of if passive bi-amping has merits, this thread's topic, the newly added amp must be one and the same, otherwise if one adds an inferior or superior design to the mix, for half of the speaker's drivers, then one isn't comparing bi-amping vs mono-amping anymore, they are instead comparing amps in general and they may differ in many regards such as power, headroom, hiss, frequency response, gain factor, than other matters.
 
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#24 · (Edited)
If this post was directed at me, I must inform you that I have stayed within your depicted, and recently added guidelines...

If you have one 50 watt amp then you have a 50 watt, useable power potential, if you will (taking the manufacturer rating at face value). If you add a second identical amplifier, you then have a 100 watt power potential. If you are able to add a third identical amp, you would have a 150 watt potential...

So how did we get to having 3 times the power, if as you keep pointing out, the voltage will theoretically remain the same (ignoring sag)...? Obviously due to the presence of three times the current.

In this example, you would in fact have 3 power supplies, powering 3 discrete circuits; and the benefits that would be produced, would be precisely as I have depicted above in other posts.

However, it should be blatantly obvious, that having 3 x the current now available, does directly translate into having more available power. Overlaying this fact one should also note that the isolation between pass band circuits produces major decrease in IMD & TIM, while also permitting superior transient headroom capabilities, when compared to scores produced by one power supply (amplifier). Having all of which can and do permit higher output levels with lower audible distortions.

All standards base their power ratings on IMD & THD limits. The most widely used limit is 1% which in fact is a point where clipping has already set in. If more current is available within a given pass band, the amplifier will not clip as soon, and the IMD & THD threshold of 1% will not be realized as soon. Isolating pass band circuits alone, greatly reduces IMD, irrespective of current demands. Ultimately, when one adheres to these objective standards, for determining power, even in part, they can only conclude that Bi/Tri amping will in fact produce, more usable power, due minimally to the presence of more current.

When one weights other factors it become obvious.

Ultimately, two power supplies are more beneficial than one, and three more beneficial then one or two...

As I am sure some of you have being also thinking about the benefits related to the isolation in back EMF, as well.:)

More current, more transient headroom, lower distortions all added to there being more usable power available; not to mention superior sonic performances, as well, and that's no baloney!
 
#8 · (Edited)
Many consumers who passively bi-amp end up using different amps and they are blissfully unaware that they quite often have different gain factors, such that they end up running their tweeters, let's say +0.5dB hotter, for example, and this perceived brightening to the sound they errantly attribute to the use of "passive bi-amping", whereas in truth what they've really done is subtly EQ'd their speakers because the tweeters and woofers aren't getting the same signal level as they normally do!
:eek:

Any proper test of passive bi-amping must set the gains identically on the two amps, using instrumentation. How often do we read of a consumer actually doing this? Pretty much never. I've personally never read of anyone using instrumentation to ensure proper levels when passively bi-amping.

Even if one sticks to the exact same brand of amplifier we know of examples were the maker specifically uses different gain factors on different models.
 
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#11 ·
Using an active electronic crossover prior to the amp so each amp sees a limited bandwidth signal [and ideally removing the speaker's passive crossover which robs power via insertion loss], indeed has some advantages but they are off topic. That method is called "active bi-amping" and this thread's topic is "passive bi-amping".

Active bi-amping is extremely rare in AVRs [as well as truly bypassing the speaker's full crossover network and going straight to the drivers via a switch or special binding posts, without major, warranty-voiding speaker modification], but passive bi-amping is quite common.
 
#12 ·
Don, my last post was written prior to reading yours above it.
 
#13 · (Edited)
I'm not so sure that would help the OP because just as many if not more people, including some with electrical engineering degrees, fall for the myth that passive bi-amping improves output power.
Power output determination is not straightforward in audio amplification. In fact, its a matter of opinions. Many ranging opinions. Hence why so many standards exist that outline the quantification of such. All said standard, produce scores from a position of compromise. Meaning, that all are based on varying limits. The prime limits are in order of importance:

1. Time - how long is a device able to output its rated power
2. Load - what type (phase angle) and how low
3. Distortion limits (Waveform) - THD, IMD, TIM, and other perspectives of the same
4. Noise - Intrinsic (thermal), Additive (Ingression, Egression)

The aforementioned are the prime determinants most predominantly used by all modern test standards: IHF, CEA, FTC, EIA, UL and others.

See: http://www.avsforum.com/forum/91-audio-theory-setup-chat/2735785-what-watt-really.html#post50383929

Bi-amping can produce improvement in all of the noted prime limiting factors. Therefore, improvements in power score can result from bi-amplification, and always do.

Are they always audible to the recipient of said improvements, nope, but they are equally, not always inaudible either, and in the landscape of higher quality, traditional 2-channel reproductions, pursued by 2-channel lovers, they typically are audible to the recipients.

It doesn't. And I don't mean "by much", I mean the traditional FTC 5-rule power rating spec of 20-20kHz, at X% distortion or less, continuous, into an X ohm load (often 8 or 4), X number of stated channels driven, does not increase by even a fraction of a dB!
---
This comes down to actual measured comparisons, between devices, and such, more so than anecdotal sharing's, as the differences can, with careful amplifier selections and gain setting, be more than marginal, as you are striving to purport in here.

Please keep an open mind and examine the evidence I will present for yourselves, everyone. It's not all that hard to understand with the following graphic I have made of an actual consumer speaker impedance load with and without the tweeter to woofer jumper bars (straps) removed (to allow a bi-amp connection). Let's look at a typical bass frequency which is easy to read on both of the charts I am about to produce, 200 Hz, found in nearly all normal music.
Amplifier performance is based on reactive, varying loads, which produce ever changing phase angles and current demands, which invariably promote voltage sag. The largest demands (losses) being promoted / produced from woofers. If one was to remove / separate the power supply for the say the mid/tweeters, from that of the woofer section, improvements in not just linear power production would occur, but reductions in THD, IMD, TIM, would also occur.

And lets face it, voltage sag = direct power loss. If sag can be reduced or eliminated for any or all pass bands, more power is in fact realized via bi-amplification.

See: http://www.avsforum.com/forum/91-au...ouble-when-impedance-halved.html#post50337617

As we all know when passive bi-amping the two amps [the "bass" amp and the "treble" amp] in truth receive the exact same incoming full range signal. So people need to dispel this notion that the bass amp is less burdened because it doesn't "see" the full frequency range. Baloney. BOTH AMPS SEE THE FULL RANGE coming in. So in determining what an amp can do and how loud it can play before the onset of clipping we need to know two simple things:
Baloney - heavens no!

More current demand is more current demand. Two power supplies have more current than 1 - fact not fiction. Therefore if a woofers load promoted or brings about heavy and prolonged events of signal clipping, and with it the intrinsic increases in THS, IMD, TIM, etc. The high pass circuits will suffer in same.

However, if their respective powers supplies are discrete, even though they share the same input signal, if you will, their output stages are isolated, and will perform independently of one another.

Now, If a woofer has its own power supply, and a mid/tweeter have their own power supply, each producing heat, creating losses, current withdrawals, etc., from their respective power supplies, instead of one shared power supply, how is it you believe that with twice the power supplies that the onset of clip isn't in fact, pushed further out?

It is, and it is an academic truth. Twice the available current, is current now made available to the same channel, even thought the Voltage theoretically should remain the same. Separating or adding more power supplies, will always push the onset of clip, further out, within each pass band.

Look at it this way. If your amp has a fuse rating of 4 amps, you only have 4 amps. if you add another identical amp, you have 4 more amps, equaling 8 in total, to feed your two speakers. In this way, the onset of clip will become pass band dependent, and further out, equaling more useable power - more power period!

Making the title of this thread BALONEY: Learn WHY passive bi-amping isn't actually more powerful:

See this link:http://www.avsforum.com/forum/91-audio-theory-setup-chat/2735785-what-watt-really.html#post50383929

And this one: http://www.avsforum.com/forum/91-au...ker-excursion-what-causes-5.html#post50887169

And this one too: http://www.avsforum.com/forum/91-au...ouble-when-impedance-halved.html#post50337617

A) The incoming signal content including its frequency, duration, and level [there's no change there]

and

B) The load the amp sees when reproducing that frequency. [OK, that one does change a bit but not in a significant way for the hardest part of the audible spectrum the amp has to drive, the low bass, as I will now demonstrate.]

Here's the animated GIF I made of a fairly typical 2-way, bi-amp capable speaker [a KEF Q100 IIRC] from another poster (AJ in Florida) . This measurement was made with good, but affordable equipment and there is a little bit of measurement slop (minor inconsistencies) which should be ignored [even how tightly you screw down your speaker wire posts, reading to reading, which alters the electrical connection's contact area, can make this sort of change] plus my Photoshop skills of combining the two images into a single, perfectly overlapped one which alternates as an animation is not so great, but I think people will get the picture.

The two alternating images show the impedance load change in ohms [0-100] on the vertical axis vs. frequency [20-20kHz] on the horizontal axis, measured at the woofer section's speaker terminals with, and then without, the jumper bars to the tweeter in place [i.e. the load the amp will see when using traditional mono-amping vs. the load when passive bi-amping]:

Notice the major changes are in the high frequencies but the low bass stays pretty consistent.

OK, that's what the load appears as to the amp under the two scenarios. Now let's use an Audio Precision analyzer [thanks to Audioholics for posting this detailed graph], to measure what a typical AVR amp channel, in this case from a Denon AVR-4310CI, can do at any given frequency in terms of maximum, continuous power output, measured in watts, in this case into the 4 ohm load the speaker poses in much of the bass range:


OK, now that way have the raw data in front of us, let's do some analysis!

Question 1: When the jumper bars to the tweeter are disconnected so we are just driving the woofer section from this amp by itself, what is the maximum continuous output level in watts this amp channel can produce at 200 Hz, into the speaker's 4 ohm load found at this frequency, before it will start to clip?

The Correct Answer: about 267 watts into the 4 ohm load

Question 2:
When the jumper bars to the tweeter are connected so we are driving both the woofer section and also the tweeter section, i.e. conventional mono-amping, what is the maximum continuous output level in watts this amp channel can produce at 200 Hz, into the speaker's 4 ohm load found at this frequency, before it will start clip?

The Correct Answer: also about 267 watts into 4 ohms!

So if our music contains the exceedingly common frequency of 200Hz, how many dB louder can the bi-amped speaker play this frequency before the onset of distortion compared to the same speaker reproducing the same music content but through mono-amping?

The Correct Answer: 0 dB louder, none, i.e. the bi-amped scenario will have clipping problems at the exact same point: that is to say it can not play normal, full range music any more loudly before it will distort (clip).

For those of you who might not know, bass is the hardest part of the frequency range for systems to reproduce, not the treble, which is why using weaker amps for the tweeters in active bi-amp setups can be a useful cost cutting move that usually won't compromise performance. But suddenly having huge amounts of reserve power for the treble, by using an equally powerful tweeter amp when bi-amping, doesn't help us for normal music reproduction because our bottleneck of how loud we can play before we start to clip is pretty much always due to the bass, such as the 200Hz example I just gave.

Passive bi-amping's claim to "improve maximum power output" is baloney, folks. You can neither measure a greater output [with normal full range music] nor hear it. People who claim otherwise are suffering from expectation bias, which is common to every single human on the planet, without exception, including myself.
Like I said, we need to explore real measurements, so let's look at mine, I will post them in a moment.

Or just visit this link:
http://www.avsforum.com/forum/91-au...ker-excursion-what-causes-4.html#post50872409
 
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#15 · (Edited)
Like I said, we need to explore real measurements, so let's look at mine, I will post them in a moment.
Yours? Assuming it's even your actual work, I can tell you in advance I doubt I'll be responding because of my respect for Bruce Hofer, co-founder of Audio Percision, regarding this very serious matter:
Based on what I uncovered and documented about your recent behavior in our forum in this post and the ones immediately following it, don't be surprised by my limited responses, if any:

http://www.avsforum.com/forum/91-au...ught-i-d-share-under-review.html#post50912513
 
#14 · (Edited)
Don, yes there are many perks to active bi-amping, which I myself have done as well, but the selling point that naïve consumers fall for is that passive bi-amping will net them a +3db gain since they've, um, "doubled the power". Oy.

Not only not true, they don't even gain a half dB over the full 20-20kHz range. That 200Hz note in my example will clip at exactly the same point in both the mono and bi-amp scenarios.

And I like your point that AVR's per channel power capability is actually worse when all channels are driven instead of just two, BTW. I've thought about that too but decided to focus on why passive bi-amping an AVR is a bad idea assuming a best case scenario where all the amps have the same power no matter how many you use. . . . Migrating people to understanding that passive bi-amping is actually worse is a hurdle for another day.
 
#16 · (Edited)
Yes there are many perks to active bi-amping, which I myself have done as well, but the selling point that naïve consumers fall for is that passive bi-amping will net them a +3db gain since they've, um, "doubled the power".
Not only not true, they don't even gain a half dB over the full 20-20kHz range.
What about at the usable power? A heavy load can cause a power supply to clip very early, producing THD scores well above 1% and in some cases, can truncate the usable power score by 50%.

In these cases, adding one or more amps (if possible), could potentially realize an improvement in useable power to the tune of the 50% lost, equalling 3dB and thats before we factor contributions made from the improvements in transiant headroom, that the second or third power supply intrinsically present.

Zillich, don't get me wrong mate, I am mostly with you. But, when you use terms like baloney, myth, fool, hog wash and the alike, as to suggest something to be utter nonsense, delivered as to degrade another member, you will always find me debating against you as an outlier.

Of coarse in most settings, adding a second amplifier, won't result in a doubling of output power, but in some it most certainly can. Therefore there is no need to use such inflammatory and defamatory terminology.

A power supply is a current and not just a voltage supply. If I have two current/power supplies of the same geometry, I in fact have twice the current present to feed the same speaker circuits, which will not only result in less voltage sag, THD, IMD, TIM etc., it will result in such occurrences being independent, one discrete pass band from another.

Larger 3/4 ways speaker systems could easily gain a 3dB gain in usable power output by removing the high pass drivers from the woofer section.Not so much from the woofers being able to be played louder, before audible distortion sets in, but from the high pass being able to; now having less THD IMD etc, present, and therefore being able to be played louder, before you can't personally deal with the distortions. Short of full on clip, most of us hardly notice the massive THD coming from our woofers, but from our mid and tweeter, we seem to be hyper intolerant.

For those of us that like to play our systems out past 90dB, bi-amping is a no brainer!
 
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#25 · (Edited)
@DonH50 Just to be sure you understand I am looking for an answer regarding my last post from you and you alone. I ignore the posts this guy above writes [and have only scanned them briefly] because of his behavior in not one but two distinct posts, separated by two days time so it can't be a "failure to remember how to quote others", which I documented in three posts of my own starting here. This is out of my deep respect for Bruce Hofer, an important person in audio.

If I haven't provided the sufficient data necessary showing the output of this amp at 200Hz into a certain load, 4 ohms, and the impedance load of this speaker at 200Hz for the two different states, connected to the tweeter network input and not connected, also happening to be conveniently 4 ohms in both states, then I would like you to please tell me what else is necessary to determine this amp's maximum continuous output at this frequency, using this speaker. Thanks.

P.S. There's no way I'm going to find a PowerCube measurement of this amp on line but I suspect that's not really necessary to get a ballpark figure and that we can make certain assumptions about the performance into typical speakers seeing only their impedance graph by frequency, which I have provided.
 
#26 · (Edited)
@DonH50 Just to be sure you understand I am looking for an answer regarding my last post from you and you alone. I ignore the posts this guy above writes [and have only scanned them briefly] because of his behavior in not one but two distinct posts, separated by two days time, which I documented in three posts of my own starting here. This is out of my deep respect for Bruce Hofer, an important person in audio.

If I haven't provided the sufficient data necessary showing the output of this amp at 200Hz into a certain load, 4 ohms, and the impedance load of this speaker at 200Hz for the two different states, connected to the tweeter network input and not connected, also happening to be conveniently 4 ohms in both states, then I would like you to please tell me what else is necessary to determine this amp's maximum continuous output at this frequency, using this speaker. Thanks.

P.S. There's no way I'm going to find a PowerCube measurement of this amp on line but I suspect that's not really necessary to get a ballpark figure and that we can make certain assumptions about the performance into typical speakers seeing only their impedance graph by frequency, which I have provided.
Ignoring my comment(s) is to ignore the facts at hand.

You have produced a massive volume of posts within this forum, putting forth innumerable assertions, and here you are before us now, clearly evidenced as not understanding AC power measurements, looking for a life line from a well know EE in these forums.

For him to come to your compete aid, he would have to retract some of his statements, relating to the need for frequency based, impedances measurements derived from actual speaker loads (in this and other threads).

More specifically the very one that you are asking clarification from him for...

Your measurements are not your own, but a mish mash of others work, strung together in an attempt to support your assertions within the thread.

What you have failed to realize is that the two graphs are not related - AT ALL!

The Amplifier power graph is based on a short term, sweep, while connected to a non-inductive resistor, not a speaker, and most certainly, not the speaker that you have presented to based your calculations on.

Your assertions cannot be upheld with what you have presented, sorry, but that is simply how it is...:confused:
 
#29 ·
If there is no crossover then the original test case will show the amplifier clips at the same level, of course.

I'm going to try once more with a hand-waving example; I need to get to church so please forgive if I miss something or make a bone-headed error.

Ignoring the reality of absolute levels let's say we have two identical signals spaced well above and below the crossover point. Make them both 1 Vpp and let the load be 1 ohm just for fun with an ideal crossover. If they are in phase then the amplifier must deliver 2 Vpp into 1 ohm, a maximum of 2 App and 4 W instantaneous. Apply the same signal to two different amplifiers, and both must deliver 2 Vpp to stay linear no matter the load. Now take the output of the two amplifiers and send them through a crossover. The woofer no longer sees the high-frequency signal, and assume to the woofer amp the crossover is ideal and presents an open circuit at the higher frequency. Then, the HF is filtered out, and the woofer amp is only delivering 1 Vpp, 1 App, and 1 Wppi to the woofer. Note the amplifier still has 2 Vpp at its output, and 1 App is delivered to the woofer, so 2 W comes out of the amplifier. The same analysis holds for the tweeter amp, in that the LF signal is filtered out, so it also only delivers 1 Vpp, 1 App, and 1 Wppi to the tweeter whilst 2 Wppi is at the output of the amplifier. So, our two amplifiers, driven by the "passive bi-amp" outputs of an AVR, both generate 2 Vpp at their output, but the actual power delivered by each amplifier is reduced in this scheme. The voltage delivered does not change, so to the extent that the amplifier's output is voltage-limited, there is no benefit to passive bi-amping. If headroom is limited by current delivery, you can gain a bit, but in practice that is generally very small given a reasonable power supply (limited voltage sag) and output devices (limited IR drop). In an AVR, there is no net reduction in demands upon the power supply, and in fact the overall power requirements increase somewhat since the amplifiers are not 100% efficient. Ditto thermal demands. So for an AVR using passive bi-amping there is a net loss in overall power available.

In the real world, bass signals tend to use significantly more power than high frequencies, so the actual power difference is much larger. HF signals may contribute little to the actual output voltage swing and thus passive bi-amping has even less impact on overall performance.

If you stick a crossover before the power amps, the situation is completely different, and now you can take advantage of splitting the signal frequencies to benefit the amplifiers. Still doesn't double the power, though, unless you double the size (power) of the amplifiers.
 
#32 · (Edited)
Thank you Don, for taking a moment before you head out to worship this morning.

I believe in the context of a so-called passive bi-amp config, using a single AVR, the pros and cons are clear and agreed upon. Outside of such, and more directly to the implications that the title of the this tread implies, still seem to be a little up in the air, at least to the OP.

Beyond his presentation of a title for this thread, he defined measurement standards, and using them stated that absolutely no power gains can be realized from moving to a bi-amped configuration, of any kind. He further, defined the kinds of bi-amping, as to include in the discussion, but limited such other topologies, to only include identical amplifiers: make, model etc...

It has been with regards to these additional topologies that I have taken exception to his assertions.

For clarity sake, I have been speaking into passive bi/tri amping using only passive networks, not active, which promote even greater sonic potentials.

Using Zillch's cited FTC metric for power determination, one can easily measure power gains, by adding discrete, identical power supples to each passband. Using the FTC standards, and the actual reactive loads for each passband, combined vs discrete IMD and THD scores, will significant shift, as to increase the final useable power score using the cited FTC metric. Those gains are greater than zero as Zillch has claimed.

Zillch claims that there would be absolutely no gains in power, framed with a cited metric, and conditions..., within them he's, ultimately, wrong.

His posted measurements, are not made within the context that he set forth, nor are they representative of anything relevant, as they lack phase angle information, and frequency based impedance/resistances, as you mentioned early on (the sweep provided is based on a 4-ohm non-inductive resistor, not the speaker impedances and phase angles that the amplifier would in fact see, iff you will. Making his posted power estimates bogus!).

Now here he stands, confused as to why I keep stating that his measurements are not only not related to each other, but also, not supportive towards his assertions.

Ultimately, what irks me the most, he seem to be casting a dark shadow over those of whom that claim to have gained sonic betterment by shifting to discrete channel amplification of more passbands. If done correctly, sonic betterment is alway the outcome, even using a single AVR (now I am speaking more towards fidelity than anything else).

Again, thank you Don for chiming in before you head out, presumably with others.

Cheers, jj:)
 
#30 · (Edited)
@DonH50 I look forward to you answering my question which was directed specifically to you and nobody else, when you return and have the time to respond to it, thanks.
 
#43 ·
Mr Zilch's example is utilizing a lot assumptions and within those constraints I do not disagree with most of his conclusions. The important thing to remember is why we are having this discussion, and that is the benefit of vertical bi-amping, which most people agree is negligible. So even in the perfect world where vertical bi-amping provides a 3db increase in system power the benefits are still suspect at best. Mr. Zilch wants to further define this as less worthwhile, while at the same time most agree that it isn't worthwhile under the perfect scenario.
 
#44 ·
So you agree with the use of assumptions, to reach an objective conclusion. Good to know:eek:

Zillch introduces much in the way of assumption, no argument from me; however, he nails them all to the floor, of objective scrutiny, by means of citing power measurement standards, and making claims that absolutely zero increases in power can be measured, via bi-amping, period!

Well that dog doesn't and didn't hunt so well within this thread.;)
 
#45 · (Edited)
Vertical passive biamping and horizontal passive bi-amping are similar in that they are worthless in an attemptt to get higher output and neither provides 3dB greater output over a singular stereo amp.
 
#46 · (Edited)
Vertical passive biamping and horizontal passive bi-amping are similar in that they are worthless and neither provides 3dB greater output over a singular stereo amp.
We are still waiting for technical evidence, relevant measurements, made from your own hand / review in support of your claims in here (now adding 'worthlessness' to the list). The measurements that you have posted thus far don't uphold your assertions, they don't even apply!

If you can produce such objective evidence, i will be the first to spot it, point it out, and up hold; while at the same time rescinding my original positions.

I have posted and linked much technical support, which up holds my assertions, and I can most certainly present more.

The proof that you require can only be measured, and in a specific way. You have cited the FTC standards body. Please present proper measurements, utilizing FTC guidelines to uphold your assertions.

Thank you:)
 
#49 · (Edited)
Vertical passive bi-amping and horizontal are so passé,

all the cool kids are now running criss-cross passive bi-amping: The L ch of stereo amp A does the HF of the L spkr., the R ch does the LF of the R spkr, and the L ch of stereo amp B does the HF of the R spkr., and the R ch. does the LF of the L spkr.

It can be confusing but it reduces crosstalk frequency exchange overlap distortion.:p
 
#52 ·
Vertical passive bi-amping and horizontal are so passé,

all the cool kids are now running criss-cross passive bi-amping: The L ch of stereo amp A does the HF of the L spkr., the R ch does the LF of the R spkr, and the L ch of stereo amp B does the HF of the R spkr., and the R ch. does the LF of the L spkr.

It can be confusing but it reduces crosstalk frequency exchange overlap distortion.:p
CFEOD is evidently a new form of distortion. Please elaborate.....
 
#54 · (Edited)
Zillch:

You introduced this thread and set the context to measurement!

But your measurements don't hunt, so now all we get is more anecdotal infusions?

Where are the actual, relevant measurements that you are basing your assertion on. You have only proved that you don't understand AC power calculations, by drawing summaries based on measurements that are not related, one to the other. Making your summaries, invalid!

You claim repeatedly that Bi-amping not only does not increase the usable power within a given circuit, put that it's worthless on the whole, as to suggest it has not sonic benefits. Do you require me to cite all of your posts in which you make such invalidated and derogatory statements?

Here's how you opened the thread...

Your text RED & BLACK

My text BLUE


I'm not so sure that would help the OP because just as many if not more people, including some with electrical engineering degrees, fall for the myth that passive bi-amping improves output power. It doesn't. And I don't mean "by much", I mean the traditional FTC 5-rule power rating spec of 20-20kHz, at X% distortion or less, continuous, into an X ohm load (often 8 or 4), X number of stated channels driven, does not increase by even a fraction of a dB! - You greatly encumbered yourself here, specifically to an FTC measurement metric!
---

Please keep an open mind and examine the evidence I will present for yourselves, everyone. It's not all that hard to understand with the following graphic I have made of an actual consumer speaker impedance load with and without the tweeter to woofer jumper bars (straps) removed (to allow a bi-amp connection). Let's look at a typical bass frequency which is easy to read on both of the charts I am about to produce, 200 Hz, found in nearly all normal music.

As we all know when passive bi-amping the two amps [the "bass" amp and the "treble" amp] in truth receive the exact same incoming full range signal. So people need to dispel this notion that the bass amp is less burdened because it doesn't "see" the full frequency range. Baloney. BOTH AMPS SEE THE FULL RANGE coming in. So in determining what an amp can do and how loud it can play before the onset of clipping we need to know two simple things:

A) The incoming signal content including its frequency, duration, and level [there's no change there] - hang on here as well, you are inferring that the input signal irrespective of the load demands, is somehow equal in significance. it isn't. If the speaker is prevented or intrinsically doesn't present a significant load within a particular bandwidth, the amplifier doesn't produce sufficient current, as to produce significant Wattages, irrespective of the voltage present. Therefore, by using two amps/power supplies, the bandwidth burden, if you will, that was once assigned to just the one power supply has effectively been isolated over two, and as a result, the overall current demand are lessened (split / shared - however you like to understand it), and a host of related benefits, enter the picture, if you will. Objective bench measure bring this to clear evidence. A crossover effectively divides loads as well as frequencies, as they're intrinsically connected at the hip, if you will. This allows / brings about increases in FTC power scores.

and

B) The load the amp sees when reproducing that frequency. [OK, that one does change a bit but not in a significant way for the hardest part of the audible spectrum the amp has to drive, the low bass, as I will now demonstrate.] - Well we haven't actually seen either, a the speaker impedances that you provided (without phase angle data i might add) are based on less than 1-watt. At 267 or so Watts, I promise you that a) the speaker will fail and B) if they don't the curve wouldn't look near the same, but I digress!

Here's the animated GIF I made of a fairly typical 2-way, bi-amp capable speaker [a KEF Q100 IIRC] from another poster (AJ in Florida) . This measurement was made with good, but affordable equipment and there is a little bit of measurement slop (minor inconsistencies) which should be ignored [even how tightly you screw down your speaker wire posts, reading to reading, which alters the electrical connection's contact area, can make this sort of change] plus my Photoshop skills of combining the two images into a single, perfectly overlapped one which alternates as an animation is not so great, but I think people will get the picture. - Great, a poor measurement, taken from less than lab grade gear, without the citation of conditions, presented with photos shopped alterations! But let's take it a face value for now.

The two alternating images show the impedance load change in ohms [0-100] on the vertical axis vs. frequency [20-20kHz] on the horizontal axis, measured at the woofer section's speaker terminals with, and then without, the jumper bars to the tweeter in place [i.e. the load the amp will see when using traditional mono-amping vs. the load when passive bi-amping]:

Notice the major changes are in the high frequencies but the low bass stays pretty consistent. - Yes, we all noticed the changes.

OK, that's what the load appears as to the amp under the two scenarios. Now let's use an Audio Precision analyzer [thanks to Audioholics for posting this detailed graph], to measure what a typical AVR amp channel, in this case from a Denon AVR-4310CI, can do at any given frequency in terms of maximum, continuous power output, measured in watts, in this case into the 4 ohm load the speaker poses in much of the bass range: - there is so much wrong within this paragraph, its difficult for me to decide where best to start. so please forgive me for a clumsy entrance: a) it isn't the load that the amp will see at all drive levels, it isn't even the load that was presented to the amp at all. b) the load presented was a non-inductive resistor, nothing like a speaker load. c) it isn't max continuous power, its dynamic power! d) no speaker load was presented to this DUT, but yet you keep making that claim.

Please read through this! http://www.avsforum.com/forum/91-audio-theory-setup-chat/2735785-what-watt-really.html#post50383929



OK, now that way have the raw data in front of us, let's do some analysis!

The raw data is incomplete and skewed, making it of no value.

Question 1: When the jumper bars to the tweeter are disconnected so we are just driving the woofer section from this amp by itself, what is the maximum continuous output level in watts this amp channel can produce at 200 Hz, into the speaker's 4 ohm load found at this frequency, before it will start to clip?

The Correct Answer: about 267 watts into the 4 ohm load - NOT SO - You are missing the Phase angle data!!!AND - the graph is dynamic power, not continuous... You aren't properly understanding what you're posting, into evidence! The dynamic score is also based on a sweep, not real music, and the load is a non-inductive resistor - NOT a reactive load, such as a speaker would present! The amps continuous power (based on FTC standard) will be much-much less, likely a third, with a phase angle of zero. Speaker do not present phase angles of zero outside a few frequencies.


Question 2:
When the jumper bars to the tweeter are connected so we are driving both the woofer section and also the tweeter section, i.e. conventional mono-amping, what is the maximum continuous output level in watts this amp channel can produce at 200 Hz, into the speaker's 4 ohm load found at this frequency, before it will start clip?

Now hang on, the amp test that you have posted, was not made as you are describing, it was made instantaneously, while connect to a 4-ohm, non-inductive resistor, not the speaker that you keep referring to. Making it a depiction of the dynamic power of the DUT vs frequency while connected to a resistor, not a speaker, therefore the phase angle is typically considered to be zero!

The Correct Answer: also about 267 watts into 4 ohms! NOT SO - you are missing the phase angle data!!! AND - the graph is dynamic power, not continuous... YOu aren't properly understanding what you're posting, into evidence! The dynamic score is also based on a sweep, not real music, and the load is a non-inductive resistor - NOT a reactive load, such as a speaker would present! The amps continuous power (based on FTC standard) will be much-much less, likely a third, with a phase angle of zero.

Looking at your posted graph, the amp is suffering from frequency truncations at the bottom and the top (which you note), with a non-inductive load, and a basic (meaning light) frequency sweep as the agitation! With a real load and a real signal, the performance gets worse, not better.


So if our music contains the exceedingly common frequency of 200Hz, how many dB louder can the bi-amped speaker play this frequency before the onset of distortion compared to the same speaker reproducing the same music content but through mono-amping? Your measurements don't tell us, so nor can you! And what makes '200Hz exceedingly common place' in your mind, and what relevance are you hoping that it would bear if fact?

The Correct Answer: 0 dB louder, none, i.e. the bi-amped scenario will have clipping problems at the exact same point: that is to say it can not play normal, full range music any more loudly before it will distort (clip). - You have not presented one piece of relevant information. You have strung together questionable measurements, and have drawn conclusions that cannot hold up to objective scrutiny! In other words, you have posted a slew of false statements, and failed to prove your assertions.

And from here on out, you continue in more of the same...

You really also need to review this post. It will help you understand what proper measurement and documentation looks like.: http://www.avsforum.com/forum/91-au...ker-excursion-what-causes-5.html#post50887169

You started this thread with a call to and a presentation of measurement. Now that you know your measurements are invalid as they don't adhere to the FTC standards that you cited, would you please start over...?:)

For those of you who might not know, bass is the hardest part of the frequency range for systems to reproduce, not the treble, which is why using weaker amps for the tweeters in active bi-amp setups can be a useful cost cutting move that usually won't compromise performance. But suddenly having huge amounts of reserve power for the treble, by using an equally powerful tweeter amp when bi-amping, doesn't help us for normal music reproduction because our bottleneck of how loud we can play before we start to clip is pretty much always due to the bass, such as the 200Hz example I just gave.

Passive bi-amping's claim to "improve maximum power output" is baloney, folks. You can neither measure a greater output [with normal full range music] nor hear it. People who claim otherwise are suffering from expectation bias, which is common to every single human on the planet, without exception, including myself.
Vertical passive bi-amping and horizontal are so passé,

all the cool kids are now running criss-cross passive bi-amping: The L ch of stereo amp A does the HF of the L spkr., the R ch does the LF of the R spkr, and the L ch of stereo amp B does the HF of the R spkr., and the R ch. does the LF of the L spkr.

It can be confusing but it reduces crosstalk frequency exchange overlap distortion.:p
But your benefits, IIRC, were from running individual drivers hotter hence you were EQing your system. The question is does passive bi-amping play louder [read the thread title]. It doesn't. Sure EQ is audible and has benefits but there are other ways to do it that are better in my opinion (and instantly defeatable at the touch of a button, let alone millions of times more flexible in terms of selecting frequencies, many of them, slopes, ranges, Q, shelving, etc.) 99% of the records you buy have gone through some degree of it in the studio, BTW.
You never gain 3 dB with passive biamping*. Substituting a 50watt amp with a stronger one can do stuff though, sure, but then you aren't testing if bi-amping is stronger, you are testing if stronger amps are stronger. They are.


*Meaning you have a 50w/ch stereo amp and then you buy another one of the same to use in bi-amp configuration, so you have a total of 4x 50w/ch individual channels. The net gain for the complete, 20-20kHz reproduction range in toto is 0dB.
 
#58 ·
This is a very informative discussion on this subject. If you go back and research this topic here when this subject is brought up, it is usually met with responses of "fools biamping", "snake oil", etc. I am by no means an expert or can even say I have a lot of knowledge on the subject of audio amplifiers or loudspeakers or their design and operation. I have read and researched this subject on a variety of different sites and would like to sum up what I have read and learned and perhaps the more knowledgeable members can explain how I am right or wrong in what I believe to be the answer to this subject.

Usually this begins by a member asking if it is of any benefit to passively biamp their speakers. As I stated above, they are usually given the response of it is a waste of speaker wire, time, a marketing ploy, etc. Perhaps in most cases they are correct. But as we all know there are very few instances where words like always and never apply 100% of the time. I believe they should ask the member some specifics on their equipment before answering if they truly want to answer the member's question correctly. I do understand that this is not the case with this thread.


What speakers do you have? I tend to agree that most 2 and 3 way speaker systems will not benefit very much from passive biamping. It seems as a general rule the lower frequencies put the most electrical strain or demand on an amplifier. The woofer will require the most power being supplied to the speaker from the amplifier. To keep the sound from the speaker even if passive biamping, 2 amps either identical or with the same gain level should be used. If they are 2 identical amps, say 50 watts per channel each, you would have 100 watts capacity feeding that speaker. But due to the fact that the mid/high frequency drivers do not require 50 watts to power them to levels matched to the 50 watts the woofer is receiving, you do indeed have 100 watts but that level will never be reached. In this situation I would agree 100% that using a single 100 watt amp would be more beneficial than 2 amps at 50 watts each.


What kind of amps do you have? Most of the time it is stated that they have a 5.1 set up and recently bought a new 7.1 receiver and read that they can use the 2 unused channels to biamp their front speakers. Unless it is a very high end receiver, they would probably see no to little benefit as all 7 amps probably share the same power supply. If they are using mono block amps or an external multi channel amp then there could be some benifit. The mono block amps definitely have their own power supply. The multi channel amp would depend on its construction. Some just have 1 large shared power supply while others are constructed as individual mono block amps in 1 chassis.


Since I lack total understanding of audio amps and speakers, I will try to explain as best as I can. A speaker driver is comparable to a motor. The amp is the power supply to the motor. I do know that a speaker is a lot more complex than a motor due to its constantly changing input signal and impedance. The crossover sorts out the electrical signal and sends it to the driver most suited to reproduce it. When passive biamping, the crossover will for example block the high frequencies to the woofer by increasing the impedance of those frequencies to the point that the woofer will not see them to any usable extent. I have seen it stated that both amps will clip at the same point. I don't quite understand clipping technically, but an amp usually will not exhibit audible distortion until its putting out more power than it was designed to. Using the 50 watt amps as an example, if the woofer amp is putting out say 75 watts, mid/high amp would only be putting out maybe 30 watts. How could it distort if it hasn't come close to exceeding its rated output? The mid/high amp is not putting the electrically demanding low frequencies to a speaker coil but is just dissipating that in the crossover. Therefore the current requirement to do that is minimal. The woofer amp would obviously be distorting.


My interest in this subject is due to the fact that I have been running a passive biamp set up for over 15 years on my front speakers. They are an old pair of JBL L7 speakers. They are a 4 way system with a 12" side firing sub with a mid bass, mid range and tweeter. The internal crossover is made up of 2 separate boards which are separated by the jumpers on the speaker terminals. These can be modified to be used with a preamp level crossover if desired. The cutoff frequency is 160HZ in a passive biamp set up. When I first did this, anyone who heard it before when driven with 1 amp then with the biamp wanted to know what I did to make it sound so much better. The question was brought up before I had said that I did anything. I also have matching speakers from the same line in my 5.1 set up. When I listen to music, if it is a stereo source, I listen in all channel stereo. My L5 surround speakers are a smaller 4 way design with a smaller sub but do not have the biamping capability of the fronts. I would have to eliminate snake oil and marketing ploy in this case. The L7 was top of this line and the L5 was 2nd. They do share the same mids and tweeters. I do have to increase their level from audussy setting of -3 to +3 or they are drowned out by the fronts even though they are 10' closer to the MLP. The L7's efficiency rating is only 1db higher than the L5's. Anyone who has heard my set up says the same.


This may be a little off topic but I would like to get some thoughts on something closely related to this question. Sometimes it is usually asked why the need for more power? Casual listening usually only requires a few watts of power delivered to any moderately efficient speaker system. Doubling the power will only result in a 3db increase in sound. What about transient peaks? I saw in a demonstration of a very expensive Macintosh 2 channel system. It had mono blocks with watt meters. Although the average output was around 10 watts, it was a fairly large room, peaks were regestering at 200-300 watts. I think this may be why some people ask about passive biamping because it seems to be the easiest way to get more power out of their existing equipment without buying additional equipment.


Thanks for reading all this and for any responses given. I appreciate any knowledge shared.
 
#59 ·
Great post, well written, and you made some good points about properly qualifying the gear, and what not; as well, you presented many great questions. So many, it might help if you picked one for us to start with (they are all somewhat interrelated, but having you pick the point of entry might make our initial response more interesting to you).

Great post!:)
 
#65 ·
I guess the first question would be about the amp ratings. It is mentioned that 50+50=50. I believe it would actually be 50+50=100. Only the woofer may see 50 watts while the HF would not at the same gain levels. Wether or not the the HF amp would ever be called upon to deliver its entire 50 watts, it still has the potential to do so. It would seem to me that it would make more sense to just use a 100 watt amp. In doing so it would give more power to the woofer than the 50 watt dedicated amp would. But I believe to say it is TOTALLY useless to do this is somewhat misleading. It should give you some more power. As to wether it would make a sonic difference I would think would be dependent on your speakers and the signals or program material being amplified.

To put it another way, if you drive a 707HP Hellcat 70MPH on the highway, you are not using 707HP. Would that mean it is not 707HP just because you are not using it? Is it not 707HP if you never go over 70MPH?
 
#71 ·
Agree with m.zilch in principal. This has been thoroughly discussed before, and nothing has since changed. There may be minimal increase in total output power in cases where the one amp power supply is sufficiently current limited that adding a second power supply removes a little demand. Minimal, because the most current hungry low frequencies stay with one amp so the effect isn't great. Fraction of a dB in potential increased output.
 
#75 ·
I am not sure about one thing.
If you have a passively bi-amped setup, two 100 W amps, one on woofer and one on tweeter. Lets say I play a 70Hz sinewave that requires more then 100Watts, effectively pushing amp(s) into clipping. Will amp connected to tweeter also be clipping, given that tweeter really doesn't do any work?
 
#76 ·
With a passively bi-amped system as used by most AVRs the voltage will be clipped by both amps since they get the same input signal. The crossover in the speaker will prevent out-of-band current flow into the tweeter, and thus little to no power (remember clipping does generate higher harmonics), but the voltage is essentially the same at the amplifier output terminals. Most amplifiers are designed to be voltage sources. That is perhaps the biggest argument against "passive" bi-amping. If you had a crossover before the amplifiers, the tweeter amp would not see the large bass signal, and would not clip.

HTH - Don
 
#79 · (Edited)
I think perhaps where this discussion got off track is in M.Zillch making what appear to be absolute statements. I can understand that, and see his points and agree with him in general.

If M.Zillch has said - generally yada-yada - then most of this conversation would not have occurred, though in occurring a great many important points were made and informative links provided.

I think a large part of the dispute is in MACRO vs MICRO. On the larger Macro scale, M.Zillch is right. There is not actual gain. Though perhaps on the Micro and Subtle scale there can be some real advantages.

But, very likely, in doing this, one is not going to use two 50w/ch amps. More likely one is going to use ...say... 100w/ch on the bass, and a 50w/ch amp on the Mid/High because the power demands are not as great for Mid/High.

Here is a graph of Power distribution across the spectrum for full orchestral music -



Notice above 2khz, you are using about 1/10th the power relative to the peak power region. Above 4khz you are using 1/20th of the power.

If you were building a 3-way speaker, you could very well use a 100w woofer, a 50w midrange, and a 25w tweeter and still call the rate the entire speaker system at 100w.

So, the point is, in a multi-amping system, the amps can be scaled to fit the power demand of a given frequency region. In a 3-way system Tri-Amped, you could put 100w on the bass, 50 on the mid, and 25w on the highs and still have a workable system. Though more likely you would have 100w on the bass and 50w on the Mid/High.

But that 100w on the bass still doesn't give you a +3db gain. It might give you that gain potential, but whether active or passive, you are going to balance the amp so the output of the speakers is balanced to your taste or to the balance that existed before you Bi-Amped. And Balanced Bass+Mid/High does not yield any additional gain, at any give volume.

I conceded much earlier that there are potential gain to Bi-Amping, but most of those gains are on the Micro Scale, not the Macro Scale.

There is also the potential, assuming you know enough about various amps to do so, to use amps uniquely suited to the frequency range they are assigned to. In my case, that was a Onkyo on the Mid/High and a Yamaha on the Bass. That worked exceptionally well, but that was not based on superior knowledge of amps, but rather by pure random chance as those are the amps I happened to have.

So, yes, there are advantages to Passive Bi-Amping, but those advantages are on the Micro-Scale.

Next, you can expand an existing system in this fashion, but it doesn't make economic sense when buying a new system, with very rare exceptions. Rather they buy two so-so amps, it makes more sense to buy a new better quality more power amp and forget Bi-Amping.

Bi-Amping does give you some limited ability to tune the system more to your personal tasted ...some times and on the assumption that the amps allow for this tuning.

I tried it ... I liked it ... but with my system in my space, it wasn't practice, so I went back to one amp per speaker system.

It can work, but for it to work to any great and noticeable degree, a whole lot of factors have to fall into place. It is far more a case of serendipity than synergy.

As to whether 50w+50w=50w or 50w+50w=100w, that is a matter of context. Electrically no, it is 50w+50w in the context of Bi-Amping, the answer is 50w. But there is another context in which it could be 100w, but that is a general non-technical conversational context. To have more power, you need more voltage, and two 50w/ch amps does not increase the voltage potential of the amps.

As to complex impedance, phase angle, and similar, those same factors are there whether Bi-Amping or Single Amping. Aspect of complex impedance can be isolated to one amp while not effecting the other in Bi-Amping, but these are Micro aspects, these are Subtle and not easily hearable things.

...in my opinion.

Steve/bluewizard
 
#81 ·
Notice above 2khz, you are using about 1/10th the power relative to the peak power region. Above 4khz you are using 1/20th of the power.

If you were building a 3-way speaker, you could very well use a 100w woofer, a 50w midrange, and a 25w tweeter and still call the rate the entire speaker system at 100w.

So, the point is, in a multi-amping system, the amps can be scaled to fit the power demand of a given frequency region. In a 3-way system Tri-Amped, you could put 100w on the bass, 50 on the mid, and 25w on the highs and still have a workable system. Though more likely you would have 100w on the bass and 50w on the Mid/High.
You could do this if you were building a 3 way ACTIVE multi-amp system where by the use of a line level xover you reduce th amplitude of the signals going into the MF amp and further with the signals into the HF amp.

In a 3 way PASSIVE multi-amp system, all channels will receive the same full bandwidth signal and due to the lower voltage rails on the smaller amps, they will clip first so the max otput will be determined by the smallest amp in system.
 
#85 ·
The bad news is, since the tweeter amp also clips, the high frequencies will also sound bad and more energy will be dumped into the tweeter as well since the HF signal is riding on the LF signal. So you can clip the LF signal and still blow both drivers, how cool is that? :)
 
#89 ·
In the example, 70hz was used, while the Tweeter amp will clip in the framework of the example, the tweeter will never see any of that signal, it will be blocked by the Crossover. So, there will be no sound from the Tweeter - good or bad.

At frequencies that are allowed to reach the tweeter, it would be extremely unlikely that any of those signals would clip, and therefore the tweeter would sound fine.

Plus, there are potential ways to limit the signal range to each amp. A bit convoluted, but it could none the less be done if a person were interested in investing an additional $50 to $60.

Again it is a bit convoluted because the system will have many sources. With a Pre-Amp Power amp arrangement, or where the main integrated amp has a break between the Pre and Power sections, additional passive filters could be added.

Harrison (Parts Express) makes passive in-line filters. It probably doesn't matter that high frequency signals are applied to the Bass Amp, and low frequencies could be reduced in the Tweeter Amp. If we assume a 2-way speaker crossing over at 2500hz.

A Harrison High Pass at 500hz should reduce the bass load on the Tweeter Amp.

http://www.parts-express.com/cat/binding-posts-plates/309

Probably more ideal would be a High Pass in the 1000hz to 1500hz range. But I don't see those listed.

It is not an insurmountable problem, but it is a concern.

The presence of a clipping signal is there, but it matters little because that signal never reaches the Tweeter.

Steve/bluewizard
 
#100 · (Edited)
Oh I forgot the most important one:

C) It demonstrates that although the treble amp is burden by having to reproduce the bass, the bass amp is hardly burdened by having to reproduce the treble! This is key. Lightening the load in the high frequencies doesn't effectively help the bass amp when passively bi-amping, at all, and it will still clip on that 200Hz note at the same level it always does, regardless of if it is connected to the speaker's tweeter section with the jumper bars or not, because the load it sees doesn't change in the range it has to reproduce:


So in reproducing the entire 20-20kHz range your bottleneck is always how loudly you can potentially play the bass notes. Gaining tons of reserve power for the treble doesn't get you anywhere if what you care about is full range music reproduction.

Q: How much louder can a passive bi-amp system potentially play full range music, 20-20kHz?
A: 0 dB louder, because you get bottlenecked by what you can potentially do for the deep bass and that doesn't increase.
 
#104 · (Edited)
I'm sorry my animation doesn't show phase angles too, folks. I made the animated image years ago and since I don't own the necessary gear to make such measurements on my own (and never claimed otherwise) I'm extremely limited by having to make measurements/readings only from graphical images I happen to be able to find on the web.

Speaking of which, here are two random speaker examples which illustrates that having a nice, easy 0 degrees phase angle at about 200/250Hz, or so, into a ~4 ohm load, is not unusual at all, hence the 4-ohm CPF-BW graphic I showed from Audioholics depicting the amp's maximum continuous power output in watts, measured into a non-inductive, 4-ohm dummy load (being about 267w measured at 200/250Hz, under both bi-amp and single amp scenarios), is absolutely representative of what this actual amp could potentially do if playing such a 200/250Hz tone, or so, into such a speaker's actual load:

[For those who might not know the impedance curves are the solid lines measured on the left edge and dotted lines are the phase angles measured on the right edge.]



Sources:
http://www.stereophile.com/content/polk-audio-lsi7-loudspeaker-measurements#kuqwpWczRllAQm9K.97
http://www.stereophile.com/content/...-loudspeaker-measurements#1p89MsvL1yUc6wxe.97
 
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