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post #1 of 184 Old 03-04-2017, 12:13 AM - Thread Starter
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Arrow Learn WHY passive bi-amping isn't actually more powerful:

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Originally Posted by A9X-308 View Post
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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post #2 of 184 Old 03-04-2017, 09:13 AM
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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!
Quote:
Originally Posted by m. zillch
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...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #3 of 184 Old 03-04-2017, 09:57 AM - Thread Starter
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Quote:
Originally Posted by DonH50 View Post
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.

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post #4 of 184 Old 03-04-2017, 10:17 AM
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Yah, and as you say that is a tiny increase in maximum power, well beyond where anybody would notice, nothing that would be heard during normal listening...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #5 of 184 Old 03-04-2017, 11:02 AM - Thread Starter
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Quote:
Originally Posted by DonH50 View Post
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.

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Quote:
Originally Posted by DonH50 View Post
Yah, and as you say that is a tiny increase in maximum power, well beyond where anybody would notice, nothing that would be heard during normal listening...
Hi Don

In the case of three way designs such as some of the large Paradigm Reference series, would you not agree that shifting from a single channel power source such as an AVR to at least 2 separate/discrete channels, could produce sonic improvements, by means of eliminating linear and non-linear voltage sags in say the mids-through to the high pass circuits?

Would you not also agree that the probability of their being less THD, IMD and TIM being outputted from the high passed amp(s), would be significant, and likely port sonic benefits?

In the way of moving from AVR power sources to separates, there is typically an improvement in channel separation and S/N scores as well. In that channel separation scores directly correlate to the quality of stereo sound field development, would you not agree that moving into a bi-amped configuration could also port these improvements as well (amplifier quality being prime)?

I also noted signal to noise scores and suggested that moving from an AVR to an external power amplifier can present better signal to noise ratios. It has often been stated that the music resides in the difference between the signal and the noise! Would you not also agree that such potentials should be explored?

In fact, all of these potential benefits are available through bi-amplification (and more). Careful amplifier selection is prime, as is subsequent gain / level setting, but all of these benefits and more, are in reach.

Less noise, less THD-IMD-TMD all sum to equal more useable power. After all, all power measurement standards use the aforementioned scores to limit / govern their respective post power ratings.

When it comes down to channel separation, more is always better. With -50dB of separation being effectively equal to mono, score of -60, -70, aren't much better. In fact scores of -80dB are considered the minimum for high quality, so called stereo reproductions. Scores of out pas -90dB are prime. Therefore, major improvements in a stereo sound field can be realized from careful bi-amped upgrades as well. Better stereo power, if you will.

Just thinking out loud, any thoughts?

Thanks

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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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post #8 of 184 Old 03-04-2017, 11:21 AM - Thread Starter
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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!


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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post #9 of 184 Old 03-04-2017, 11:41 AM
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Quote:
Originally Posted by Jady Jenkins View Post
Hi Don

In the case of three way designs such as some of the large Paradigm Reference series, would you not agree that shifting from a single channel power source such as an AVR to at least 2 separate/discrete channels, could produce sonic improvements, by means of eliminating linear and non-linear voltage sags in say the mids-through to the high pass circuits?
That is a different scenario from passive biamping using an AVR and its single power supply. And of course it depends upon how severe the sags, and the extent to which they are alleviated by independent supplies, assuming that is your argument. Passive biamping using an AVR, even with external amplifiers, still affords essentially no improvement in voltage headroom since every channel has the same input signal. Most AVRs do not place a line-level crossover before the power amps -- that is what took me by surprise when I first heard about this scheme. Using a crossover before the power amps, which is the way I have always done it, can provide significant benefits. Maybe I am not understanding your point?

Quote:
Would you not also agree that the probability of their being less THD, IMD and TIM being outputted from the high passed amp(s), would be significant, and likely port sonic benefits?
It sounds like you are talking about placing a HPF before the amplifiers; that is not what most AVRs do. Placing a crossover before the power amps can certainly bring measurable and potentially audible improvement.

Quote:
In the way of moving from AVR power sources to separates, there is typically an improvement in channel separation and S/N scores as well. In that channel separation scores directly correlate to the quality of stereo sound field development, would you not agree that moving into a bi-amped configuration could also port these improvements as well (amplifier quality being prime)?
Same answer as above. This is apples to oranges. Although channel separation is usually much, much higher than the source material even in an AVR. But the point m. zillch raised is about "passive" biamplification as implemented by most AVRs, wherein they simply drive two amplifiers in the same chassis with the same input signal, and depend upon the speaker's crossover just as if a single amplifier was used.

Quote:
I also noted signal to noise scores and suggested that moving from an AVR to an external power amplifier can present better signal to noise ratios. It has often been stated that the music resides in the difference between the signal and the noise! Would you not also agree that such potentials should be explored?
Depends upon the amps and all that jazz. Again, not the focus of this thread. I must have missed something.

Quote:
In fact, all of these potential benefits are available through bi-amplification (and more). Careful amplifier selection is prime, as is subsequent gain / level setting, but all of these benefits and more, are in reach.

Less noise, less THD-IMD-TMD all sum to equal more useable power. After all, all power measurement standards use the aforementioned scores to limit / govern their respective post power ratings.

When it comes down to channel separation, more is always better. With -50dB of separation being effectively equal to mono, score of -60, -70, aren't much better. In fact scores of -80dB are considered the minimum for high quality, so called stereo reproductions. Scores of out pas -90dB are prime. Therefore, major improvements in a stereo sound field can be realized from careful bi-amped upgrades as well. Better stereo power, if you will.

Just thinking out loud, any thoughts?

Thanks
I think your points are valid but do not generally apply to the argument against passive bi-amping as implemented by most AVRs. Maybe I misunderstood the scope of the argument; I was addressing the case wherein an AVR's unused channels are utilized to drive a speaker. The amplifiers are in the same chassis, have the same input signal, and drive the high and low inputs of the speaker's passive crossover. The voltage in and out is essentially the same for both amplifier channels, i.e. no frequency division occurs in the voltage signals, so the primary advantage is that less output current is required from the individual amplifiers. How much less depends upon the frequency content of the source and crossover frequency of the speaker, and how much of an advantage it offers depends upon the AVR's design. The net impact on the power supply is a loss since, assuming less than 100% amplifier efficiency, using an extra amplifier channel places additional demands upon the power supply (more bias for driver and output stages in the second channel, which could of course also increase crosstalk etc.)

If you took the preamp output of an AVR and drove two amplifiers, e.g. using a Y splitter from one output to drive two discrete (mono) power amps, then some of the benefits you propose could occur, but I still think they'd be slight and that's a big change from the original premise. If I were to do that, I'd stick an external crossover before the power amps, and then most if not all of your arguments would apply.
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Quote:
Originally Posted by m. zillch View Post
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.
The reasons for active bi-amping when I have done it have little to do with power. Or actually more about reducing overall power and size and weight of the amp rack. It is usually about "right-sizing" the power amps (usually don't need a 1 kW amp on the tweeters, could need it on the woofer) but more importantly enables much steeper crossovers than typically achieved by passive designs, with greater control of signal levels and phase/time alignment, to improve overall system performance. You also do not have the loss associated with passive crossovers (which can range from negligible to rather large depending upon the speaker). If you need twice the power, you need to buy twice the amp.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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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.
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Don, my last post was written prior to reading yours above it.

In A/V reproduction accuracy, there IS no concept of "accounting for personal taste/preference". As art consumers we don't "pick" the level of bass, nor the tint/brightness of a scene's sky, any more than we pick the ending of a novel or Mona Lisa's type of smile. "High fidelity" means "high truthfulness", faithful to the original artist's intent: an unmodified, neutral, accurate copy of the original master, ideally being exact and with no discernable alterations, aka "transparency".
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[quote=m. zillch;51228609]

Quote:
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: https://www.avsforum.com/forum/91-aud...l#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.

Quote:
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.

Quote:
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: https://www.avsforum.com/forum/91-aud...l#post50337617

Quote:
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:https://www.avsforum.com/forum/91-aud...l#post50383929

And this one: https://www.avsforum.com/forum/91-aud...l#post50887169

And this one too: https://www.avsforum.com/forum/91-aud...l#post50337617

Quote:
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:
https://www.avsforum.com/forum/91-aud...l#post50872409
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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.

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Quote:
Originally Posted by Jady Jenkins View Post
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:
Quote:
Originally Posted by m. zillch View Post
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:

https://www.avsforum.com/forum/91-aud...l#post50912513

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Originally Posted by m. zillch View Post
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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Quote:
Originally Posted by m. zillch View Post
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:
Hey I thought that you weren't going to respond to me.

Serious? How so?

Facts are facts, regardless of the inclusion of citation Zillch, just like statements of errors are errors, regardless of citation, meaning who presented them.

My point about me having to post measurements is based on what Don presented:

Quote:
DonH50: You need a frequency-dependent load to demonstrate the theoretical (and measurable) differences of passive bi-amping.
Your measurement don't objectively support your assertions for the prime reason that he stated above. They are an incomplete, inaccurate depiction and therefore wholly unusable.

Here's a link to what proper measurement and summary looks like: https://www.avsforum.com/forum/91-aud...l#post50872409

I have never posted, in technical error. Regardless... but you have!

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Originally Posted by Jady Jenkins View Post
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%.


Useable power is already stated in the amplifiers specs. If a user is always in your near clipping scenario the correct advice is that a more powerful amplifier is needed.


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

No, the speakers power is already balanced out between the low and the high frequency range.
With bi-amping the removal of the connections between high and low sections doesn't change the low section into a "A heavy load " requiring another amplifier.


Quote:
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.

No, it can't. Not without adding a second set of identical speakers.


Quote:
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 desecrate pass band from another.

See above, If amplifier can't cope with the current demand of the loudspeaker to be bi-amped trade in amp and buy a more powerful amplifier.


Quote:
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, but from the high pass 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 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!

"Easily gain 3dB in usable power" is nonsense. In a passive bi-amping setup preventing powerline voltage sag is not going to materialize in 3dB more power. Play louder and run 2 amps into clipping.
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[quote=Frank Derks;51240537]
Quote:
Useable power is already stated in the amplifiers specs. If a user is always in your near clipping scenario the correct advice is that a more powerful amplifier is needed.
Well, short-term, dynamic power is noted based on a non-inductive load (resistor), so usable power isn't actually listed (well at least 90% or more of the time) - Agreed, with regards to the second half of your post.

Quote:
No, the speakers power is already balanced out between the low and the high frequency range.
With bi-amping the removal of the connections between high and low sections doesn't change the low section into a "A heavy load " requiring another amplifier.
- I'm not saying that but thanks!

Quote:
No, it can't. Not without adding a second set of identical speakers.
- In my context it is possible! But thanks for you opinion.

Quote:
See above, If amplifier can't cope with the current demand of the loudspeaker to be bi-amped trade in amp and buy a more powerful amplifier.
Obviously, and bi-amp if you can afford too.

Quote:
"Easily gain 3dB in usable power" is nonsense. In a passive bi-amping setup preventing powerline voltage sag is not going to materialize in 3dB more power. Play louder and run 2 amps into clipping.[/
In my well framed context - absolutely.

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Originally Posted by DonH50 View Post
That is a different scenario from passive biamping using an AVR and its single power supply. And of course it depends upon how severe the sags, and the extent to which they are alleviated by independent supplies, assuming that is your argument. Passive biamping using an AVR, even with external amplifiers, still affords essentially no improvement in voltage headroom since every channel has the same input signal. Most AVRs do not place a line-level crossover before the power amps -- that is what took me by surprise when I first heard about this scheme. Using a crossover before the power amps, which is the way I have always done it, can provide significant benefits. Maybe I am not understanding your point?



It sounds like you are talking about placing a HPF before the amplifiers; that is not what most AVRs do. Placing a crossover before the power amps can certainly bring measurable and potentially audible improvement.



Same answer as above. This is apples to oranges. Although channel separation is usually much, much higher than the source material even in an AVR. But the point m. zillch raised is about "passive" biamplification as implemented by most AVRs, wherein they simply drive two amplifiers in the same chassis with the same input signal, and depend upon the speaker's crossover just as if a single amplifier was used.



Depends upon the amps and all that jazz. Again, not the focus of this thread. I must have missed something.



I think your points are valid but do not generally apply to the argument against passive bi-amping as implemented by most AVRs. Maybe I misunderstood the scope of the argument; I was addressing the case wherein an AVR's unused channels are utilized to drive a speaker. The amplifiers are in the same chassis, have the same input signal, and drive the high and low inputs of the speaker's passive crossover. The voltage in and out is essentially the same for both amplifier channels, i.e. no frequency division occurs in the voltage signals, so the primary advantage is that less output current is required from the individual amplifiers. How much less depends upon the frequency content of the source and crossover frequency of the speaker, and how much of an advantage it offers depends upon the AVR's design. The net impact on the power supply is a loss since, assuming less than 100% amplifier efficiency, using an extra amplifier channel places additional demands upon the power supply (more bias for driver and output stages in the second channel, which could of course also increase crosstalk etc.)

If you took the preamp output of an AVR and drove two amplifiers, e.g. using a Y splitter from one output to drive two discrete (mono) power amps, then some of the benefits you propose could occur, but I still think they'd be slight and that's a big change from the original premise. If I were to do that, I'd stick an external crossover before the power amps, and then most if not all of your arguments would apply.
Thank you Don, for your carefully expressed comments.

FYI my comments have been in response to Zillch's related assertions put forth to uphold his threads title: Learn WHY passive bi-amping isn't actually more powerful:

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Quote:
Originally Posted by m. zillch View Post
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. ....
You are pointing out the biggest misunderstanding in Passive Bi-Amping. If you apply 50w to the woofer, and 50w to the Tweeter then the total is 50w not 100w.

If you use a single 50w amp and apply it to a complete speakers, then both the woofer and the tweeter have 50w of potential applied to them. If you break the Woofer/Tweeter apart and apply a 50w amp to each of them, then the woofer still have 50w of potential applied to it, and the Tweeter still have 50w of amp potential applied to it. The originally had 50w each and they still have 50w each, it is just that in the second case, they have a separate and different 50w amp applied but it is still 50w.

Using math, the rail or peak voltage of a 50w amp is P = SqRt(P x R). We will assume that the power was rated at 8 ohms, and so use an 8 ohm load.

P = SqRt(50 x 8) = SqRt(400) = 20 VOLTS

Now we do the same for 100w amp -

P = SqRt (100 x 8) = SqRt(800) = 28.28 VOLTS.

If you have a 50w amp on the Woofer, and a 50w amp on the Tweeter, the maximum voltage potential is limited to 20v. It doesn't go up because there are now two amps.

But, there could be some advantage in having independent control of the Woofer and Tweeter, that is, assuming the Amp used allow some degree of independent control. For example, if the tweeter is overly bright, you can turn that amp down just a small amount to smooth the response relative to your personal taste, and of course, you can always turn the bass up a bit too.

The above has an advantage over the tone controls as the tone controls tend to work on a slope. That is the change is not uniform across the effected frequency. But by turning the Amp up or down, it is uniform across the range that the drivers the amp is connected too.

As in my example, on the other thread, by random change I use two amp that were very suited to the task they were assigned. The Onkyo Amp was very well suited to clear Mid/High, and the Yamaha was very well suited to bass. Between the two I have never heard my speakers sound better.

Did I level match? Yes, I connected only the Mid/High section and played Pink noise, The Right speakers was standard single amp wiring, the Left speaker was Bi-Amp using the amps described. I measure the Right standard speaker, and adjusted the Mid/High to the same measured level. But at the same measured level, there was still too much Mid/High, I dialed it back a bit to suit my personal taste, and this work fantastic. Like I said, never heard those speaker sound better.

But this happened by random change. Those just happened to be the two amps I had. For someone starting cold with different amps and trying to determine which amps will sound best together is a very difficult, long, arduous, and expensive task. Unless you want to make a hobby of it.

I suspect for someone with a lot of first hand knowledge and experience with a wide variety of amps, you might be able to guess which combination would work best, but short of that, you are shooting in the dark.

Now, let's take the alternate example. Let's say you have an AV Receier and you Bi-Amp the Front speakers using previously unused Amp Channels. How is it going to sound. Well given that you are using identical amps, you can only expect it to sound identical. There could still be some very slight advantage, but while there, you are unlikely to hear it.

So, let's take another alternative. Let's say you have a Rotel Integrated Amp, and you add to it a Rotel Power Amp, and use this combination to Bi-Amp the speakers. How is it going to sound, well given that you are essentially using identical amps, logically it is going to sound identical. Though again, there would be some suble underlying advantage that is not easily heard. In this case, each amp on a given speakers is driven from a separate Power Supply so that could be an advantage if you play loud demanding music or watch movies with very high dynamic range. Likely, while it could be helping you, only in the most subtle and non-obvious way would it be helping you.

So, yes, there are circumstances where there can be some gains, but for the most part, to the average listening ear, expect it to sound pretty much the same.

For someone on a tight and limited budget, you might be able to get some sense of an upgrade using two amps. You have a amp of very modest power, and you bi-amp to that a amp of considerably more power. But, if you have an amp of considerably more power, why not just use that amp?

It is always worth doing for the experience, but experience is about the only tangible gain from the process.

And, unless you have the Technical Knowledge to effectively implement Active Bi-Amping, you would never go down this road when buying a new system. Rather they buying two new amps, simply pool that money into one better more powerful amp. This is something a poor person can do out of desperation, but it is never something a person who can afford quality new equipment does. It simply makes no economic sense.

In my case, I just had amps laying around, so I gave it a try. I liked what I heard, but from a pratical sense, I just couldn't make it work on a day to day basis. So, I went back to the original configuration. I don't regret trying it, but practically, it wasn't worth keeping it that way.

But to the original point, the power is not additive. Each driver gets the power potential of the amp you attach to it. They do not add together. TWO 50w Stereo amps is still just 50w per driver or driver section.

Within the limited context I've laid out here, there could be circumstances where Bi-Amping might work for the individual. But, it makes more sense to simply buy a new more powerful amp.

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Quote:
Originally Posted by DonH50 View Post
You need a frequency-dependent load to demonstrate the theoretical (and measurable) differences of passive bi-amping. .
@DonH50 , so you disagree with my power readings at 200Hz in my opening post or no? I'm getting 267 continuous watts into the speaker's load as presented at 200Hz in mono-amp mode [jumper bars left in place] and 267 watts into the speaker's load as presented at 200Hz when the jumper bars are removed [bi-amp mode].

What are the two wattage figures you are getting for these two different modes, at 200Hz?

Note: Both of my charts are frequency dependent on the horizontal axis but the animated one shows the impedance on the vertical axis and the large one from Audioholics is the Continuous Power output, in watts, if the theoretical load used was 4 ohms.
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Originally Posted by m. zillch View Post
@DonH50 , so you disagree with my power readings at 200Hz in my opening post or no? I'm getting 267 continuous watts into the speaker's load as presented at 200Hz in mono-amp mode [jumper bars left in place] and 267 watts into the speaker's load as presented at 200Hz when the jumper bars are removed [bi-amp mode].

What are the two wattage figures you are getting for these two different modes, at 200Hz?

Note: Both of my charts are frequency dependent on the horizontal axis but the animated one shows the impedance on the vertical axis and the large one from Audioholics is the Continuous Power output, in watts, if the theoretical load used was 4 ohms.
Your measurements are lacking phase angle information. AC Power cannot be calculated without inputting phase angle scores.

Quote:
The Straight Goods:

A Watt is only a Watt, when the Current & Voltage angles are in phase, everything else is quite literally a waste, as in a waste of energy! Incidentally, the Power Factor of any circuit in which the Current & Voltage envelopes are running in phase, have a Power factor of 1, and when its 1, work can be done!

Unfortunately, figuring all of this out, is very complicated, and as such; consumers don’t honestly have any idea, what the Real Power capabilities of their amplifiers are, which has resulted in them calling just about anything a Watt!

Please review this: https://www.avsforum.com/forum/91-aud...l#post50383929

Then review actual and proper AC measurements and calculations: https://www.avsforum.com/forum/91-aud...l#post50887169

The graph that you posted is based on non-inductive loads - phase linear, resistive loading, not actual reactive loading, as in while connected to the speaker in question / review.

They are not related - at all!

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Originally Posted by m. zillch View Post
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.
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!

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post #25 of 184 Old 03-04-2017, 08:30 PM - Thread Starter
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@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.

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post #26 of 184 Old 03-04-2017, 09:01 PM
 
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Originally Posted by m. zillch View Post
@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...

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post #27 of 184 Old 03-05-2017, 06:12 AM
 
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Originally Posted by bluewizard View Post
If you apply 50w to the woofer, and 50w to the Tweeter then the total is 50w
If you apply 50w to the woofer and 50w to the tweeter you'll have a dead tweeter.
At best a tweeter might consume 10% of the total system power.
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post #28 of 184 Old 03-05-2017, 07:45 AM
 
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Originally Posted by Bill Fitzmaurice View Post
If you apply 50w to the woofer and 50w to the tweeter you'll have a dead tweeter.
At best a tweeter might consume 10% of the total system power.
I took BW to infer potential, which is obviously governed by the same passive crossover network section that is interconnected when just one power supply /amp is used.

When just one amp channel / power supply is connected to a 2 or more way speaker system, the passive crossovers typically include voltage dividers, and often a protection circuit for the tweeter. Using the same network in a bi-amped configuration doesn't negate these inclusions.

Where he is a drift in my book, is that he has failed to add 50w + 50w = 100W in potential; again the potentials is governed / padded by the respective passive crossover networks, placed in front of each driver, if you will, and the respective impedances of each driver, and yes, ultimately, by the respective gain structures.

You would be completely correct however, if he simply took one tweeter and one woofer, and connected them each to a 50watt amp, set the gains as such to permit full output, and inputted the identical signal to each. In this setting the tweeter would likely not last very long thermally or mechanically.

But that isn't the context/setting that he is speaking into.

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post #29 of 184 Old 03-05-2017, 08:07 AM
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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.
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post #30 of 184 Old 03-05-2017, 08:25 AM - Thread Starter
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@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.

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