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Question on bi-amping - Page 14

post #391 of 1039
Quote:
Originally Posted by stereoforsale View Post

Quote:
Originally Posted by mcnarus View Post

No.

Ok, another thought. The speaker's internal crossover blocks the unused part of the signal, hence there isn't a complete circuit at those unwanted frequencies, and therefore that part of the signal is simply not part of the signal sent to the speaker: no circuit = no current (at the blocked frequencies). The part of the signal that is blocked by the internal crossover is never amplified and never leaves the amp since there is no where for it to go (no circuit). So the only signal going to the HF post is HF signal, and the only signal going to the LF post is the LF signal. Yes? No? smile.gif

Depends on the order of the crossover.

6 dB/octave filters (common on lower cost speakers) work as you say.



12 dB/octave and higher order filters (common on lower cost speakers) don't work exactly that way.



C1 and L2 bypass some of the input signal to ground.
post #392 of 1039
Hi Stereoforsale,
Quote:
Ok, another thought. The speaker's internal crossover blocks the unused part of the signal, hence there isn't a complete circuit at those unwanted frequencies, and therefore that part of the signal is simply not part of the signal sent to the speaker: no circuit = no current (at the blocked frequencies). The part of the signal that is blocked by the internal crossover is never amplified and never leaves the amp since there is no where for it to go (no circuit). So the only signal going to the HF post is HF signal, and the only signal going to the LF post is the LF signal. Yes? No? smile.gif
Well, you're getting there . . .

More specifically: All frequencies are being amplified by the amplifier, and if you could look at the voltage coming out of the amp, that voltage has all frequencies represented.

When you get to the filters that make up the crossover, however, those filters block any current for those frequencies that are not meant for that driver, so although there is voltage for the unwanted frequencies, there is no current.

Since power equals voltage times current ( watts = volts x amps ), when you have no current, you have no power.



And as an aside, the power-supply is always supplying voltage, and amplifying the voltage of a signal that then draws no current is no extra work for either the amplifier or its power-supply.


And as a second aside: When passively bi-amping with identical amplifiers, the voltage output of the two amps are identical. If you disconnected one amplifier and jumpered the high and low speaker inputs together (no bi-amping), then the current through each driver would be the same as when you were passively bi-amping. It's just that it is now all supplied by a single amp instead of two amps. That is why there is no difference in total power, whether bi-amping or not.

But if a single amplifier can't produce enough power in the first place, bi-amping might work as a band-aid, maybe by simply doubling the available heat-sink area. But it would be a marginal fix, as most of the power is needed by the low-frequency amp, and you are only siphoning off the high frequencies from that amp when passively bi-amping.
post #393 of 1039

Hi Mark,

 

You seem very knowledgeable on this topic. Just have a question for you. I have a Denon receiver in my bedroom that offers the ability to bi-amp. Apparently I need to use the rewrite the surround back channels in order for this to happen.

 

Does power not increase at all with receiver bi-amping?

post #394 of 1039
Hi Shaun,

Here is my attempt at an explanation:
Quote:
Originally Posted by Shaun B View Post

Does power not increase at all with receiver bi-amping?
I don't know what Denon is offering, so I will give you to the passive bi-amp answer. The active bi-amp answer would not be much different, if at all.

If the single amplifier was not over-taxed and you use the same volume levels in both cases, then the power would be identical, as the voltage going to the drivers would be identical, the filters in the speakers have not changed, so the current going through each driver would also be identical. Ohms law.

Now, if the single amp did not have enough power in the first place, then a second amp might help out. However, since the amount of power used by the upper frequencies is so much less then the lower frequencies, it can only help a little. A bigger amp is really what is called for.


Ok, the active answer as well: Assuming that the frequencies are split the same as in the passive bi-amp mode, again the power would be the same. Since the active crossover might equalize a little differently from the passive, there might be a slight variation in power, but it would be tiny and also dependent on the music. Changing the crossover frequency (bad idea, as it was likely correct before) would shift the power between amps, but the total would still be the same.

The thing to note is that neither active nor passive bi-amping changes the power from a properly working single-amp system.
Edited by MarkHotchkiss - 11/18/13 at 7:46am
post #395 of 1039
I am just going to add to what Mark said and build on an earlier point regarding one of the advantages of bi-amping (passive or active) which is the isolation of the two devices. Let's take the case of a 12 db/octave crossover and model it together with the tweeter represented by a fixed 8 ohm resistor. Here is the spice simulation of that:

i-mV7R4qf-XL.png

The Teal color is the the voltage as seen by the tweeter. The green line which is hidden is the current that is going to the crossover from amplifier. The red is the product of the amplifier output voltage times this current (i.e. power drawn from amp). Since in this simulation the source is constant at all frequencies the power curve in red simply overlays the current. In other words, as Mark post in his good explanation, and combining it with the fact that spectrum of low frequencies is a lot louder in content than highs, we can conclude that the amp driving the tweeter will be coasting. It will have very little work to do relative to the one driving the woofer.

Now let's say I have maxed out my power for the bass frequencies and that amp is creating harmonic distortion (for a variety of reasons and not just clipping). As I explained earlier if you have a single amp, the harmonics of strong low frequencies will create frequencies played by the tweeter and create a harsher sound. Using passive bi-amping we isolate the two drivers so that can't happen. Question is, did the distortion reduce? Answer is that it did. The amp driving the woofer is under severe load. It is running past its maximum load experiencing non-linearities. In addition, its protection circuit which attempts to save the output stage may be current limiting on and off (very quickly). Similarly, the heatsink temps may be excessive causing the same reduction in current. All of this will lead to non-linear distortions with components above the tones in the content. In the single amp situation, these would bleed into the tweeter. But not in passive bi-amp. The connection is no longer there. The amp driving the highs is running at just a handful of watts and way below its non-linearity, max current, or max temp limits. In addition, the lower temps would help reduce its noise level and accuracy of the front-end stage both of which probably matter for the tweeter drive than woofer.

So as we see, it is not the addition of the watts from each amp that is of value but rather isolation of distortion. One of the nice things about passive or active bi-amping is this factor. They will max out in power with gentler rise in distortion than if you used a single amp. You will notice that as you turn up the volume you are not getting louder sound necessarily but harshness/distortion is not increased nearly as much.
post #396 of 1039
Mark, thanks for the explanation. I like the point that if one amp isn't powerful enough to drive your woofer, then cutting out the HF isn't gonna give you much additional power for that underpowered woofer anyway. But I also posed a question earlier that passive biamping is essentially the only way for me to also biwire, which B&W says is a must. Some have strongly disagreed, but I also note the Vandeersten also highly recommends biwiring and they have done extensive testing to prove its benefits.
1) What's your view on biwiring?
2) And would you accept that passive biamping is beneficial even if solely for the fact that it may be the only feasible way for some people to biwire?
post #397 of 1039
Hi Stereoforsale,
Quote:
Originally Posted by stereoforsale View Post

1) What's your view on biwiring?
I feel bi-wiring is a waste of time and money, but not of copper. As long as you have enough copper, how that copper is distributed makes little difference. Bi-wiring with 4 wires of 15AWG would be the same as not bi-wiring with 2 wires of 12AWG.

The difference in inductance and capacitance, which would be the only parameters that would have an effect, would be so small as to be insignificant compared to the inductance and capacitance inherent in the speaker circuit already. Like topping-off a lake with a garden hose.

I would like to hear B&W's justification for having to bi-wire. It sounds like they are saying that their speakers are somehow defective.
post #398 of 1039
Quote:
Originally Posted by MarkHotchkiss View Post

I would like to hear B&W's justification for having to bi-wire. It sounds like they are saying that their speakers are somehow defective.

For what it's worth, here is what Vandersteen says about biwiring (scroll about 1/2 way down the page)... sound like their experiement found that doubling the thickness of wire did not have the same improvement as biwiring:

http://www.vandersteen.com/vandersteenfaqs.htm
post #399 of 1039
Not sure I followed that, Amir. If both amps have the same input signal, as is true in passive bi-amping, then assuming adequate current capacity (maybe that is the implication of your post) both amplifiers will be clipping due to the large bass signal, and both amps will have distortion spectra that impact tweeter frequencies.

An active bi-amp system with two identical amps adds no power to the system, but now the tweeter amp is not overdriven by the bass frequencies (since the active crossover before the amps prevents those frequencies from reaching the tweeter amp) and as a result does have lower distortion.
post #400 of 1039
Quote:
Originally Posted by DonH50 View Post

Not sure I followed that, Amir. If both amps have the same input signal, as is true in passive bi-amping, then assuming adequate current capacity (maybe that is the implication of your post) both amplifiers will be clipping due to the large bass signal, and both amps will have distortion spectra that impact tweeter frequencies.
Yes, I am looking at current usage and real amplifiers with protection circuits and such as opposed to ideal. Let's take the simple case of current limiting in the protection circuit. As I showed in the simulation, the high-frequency amp sees none of the base energy with respect to that current. Therefore its current limiter in the protection circuit would not kick in. Likewise if it was a separate amp with its own power supply (like someone who said he had bought two 80 watt amps), it would be drawing very little from it. The one driving the bass though could be pounding on its power supply causing its voltage to sag and clip whereas the high frequency one would not. As you know with some rare exceptions output stage power supplies are not regulated so this fluctuation would be there for the one driving the woofer but not for the one driving the tweeter. All of this would be sources of nonlinearities.
post #401 of 1039
OK.

"base energy" = bass energy -- I hate when spellcheck misses a correctly-spelled word that is still wrong in context. smile.gif
post #402 of 1039
Quote:
Originally Posted by DonH50 View Post

Not sure I followed that, Amir. If both amps have the same input signal, as is true in passive bi-amping, then assuming adequate current capacity (maybe that is the implication of your post) both amplifiers will be clipping due to the large bass signal, and both amps will have distortion spectra that impact tweeter frequencies.

An active bi-amp system with two identical amps adds no power to the system, but now the tweeter amp is not overdriven by the bass frequencies (since the active crossover before the amps prevents those frequencies from reaching the tweeter amp) and as a result does have lower distortion.

Given other info I've read, which I think is supported by Mark above, this descrption of how passive biamping works is incorrect, and probably the reason why many people (incorrectly) oppose passive biamping. In passive biamping the tweeter does NOT see ANY bass frequencies since there is no current. Just becasue the amp "amplifies" the bass frequencies, it does NOT mean there is a circult for it to flow... no flow, no current, therefore no watts. The tweeter only get HF signals. And the opposite is true of the woofer.
post #403 of 1039
Quote:
Originally Posted by stereoforsale View Post

Quote:
Originally Posted by MarkHotchkiss View Post

I would like to hear B&W's justification for having to bi-wire. It sounds like they are saying that their speakers are somehow defective.

For what it's worth, here is what Vandersteen says about biwiring (scroll about 1/2 way down the page)... sound like their experiment found that doubling the thickness of wire did not have the same improvement as biwiring:

http://www.vandersteen.com/vandersteenfaqs.htm

They don't specify their criteria for "sounded better" was, so it was no doubt sighted evaluations.

This paragraph: "Additional experiments with a Hall Effect probe revealed that high-current bass frequencies created a measurable field around the wires that expanded and collapsed with the signal. We believe that this dynamic field modulates the smaller signals, especially the very low level treble frequencies. With the high-current signal (Bass) separated from the low-current signal (Treble) this small signal modulation was eliminated as long as the cables were separated by at least an inch or two. (To keep the treble cable out of the field surrounding the bass cable.)"

They unfortunately mix a truism (any alternating current does create a measurable field around the wires) with what appears to be a spiritual belief that there is audible modulation distortion in ordinary copper wires for this reason.

Whatever this modulation is, it is not predicted by science and it isn't measurable.

The FAQ says "The effects of bi-wiring are not subtle. The improvements are large enough that a bi-wire set of moderately priced cable will usually sound better than a single run of more expensive cable."

This is another one of those things that only shows up in sighted evaluations.

There are a number of other items in their FAQ which run contrary to accepted science, as well. Their speakers seem to sound good despite it. ;-)
Edited by arnyk - 11/18/13 at 6:15pm
post #404 of 1039
Quote:
Originally Posted by MarkHotchkiss View Post

However, since the amount of power used by the upper frequencies is so much less then the lower frequencies, it can only help a little.

Not necessarily so. Given that the halfway point for power demand is around 300hz, then yes, for a 2-way receiving full range and a crossover to the tweeter around 2k that statement would be true.

But how about a 3-way with double binding posts? The woofer driver in a 3-way is usually crossed around 300hz and is feed from one set of posts and the other set goes to the midrange and tweeter drivers. That would make a 50/50 split.

Or in the case of my 2-ways; 80hz and below goes to subs. That will raise the halfway point for power demand considerably closer to their 1k crossover to the HF ribbons.

So to say that the LF posts will be drawing most of the current compared to the fraction used by the HF posts as if that's always the case is a bit misleading.
post #405 of 1039
Quote:
Originally Posted by amirm View Post

Quote:
Originally Posted by DonH50 View Post

Not sure I followed that, Amir. If both amps have the same input signal, as is true in passive bi-amping, then assuming adequate current capacity (maybe that is the implication of your post) both amplifiers will be clipping due to the large bass signal, and both amps will have distortion spectra that impact tweeter frequencies.

Yes, I am looking at current usage and real amplifiers with protection circuits and such as opposed to ideal. Let's take the simple case of current limiting in the protection circuit. As I showed in the simulation, the high-frequency amp sees none of the base energy with respect to that current. Therefore its current limiter in the protection circuit would not kick in. Likewise if it was a separate amp with its own power supply (like someone who said he had bought two 80 watt amps), it would be drawing very little from it. The one driving the bass though could be pounding on its power supply causing its voltage to sag and clip whereas the high frequency one would not. As you know with some rare exceptions output stage power supplies are not regulated so this fluctuation would be there for the one driving the woofer but not for the one driving the tweeter. All of this would be sources of nonlinearities.

The above statement presumes that current limiting is the major source of distortion, which is in fact quite rare. The usual source of distortion in amplifiers is voltage limiting. There was a day early in the development of solid state amplifiers (early 1970s) when current limiting was far more of an issue than it is today.
post #406 of 1039
Quote:
Originally Posted by stereoforsale View Post

Quote:
Originally Posted by DonH50 View Post

Not sure I followed that, Amir. If both amps have the same input signal, as is true in passive bi-amping, then assuming adequate current capacity (maybe that is the implication of your post) both amplifiers will be clipping due to the large bass signal, and both amps will have distortion spectra that impact tweeter frequencies.

An active bi-amp system with two identical amps adds no power to the system, but now the tweeter amp is not overdriven by the bass frequencies (since the active crossover before the amps prevents those frequencies from reaching the tweeter amp) and as a result does have lower distortion.

Given other info I've read, which I think is supported by Mark above, this descrption of how passive biamping works is incorrect, and probably the reason why many people (incorrectly) oppose passive biamping. In passive biamping the tweeter does NOT see ANY bass frequencies since there is no current. Just becasue the amp "amplifies" the bass frequencies, it does NOT mean there is a circult for it to flow... no flow, no current, therefore no watts. The tweeter only get HF signals. And the opposite is true of the woofer.

You seem to have the belief that current is the most common cause of amplifier clipping. In fact that is quite rare. Voltage limiting is the most common source of amplifier distortion by far. Just because current is flowing doesn't mean that the amplifier is distorting.
post #407 of 1039
Quote:
Originally Posted by kiwi2 View Post

Quote:
Originally Posted by MarkHotchkiss View Post

However, since the amount of power used by the upper frequencies is so much less then the lower frequencies, it can only help a little.

Not necessarily so. Given that the halfway point for power demand is around 300hz, then yes, for a 2-way receiving full range and a crossover to the tweeter around 2k that statement would be true.

But how about a 3-way with double binding posts? The woofer driver in a 3-way is usually crossed around 300hz and is feed from one set of posts and the other set goes to the midrange and tweeter drivers. That would make a 50/50 split.

Or in the case of my 2-ways; 80hz and below goes to subs. That will raise the halfway point for power demand considerably closer to their 1k crossover to the HF ribbons.

So to say that the LF posts will be drawing most of the current compared to the fraction used by the HF posts as if that's always the case is a bit misleading.

Your analysis seems to be based on the idea that the energy split is only based on the choice of crossover point. In fact the spectral content of the music is just as relevant and varies all over the place. In many cases the tweeter has higher efficiency than the woofer and/or higher impedance. Thus crossover points are only one of three major influences and any analysis based on just crossover points has major blind spots.

Here's a typical speaker:



Note that from 80 to 1 KHz the speakers impedance averages to about 4 ohms, and from 2 KHz on up, the impedance is 4.7 ohms or more. This is a common trend because the efficiency of woofers is limited by Hoffman's Iron Law, which does not apply to midranges and tweeters because their enclosures are always far smaller and be therefore easily made proportionately larger.
post #408 of 1039
Quote:
Originally Posted by arnyk View Post

Your analysis seems to be based on the idea that the energy split is only based on the choice of crossover point. In fact the spectral content of the music is just as relevant and varies all over the place. In many cases the tweeter has higher efficiency than the woofer and/or higher impedance. Thus crossover points are only one of three major influences and any analysis based on just crossover points has major blind spots.

Here's a typical speaker:..

Of course the musical content is also going to govern where power is needed.!

And no, the PSB T2 is not your typical speaker in what it does with the lower octaves with its crossovers and impedance.
post #409 of 1039
Quote:
Originally Posted by arnyk View Post

The above statement presumes that current limiting is the major source of distortion, which is in fact quite rare. The usual source of distortion in amplifiers is voltage limiting. There was a day early in the development of solid state amplifiers (early 1970s) when current limiting was far more of an issue than it is today.

Arny, I need some 'splainin' here. I'll lay out my meager understanding in hopes you can school me.

No problem with the reality that a given transistor (or to relate to output devices I've held in my hand, tube) can only swing so much voltage, and any time you exceed that voltage you'll be distorting (not going to get into how much distortion constitutes clipping). But if it's just the voltage of the devices, then, it seems to me, an amplifier should be able to "double down" from 8 ohms loads to 4 ohm loads because, by definition, the same voltage with half the impedance equals twice the power.

But that doesn't happen in the real world. My just barely there grasp of the issue has been that when you push the output device at lower impedances, something (I guess I'd guess the power supply) cannot keep up with the current demands.

Now Ohm's law would prevent the amp from swinging the full voltage if it can't supply the current, so voltage for the output devices sags. Maybe the power supply sags to cause some or all of this (I know it does in some of those lovely 50's Fender Tweed amps, but THAT distortion profile has input everywhere from the preamp tubes to the PI to the output stage and is, AFAIK, not especially relevant to solid state equipment appropriately designed for music reproduction).

Maybe it's just semantics. If voltage sags because the amp cannot source enough current, I guess it's fair to say you've maxed out the voltage, but it's not accurate to say the output devices are outputting their maximum designed (clean) voltage. Instead, system voltage has been compromised because the system cannot source enough current. At least that's how it looks to me at this moment. Perhaps soon I shall be more enlightened.
post #410 of 1039
Hi Kiwi,
Quote:
Originally Posted by kiwi2 View Post

But how about a 3-way with double binding posts? The woofer driver in a 3-way is usually crossed around 300hz and is feed from one set of posts and the other set goes to the midrange and tweeter drivers. That would make a 50/50 split.

Or in the case of my 2-ways; 80hz and below goes to subs. That will raise the halfway point for power demand considerably closer to their 1k crossover to the HF ribbons.
You're right - I over-generalized.

Especially when it comes to subwoofers, you can get a more even split than I indicated. And you could certainly select your drivers and pick your crossover-point to try to optimize the split, which would make sense if you were designing specifically for bi-amping, whether active or passive.
post #411 of 1039
Quote:
Originally Posted by JHAz View Post

Quote:
Originally Posted by arnyk View Post

The above statement presumes that current limiting is the major source of distortion, which is in fact quite rare. The usual source of distortion in amplifiers is voltage limiting. There was a day early in the development of solid state amplifiers (early 1970s) when current limiting was far more of an issue than it is today.

Arny, I need some 'splainin' here. I'll lay out my meager understanding in hopes you can school me.

No problem with the reality that a given transistor (or to relate to output devices I've held in my hand, tube) can only swing so much voltage, and any time you exceed that voltage you'll be distorting (not going to get into how much distortion constitutes clipping). But if it's just the voltage of the devices, then, it seems to me, an amplifier should be able to "double down" from 8 ohms loads to 4 ohm loads because, by definition, the same voltage with half the impedance equals twice the power.

But that doesn't happen in the real world. My just barely there grasp of the issue has been that when you push the output device at lower impedances, something (I guess I'd guess the power supply) cannot keep up with the current demands.

That is all correct. The question is not whether there is a current limit because there is. The question is about the location of the current limit. If the current limit exceeds the needs of the load, then there may be a slight increase in nonlinearity but there is no audible distortion..
Quote:
Now Ohm's law would prevent the amp from swinging the full voltage if it can't supply the current, so voltage for the output devices sags. Maybe the power supply sags to cause some or all of this (I know it does in some of those lovely 50's Fender Tweed amps, but THAT distortion profile has input everywhere from the preamp tubes to the PI to the output stage and is, AFAIK, not especially relevant to solid state equipment appropriately designed for music reproduction).

Maybe it's just semantics. If voltage sags because the amp cannot source enough current, I guess it's fair to say you've maxed out the voltage, but it's not accurate to say the output devices are outputting their maximum designed (clean) voltage. Instead, system voltage has been compromised because the system cannot source enough current. At least that's how it looks to me at this moment. Perhaps soon I shall be more enlightened.

In an AVR the power supply is shared among all of the amplifiers, and frankly you don't want it any other way. If the AVR's power supply suffers with current induced power supply voltage sagging when run the regular way, passive biamping is no help because the current still comes from the same power supply.
post #412 of 1039
Quote:
Originally Posted by stereoforsale View Post

Given other info I've read, which I think is supported by Mark above, this descrption of how passive biamping works is incorrect, and probably the reason why many people (incorrectly) oppose passive biamping. In passive biamping the tweeter does NOT see ANY bass frequencies since there is no current. Just becasue the amp "amplifies" the bass frequencies, it does NOT mean there is a circult for it to flow... no flow, no current, therefore no watts. The tweeter only get HF signals. And the opposite is true of the woofer.

The tweeter may not "see" the bass frequencies as the high pass filter in the crossover blocks these, but that doesn't change the fact that you are still feeding a full range signal into both the bass amp and tweeter amp - this signal is amplified by both amps and if the signal is too large it will clip (assuming the amps are the same at the exact same time). Not because the voltage on the power supply is sagging, but because the output voltage exceeds the voltage rail of the power supply in both amps exactly the same - bench testing will show the voltage at clipping and it can be verified that it is not because the rail voltage is sagging. Now those dreaded distortion harmonics are present at the output of both amps and high order harmonics that are high enough frequency enough to pass through the high pass filter of the crossover WILL be seen by the tweeter.

Passive bi-amping only increases the total current output to the speaker and the total thermal capabilities of the combined amps very slightly (only the amount removed by not driving the tweeter) - which will only help you if you have very low impedance dips at high energy bass frequencies or your amps cannot handle the thermal load presented by low impedance speakers. This may be a good thing for some low impedance exotic speakers but this isn't the normal case for "easy to drive" 4 - 8 ohm range speakers with a high quality amplifier.
post #413 of 1039
Hi Stereoforsale,

I started writing this post a few minutes after you made your post, but then I was interrupted by work (I hate when that happens), and Arny did a better job of saying what I was going to say. But since I've typed most of it already, I will say it anyway, at the risk of being a little redundant.
Quote:
Originally Posted by stereoforsale View Post

For what it's worth, here is what Vandersteen says about biwiring (scroll about 1/2 way down the page)... http://www.vandersteen.com/vandersteenfaqs.htm
My first issue is that that particular FAQ answer sounds more anecdote then science. They may be very good speaker designers, but they certainly aren't electrical engineers. Specifically:
Quote:
We began experimenting with . . .
We noted that speakers sounded better . . .
We initially believed that . . .
Finally we heard the sonic improvements . . .
We believe that this . . .
Although it's possible that they were more scientifically rigorous than these phrases imply, it sounds like they were depending on their flawed sense of hearing rather than measurements.


But this is what really bothers me:
Quote:
We believe that this dynamic field modulates the smaller signals, especially the very low level treble frequencies. With the high-current signal (Bass) separated from the low-current signal (Treble) this small signal modulation was eliminated as long as the cables were separated by at least an inch or two. (To keep the treble cable out of the field surrounding the bass cable.)
What they believe is contrary to the laws of physics. Small signals are not "modulated" by larger signals. This is an audio myth with absolutely no basis in science. If larger signals could modulate smaller signals, our whole communication system would fail to operate. Cable TV stations would interfere with each other over the wire. The phone company could not use frequency-division multiplexing to carry your calls. Radio stations would scramble each other.

Then they bring up the requirement that, when bi-wiring, the two cables need to be separated by at least two inches, which is not what most high-end audio shops sell. So they are perpetrating a new audio myth. Now we need multi-tiered cable risers (keep the highs high, and the lows low).

Quote:
Because of the different reflected impedances of the cables, the crossover between the woofer and midrange actually occurs at the wire ends where they connect to the amplifier.
"Reflected impedance" is insignificant because, as I said in an earlier post, the cable impedance is minuscule compared to the speaker's impedance.

Quote:
The low-current signal to the midrange and tweeter drivers does not have to travel on the same wire as the high-current woofer signal. The field fluctuations and signal regeneration of the high-current low-frequencies are prevented from distorting or masking the low-current high-frequencies. The back EMF (Electro-Mechanical Force) from the large woofer cannot affect the small-signal upper frequencies since they do not share the same wires.
First-off, why are they saying the high frequencies are low current? Do they think we only listen to hip-hop? (Ok, so I do, but I still like my highs).

Second, the speaker cable is not an isolator. Even if such "distorting or masking" was a physical possibility, the separate cables are still connected together at the amplifier's end, and since the cable is low impedance, that direct coupling will outweigh any EMF coupling by many orders of magnitude. These are not radio frequencies. Maxwell's equations would allow you to quantify exactly how tiny this EMF coupling would be, so it is not something that needs to be found empirically, as they seem to think they have done. And again, any such coupling would be benign, as large signals do not "modulate" smaller signals anyway.

Sorry for the delay in answering.
Edited by MarkHotchkiss - 11/18/13 at 5:24pm
post #414 of 1039
Quote:
Originally Posted by kiwi2 View Post

Quote:
Originally Posted by arnyk View Post

Your analysis seems to be based on the idea that the energy split is only based on the choice of crossover point. In fact the spectral content of the music is just as relevant and varies all over the place. In many cases the tweeter has higher efficiency than the woofer and/or higher impedance. Thus crossover points are only one of three major influences and any analysis based on just crossover points has major blind spots.

Here's a typical speaker:..

Of course the musical content is also going to govern where power is needed.!

And no, the PSB T2 is not your typical speaker in what it does with the lower octaves with its crossovers and impedance.

Really? Its the first speaker that I found on the SP site when I googled it. No cherry picking.

Here's the second:



The numbers are a little different but again the tweeter range has a significantly higher impedance than that of the woofer.

And the third:



The numbers are again a little different but again the tweeter range has a significantly higher impedance than that of the woofer.

...well you get the idea?
post #415 of 1039
Quote:
Originally Posted by mtn-tech View Post

The tweeter may not "see" the bass frequencies as the high pass filter in the crossover blocks these, but that doesn't change the fact that you are still feeding a full range signal into both the bass amp and tweeter amp - this signal is amplified by both amps and if the signal is too large it will clip (assuming the amps are the same at the exact same time).

My understanding is that this is incorrect. The bass signal is not amplified at all. No signal moves until it has a complete circuit. Yes, the signal is "blocked" by the crossover, but it doesn't "stop" at the crossover. Since the bass frequencies have nowhere to go, it doesn't get amplified in the first place (if I suggested/implied otherwise, I misspoke). Passive biamping works since it denies the unwanted signal a complete circuit and therefore it is completely eliminated from the path taken by the wanted signal. This is unlike a single amp system where the combined signal SEPARATED by the crossover, so both the HF and LF have a complete path, just in different directions (one to the tweeter and one to the woofer). If a signal is denied a complete path, then it never moves, and it cannot be amplified. To suggest otherwise is science fiction. Or at least that is what I'm told.
post #416 of 1039
Quote:
Originally Posted by stereoforsale View Post

Quote:
Originally Posted by DonH50 View Post

Not sure I followed that, Amir. If both amps have the same input signal, as is true in passive bi-amping, then assuming adequate current capacity (maybe that is the implication of your post) both amplifiers will be clipping due to the large bass signal, and both amps will have distortion spectra that impact tweeter frequencies.

An active bi-amp system with two identical amps adds no power to the system, but now the tweeter amp is not overdriven by the bass frequencies (since the active crossover before the amps prevents those frequencies from reaching the tweeter amp) and as a result does have lower distortion.

Given other info I've read, which I think is supported by Mark above, this descrption of how passive biamping works is incorrect, and probably the reason why many people (incorrectly) oppose passive biamping. In passive biamping the tweeter does NOT see ANY bass frequencies since there is no current. Just becasue the amp "amplifies" the bass frequencies, it does NOT mean there is a circult for it to flow... no flow, no current, therefore no watts. The tweeter only get HF signals. And the opposite is true of the woofer.

What Amir described was amplifier clipping, which generates higher-frequency distortion that falls into the tweeters frequency range (after the crossover's HPF). That is what I meant by "distortion spectra". His post assumed current clipping; I think all the other posts (at least all of mine) assume voltage clipping is the primary source of distortion. It does not matter for his main point, that clipping produces higher-frequency energy that can be passed to the tweeter. What does matter is the isolation premise of his post. If the clipping is caused by voltage there is essentially no isolation; if it is caused solely by current limits, then bi-amping can reduce the impact of clipping as he stated.
post #417 of 1039
Quote:
Originally Posted by stereoforsale View Post

Quote:
Originally Posted by mtn-tech View Post

The tweeter may not "see" the bass frequencies as the high pass filter in the crossover blocks these, but that doesn't change the fact that you are still feeding a full range signal into both the bass amp and tweeter amp - this signal is amplified by both amps and if the signal is too large it will clip (assuming the amps are the same at the exact same time).

My understanding is that this is incorrect. The bass signal is not amplified at all. No signal moves until it has a complete circuit. Yes, the signal is "blocked" by the crossover, but it doesn't "stop" at the crossover. Since the bass frequencies have nowhere to go, it doesn't get amplified in the first place (if I suggested/implied otherwise, I misspoke). Passive biamping works since it denies the unwanted signal a complete circuit and therefore it is completely eliminated from the path taken by the wanted signal. This is unlike a single amp system where the combined signal SEPARATED by the crossover, so both the HF and LF have a complete path, just in different directions (one to the tweeter and one to the woofer). If a signal is denied a complete path, then it never moves, and it cannot be amplified. To suggest otherwise is science fiction. Or at least that is what I'm told.

This is also false. If you feed a bass signal into the amplifier, it will amplify it even if the speaker does not use any power at LF. The bass signal (voltage) at the output of the amplifier is as large (actually a hair larger) when there is no LF load. The circuit is closed inside the amplifier irrespective of the load. There will be little if any current flow at LF but the signal voltage is still present.

P = power
V = voltage
I = current
R = resistance

P = V * I = V^2 / R = I^2 * R

If the load was an open circuit R is infinite and power delivered is zero but voltage can be as high as it wants to go. Given a real amplifier with finite voltage (power supply) rails it is easy to see that a large input signal can cause the output to clip even if there is no load.
Edited by DonH50 - 11/18/13 at 6:54pm
post #418 of 1039
Quote:
Originally Posted by DonH50 View Post

This is also false. If you feed a bass signal into the amplifier, it will amplify it even if the speaker does not use any power at LF. The bass signal (voltage) at the output of the amplifier is as large (actually a hair larger) when there is no LF load. The circuit is closed inside the amplifier irrespective of the load. There will be little if any current flow at LF but the signal voltage is still present.

P = power
V = voltage
I = current
R = resistance

P = V * I = V^2 / R = I^2 * R

If the load was an open circuit R is infinite and power delivered is zero but voltage can be as high as it wants to go. Given a real amplifier with finite voltage (power supply) rails it is easy to see that a large input signal can cause the output to clip even if there is no load.

With respect to voltage, yes I believe this is correct. I assume you believe this to be the primary concern, but as I understand it, it is not the main concern, but it is probably true from your perspective that biamping has no benefit. But the key to the benefits of passive biamping have to do with current, not voltage... but if you doubt this premise, then yes, biamping is pointless.
post #419 of 1039
Guys, bottom line I think comes down a cost benefit analysis. There is at least some reason to believe there are at least some potential benefits to passive biamping. But having said that, it is certainly not great enough for someone to double their budget to do it (note: if you're gonna double your budget, then get better equipment to start with! I think we can all agree on that! smile.gif But if you have the equipment and wire on hand (or available at a reasonable cost... consider buying used if need be) and you still rfuse to passively biamp then you are not doing everything you can to get the very most out of your system... and that's a fact. You may argue the improvement are minimal, but if you're on this thread then you are probably already well down the road of diminishing marginal returns and IMHO you'd be foolish not to take yet another sliver of improvement (it all adds up, after all). If we were so critical of every marginal benefit of system building (many of which are equally dubious), then we'd all be using some dreaded "HT in a box"! I am, however, thoroughly satisfied that those who say there is ABSOLUTELY ZERO benefit WHATSOEVER to passive bimaping (aka "fools amping") based on supposed scientific principles are perpetuating a bald faced myth.
post #420 of 1039
Quote:
Originally Posted by MarkHotchkiss View Post


But this is what really bothers me:
What they believe is contrary to the laws of physics. Small signals are not "modulated" by larger signals. This is an audio myth with absolutely no basis in science. If larger signals could modulate smaller signals, our whole communication system would fail to operate. Cable TV stations would interfere with each other over the wire. The phone company could not use frequency-division multiplexing to carry your calls. Radio stations would scramble each other.

TV/radio/phones don't suffer interference? That's news to me! I'll be sure to tell that to the repair man the next time he comes over! lol wink.gif
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