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#293398 - 02/22/10 03:59 PM Re: M80 Questions [Re: donlboy]
ClubNeon Offline
connoisseur

Registered: 02/06/09
Posts: 3448
Loc: Western Maryland, USA
Except you're forgetting what happens in the speaker with the passive crossover network. When one amp is driving the full "system" inside the speaker all frequency ranges are going to some driver with an impedance with allows for easy current flow. But when you remove the straps; you separate the system into a high-frequency range with a high-pass filter, and a low-frequency range with a low-pass filter. The other half of those ranges basically end up seeing a very high impedance, and turning the amp's energy to heat.

So when driving the speaker system 100 Watts, across the range, drives some part of the speaker's full system. When bi-amping, 100 Watts drives the highs, and 100 Watts, drives the lows. You're still only getting 100 Watts to any part of the speaker.

If you were to use the pre-outs on a receiver, input them into an active crossover network, remove the crossovers components from the inside of the speaker (make sure your active network matches the passive parts in point and slope), then get separate amps, with fine grained gain control, along with a precise audio spectrum analyzer to balance the gain of each amp against the driver it is feeding for a flat response. You might get some benefit from bi-amping.

The bi-amping built into receivers, feeding a passive crossover network, is an entirely marketing based feature; one manufacturer offered it, so they all have to offer it.

EDIT: Oh, I forgot to add. In the presented scenario, with one PS providing power to multiple channels, when bi-amping, you're more likely to exhaust all that's available because you have two channels with exactly the same content being driven to the same levels, but half of it being used to make heat instead of sound. The way multi-channels amps get away with higher single channel ratings, is that in the real world it isn't common for more than a stereo pair of channels to be driven hard at one time in anything other than test signals. But with bi-amping you quickly run into cases with 4 channels being driven hard.


Edited by ClubNeon (02/22/10 04:09 PM)
_________________________
Pioneer VSX-1018AH-K, PDP-5020FD, DV-79AVi
Axiom M22s, VP150, QS8s
Sony PS3, surround backs
-Chris

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#293406 - 02/22/10 04:52 PM Re: M80 Questions [Re: ClubNeon]
Ken.C Offline
shareholder in the making

Registered: 05/03/03
Posts: 17741
Loc: NoVA
If I could figure out how to do it any more, this one would be going on my favorite posts list. I always know the simple answer, but I never remember the actual technical answer.
_________________________
I didn't do it, no one saw me, you can't prove anything.

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#293409 - 02/22/10 05:01 PM Re: M80 Questions [Re: Ken.C]
SirQuack Offline
shareholder in the making

Registered: 01/29/04
Posts: 13318
Loc: Iowa
Don, that is not true bi-amping and your still getting 100watts as Chris explained. Here is a good article....

http://www.gcaudio.com/resources/howtos/biamping.html
_________________________
M80s-VP180-QS8s-EP600-2xEP350 Denon3808 Outlaw7700
M22-OWM22-VP100-Denon2805
Audio Nirvana

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#293444 - 02/22/10 10:35 PM Re: M80 Questions [Re: donlboy]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10362
Don, a further comment would be that you used "amps" and "channels" as if the two were synonymous. A receiver has only one amplifier with several channels to distribute its output. The output transistors in each channel simply act as valves to measure out the required voltage from the power supply section. They have no power of their own to create a doubling or any other increase.
_________________________
-----------------------------------

Enjoy the music, not the equipment.



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#293445 - 02/22/10 10:45 PM Re: M80 Questions [Re: Wizardz]
terzaghi Offline
connoisseur

Registered: 04/04/07
Posts: 4842
Loc: Tulsa, Oklahoma
 Originally Posted By: Wizardz

again, sorry for the long post, and thanks for your very valuable input.


You should read the Mother of all Posts... I made an attempt, but after the 2nd sentence I went over to the "Who I am and Why I'm Here" post and never made it back
_________________________
-David

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#293468 - 02/23/10 09:37 AM Re: M80 Questions [Re: terzaghi]
Wizardz Offline
newbie

Registered: 02/21/10
Posts: 3
Loc: QC, Canada
wow, that is ONE BIG POST. \:\)

but i kinda like those, especially the "i'm building my theater" type one.

i just bought a new house and will be building mine shortly. i need ideas :P

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#293561 - 02/23/10 07:44 PM Re: M80 Questions [Re: JohnK]
donlboy Offline
buff

Registered: 11/08/09
Posts: 41
 Originally Posted By: JohnK
Don, a further comment would be that you used "amps" and "channels" as if the two were synonymous. A receiver has only one amplifier with several channels to distribute its output. The output transistors in each channel simply act as valves to measure out the required voltage from the power supply section. They have no power of their own to create a doubling or any other increase.

John- I may be living in the past (I have plenty of it!). In my experience the output stage does have gain, that is, it amplifies the signal coming into it. A (relatively) small voltage at the input of the final (output) stage causes a larger voltage at the output of that stage. Also, the impedance that the final stage is driving is usually much lower than what the prior stage drives (the input impedance of the final stage), so the power gain is considerable. Your description would mean that the final stage has unity power gain, is that the way modern amps are built? I'm familiar with 1-output per channel stereo amps, but not 5 or 7 output per channel amps, maybe this splitting of the signal is where the unity gain comes in.
_________________________
Don

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#293568 - 02/23/10 08:20 PM Re: M80 Questions [Re: ClubNeon]
donlboy Offline
buff

Registered: 11/08/09
Posts: 41
 Originally Posted By: ClubNeon
Except you're forgetting what happens in the speaker with the passive crossover network. When one amp is driving the full "system" inside the speaker all frequency ranges are going to some driver with an impedance with allows for easy current flow. But when you remove the straps; you separate the system into a high-frequency range with a high-pass filter, and a low-frequency range with a low-pass filter. The other half of those ranges basically end up seeing a very high impedance, and turning the amp's energy to heat.

So when driving the speaker system 100 Watts, across the range, drives some part of the speaker's full system. When bi-amping, 100 Watts drives the highs, and 100 Watts, drives the lows. You're still only getting 100 Watts to any part of the speaker.

If you were to use the pre-outs on a receiver, input them into an active crossover network, remove the crossovers components from the inside of the speaker (make sure your active network matches the passive parts in point and slope), then get separate amps, with fine grained gain control, along with a precise audio spectrum analyzer to balance the gain of each amp against the driver it is feeding for a flat response. You might get some benefit from bi-amping.

The bi-amping built into receivers, feeding a passive crossover network, is an entirely marketing based feature; one manufacturer offered it, so they all have to offer it.

EDIT: Oh, I forgot to add. In the presented scenario, with one PS providing power to multiple channels, when bi-amping, you're more likely to exhaust all that's available because you have two channels with exactly the same content being driven to the same levels, but half of it being used to make heat instead of sound. The way multi-channels amps get away with higher single channel ratings, is that in the real world it isn't common for more than a stereo pair of channels to be driven hard at one time in anything other than test signals. But with bi-amping you quickly run into cases with 4 channels being driven hard.


Chris- I (mostly) agree about only having 100 watts available to any part of the speaker system. What I was thinking, but didn't say clearly, was that if you bi-amp (passively) the speaker you unload each amp from having to drive all speakers. For example, if a signal has 90 watts of 100 Hz content and 10 watts of 10,000 Hz content for a total of 100 watts a single channel/amp has to drive that total power. But if you separate the highs from the lows than the tweeter amp is only driving 10 watts. The 90 watts of low frequency power on that amp sees the very high impedance of the HPF so is delivering only very low power at that frequency. Related to that, I don't really understand your statements about the crossovers dissipating lots of heat. If you define the crossover as just the reactive components (inductors and capacitors), then the only heat generated is due to the resistive and parasitic losses in those components, which is very low for high quality parts. The high impedance of the HPF at low frequencies and the LPF at high frequencies presents a high impedance load to the amp, so very little power goes to that section. (It's true that the resistive elements, which aren't really crossover but are for gain balancing, etc. do dissipate power, but that is equally true whether or not the speaker is bi-amped.) Of course, as you said, using an electronic crossover ahead of the amps allows all equalization and gain matching to be done without any passive components, so no losses.
_________________________
Don

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#293576 - 02/23/10 09:29 PM Re: M80 Questions [Re: donlboy]
JohnK Offline
shareholder in the making

Registered: 05/11/02
Posts: 10362
Don, of course gain does take place in the output stage(typically 25-30dB), but the point is that the voltage to boost the incoming voltage by that amount comes from the one main power supply section. The output transistors simply act as valves to let through enough voltage to increase the incoming voltage say, for example, 28.28 times so that a tenth of a volt input would result in a 2.828 volt output and into an 8 ohm load would produce 1 watt(the usual speaker sensitivity measurement standard, of course)following Ohm's Law(power=voltage squared/resistance). So an amplifier is a power supply section plus one or more channels of output transistors. The output transistors themselves aren't complete amplifiers, and it isn't correct to describe a 7.1 receiver as having seven amplifiers.
_________________________
-----------------------------------

Enjoy the music, not the equipment.



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#293579 - 02/23/10 10:38 PM Re: M80 Questions [Re: JohnK]
CatBrat Offline
axiomite

Registered: 08/05/09
Posts: 5798
Loc: Some random location
I'm sorry, but this conversation has me bored to tears. ::walks away and hopes nobody notices::

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