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Bi-Amping speakers

Berwhale

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As the drivers are outside the amplifier (unless included in some sort of feedback), they have no effect on the amplifier, Back emf from the bass driver won't get through the crossover to affect the tweeter, and anyway, will be hugely attenuated by the amplifier's low output impedance, so there's no effect there.

As nothing is perfectly linear, nor is the amplifier's output impedance actually zero, there is always some residual effect of non linearity, but with any even half decent amplifier being 99.99% linear or even 99.999% linear, any non linearity can be safely ignored.

S

You seem to have dodged the question. I think the system in question comprises of both the amplifier and the driver. Using your example from Wikipedia, the input A is going into the amplifier and the response X is comming out of the speaker. If either the amplifier or the speaker is non-linear, then the system must also surely be non-linear and the Superposition Principle would not necessarily apply?
 

Chrispy

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Always makes me wonder, who started this passive bi-amping nonsense anyways?
 

bigguyca

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What is your point here as relates to bi-amping? What does amplifier power have to do with the superposition principle?

Nothing at all. Power isn't an issue with passive biamping.

S

In re-reading the question it seems apply to bi-amping (not biamping) in general, which was the intention. There is no passive in the question. Do you see the word passive?

You raised the subject of active bi-amping. You noted that you converted, for some unknown reason, some 801's to active bi-amping. How does superposition apply in that case, or do you just like to quote Wikipedia?
 

Vini darko

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I run my three way towers passive bi-amp and its a decent improvement over just one amp. However the plan is to go active tri-amp this year wich will be better again hopfully. At the least I'd like to get a dsp amp on the woofers that's 2 ohm stable and having serious power. Crown is the likey candidate.
 

bigguyca

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Always makes me wonder, who started this passive bi-amping nonsense anyways?


Technically, why is passive bi-amping nonsense? Handwaving and parroting blanket statements provided by others isn't a satisfactory answer.
 

sergeauckland

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You seem to have dodged the question. I think the system in question comprises of both the amplifier and the driver. Using your example from Wikipedia, the input A is going into the amplifier and the response X is comming out of the speaker. If either the amplifier or the speaker is non-linear, then the system must also surely be non-linear and the Superposition Principle would not necessarily apply?
I need to think about that.

My thinking is that Superposition applies totally to the amplifier(s). What the amps are driving is not relevant to the amplifiers, they remain linear. The drivers are two separate systems, each one separated from the other by the crossover and each one has it's own levels of linearity. So, consider the woofer alone, there could be intermodulation between, say, 500Hz and 600Hz due to non linearity, but that can't affect the tweeter because of the crossover, the amplifier's low output impedance and the poor electrical coupling between the cone generating the intermodulation and the back emf. Ditto with the tweeter. So, within each driver system, superposition only holds to the extent of each driver's linearity, and the two systems are sufficiently isolated that they don't interact.

If you see any flaw in this, please let me know. My head hurts having thought this through, so time for bed.
S
 

Chrispy

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Technically, why is passive bi-amping nonsense? Handwaving and parroting blanket statements provided by others isn't a satisfactory answer.

For a variety of reasons, how about an example of where it's a benefit? As far as avr and speaker marketing goes, its mostly just that IMO.
 
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Ben23

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what are the downsides of bi-amping speakers with a single multiple channel amp (4 or more channels) ? Is it worth it or are 2 separate amplifiers really that much better?
Thank you all for three replies. They are much appreciated There reason I wanted to know is because my Sonus Faber bookies are 86db sensitive and 6ohm load and my thought was bi-amping would benefit sound at lower levels regarding transparency and detail. Any truth to that?
 

Vladimir Filevski

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what are the downsides of bi-amping speakers with a single multiple channel amp (4 or more channels) ? Is it worth it or are 2 separate amplifiers really that much better?
Downsides are: double price and no improvement. There may be some difference in sound, usually to worse. Below crossover frequency amplifier for the tweeter will see capacitive impedance and big phase change, which may be problematic for some amplifiers. Amplifier for the midbass driver will see inductive impedance and big phase change above the crossover frequency. On the other hand, amplifier connected to a conventional "single-amping" loudspeaker will see only moderate phase change (but there are some exclusions).
Advice - if you are intending to invest more money to improve your audio setup, then sell your old stuff and buy one pair of better loudspeakers and only one better amplifier.

...my thought was bi-amping would benefit sound at lower levels regarding transparency and detail. Any truth to that?
No.
 

Berwhale

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superposition only holds to the extent of each driver's linearity

Yes, I thought that myself after posting. If speaker is only being driven over it's linear range, then the amp + speaker system would be considered linear. It also occurs to me that by actively driving the speaker, one could ensure that the transducer remained mostly linear.
 

Wes

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highly unlikely if not impossible

use the $$ for something like a UMIK-1 mic., sound tmts. or a pretty pre-amp
 

NTK

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If the amplifier is to output 2 superimposed sine waves, say, one 10 V @ 33 Hz and one 10 V @ 4000 Hz. When the two sine waves are in phase, the peak output voltage will need to be 20 V, regardless of what the load impedance is.

Therefore, if the clipping voltage of the amplifier is less than 20 V, it will clip regardless of whether the amplifier load impedance is 100 Mohm @ 33 Hz and 8 ohms @ 4 kHz, or vice versa. That's why, to take full advantage of using 2 separate amplifier channels, we need to have a cross-over upstream of the amplifier to remove the out-of-band portion of the signal. Without this upstream cross-over, you will see very little benefits* in terms of increased output capability.

* [Note]: If the amplifier is current limited instead of voltage limited, then "passive bi-amping" can reduced the current demand and provide some (probably small) amount of output increase.
 
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voodooless

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dfuller

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Nothing is nearly so dumb as bi-wiring, though. And really, biamping only makes sense with active crossovers IMO (be they analog or DSP based).
 
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I need to think about that.

If you see any flaw in this, please let me know. My head hurts having thought this through, so time for bed.
S
More practical thought and experimentation, and less theorizing and your head wouldn't hurt so much. :)

The reduced current requirement placed on either amplifier in a passive bi-amping scheme should be obvious to anyone thinking about this logically. But, if you need proof, simply wire a current meter into the speaker lead of an amplifier playing a speaker full range and then repeat just powering the tweeter portion of the same speaker. Note the difference. There's your answer.

Dave.
 

Kvalsvoll

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I visited someone who did this - using 2 stereo amplifiers, 1 channel for HF, and one channel for the woofer. Since there was no dsp or active crossover, all passive networks were still in use, this was "bi-amping".

I wondered why. Then it ocurred to me, there actually was a reason for this arrangement. He had just bought some new, excellent, powerful amplifiers. But - the new amplifier cost less than the one it replaced. Since the most important specification for an upgrade is higher price, this was a no-go. Finding a way to use 2 amplifiers solved this issue - now the total cost was higher than the single amplifier they replaced. The system was upgraded.

No, I did not ask, I did not explain why this was very unlikely to give any audible benefits. He had already bought the amplifiers, he was happy with this solution.
 

Th0805

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What if it’s simply to gain more power? For example let’s say you have an 86db 4ohm speaker and a Purifi stereo amp 227 watts at 8ohms. You just want a little more juice for the speakers. What would it cost to get a 300-400 watt amp or comparable perform to that module? Adding a second would be about as good as one could do I would think for a very reasonable price.

bad logic?
 
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