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Bi-amp benefits with active crossover

Hello All,

What are the benefits of an active crossover from the amplification point of view?  Will a given amplifier sound better if it's input is of a limited frequency spectrum?  Is there an assumption that if an amplifier is driving a limited spectrum, and therefore not working as hard as it would in driving full spectrum, it will drive the limited spectrum "better" than it would if it was driving the full spectrum?

What I am considering is bi-amping, with speakers that have separate terminals for lows and mid/highs, and whether or not there would be a benefit in actively crossing over the frequencies before they get to the respective amplifiers.  This scenario would NOT include bypassing the passive crossovers in the speakers in any way.  I want to retain the speaker designers intent regarding the speaker as a whole.  My focus is whether or not there is an advantage to actively crossing over as opposed to simply using separate amplifiers for the lows and mid/highs, with all the amplifiers driving the same full spectrum signal.  My initial thoughts were that it seems a shame to make the amps work that hard, only to have the spectrum limited by the passive crossover.  But then, in crossing over actively there's all those extra cables and connections and circuits that the signal needs to go through to consider.

The equipment I'm using:
Triangle Volante 260 speakers
Parasound JC 1 mono block amps (would need to add two more channels of amplification, obviously, but the particulars on that are in the next questions: tube? Solid state? Matching levels?  Input sensitivities?  etc.)
Sonic Frontiers Line 1 preamp
Arcam UDP 411 universal disc player
Pro-Ject Carbon Debut w/Ortofon 2M Red cartridge, soon to be 2M Blue.

Thanks All!


dprincipato
10 responses Add your response
nekoaudio's avatar
nekoaudio
105 posts
 
https://www.audioholics.com/frequent-questions/the-difference-between-biamping-vs-biwiring has a decent section on active and passive bi-amping.
erik_squires
5,268 posts
 
If you are going to keep the original crossover I'd suggest then is you bi-amp at points far from the speaker's crossover.

For instance, if the speaker is designed with a 2 kHz, set the high pass at 500 Hz, and low pass at 5 kHz. Your high amp will eliminate most of the power hungry bass.

Otherwise, the crossover slopes will get altered.
ivan_nosnibor's avatar
ivan_nosnibor
782 posts
 
As long as you keep using your passive crossovers, then I'm afraid there is audibly not going to be any real-world justification for this change. None whatsoever IMHO. The reduction in bass frequencies are largely redundant here...and the only point at which they might audibly change anything will likely be at the point at which the crossover values are being altered, as Erik pointed out. The only real advantage with bi-amping with active crossovers AFA the amps are concerned is more that (if you're using boxed, dynamic speakers, that is) the bass frequencies from the enclosed woofers that are bouncing back through the cone and creating increased EMF are no longer as adversely affecting the higher frequencies as they do in a single amp.

But, even that advantage I'd say would pale in comparison to the advantages that replacing your passive crossovers at the same time you go active, would bring you - even if all you did was replicate original factory values throughout the crossover range...a much more coherent sound in terms of dynamics, tone and sound staging/imaging all the way through the crossover zone. So, if you were to consider replacing your passive crossovers with (fully) adjustable active ones, then that might be another matter...quite recommendable - IF you're both willing and able to take things that far...and there will be a learning curve for all that, as well. But, if otherwise, then I would certainly recommend against this move...just far more cost and complexity IMO than the miniscule amount of gain would be worth. Hope this helps.
ivan_nosnibor's avatar
ivan_nosnibor
782 posts
 
IOW, we only need consider an amp to be ’overworked’ by thinking purely in terms of its "output" (volume level), not its "input". That is, any crossover, passive or active, is perfectly sufficient to reduce the amp’s normal workload (as long as it’s connected to appropriate speakers) to limits well within the design specs of the amp - both operationally and audibly. Any full-range amp seeing duty as a "mid", or "tweeter" amp is indeed loafing along (if power ratings have been taken into account) and is having a far easier time of it than the full-range amp or even the "bass" amp in the same system. And it matters not where the division of the frequency spectrum occurs.
erik_squires
5,268 posts
 
@ivan_nosnibor
No, that's not correct.
Consider a speaker with the woofer section (crossover and driver) removed.

The amp still produces the complete voltage swing. However, there is very little current flowing at low frequencies. So, power is greatly reduced. However, the dynamic range of the amp is not affected by much.
By eliminating bass from the amp intput, you greatly reduce the voltage swing, allowing greater dynamic range in that amp.

Put another way, you could run around a 30 watt top amp and 200 watt bottom amp, and have balanced dynamic range, and more of it. :)
ivan_nosnibor's avatar
ivan_nosnibor
782 posts
 
@erik_squires 

Forgive me if I've failed to grasp something here that I did not know before, I'm feel sure it might be something simple, but I'm still having trouble discerning what that is. Can you elaborate a bit more for me here?

If as you say "the dynamic range of the amp is not affected by much", then how is it again that eliminating the voltage swing" will allow "greater dynamic range in that amp"? Again, not arguing anything, just trying to figure out where my interpretation of what you're saying has gone off track for me. I figure I'm just hung up on the semantics somewhere or something.

Thanks
jburidan
672 posts
 
No benefit whatsoever.
erik_squires
5,268 posts
 
Hi @Ivan_nsnibor

Instead of thinking of amplifiers as amplifying power, think of them as amplifying voltage, as indeed, the ideal amp is a voltage amp with infinite power.


So, take an amplifier that can produced a maximum of 10V rms. In music, most of that will be used by the bass, below 200 Hz. A lot of it. Maybe 8 V rms. If the bass takes all 8, you are left with 2 V for the rest.


If you put a high pass filter before it, the amp is now able to reserve all of the 10V for mid to treble.


Does that help?

Best,
E
ivan_nosnibor's avatar
ivan_nosnibor
782 posts
 
Ok, gotcha I believe. This then is the problem unless the active crossovers (or filters that you guys were talking about above) are applied at the input, yes?...not the output. And if they were applied at the input, then all 10V would be available for whatever portion of the frequency spectrum the amp was being fed, do I have that right? Just making sure.

IOW it all depends on whether the filtering is being applied after or before the input...(which is apparently how it is for my own amps or otherwise I might have run into this problem already, since my system active tri-amped).

Regards
dprincipato OP
2 posts
 
Thanks to all for the insights.  Nekaudio, interesting articles, thanks for the links.  Erik, I’m inclined to agree with you, and if I were to go down the road of actively crossing and leaving the passive crossovers in place, the active cross point should be at least an octave away from the passive’s crossover point. I’m thinking now that the best move would be to keep eyes pealed for bargians that fit the future scheme for active three-way, with speakers that I build, designed with no passive, or very minimal passive crossovers. I really like the Triangle Volantes, although they can be a bit bright on some recordings. And I definitely don’t want to blow up thier resale value by digging around inside them. As far as I can see right now, it would be a Marchand crossover, three-way, with 24dB slopes, that allows signal attenuation for the frequency bands. Now, amps for this scheme are an area I could definitely use some ideas on, I love my JC 1’s, would consider them good choices for bass, but could use suggestions regarding mids and highs, amp-wise.  I’m thinking of tubes for the highs, and I have a Bob Latino ST-120 tube kit that may fit the bill for the highs quite nicely.  Any thoughts are appreciated, and thanks again to all for th fine information..
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