Bi-amping

[admin_exported]

So technology in the hi-fi world is crazy at the moment with DAC's and more settings on amplifiers that we could ever dream of. Not that i'm complaining but i want to go back to something that has been around for a while. Bi-amping. I've been bi-amping for about 4 years now with 2 Cambridge Audio 640A's. It sounds great but i've read that this is not true bi-amping. True bi-amping is when you remove the passive crossovers inside your speakers and split the signal before you amplify with an active crossover. One amplifier will only amplify low's and the other one high's. Now this is where I have questions. Why are speaker manufacturers not manufacturing speakers without passive filters and why don't you get amplifiers with crossovers built in (I think one of the Onkyo's have one built in now). My point is that to actually do true bi-amping is quite a mission and you will have to buy an active crossover. Has someone here tried this and what is the result? Is it worthwile to investigate? I've heard you double your output. It almost seems like removing your passive filters is a mod that manufacturers dont want you to do and that we have to stick with bi-wiring (which in my opinion makes no difference) and bi-amping with the full audio spectrum.

 

[kevinJ]

I believe B&W's Nautilus uses such an external crossover, and needs 4 stereo amps to drive a pair of speaker.

The problem is, you'll need to design your own crossover (so you'll need the equipement to measure everything) because there's no "one size fits all", make sure you have a whole bunch of replacement speakers for when things go wrong, and you need a lot of amps.

But I guess it's possible to build a system that way, I just don't think it's worth the trouble/time/expense.
Most speaker manufacturers know how to design a crossover these days. But there are still a few "tweakers" out there.

 

[Anonymous]

I've been bi-amping for about 4 years now with 2 Cambridge Audio 640A's. It sounds great but i've read that this is not true bi-amping. True bi-amping is when you remove the passive crossovers inside your speakers and split the signal before you amplify with an active crossover

Haven't heard of that definition. Sure, bi-amping with active crossover will arguably produce better results than with the passive crossover still in place, but it's still bi-amping to me.

Why are speaker manufacturers not manufacturing speakers without passive filters and why don't you get amplifiers with crossovers built in

Because the crossover is part of the speaker design. Every speaker has a different crossover filter that's tuned to the drivers, cabinet and other characteristics of the speaker. It's like wanting to fit a Fiat's gearbox into an Aston Martin...

My point is that to actually do true bi-amping is quite a mission and you will have to buy an active crossover.

You can't buy them off-the-shelf. Active crossovers are bespoke items that must be built into your amplifier(s) to match the passive crossovers in your speakers.

It almost seems like removing your passive filters is a mod that manufacturers dont want you to do and that we have to stick with bi-wiring (which in my opinion makes no difference) and bi-amping with the full audio spectrum.

I think you're wrong there. The hardest part for an amplifier is not raising the output voltage, but delivering enough current so that the speaker can do what it needs to do. If you bi-amp with the full audio spectrum, then yes, the amplifier will amplify the full audio spectrum. But the passive crossover in the speaker will not draw any current for frequencies outside of its driver's range.

 

[FennerMachine]

Linn do active crossovers and speakers designed for this.

It looks like you can build your system gradually, adding power amps and active crossovers as needed. Other manufacturers may also do this.

 

[lindsayt]

Jakesb: Speaker manufacturers (for non-active speakers) always put crossovers in to prevent damage. If you supply the full frequency range or bass signal to a tweeter with no crossover protection you wil break it.

There are some amplifiers with active crossovers built into them as optional cards. This is not an approach that I like as it ties you into one particular set of amps and speakers.

I don't think that active bi-amping is quite a mission. It's easy peasy. All you need is some speakers where you can get at the crossovers easily or speakers that already wired for easy conversion to active bi-amping. Every 1960's to 1970's American speaker that I've come across (I'm only interested in the stuff that would have been high-end when new) has been designed for very easy conversion to active bi-amping and also for active tri-amping (and quad-amping for the 4 way that I bought). So, in the old days speaker manufacturers were only too happy for you to use passive or active amplification.

Adjustable active crossovers are not expensive. I bought a 2nd hand Ashly for £120. I also bought a Pioneer SF-700 for £180. There are plenty of other brands who made or still make adjustable crossovers. You can also buy speaker specific non-adjustable active crossovers for certain speakers. Good quality 2nd hand power or integrated amps can be bought for very reasonable prices too.

You are right in thinking that you double your output - due to the power amps not having to deal with low frequency transients / waves imposed on top of in phase higher frequency transients / waves. A doubling of output results in an extra 3dbs. Is it worth investigating? I think it largely depends on your speakers. If your speakers have a crossover somewhere between 100 hz and 1.2 khz then I think that this lends itself better to active bi-amping because you'll have a vaguely equal division of the load. If you have 2 way speakers that crossover at 2khz or higher then you'll have the mid-bass amp doing all the work and the tweeter amp having a really easy time. I have a pair of speakers that are generally acknowledged to sound better when actively bi-amped. When I did this to them I gained dynamic ease plus some control over the tonal balance. I lost a bit of midrange detail due to the active crossover introducing some transistorised hash. Overall I prefer them bi-amped. Whether you will prefer your speakers actively bi-amped or not will depend largely on your speakers and to a lesser extent on how transparent an active crossover you can get as well as what sort of power amplification you're using.

One myth with active bi-amping is that you should use the same amps for lower and higher frequencies. This is nonsense. All you need is a volume knob on the active crossover itself (which you get on adjustable active crossovers) or between the active crossover and the amp with the most gain. In my active bi-amp set-up I'm using an 80 watt solid state amp below 400hz and an 8 watt SET valve amp above 400hz. This works very well as a pragmatic horses for courses solution.

 

[Anonymous]

Thanks for the replies and discussion guys

KevinJ: I do agree with you that it's defnitely a "tweaker" type of thing to do. Unfortunetaly i'm a bit of a tweaker so guess i will do it at some time. Guess its just part of the hobby to read and investigate it first. I'm also just worried about the expense and trouble.

tremon: Do you mean that you havent heard about true bi-amping? Its just wording i'm using what others have used. I see others refer to it as active bi-amping. I agree with you that the speakers passive crossover from the manufacturer must have the best crossover filter for the speaker and cabinet but i'll do some testing with a frequency generator and a scope on the passive filters to determine the crossover. You can buy active crossovers off the shelf http://www.behringer.com/EN/Products/DCX2496.aspx and there's a few more out there. Surely there must be power lost into the passive crossover. Interesting what you say about passive crossovers in the speaker will not draw any current for frequencies outside of its driver's range.

lindsayt: Intresting that you refer to 1960's and 1970's high end speakers that were active bi-amp friendly. I didnt know this. Its also good to hear from someone that has actually done active bi-amping. I sometimes wish I worked at a high end hifi shop with lots of listening rooms. Then i'll be able to test without spending money and wondering about it. I have KEF iQ 5's by the way. They defnitely sound better when I passive bi-amp them.

I'm sure that passive filters are designed very well these days by manufacturers. Just wish I had a switch that I can quickly switch between passive and active bi-amping and hear the diffence. 😛ray:

 

[lindsayt]

There are hi-fi enthusiasts who have redesigned and replaced the passive crossovers that came with their speakers and have gotten better sounding speakers as a result. This makes me think that there's nothing particularly special nor magical with the crossovers inside many speakers, and that they can be improved upon with some careful design work and selection of good quality components. The crossovers in speakers like the IQ 5 will have been designed and built down to a cost.

 

[Anonymous]

i know this had been dead for a while but ..

i have just bought a behringer active crossover for a play around with, i removed crossovers from my old tdl rtl3 se loudspeakers. I have only really listened for a few hours and tweaked for a few more. but the sound is quite improved. the speakers are painting with a finer brush if you get me. if you have two amps already id definitely recommend it.

it is true that crossovers are tuned to the speakers but there is no reason why an active crossover cant do the same thing better. if you know the crossover frequency (that is listed most of the time on a speakers specification) and you use the same frequency that’s a good starting point and you wont damage the hf unit. Then you have to pad down the hf unit to the level of the lf unit as they are usually more sensitive .

The below article is good at explaining active crossovers .

http://www.tubecad.com/articles_2001/Active_Crossovers_and_Filters/Active_Crossovers_and_Filters.pdf