How would you modify a speaker to biamp?

soiset

I'm curious: If I wanted to modify the LS50 or the CS350LS for biamping (I've heard of the 350 being modded in this fashion) what would be the best way to do it?

VR3

Youd have to make two seperate xovers, one for the tweet, one for the midbass(es)...

soiset

Well, the closest I could come to the original crossover frequency would be to approximate what is roughly shown in the s/ls series brochure, which is shown at 4500 Hz. I know approximately jack about speaker building, but that seems a little high to me.

So I guess you would have to use two identical crossovers, one of which would act as a high-pass and the other as a low-pass filter(?)

Are there any external crossovers, perhaps with adjustable crossover freqs, that would work?

Zen Dragon

Vr3MxStyler2k3 wrote:

Youd have to make two seperate xovers, one for the tweet, one for the midbass(es)...

I'm not entirely certain that new crossovers would be needed. Both the low and high pass circuits alread exist in the crossover. I think one would only need to find the place on the PCB board where the two circuits are connected and cut the run.
At this time you would have two separate crossovers in the speaker and could run the wires from each back to a pair of input terminals.
Connecting the input terminals would be in essence the same thing as reconnecting the circuit run that was cut.
I have looked at the schematics for Polk speakers that are biampable, and ones that are not, and the same basic configuration appears to exist, with the difference that the high and low pass filters are not connected together on the crossover for the biampable speakers.
Naturally I would not recommend attempting this on any speaker still under warranty. In fact if you wanted to test the theory, you might go pick up like a pair of realistics at a thrift store for $10.
Anyone else have thoughts on this?

VR3

Well I was going for the "correct way"...

Not the rigged way...

Zen Dragon

I would not call this the rigged way. You will be using the original Polk crossovers and the components they selected.
Separating the circuit runs is necessary to separate the two networks which are connected in parallel from the factory by default. It is what would be necessary to acheive the correct electrical circuit. No sense buying the same components you already have.
When someone sends a unit out to have several hundred dollars of mod work done to it they do not call it "rigged" when they get it back.

VR3

I dunno, if I was going to spend several hundred on a crossover to be redone into a biamp option type deal - I would be expecting to receive a new xover with two seperate boards. Thats the whole idea behind biamping - keeping things seperate.

Zen Dragon

As I read it Soiset is looking for a mod he can perform himself. By cutting the circuit run you are effectively isolating and separating the circuits. It is no different than building the original circuits up from scratch on separate boards.
The concept of biamping is actually an efficiency oriented function. By allowing separate amps to drive the low and high frequencies you reduce the overall strain on each amplifier.
It also allows you to use more of a powerhouse amp on the lows, where most of the power is required due to the impedance dips, and more of a detailed amp, even tube perhaps if you want to soften the upper frequencies, on the highs where more detail and less power is required.

VR3

Lets just say it would be nothing I would ever do.

Bi-amping isnt that simple either. You have to cross your amps over (high frequency amp) or the amp is still seeing the signal as full range, therefore its not really in theory biamping.

There are in line crossovers you can buy for the amps though, but thats just another piece in the signal path.

If you want to end the circuit path on a crossover, I say go for it - but that just sounds like you're rigging it up to me, its my opinion on that one.

And one of *my* reasons for biamping (when/if I do it) - I want everything seperate. I want my tweeter network away from the midbass network, I want my tweeter network to have its own post, its own wires, its own board.

Active crossovers would be fun to.

soiset

Please, continue; I'm enjoying this!
As far as the amps reproducing a full bandwidth signal, and thereby being used inefficiently, I don't think that is the case (from the little I've read). If the work is not being done (either by heat or mechanically), then the power is not being used.

Also, as I understand it, one of the benefits of biamping is to prevent current generated by the movement of the drivers from feeding back through the network to the other drivers, muddying the signal.

VR3

The idea behind biamping is to free up the amps. Plain and simple.

Have a dedicated amp to the lows and then to the highs.

The preamp/receiver is what sends the amps this signal. If the preamp is sending a full range signal, the amp dosnt know what its plugged into. The amp sends all its power to the speakers because its told to do that full range signal. Once it reaches the speaker, the crossover stop the drivers from playing to much.

Thats why crossing the high frequency amp is so important. Its kind of a waste of amp if you dont because you are gaining no real benefits.

Zen Dragon

I have done some reading on active crossovers and bi-amping . It is an interesting concept.
In the ideal active crossover you completely disable the crossover in the speaker and install a crossover between the pre-amp and the amp. By performing the crossover pre amplification the amplifier never has to reproduce the unwanted signals in the first place.
The amplifier is freed up from the extra frequency, and doesn't end up driving any unwanted frequencies into the high impedance of a crossover that is rejecting portions of the frequency.
This also allows for better control of the drivers as less damping is required because the amplifier is not seeing the push back from a high impedance above the crossover point.
I'd like to experiment with active crossovers one day.

VR3

You can do it passively with connectors.

Go to parts express and type in Crossovers and scroll down to In-Line.

Its the same concept, just cheaper - but it also puts nasty connectors in the signal path.

Zen Dragon

Interesting. Thanx for pointing the parts express units out Sid. The F Mod active crossover simulators would be neat to experiment with. Just to see if there is a difference in sound.
I would never use them as a final solution however. The speaker Mfr generally chose the components they did for a good reason after much engineering, and the reading I have done states you should use the same quality and value of components in an active crossover that were used in the original speaker passive crossover.

Brian

VR3

The manufacture uses CRAP components 90% of the time (and when they dont, they generally costed ALOT.)

The best upgrade you can do to a crossover is upgrade the caps and resistors.

Zen Dragon

Correct. I should have stated that using the same value is recommended, not necessarily the same quality, but equal or greater quality.
I don't know that the components used are crap, but mfrs generally try to find a cost vs performance point to keep their production costs down.
This usually means they will use components of good quality that do not impart substantial degredation into the circuits.
Very few mfrs use the highest quality components because it tends to push their price points out of the mainstream market, and is beyond what the masses require in their listening.
Of course tastes varry as to what sounds good to the individual listenener anyway, and if the best components were used up front, how would the tweaker within us get it's fix?

VR3

Im not complaining that they do - I understand why they do.

I did the ultimate tweak - I rebuilt the speaker!

unc2701

Just a point of clarification- active biamping, done right, removes the crossover from the speaker (less components in the signal path) and puts a crossover before the power amp (more components in the signal path).

I've found that biamping really doesn't do much unless you do active biamping, but there's no reason why you can't do what both Sid and Zen suggest- map out your crossover circuit and figure out where you'd put your high and low posts, then build a new xover using better componets (with the same values).

soiset

What about using a crossover from the LS/fx, which uses the same tweeter as the LS50, to steer the highs in the LS50 (or CS350)? I could disconnect the tweeter from the original crossover in the LS50, install the crossover from the LS/fx, and hook the tweeter output from that crossover into the tweeter of the LS50.

As far as biamping sans external crossovers, I have read that there are two benefits to conventional biamping: One, that you can choose your amps by their high/low characteristics, and two, and this is the big one, I think, current induced by movement of the voice coil(s) of the woofers is not fed back into the tweeter. Am I wrong?