Use of line-level crossovers for bi-amping?

[Wizard-of-Odd]

Has anyone used the Harrison Lab FMOD crossovers when bi-amping? I want to use a combinantion of low-pass/hi-pass filters between my pre/pro and amps. Good idea, bad idea, or try it and see?

thanks,
Kevin

[stewfoo]

Horrible idea for the new B&W 800 series... Their new crossover simplicity is a major reason for the drastic improvement in the new models.
Stew

[Karma]

HI Wiz,
I must disagree with my friend stewfoo. Line level crossovers (also known as active crossovers) CAN offer many advantages over the passive crossovers used in the speakers. You have much better control over the cross over slopes, phase relationships, rolloff rates, and relative driver volume.

However, for you to ask this question indicates to me that you are not experienced doing this. Biamping with active crossovers is tricky and considered to be an advanced technique. So if you are not confident you know what you ae doing I would stick with the passive crossovers.

The CAN above is important. The active crossover must be of high quality. Many are not. So, if I was going to biamp I would definitely seek a high quality active crossover. If I wasn't willing to spent the necessary money to get a good one, I would stick with the ones built into the speaker.

Sparky

[Spearmint]

Has anyone used the Harrison Lab FMOD crossovers when bi-amping? I want to use a combinantion of low-pass/hi-pass filters between my pre/pro and amps. Good idea, bad idea, or try it and see?

thanks,
Kevin

If you decided to go this way, how would you bypass the internal passive crossovers in your speakers?

[Karma]

HI,
Good point. You would have to modify your speakers. That's not difficult but it should be done professionally. It could be done such that the original configuration could be easily restored if you wanted to sell your speakers.

Sparky

[stewfoo]

Sparky, I qualified my statement by limiting my oppinion to the new 2005 800 series B&W speaker. I think it is fine if you are altering crossovers in a mid-fi speaker or below. But, I trust that the engineers at B&W are better at designing crossovers than you or I. Adjusting the slope or crossover points of such refined speakers could and probably would degrade the sound of the original speaker. Now, if you are looking to actively crossover 800 series speaker because it is a hobby and you enjoy tinkering... I say enjoy yourself. Its you stuff. Do as you please. But, if you are doing it purely in order to improve sound, I would bet that sound quality will not be improved.

[Eliav]

Sparky, I qualified my statement by limiting my oppinion to the new 2005 800 series B&W speaker. I think it is fine if you are altering crossovers in a mid-fi speaker or below. But, I trust that the engineers at B&W are better at designing crossovers than you or I. Adjusting the slope or crossover points of such refined speakers could and probably would degrade the sound of the original speaker. Now, if you are looking to actively crossover 800 series speaker because it is a hobby and you enjoy tinkering... I say enjoy yourself. Its you stuff. Do as you please. But, if you are doing it purely in order to improve sound, I would bet that sound quality will not be improved.

I would not touch such a refined piece of art as the B&W 800 series. to me It's like opening a Mercedes-Benz new engine, drilling it's rings and cylinders to get some more horse -power. I would not dare, but that's just me of course!
Eliav

[Karma]

HI stewfoo,
Sorry, I must disagree again. Passive crossovers have severe limitations. There is only so much you can do with inductors, capaditors and resistors. Surely, you understand that passive crossovers are functioning on the high current audio signal from a power amplifier. This imposes really serious problems for the crossover designer. Passive crossovers, even the best of them, are filled with tradeoffs.

Any speaker designer would love to have the precision that is available from active crossovers. It is the opposite of your opinion. You will find active crossovers in the highest of the high end systems. For example, the Wilson Grand Slams at a cool $200,000 a pop. Also the Apogee Diva's at roughly $20,000, the Infinity IRS at what ever they are now; maybe $70,000, and a few others. These are all hugely expensive systems that are bi or tri amped and use active crossovers.

Why are they not used more? Primarily cost. Remember, you must add in the cost and complexity of an amplifier for every driver. Plus, the speaker manufacturer looses control over the final result. Once the crossover is out of the box, any cowboy can screw it up. You are right about that. I don't necessarily think everybody should underatake active crossovers. Jeez, we have enough trouble just getting our subwoofer crossovers adjusted (these are active BTW). But when done right, they are the best.

Sparky

[stewfoo]

Once the crossover is out of the box, any cowboy can screw it up. You are right about that. I don't necessarily think everybody should underatake active crossovers. Jeez, we have enough trouble just getting our subwoofer crossovers adjusted (these are active BTW). But when done right, they are the best.

Sparky

Exactly. Without preset active crossovers the average audio enthusiast is gonna screw it up, especially without the equipment to calibrate perfectly. Remember, this is a B&W forum and I was referring to 800 series speakers. I grew up with car audio and I had an active crossover for my 12 speaker/driver system . I remember using a combination of active and passive xovers.... (I probably had that all screwed up) But, with 800 series speakers the stakes are higher. I personally wouldn't do it. In fact, I have limited my crossover tinkering to playing with my Velodyne DD-18 equalization and crossover settings.

[Ryx]

Just to add to the lists of speaker which use active cross-overs that Karma has already supplied, B&Ws own Nautilus (Snail shells) also use an active crossover setup.

I would have to agree that the main reason most speakers are left with passive crossovers is the cost of buying multiple amps per speaker. just imagine what it would cost to buy 8 Cam-400s in order to power a pair of snail shells 8O

[Karma]

HI Stew,
I can relate to your advice. But really, how high are the stakes? The speaker modification is easy and cheap. And it can be reversed just as easily. Damage to the drivers is not likely. The biggest down side is pure frustration. The upside is a very real possibility of a significant improvement. I really don't see a risk.

Don't forget the major advantage of biampiing. If a person is willing to spend the time, I think it is a good idea.

Sparky

[Wizard-of-Odd]

My proposed use of bandpass filters in no way replaces the speaker crossovers. I just don't see any reason for an amp to deal with the entire frequency range when it is only driving the woofer or the mids/tweeter. By splitting each channel output from the pre/pro before input to the amps, the speakers are being fed only the frequency range they use. The crossover for the mids/tweeter will still function as designed. So................. is there a problem doing it this way? I am no expert in this area. I'm just trying to get the most out of bi-amping with the hardware I have and can afford.

Kevin

[Karma]

HI Kevin,
It will work fine but you might consider eliminating the speaker crossover to gain the full benefit of the active filters. But as Stew and I said, it can be a tricky beast.

Sparky

[james_dmi]

My proposed use of bandpass filters in no way replaces the speaker crossovers. I just don't see any reason for an amp to deal with the entire frequency range when it is only driving the woofer or the mids/tweeter. By splitting each channel output from the pre/pro before input to the amps, the speakers are being fed only the frequency range they use. The crossover for the mids/tweeter will still function as designed. So................. is there a problem doing it this way? I am no expert in this area. I'm just trying to get the most out of bi-amping with the hardware I have and can afford.

Kevin

This wont work it will sound terrible. You will effectively be running both the active and passive crossovers in series which would have the effect of multiplying the frequency response curves together. This will destroy the balance of the speaker. On top of that you are increasing the amounts of electronic filtering the signal has to go through which will further degrade the sound.

There is no point using an active crossover unless you can bi-pass the passive ones. You will receive none of the benefits ( i.e. 100% phase alignment with optimal response curves) because of the passive filters you still have in place.

If your worried about your amps using power they don’t have to then you needn’t be concerned. The amp that is driving the base for example only expands power when it can see the resistive load of the driver. Once the frequency goes beyond then crossover filters band cut point then the amp is seeing an infinite resistance and therefore won’t be expanding any power. There is still some power loss in the crossover region but this small benefit will be far outweighed by the problems I have stated above.

[stewfoo]

This wont work it will sound terrible. You will effectively be running both the active and passive crossovers in series which would have the effect of multiplying the frequency response curves together. This will destroy the balance of the speaker. On top of that you are increasing the amounts of electronic filtering the signal has to go through which will further degrade the sound.

There is no point using an active crossover unless you can bi-pass the passive ones. You will receive none of the benefits ( i.e. 100% phase alignment with optimal response curves) because of the passive filters you still have in place.

If your worried about your amps using power they don’t have to then you needn’t be concerned. The amp that is driving the base for example only expands power when it can see the resistive load of the driver. Once the frequency goes beyond then crossover filters band cut point then the amp is seeing an infinite resistance and therefore won’t be expanding any power. There is still some power loss in the crossover region but this small benefit will be far outweighed by the problems I have stated above.

That's what I meant! :blink:

[Wizard-of-Odd]

I think I understand now - bad idea, won't do it. Thanks to everyone for bearing with me.

Kevin

[Karma]

HI All,
Are you guys arguing that bypassing the passive crossover and instead using an active crossover and a separate amp for each driver is a bad idea?

Or are you only warning about using an active AND a passive crossover with independent amplifiers? If this is the argument, I agree with you.

These are two entirely separate questions ( I know you know) with separate answers. I'm intrigued by the idea of using a classical biamp solution. I think it could prove very good. And I don't see that there is anything to loose except some money if it doesn't work out. But it almost always does.

Sparky

[james_dmi]

HI All,
Are you guys arguing that bypassing the passive crossover and instead using an active crossover and a separate amp for each driver is a bad idea?

Or are you only warning about using an active AND a passive crossover with indendent amplifiers? If this is the argument, I agree with you.

These are two entirely separate questions ( I know you know) with separate answers. I'm intrigued by the idea of using a classical biamp solution. I think it could prove very good. And I don't see that there is anything to loose except some money if it doesn't work out. But it almost always does.

Sparky

I have listened to Dali MS5's and B&W802D + 803D in both single and classical bi-amp configuration with the same set of amps and electronics. Its well worth it! Sounded better then the sum of the parts if you know what I mean.