Bi-amping

[diyman]

I am looking at the possibility of bi-amping without using electronic crossovers. Would it be okay if I build a passive crossover and insert it before the power amplifiers? After all, even active crossovers are a series of filters!

 

[pinkmouse]

You would be much better off using an active crossover, or putting the passive crossover components in the amp enclosure on the outputs.

 

[Bill Fitzpatrick]

I am looking at the possibility of bi-amping without using electronic crossovers. Would it be okay if I build a passive crossover and insert it before the power amplifiers?

What would be the point in doing it this way?

 

[diyman]

If I build a passive crossover using the same specifications as per the original speakers, I suppose I do not have to tweak it as the original componets were chosen with the box design in mind eg. roll-off, Xover freq etc.
The reason I want to do it this way is to split the signal before amplification as is done by electronic crossovers. This is to allow specific power amps to amplify certain frequency range only to optimize the full benefits of bi-amping.

 

[Mr Evil]

You can use a passive line-level crossover. I believe there has been quite a bit of discussion about them here before. I would recommend using an active crossover though; they have many desirable characteristics.

What would be the point in doing it this way?

I can think of two reasons: 1) Simplicity/cost. 2) Potentially lower distortion by using only linear components.

If I build a passive crossover using the same specifications as per the original speakers, I suppose I do not have to tweak it as the original componets were chosen with the box design in mind eg. roll-off, Xover freq etc...

You couldn't just use the crossover as-is, as it will have been designed taking into account the variable impedance of the drivers.

 

[Bill Fitzpatrick]

That and what are you going to do about the very large value inductors you will be needing?

 

[Mr Evil]

That and what are you going to do about the very large value inductors you will be needing?

Don't ask me, I've never done one before! I know other people have though, so it's possible.

 

[leadbelly]

I am looking at the possibility of bi-amping without using electronic crossovers. Would it be okay if I build a passive crossover and insert it before the power amplifiers?

If I build a passive crossover using the same specifications as per the original speakers, I suppose I do not have to tweak it as the original componets were chosen with the box design in mind eg. roll-off, Xover freq etc.

If you mean that you know the design details such as corner frequency, slope, etc., of the passive crossover for a speaker you are building, but want to build a passive line level crossover version instead to biamp, yes you can do that. But there are pitfalls you must overcome:

http://www.t-linespeakers.org/tech/filters/passiveHLxo.html

 

[Davey]

Passive line-level crossovers are possible, but fairly difficult to implement in most cases. Inductor values increase dramatically, but it is still possible. The impedances involved are fairly low and a stout preamp (maybe a headphone amp) would be required.Check the Marchand XM46 crossover:

http://www.marchandelec.com/xm46.html

Passive crossovers using RC circuits (vice LC circuits) are possible, but there can be significant insertion loss, Q's are limited to 0.5 maximum, slopes are realistically limited to second-order, etc. Interconnect driving ability may also be a factor. There are many variables, but if the proper combination of preamp, power-amps, and a not too challenging topology is required then passive line-level crossovers are a viable alternative.

Active crossovers solve a multitude of problems and are preferred in most cases.

Cheers,

Davey.

 

[5th element]

There is nothing wrong with using a PLLXO but you then have to involve the input impedance of the next thing in line after the PLLXO, and include the article driving the PLLXO. You can think about a PLLXO like a normal loudspeaker.

Power amplifier drives the coils, caps and resistors, and the loudpeaker drive units. The coils, caps and resistors are designed around the loudspeakers impedance curve and frequency response to achieve a desired result.

In a PLLXO the preamp drives the coils, caps and resistors, and the power amplifier input impedance. You design caps, coils and resistors in the PLLXO around the input impedance of the power amp and the drive units frequency response.

The benafit this brings is the usual coupling of the power amp directly to the loudspeakers, and xover designed around a fixed impedance that doesnt change with level. The power amp input impedance doesnt change with frequency or how many watts the amp is giving out. Loudspeaker voice coils impedance vary with frequency and increases when power is applied.

The versatility of a PLXXO is not as much as a real active xover and is harder to implement. If you want to do xover before amplifier then just throw a few opamps in the circuit too, this removes the need for large inductors (because of the power amp high input impedance) and pretty much removes the preamp having to be capable of driving a difficult load.

www.linkwitzlab.com

has some useful info on active xovers.

 

[fakeout]

I'm bumping this because it might be relevant. If I have a Lepai 2020A+ amp, two full range drivers and want to hook up a woofer, is there a quick and easy way?

 

[Moondog55]

Quick and easy is usually in my case a first order on the woofer to make a 2.5way. Takes a pretty big coil

 

[tvrgeek]

Just a hint: There are very good reasons why the standard way of doing things became the standard way of doing things. Passive crossovers at power level, or active at line level. It should be a hint that nothing past "bass blockers" for cheap car stereos are passive line level. They work like garbage too.

 

[Moondog55]

I didn't mean my post to be taken as being better than Bi-amping electronically, I am a Bi-amp user for yonks, just that using a big coil in series with a helper woofer is "Quick and Easy" Never tried PLL XOs, electronic is simply easier as you buy them off the shelf if your soldering skills are not great

 

[hazard500]

Hmm, some interesting comments in this thread - becasue I already have passive line level cross overs and it works well. That said, I only have 1st order cross over so this is an easy implementation. To be specific, I have a hybrid speaker with Magneplanar tympani bass panels, with Bohland Graebener RD75 ribbon tweeter. Cross over is 1st order at 660 Hz (my target is to get the cross over at the music half power point). My power amps (DIY) have a jfet input with impedance of 1 meg so a passive filter is easy to implement and doesn't load my (passive) pre-amp. Bass amplifier has an R-C filter, treble pre-amp has a C-R filter. Nothing hard about this. I've been using it for nearly 10 years (replaced a DIY op amp active filter) and it works flawlessly, and is totally transparent.

I can see that that there might be complexity if you have a power amp with a low input impedance, but this is a DIY site, right - haven't we all built our own power amps with high Z? And we accept challenges like this with a grin? I say go for it.