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For about a decade I've been meaning to build an active crossover and bi-wire my speakers. I liked the idea of reduced inter-modulation and increased control of the crossover characteristics, and it sounds like a cool thing to do.

However, I've just read this very intelligent argument against, basically saying that it leads to phase errors between the drivers.

However; doesn't the reactive nature of crossovers and differing speaker characteristics cause phase differences between the drivers in the crossover region anyway?

What's the general consensus?

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Fri Nov 20, 2009 12:00 pm
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Using an active x-over & bi-wiring are 2 seperate things.

Biwiring is running 2 cables from the same channel of the amp to the speaker (1 cable connects to the bass & 1 to the treble, you remove the bridge connector on the speaker). This gives some benefit as you have more copper from the amp to speakers so will have less resistance (although just using bigger cable would do the same)

Using an active crossover allows you to split the frequencies before amplification so you're not relying on passive x-overs in the speaker to do the job.
For this to work you'd need to disable the x-overs/filters in the speaker boxes.

Bi-Amping speakers is another matter as well.

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Fri Nov 20, 2009 12:37 pm
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Let me explain more clearly.

I am planning to build an active crossover and 4 way amplifier. Obviously there will be two cables running from two amps to the speakers, with the tweeters and woofers wired to their own amp. That is the only way I know of to use an active crossover. Obviously I will not be using the passive crossover in the speaker cabs.

The article is talking about bi-wiring from a single amp, but the phase error problems described apply equally to my scenario.

So, my question is: are the benefits of an active crossover with separate amps and cables to the drivers outweighed by the static and stochastic phase errors introduced as compared to a single amp with single cables?

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Fri Nov 20, 2009 7:36 pm
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I use active x-overs in my live rigs (a rather nice unit which I can program from my laptop), it gives me a much better sound & flexibility for what I need (I can 3-way/4-way it for big gigs or 2-way for smaller ones).
Most hi-fi stuff you find is done with highpass or lowpass filters instead of traditional x-overs (like you find in older kit & cheap PA speakers).

But that's just me waffling on.

Personally I'd say any phase errors introduced would be negligible compared to the phase errors introduced the lack of time & point alignment in a speaker cabinet (not to mention at potential difference from having slightly different amounts of cable between each driver)

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jonlumb wrote:
I've only ever done it with a chicken so far, but if required I wouldn't have any problems doing it with other animals at all.


Fri Nov 20, 2009 8:31 pm
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saspro wrote:
Personally I'd say any phase errors introduced would be negligible compared to the phase errors introduced the lack of time & point alignment in a speaker cabinet (not to mention at potential difference from having slightly different amounts of cable between each driver)

The phase errors talked about in the article were not due to differing cable lengths. Even with absolutely identical cables, the loading presented by the two drivers is very different. Since a cable is a reactive component, this leads to a fairly complex system.

The model used in the article simulates the cable as an 8uH + 50mR impedance, which does not seem an entirely unreasonable simplification. They simulate the woofer as 500uH + 6R and the tweeter with a rather more complicated circuit. In my scenario, the passive high and low pass filter components are absent but the reactive components of the cable and drivers are still present.

He was seeing up to 3 degrees of error introduced in the crossover region, purely because of the bi-wired cabling. I won't have the passive crossover, but the characteristics of the two amplifiers will not be identical so I guess the phase errors will still be of this magnitude.

My drivers are vertically aligned with a central separation of 250mm. With the drivers in perfect sync there would be zero phase error with ear at the central height. At 2.5Khz, 1 degree is equivalent to 340ms-¹ / 2500s-¹ / 360° =0.38mm. At my usual listening position 2.5 meters away, that represents a vertical distance of about 10mm.

Therefore, I think you're probably right. I do sometimes move my head by more than 1cm from the optimum position.

I guess if I really want to know, then I should simply wire up the speakers to a sweep oscillator and analyse the result with a dual channel scope. I suspect the mechanical response of the drivers is actually the larger issue, so testing with a mic in addition to the voltage at the speakers would be interesting.

I might even listen to it and see if it sounds better, but that means building it first.

*blows dust off 'scope and soldering iron*

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Sat Nov 21, 2009 2:38 pm
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wow I love this thread.

It's a proper geeky one, with lots of jargon and terminology I've never heard before.

It's excellent. :)

Keep it up lads.

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Sun Dec 20, 2009 12:46 pm
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Tbh I think that you'd find it impossible to hear any artifacts caused by a 3 degree phase error in even the best of listening environments. Hell you'd probably struggle to detect it beyond 2 metres.

In anything but the deadest space a 3 degree x-over phasing would be dwarfed by reflective phasing from the walls and furniture. Add in moving air, ambient noise, equipment noise, magnetic interference and other factors and I'd think this effect becomes real but negligible.

Furthermore I'd have to say that using a x-over and bi-amping allows you to restrict each driver to its optimum frequency window and the benefit should far outweigh any issues.

Just my two pen'rth

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Sun Dec 20, 2009 4:10 pm
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JJW009 wrote:
For about a decade I've been meaning to build an active crossover and bi-wire my speakers. I liked the idea of reduced inter-modulation and increased control of the crossover characteristics, and it sounds like a cool thing to do.

However, I've just read this very intelligent argument against, basically saying that it leads to phase errors between the drivers.

However; doesn't the reactive nature of crossovers and differing speaker characteristics cause phase differences between the drivers in the crossover region anyway?

What's the general consensus?


I remember someone posting that exact page on the Hifi Choice forums about 10 years ago, and it taking ages to load on 28k dial up.

Bi-Amping is good, Bi-Wiring is controversial, is what people used to say. Using Monoblocks and Bi or Quad Amping was a popular way of powering electrostatic speakers like those made by Quad.

When Bi-wire capable speakers were all the rage, particularly by Mission, about 10 years ago, the Dynaudio Audience were winning awards and they were always single wire only. I had some 42's and they were gorgeous.

These Electro's are bi-wirable though...

http://www.davidmichaelaudio.com/pc-371 ... akers.aspx

Cheap too.


Sun Jan 17, 2010 10:45 pm
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