Bi-amping SL3s with XA-50 and XA-200

[JohnA]

Ah, it's never straightforward, is it?:haha1:

I've got four Musical Fidelity monoblocs available for the task. two XA-50s and two XA-200s.
They all have the same (30db) gain so biamping should be feasible.
If these were ordinary speakers, it would have been a no-brainer: XA-200s for the woofers, XA-50s for tweeters (I actually tried it with my previous speakers and made no difference whatsoever compared to the XA-200s alone)

But the SL3s are different beasts.
Going by what I've read here and all over the net, I am leaning towards XA-50s for woofers and XA-200s for the panels.
What do you guys think?

(I know that eventually I really should get another pair of XA-200s, I'm on the lookout!)

 

[HsvToolFool]

Try both ways to see which sounds best.

I suspect big on bottom would be best. Fast woofers
integrate better with an ultra-fast 'stat panel. Either amp
should have an ample power supply to handle the wilder
impedance of a 'stat panel. But you want an amp that
grabs that woofer and makes it behave.

But I also suspect the XA-200 alone will sound as good or
better than bi-amping.

But, we won't know for sure until you try every combo and
dutifully report back.

 

[JohnA]

I've got it setup now and it sounds good. XA-50s for the bass units, XA-200s for the panels.
Hard to tell yet any definitive improvement from using the XA-200s on their own, I am still optimising the speaker location (final tilt and toe have not been found yet)

Maybe I should point out that my room is not particularly big, and frequency response is closer to flat with the SL3s on the -3db setting.
In a big room where they'd have fill a lot of space probably the XA-50s would be found lacking at high volumes, who knows...

One thing that surpised me was that the biamping ended up in 1-2db extra at the 40-150Hz range (well, zero to 1db on average). Nothing else had changed, and my readings are 100% repeateable, so I wonder where this extra oomph came from

 

[JonFo]

I've got it setup now and it sounds good. XA-50s for the bass units, XA-200s for the panels.
Hard to tell yet any definitive improvement from using the XA-200s on their own, I am still optimising the speaker location (final tilt and toe have not been found yet)

Maybe I should point out that my room is not particularly big, and frequency response is closer to flat with the SL3s on the -3db setting.
In a big room where they'd have fill a lot of space probably the XA-50s would be found lacking at high volumes, who knows...

One thing that surpised me was that the biamping ended up in 1-2db extra at the 40-150Hz range (well, zero to 1db on average). Nothing else had changed, and my readings are 100% repeateable, so I wonder where this extra oomph came from

You have the right combo of amps to driver IMHO.

The reason you see a gain in the low frequencies is due to the amp driving the low frequencies not having to deal with the reactive load of the step-up transformer the panel has.

 

[JohnA]

You have the right combo of amps to driver IMHO.

Yeah, I was thinking that at 4 Ohms the XA-50 monobloc produces 100w. Surely that is enough to drive properly a 10" driver and a low-pass filter, especially at the -3db setting.

The reason you see a gain in the low frequencies is due to the amp driving the low frequencies not having to deal with the reactive load of the step-up transformer the panel has.

I thought it would be something on those lines.
So is it the step-up transformer that exhausts the amp? I thought it was the capacitance of the panel (another theory I've read is the lack of heat dissipation a coil provides).
But then again it could be something different altogether...

 

[JonFo]

...
I thought it would be something on those lines.
So is it the step-up transformer that exhausts the amp? I thought it was the capacitance of the panel (another theory I've read is the lack of heat dissipation a coil provides).
But then again it could be something different altogether...

John, it's a combination of several factors. The crossover for the highs is pretty complex and has passive elements like coils as you note, then there is the transformer, and the panel itself does indeed have capacitance type behavior. But that amp mainly see's the transformer.
By removing all that from what the XA-50 sees, you obtain slightly better efficiency on the woofer.

And yes, 100W is plenty for that 10" driver.

This why bi-amping is popular, as one obtains much better behavior from each amp. But also, because not many do what you did and check the gain levels after the setup.
It’s probably frequent that one of the ‘benefits’ of bi-amping is a nice bass-boost. That of course is not accurate, but some rooms and people probably enjoy it.

This is why when bi-amping or doing active crossovers, it’s imperative to check and set gain and phase (don’t forget that last one, it will kill all the benefits if the phase is skewed).

 

[JohnA]

...that amp mainly see's the transformer.

ugly. A very large, reactive coil. There is a clear case for the panel to have it's own isolated power amp in my view.
With box speakers the benefits are not always clear (or cost-efficient), but here it works very nicely.

... not many do what you did and check the gain levels after the setup.

Musical fidelity amps tend to have line-out and all share the same gain, so they can be mix'n'matched, daisy-chained. Flexibility.

...This is why when bi-amping or doing active crossovers, it’s imperative to check and set gain and phase (don’t forget that last one, it will kill all the benefits if the phase is skewed).

I would definately consider an active crossover if the panel had flat response. Which it doesn't, as we know from that guy who posted the frequency graphs of the Sequel (not far technically from the SL3)

 

[JonFo]

....

I would definately consider an active crossover if the panel had flat response. Which it doesn't, as we know from that guy who posted the frequency graphs of the Sequel (not far technically from the SL3)

Uhm, boy are you talking to the right guy ;-)

I posted a thread full of SL3 measurements as I chopped one up to make my center channel. Read this thread for plenty of info and some evangelism on active crossovers

 

[JohnA]

I have to admit that I'm impressed by your DIY project.:rocker:

I'm quite hands-on as well, as you can see from my website, but more mechanically-minded. I've built subwoofers in the past even amps and an active crossover even 20 years back, based on diagrams from a HiFi mag at the time.

I'll go through that thread carefully and see what I can learn. I'm surprised that I missed it when I was going through the past threads of this forum.:cheers:

 

[JonFo]

I have to admit that I'm impressed by your DIY project.

I'm quite hands-on as well, as you can see from my website, but more mechanically-minded. I've built subwoofers in the past even amps and an active crossover even 20 years back, based on diagrams from a HiFi mag at the time.

I'll go through that thread carefully and see what I can learn. I'm surprised that I missed it when I was going through the past threads of this forum.:cheers:

thanks John.

Is my avatar too subtle?

You'd think that would pique curiousity if nothing else :haha1:

BTW- Great site. I'm also a boost-hound, what with an '04 Subaru WRX and an '05 Legacy GT estate, I dig turbo's as well. But they have to have AWD :rocker:

 

[Pcar928fan]

I dig turbo's as well. But they have to have AWD :rocker:

Porsche 911 Twin Turbo 2001 and forward! YEA BABY! The new tip will hit 60 in 3.4 sec! Faster than the Carerra GT to 60, but the GT is making up time quickly as you cross the 80mph mark and has the 911 fully handled by 100 and up! Well, what do you expect...610HP and 300 or 400# fewer vs. only 460ish HP in the 911! One day I will have one in my garage to keep the other P-cars company!