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Old 18th December 2015, 11:11 AM   #1
drtebi is offline drtebi  United States
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Default bi-amping and amplifier selection

Hello,

I am toying with the (future) idea of building a pair of 2-way speakers and using an active crossover with two amps to power them.

What I am wondering about is, whether the two amps used for such a system must each handle LF and HF separately, or if each could handle LF on the right channel, and HF on the left channel instead?

The reason why I would want to wire it this way is simply a cabling issue... it would make things much easier in my room if I could power one speaker with one amp, using left for LF and right for HF, and the same on the other speaker.

But I assume now, that this would only make sense if the power amp would be a true dual-mono design, because otherwise I would actually loose the advantage of using separate power amps for different frequencies... if I use LF and HF on the same amp?

Does this make sense, or am I overthinking this?

I have a Nakamichi PA-5... which is not a true dual-mono design as far as I understand... so I am wondering if I should get another PA-5 and do as described, or if I'd be better off with two dual-mono amps or just run long cables...
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Old 18th December 2015, 11:16 AM   #2
AndrewT is online now AndrewT  Scotland
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That's what I recommend.
Use one stereo amp located beside/behind the active speaker to power the two drivers of the 2way speaker.
Use a second stereo amplifier for the other active speaker.
Use very short amp to speaker cables.

Use long interconnects from a conveniently located Source/Buffer/Pre-amp.
The volume control is in the convenient location.

The stereo amplifier can be made from two identical amplifiers.
or you can build a two channel amplifier with two different amplifiers. Each amplifier is dedicated to it's driver and can be specially assembled to perform at it's best for that driver.
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Old 18th December 2015, 11:24 AM   #3
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Should not be a problem at all as far as I can tell.

Running non-dual monos as you suggest means that the PSU is unlikely to be unduly stressed as treble tends to need less power provided your crossover point is appreciably above 350Hz (the average equal power point in music).
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Old 18th December 2015, 08:14 PM   #4
drtebi is offline drtebi  United States
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Thanks for your responses.

I now realized that there are actually terms for this question, and I should have asked if vertical bi-amping is preferred over horizontal bi-amping. My idea of connecting would be vertical, and a couple of articles I have read so far indicate that the vertical approach is actually the preferred one—as long as one uses the same power amplifiers.

Looks like I am on the right track then.

I guess it's all about "Intermodulation distortion" of the amplifier, which I don't completely understand yet...
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Old 18th December 2015, 09:08 PM   #5
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Vertical bi-amping will reduce stereo cross-talk, and means both amps are running about as hard (ie, you're not cooking just one). Horizontal bi-amping means you can put more power where its needed.

Chris
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Old 18th December 2015, 09:57 PM   #6
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have been using old 800w/ch qsc amplifier for old rcf event 18 bass bins ,crossed over at 310hz with old rcf event 3000 tops on 150w/ch class d diy amp. in my opinion it would be waste of money/power to have qsc playing on top or all cabinets as this 150w/ch is in real life double the power of what is actualy needed, i know that suggested power at 350hz is 50/50 but in real life i never pulled more than 70w/ch from d-class while qsc would occationaly blink red lights . yeah tops are lot more sensitive than bass and thats probably why this works in this case.
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Old 18th December 2015, 10:45 PM   #7
chrisb is offline chrisb  Canada
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This is DIY, man - there's no such thing as overthinking, or a single right way to do anything in all cases.

Almost all of the 2-ways I build are basically FASTs - essentially a 3-4" fullrange driver generally operating from around 200Hz or so up, and supported by whatever number and size of mid-bass drivers strikes our whim at the time - so there may or not be a big difference in net load impedance and sensitivity of each pass band and corresponding power requirements.


I prefer horizontal bi-amping as it allows for both the very convenient and flexible- if not scrupulously matched - practice of using a pair of whatever stereo amps may be at hand, as well as more careful selection of amp type and power level to suit each driver & enclosures "personality". Some folks just love the synergy of a flea watt SET driving a high sensitivity FR / mid-tweet -when done well, myself included - while the woofers/ sub(s) may be of equal or lower sensitivity and need the torque / HP of a 60-100W SS amp for the heavy lifting

What am I saying, all amps sound the same.
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Old 18th December 2015, 11:38 PM   #8
drtebi is offline drtebi  United States
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Quote:
Originally Posted by chrisb View Post
This is DIY, man - there's no such thing as overthinking, or a single right way to do anything in all cases.
Right!

I will definitely experiment with both options when the time comes. But the thing is, if I would go for vertical bi-amping, I would think that the amps should be the same, and I may be able to get a nice PA-5 for a good price right now... hence I sort of need to know whether this works and is worth it.

I have a couple of other amps, so a horizontal setup would be no problem, it's just that I would have cables all over the place which is obviously inconvenient and not very wife-friendly
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Old 18th December 2015, 11:54 PM   #9
chrisb is offline chrisb  Canada
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Well you could certainly do a lot worse than a pair of PA5s, so provided your active XO has level controls on each pass band and there's a master level control upstream, it should work like a dream.

I wouldn't lose much sleep over the absence of dual mono power supplies - I think even back then Mr Pass had a good handle on things.
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Old 18th December 2015, 11:58 PM   #10
drtebi is offline drtebi  United States
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Yeah, the PA-5 is quite nice... mine has been restored, too.

The active cross-over I would want to use is the Ashly XR1001. I have read quite a few praises for it (on forums), and I don't see too much out there with the same features, apart from a Pass Labs crossover, which is way over my budget.
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