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Old 7th September 2006, 07:22 PM   #1
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Default tri-amping and active xover - TOTAL SEPARATES?

So I'm wanting to go to an active xover, mostly to play around with and give me more flexibility. I'm talking about something like the behringer dcx2496 programmable crossover, EQ, etc. So I got to thinking about the speakers.

Wouldn't the best possible design here be to put each drive in its own "box" best for that particular drive (woofer, mid)? Then possibly use one of those "new" external "mega" standalone tweeters with their own external connections already built on? (I know I've seen these in Voice Coil or somewhere).

In that case you could program the active xover to perfectly between drivers which were all in their "perfect" cases. Am I missing something here, or wouldn't this be the best possible configuration?

PS- I'd like to keep the amp discussion out of it, let's assume I'm using high-end monobloks (actually, I'm thinking more of something like lm3875 or Tripath chip-based as watts per channel in this config should IMO not need to be very high, 100W tops), but again, let's keep the amp part out.

Am I dreaming here, or would this not only be a fairly easy construction, but also allow incredible flexibility (could place each section of frequency range in just the right position/direction)?
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Old 7th September 2006, 07:48 PM   #2
Daveis is offline Daveis  United States
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I've been playing with active crossover(DCX2496/PC) and DIY speakers that were designed with a spirit towards modular design. I can swap mid's and tweeters in and out fairly easily because they are in separate boxes.

So far, the benefits of using active crossover are outweighed by the extreme expense of the crossover and additional amplifiers.

In hindsight, I am thinking I should have ditched the active crossover in favor of passive. This allows me to use a single amp, but the best amp I can afford rather than many smaller and cheaper amps.

I am starting to see that even expensive poly/teflon caps that you might be tempted to use in your passive speaker level crossover are still cheap compared to buying 2 or 4 more amps.
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Old 7th September 2006, 08:08 PM   #3
MJK is offline MJK  United States
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I have come to the opposite conclusion. I bought two less expensive amps, that essentially equaled the price of the high end one I was considering, and a dBx Driverack PA crossover. I will probably step up and add a third amp soon. The less expensive amps are still quite nice, I don't feel I sacrificed that much in the way of amp quality. I believe that the final system performance and flexibility is much better then what I would have achieved with a single high end amp and passive crossovers. In the future I can design and build two or three way speaker systems and dial in the best crossover performance very quickly and make changes to account for different rooms, styles of music, or even individual recordings. I can try differnt crossover settings without soldering.
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Old 7th September 2006, 08:55 PM   #4
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Your idea sounds like it could look like the Focal/JMlab Utopia line. I like the look.

You could save some expense and building time by making your baffles removable, and just replace the baffle when you change drivers. Make the largest box needed by the drivers you are considering and then fill with solids as needed - bricks, wood blocks, etc. as needed.

Digital crossovers sound like a good solution, but for now I am using analog active crossovers. How close you can get to perfect depends on the crossover and its processing power as well as your ability to measure performance.

I'm with MJK - I am more likely to keep at it and get the crossover really right when it doesn't cost a small fortune to tune it. I can stuff an active crossover with high quality polypropylene caps (or even polystyrene) for less than the cost of a single "audiophile" cap. Changes usually amount to just changing resistors.

I have a pair of Pass/Thagard A75s, a 4 channel Leach and a Hafler DH-500 in my stable. Usually I have the A75s in the main system with the Hafler covering the subs. Now that I have the amps it is easy to justify active systems. I wouldn't go back, except systems for friends without the budget to buy everything.
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Old 7th September 2006, 09:00 PM   #5
Daveis is offline Daveis  United States
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MJK,

How are you controlling the volume?

An active crossover with opamps and a single preamp could work.

Unfortunately, in my situation I am doing the crossover with either a DCX2496 or PC. In those cases, I need to be able to control volume on 6 or 8 line level channels.

It might be possible for me to control volume entirely in the digital domain. If someone knows of a VST plugin that will take 16-bit audio and simply shift it into 24-bits I'd be interested. Then I could control volume in the digital world. The downside would be that I am stealing the unused resolution from my DAC's for volume control. I do have a few SACD/DVD Audio disks that I'd actually be losing resolution with.

Im not sure this is possible. It seems that ASIO on a PC assumes that the sound card's inputs and outputs are all running the same sample rate and bit depth.

BobEllis, have you compared the A75's to any of the singleended Pass Alephs? I have a Threshold T200 and still like it better than the Aleph30.

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Old 7th September 2006, 09:11 PM   #6
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I haven't built any of the Aleph series yet - still on my to do list. I like the A75s better than the Leach bu a small margin. Low level detail is better.

As for volume control you could use a relay based stepped attenuator, like the Twisted Pear guys make or for a remote control version look up dantimax.
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Old 7th September 2006, 09:18 PM   #7
MJK is offline MJK  United States
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I use a preamp. The two amps are identical. The dBx unit has a 6 or 12 dB (I don't remember which off the top of my head) boost or attenuation on each crossover. That pretty much allows me to level match and tune to my hearts content.
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Old 7th September 2006, 09:24 PM   #8
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I'm on the active train also. I use a HTPC with kxdrivers to send SPDIF optical out to three separate DAC's then on to three separate amps.

I think it was worth every penny and I will never go back to using passive XO's in my main setup.

After playing with what is basically an on-the-fly infinitely variable crossover; I have noticed how even very small changes in the XO point can dramatically effect the sound. Building passive XO's can be a "best guess" type of scenario at times and It takes way too much effort and tweaking to get the same type of precision you can get with an active setup.

I do my volume control with a simple 6 gang 10k ALPS motor pot and an IR control board.
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Old 7th September 2006, 11:30 PM   #9
Salas is offline Salas  Greece
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I dont want to spoil it for you, but in my experience from working in sound reinfrorcement field, the Driverack PA and the DCX2496 are unatural sounding. Compared head to head with BSS and XTA its a revelation of how much they lag behind near natural.
Because both BSS and XTA are many times more expensive I would much rather go passive xo and bi or tri amping. Much better than so low grade digital as Driverack PA or Beringher.
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Old 7th September 2006, 11:46 PM   #10
MJK is offline MJK  United States
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In your work with sound reinforcement systems, are you working with high end home audio speakers or workhorse professional PA types of speakers? I don't disagree that you can get better then these two "budget" components, but I am not convinced yet that they are limiting in a home audio set-up.

With my Lowther two way OB system, I have heard the same driver as a single full range speaker with a passive BSC circuit in my ML TL enclosure. When I compare the sound of this full range speaker system with the two way OB I don't hear a significant change in the characteristics of the Lowther's sound. What the dBx allows is the addition of a strong bass presence in the overall presentation by going with an active two way.
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