foreplay with active x-over?

[madbrayniak]

Hi guys, I decided that instead of looking at some tube amps first I would get some sensitive speakers done first.  Something that I have been working on for a while now too....

anyways, I am wondering how somethign like a foreplay or quickie would work with a DCX2496 or MiniDSP?

I am partially considering just a small investment in a MiniDSP to figure out the best crossover and then get some made somehow....or make them myself....something else to learn I guess...I have a friend that should be of good help in that department.

granted with a MiniDSP or DCX I could have tons of control and be able to tweek them for what ever room I am in....but the problem becomes that you have to amplify every channel seperately....which adds to the cost SO MUCH. 

For Movies and maybe some heavy metal music I was goign to build some F5 Turbos from Pass so I can build just two monoblocks for music rather than 6 of them or an aleph...

what do you guys think of the active x-over approach?  Is it a waste of time?

[R.Mackey]

My last system incarnation was like you describe --  Foreplay III into a DCX2496, then active bi-amp into two-way box speakers.  Worked out OK.  The only hassle was that the DCX uses XLR inputs and outputs, so I had to build a simple little converter box.  The DCX also likes "professional" +4 dBu instead of the typical -10 dBV line level out of your CD player, which I handled simply by feeding the DCX a much louder signal than usual and then padding by -12 dB with passives in the converter box.

The resulting sound was a good one, particularly precise with respect to imaging.  The only room-specific tweaking I ever did with the DCX was damping some major room modes below 50 Hz, but it's not really precise enough to do this correctly.  As far as the crossovers themselves, you basically set it and forget it.

However, in my ears's opinion, you get a much bigger effect with relatively insensitive drivers and/or replacing crossovers with a lot of attentuation.  Odds are, if you're using tube amplifiers, you're not using these kinds of speakers.  With high-efficiency speakers, horn loaded and big efficient drivers, I'm not convinced it's worth the extra amplifiers. 

For my next system I'm going high-efficiency.  So, the DCX is no longer in the signal chain.  It's also not the most rugged piece of equipment.  Pretty powerful for the price, though.

 

[Paul Birkeland]

Hello Mad-b,

What kind of speakers do you intend to use?

You can totally run the FP-III into the DCX2496 (just buy some adapters as mentioned), but there may be analog options for you also.

-PB

[madbrayniak]

sorry for the delayed response.  I have decided to go with the quickie for now but this is still an option in the future.

The speakers I am going to be using are of my own design that I am working on.  It will use a Beyma TPL-150(99db 1w/1m) and this B&C 10" Driver:

http://www.usspeaker.com/B&C-10PLB76-1.htm

Which is rated at 98db 1w/1m

I know that the sensitivity of the drivers alone dont dictate how sensitive they will be in the box but by choosing these drivers I should be able to easily allow me to have high sensitive monitors....my goal was 95db 1w/1m or more.....With this design as well I can also turn it to a WTW design to add another 3db in the range of the 10" and horn the TPL for about 100db 1w/1m.

Edit: I forgot to add that I may also go with a 8" in a WTW setup to start with if I can find some that measure well and dont cost a kidney.

I havent run any simulations yet as I am also studying to get my Pest Control Advisor license (plant doctor for farmers basically) and that has been taking up most of my time.

When I do build these monitors though I was thinking that I will probably use a minidsp to determine the best crossover points and then either build one myself or have one made....I will keep it external though for easy access and modifications.

After the speakers I am planning to build some amps specifically for the preamp for music....wether that is a bottlehead amp or a Pass Labs design like the F5 or some other version.

[cvandyke]

I've been using an active crossover for years and I'm hooked on the basic approach. You can also change crossover parameters at a whim which makes it easy to try different drivers. I think performing the functions of a crossover in the digital domain is better since you can avoid phase-shifts inherit in an analog design and can achieve stepper crossover slopes (this does require that all signals be digitized so I know that's a non-starter for some).  To be fair, some of this may be due to the fact I've never been able to build a traditional speaker crossover that I was really satisfied with.

I'm currently using the DCX2496 and I think it's an impressive unit but the A/D and D/A are it's biggest weakness. I was already feeding it a digital signal so I've never looked into changing that aspect of it. The D/A section is OK by itself but I think that the analog circuitry that follows it is really sub par. I've modified my unit and removed the analog output stuff which is relatively easy to do since it's all on a separate card. If you are interested in this, I'd be happy to share my experience.

One issue that you might not have considered is volume control. If you control the volume by lowering the analog signal you feed the DCX, you will get poorer performance at low levels since you are "throwing away" the upper bits of the digital conversion. Ideally, you would want to control the volume after the crossover. For this I built a six channel preamp that uses ganged, stepped potentiometers so I control all three "right" channels with a single knob. Note that the DCX does allow you to change the gain on individual channels but it would rather cumbersome for use to control volume and you will still throw away bits if you need to attenuate to a great extent.

One way you can save some money is by reusing a solid state amplifier for the woofers. Here, some of the properties of a sand amp can be valuable such as a high dampening factor and cheap watts for the lower efficiency common to woofers that actually play solidly in the 20-30 Hz range. I've actually wanted to build a tube amp for the woofers but my reel to reel habit has been consuming my time and budget.