Recommendations for active crossovers

  • Thread starter Thread starter Bigus Dickus
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Well, I don't want to get into a lengthy debate about the merits of active crossovers, but suffice it to say that it is my opinion that active crossovers and biamplification does provide for the simplest and cleanest signal chain.

I also don't believe cost is an accurate indicator of quality. While high cost usually indicates a certain level of quality can be expected, low cost doesn't dictate a lower level of quality. I buy components based on performance, not price - hence the Rotel gear in my system instead of Krell or Levinson. If the dbx XO sounds bad, I'll sell it. If it sounds good, it will have a happy home beside Rotel, Marantz, Denon, B&K, Anthem, or whatever other gear I might have.

What preamp I am using is really a non-issue at this point. None on the market provide the level of signal control that I think is necessary, so no upgrade will currently fulfill my requirements. The only difference between my current 5.1 setup and a future upgrade to 7.1 is that the side/rear surrounds will be duplicated instead of discrete channels until I make that upgrade. However, I will still want essentially full range, bi/tri-amplified speakers at each of the seven channels. You can't accomplish that without active crossovers, and I doubt I will be able to purchase a prepro that can do this in the next couple of years.

I am a bit perplexed about your comments concerning "voltage or current dividers." There isn't anything special an amp needs to do or have to be bi-amp capable. You are simply using an amplifier channel to drive a speaker. It's really that simple. Biamplification is more a function of what happens upstream from the amp - i.e., active crossovers.


And about that sub... I don't care what their marketing department claims - if the sub is in an enclosure, which that one certainly is, then by definition it's not an infinite baffle sub.










Anyone else that might still be reading this, I'm still all ears for other suggestions on active crossovers. After reading a bit about John Elliot's DIY designs, I may take a serious look at that route. Building my own crossover networks will give me the performance I demand at the price I desire, but such designs will always be inflexible. I'd have to essentially build another channel if I wanted a difference XO frequency. The main attraction of the dbx/Behringer/Rane units at the moment is their tremendous flexibility ("dialing in" a crossover frequency is very appealing).
 
I am a bit perplexed about your comments concerning "voltage or current dividers." There isn't anything special an amp needs to do or have to be bi-amp capable. You are simply using an amplifier channel to drive a speaker. It's really that simple. Biamplification is more a function of what happens upstream from the amp - i.e., active crossovers.
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Not if your going the simple route and have biwired speakers and amp(s).
On many hifi speakers there are 4 posts, and the appropriate wires come from 2 different sets of outputs on the amp for each biwired channel, so you have 4 speaker wires going to each speaker from the amp. They are the (+,-)voltage and current outputs. In this case there are of course built in crossovers in your speakers and they accept both voltage and current to run at their peak efficiency.

If you want to take the crossover route, like you said, I'd look into building my own or buying kits, or finding the specs you want in the crossover in one that is already produced for other speaker systems.

Good luck. Let us know how it turns out!:)
 
Well, when you biwire, you can just connect both sets of cables to the same amplifier binding posts. There is really no difference when an amp is "biwire ready." All that means is that internally, just inside the chassis, the two sets of posts are connected by a hard, conductive link - usually a copper bus bar, which gives exactly the same result as just connecting two sets of biwires to a single pair of binding posts.

Though I'm not biwiring - I'm biamping. Big difference; primarily that my crossovers will move out of the amp--speaker path and move into the preamp--amp path.

Looks like a complete DIY crossover of high quality components can be built for roughly $40 per channel, including output gain adjustments and input buffering. That is comparable to the cheapest of the prosound units (the Behringer). The drawback is that the crossover frequency(s) will be "built in" and difficult to modify. I'll probably make use of the dbx unit I ordered for (at the very least) finding the appropriate crossover frequencies.
 
My amp offers biwiring and biamping capability. I guess I forgot the difference, or I thought they were the same. Although it does say in my manual that connecting the voltage source to the woofers and current source to drive the upper range will offer "improved performance", I see what you mean about biamping. I'd love to have speakers that could handle biamping my amp. I'm sure it would offer more depth and clarity, but I get a little heavy handed with the remote sometimes and at over 800 watts per channel I'm afraid I might hurt something... Plus I'd have to get another amp for my rears then.:( And possibly a new foundation.

Let us know how the xo's work out.
You should post a pic!
 
Actually, yes, that's very close. That was one of the first units I looked at. It's very flexible compared to most things on the market, but is still limited to two way on each channel, and doesn't have the variety of low frequency summing options I need (it only sums mono or stereo, and I need a few summed to stereo and some not summed at all).

Also a limited amount of crossover frequencies.

And it doesn't have output gain adjustment, so matching amplifiers with different gains or loudspeakers with different sensitivities would be next to impossible. The ICBM-1 is really meant to just separate out low frequencies for a common subwoofer. I need that and a split of midrange/high and midbass frequencies on several channels.

I'll definitely let you guys know how all this turns out. Will be several months unfortunately, but that gives me time to determine the proper crossover fequencies and build all the channels I need.
 
I'd say the diy route is the way to go. I'm surprised that there aren't crossover units out there like that. I looked everywhere and that's the only one I could find. And that's strange because the manual on my sunfire amp even mentions the merits of using one. It just seems they don't exist in the hifi realm.
Good luck!
 
Report on my initial impressions of the dbx 234 3-way active crossover:

Using Magnepan SMGc speakers, Rotel preamp and amplifier, Velodyne FSR-10 servo-subwoofer. For initial "quick" setup and testing, I only used two-channel stereo, and only used the crossover in 2-way mode, with high-pass going to the Magnepans and low-pass summed going to the Velodyne.

Level matching: No problem. The dbx has an input gain of +/- 12dB, and output gains on each passband section of +6dB/-infinity. Using unbalanced connections (with RCA to TR connector adaptor) at -10dBv (instead of the +4dBu the unit was designed for) didn't seem to be a problem. The detents are fine enough to allow fairly precise gain matching. Using pink noise, I was able to very quickly match the signal level I had measured (using A-weighting on 75dB SPL reference) previously without the dbx in the signal path to within .5dB. In fact, I was able to match left and right channels more precisely than was the case without the dbx (due to gain from a wall reflection on only one side of the room).

Noise: Didn't seem to be an issue. With gains set at 0dB on both input and output, there was a very small amount of high frequency noise coming from the dbx. Setting input gain to max (+12dB) and using the output gain to match reference levels (approx. -12dB), the noise diminished significantly. It was well below the noise floor of my listening environment. My very scientific testing methods determined that with proper gain settings this noise was vanishingly small (i.e., placing my ear directly on the tweeter element, I could barely hear it 75dB reference level - six inches away it had dropped below the room noise floor). In fact, the crossover itself was noisier (physically!) than the signal noise introduced, even at very high volume settings. I'm not joking... there is a very low transformer hum or something coming from the dbx that, while quiet, is significantly louder than the signal noise.

Crossover functions: What can I say? That thing is a dream. I am seriously considering building 8 channels of high quality fixed frequency 3-way crossovers (based on Rod Elliot's design), but it's going to be tough to live without the flexibility of the dbx. Want to change crossover frequency? Turn a knob. Low/Mid XO frequency is adjustable from 45Hz to 9600Hz, Mid/High XO frequency is adjustable from 450 to 96000Hz. Want to balance gains to adjust for different amplifiers or speaker efficiencies? Turn a knob. Want to invert the phase of just one passband? Stereo sub output? Summed mono? 2-way? 3-way? 4-way (really...)? That thing can do it.

Sonics: I've only done a couple of hours of listening, and none of it is blind (obviously, no one is here to help me with this), but so far I don't think I can distinguish any degradation of the sound in any way. To test the sonics of just the XO, I ran only the high-pass to the Maggies but with a crossover frequency of 45Hz (below their low limit anyway) and went straight from the preamp to the Velodyne using its internal crossover (as I have been running it in the past). I could not hear anything worth noting between the XO in or out of the signal chain. I thought perhaps the noise would muddy the sound a bit, or perhaps dropping the lowest frequencies out of the amplifier would clear up the sound (less IM distortion), but I couldn't go either way on that one. If I had to put a name on the sound of the dbx, I'd say transparent... it didn't alter the sound in any meaningful way being in the system.

Sonics part 2: Swapped the sub from the preamp to the summed mono low frequency output of the dbx crossover. Turned the Velodyne's internal crossover off. Setting the dbx to a crossover frequency of 80Hz (a little below where I had been running the sub), the sub integrated very well. In fact, I'd say it sounds better as a whole now than it did before. If I had to guess, I'd say there were phase problems between Maggies and sub before (since they were covering the same frequencies - also not sure what the Velodyne XO slope is, but that would shift the phase of the sub but not the Maggies... using the L-R alignmnet, both are phase shifted the same now) that have been at least reduced with the use of the dbx. And since there's no overlap causing a peak in the frequency response of the crossover region, that could contribute to the better integration I'm hearing. I'll play around with crossover frequency a bit (since it's easy now...) over the next week or two and find what I like the best.


Conclusion: On first impressions, I could live with this crossover permanantly. I don't think I could ever hear the noise generated by the dbx (not over the noise of the chassis itself anyway), especially with my relatively insensitive speakers. Perhaps in a very very quiet room, with efficient speakers, with someone who likes keeping the volume cranked, you might pick up the high frequency noise at the listening position. Unless I hear something I missed in the upcoming weeks, I wouldn't feel bad at all pairing this crossover with $5000 speakers and $5000 amplifiers. If someone was looking for a flexible quality subwoofer crossover, I would definitely give the dbx my stamp of approval and it would get a strong recommendation (actually you'd only need the dbx 223 for that - at a street price of $150 vs. the $180 price of the 234). If someone was looking for a quality full range 2/3/4-way crossover at a very good price, I would say it would be well worth the money to give this piece an audition.

I know the state variable design that gives the crossover its flexibility is supposed to have higher noise etc. I know using gear designed for +4dBu balanced connections is supposed to be a "no-no." But to be perfectly honest, I'm now debating whether to buy two more of these, or spend the time to build half a dozen channels of "audiophile quality" 3-way crossovers, output adjustment sections, and power supplies. I'm skeptical that I would hear an improvement, and I would without a doubt lose flexibility.

Perhaps when I find the best crossover points (using the dbx) then I'll be more comfortable with a hard-set XO point DIY crossover.
 
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