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Discussion Starter · #1 ·
 dbx 234


Looks pretty nice to me, especially at $180. In stereo operation, it is a three-way XO for each channel, using 24db/oct L-R crossover design, with the option to sum the low frequency output of the two channels into a single LF output. Independent XO points for each channel.


It uses balanced TRS connectors. If I'm not mistaken, can't you just use TR unbalanced connectors in TRS equipment? If so, then Phono to 1/4" TRS adaptors should let this thing work for standard consumer audio gear... ??




Opinions? Does this look appropriate for bi-amp/tri-amp projects?
 

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Discussion Starter · #2 ·
Here's a very similar Behringer alternative that goes for about $80. It also can function as a three-way stereo XO, with the difference being that in the Behringer solution the low frequency output is always summed mono from the stereo inputs, whereas in the dbx it is selectable stereo/mono output.


$80? That really seems like a bargain. Again, the only negative is the somewhat low S/N ratio just as is the case with the dbx - from ~91db to ~93db. Oh, and the Behringer uses XLR connections, so that could be somewhat of a pain.


Thoughts?
 

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Discussion Starter · #3 ·
As a comparison, Rane has an equivalent alternative to the dbx and Behringer options, but at a street price of nearly $400, it doesn't offer any more flexibility, or greater S/N ratio, or anything else that would indicate that it is a superior choice to the other two.


The Behringer looks terrific, except that XLR thing could be a pain. Both dbx and Rane make 1/4" TRS models, but apparently Behringer doesn't. :(
 

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Discussion Starter · #4 ·
Hmm... guess people don't think too much of them! :D
 

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I had a Behringer super-X pro in my system a while ago. I got rid of it (actually I gave it to a friend) because it introduced audible high-freq hiss on my monitors. These pro tools are not alway very easy to integrate in audiophile systems: due to the difference of levels used (pro use much higher levels) the S/N ratio may not be optimum in non-pro environment.


Michel
 

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I like (and own) the Marchand Xovers better, higher S/N ratios and rated excellant by the audiophile community for being very quiet.


They have various models and even offer kits for less money.

Marchand
 

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Discussion Starter · #7 ·
That's a pretty large difference in price. The Marchand XM9 3-way (which I would need) runs $400 per stereo pair in kit form. Even the dbx is less than half that.


Maybe I'll try and find a used dbx or behringer piece on ebay and see if I can detect any hiss or distortion. I talked to an EE friend of mine, and the only thing we could come up with to explain the higher noise of the prosumer units was the potentiometer vs. metal film resistor. You wouldn't think that would cause noise though... Noise would come in the op-amp stage, but how do you screw that up?


I think the Marchand is just price prohibitive for me. They're also very inflexible, and that is a real downer. I'd make my own XO's before I went that route.
 

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Pro equipment are running at much higher nominal level than consumer equipment. Pro: +4dBu, Consumer: -10dBv. Actually that's something like a 12db difference (note the different units dBu vs. dBv). If you put a pro unit in a consumer system, it will "see" very low levels coming from the consumer units and thus its own noise will be high as compared to the signal and this will then give a bad S/N ratio.


On the contrary, in a "all-pro" system, all the nominal levels are the same (and much higher than the consumer levels) and thus the S/N level will be optimal.


Michel
 

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Discussion Starter · #9 ·
Interesting.


I've decided the only way I'll ever find out how bad this self noise can be is to listen for myself. For such a low price, I ordered a dbx XO to play with and test. If it turns out to be incompatible or overly noisy, I'll sell it on ebay for a small loss. I think it's worth the $40 bucks or so it will cost me to really know how these prosumer pieces perform. If that saves me the thousands I would spend on Marchand equipment... great! If not, what's another $40 compared to what I'll have to spend! :( ! :D


I'll report all my findings. I don't have the quietest listening room at the moment, and only a RatShack SPL meter to take measurements on noise levels, but I'll see what I can come up with. Hmm... my recording room might be quiet enough to get useful results from measurements... At the very least, I'll let you guys know what my ears tell me.
 

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It will of course also depend on the associated equipment, if your other consumer units are not the quietest, you may not notice the inclusion of the dbx. Surely you won't notice on the bass, you should notice the inclusion of the crossover on the highs (tweeter). I have "audiophile grade" and dead quite equipment and I could immediately notice the Behringer and it was unacceptable.


In anycase try to make the input of the dbx as "hot" as possible and reduce it at the output if needed. The problem of mixing pro and consumer units is very well known. There are even adapters for that (Rane BB22 for example http://www.rane.com/bb22.html ). But at the end I decided to go the full consumer way... but indeed much more expensive.


Good luck.


Michel
 

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Discussion Starter · #11 ·
The dbx allows up to +12dB of input gain, but only -6dB output attenuation [edit: I realize now that the output gain goes from +6dB to -infinity]. I'll play with it and see how it goes. My gear is pretty damn quiet, and my maggies should let me know if there is any high frequency hiss going on!
 

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Discussion Starter · #12 ·
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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A State Variable design that utilize VCAs are nortorously bad sounding. No company that cares about sound quality touches VCAs. You could only find them in the cheap low pass crossovers of subwoofers.
 

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Quote:
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.
I think a Marchand used as a 2-way xover like you state above would provide superior sound to anything else you are comtemplating.


The xover frequency is easily adjusted with small resistor dips that are easy to change.


The kits or raw boards could provide you with higher quality that what you are currently testing.
 

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Discussion Starter · #15 ·
Quote:
Originally posted by lwang
A State Variable design that utilize VCAs are nortorously bad sounding. No company that cares about sound quality touches VCAs. You could only find them in the cheap low pass crossovers of subwoofers.
That's what I've heard, and that's what I expected to hear, but to be honest I don't think I could say the sound was worse based on my listening. Perhaps in an A/B comparison where I could switch it in and out of the signal chain quick enough I could pick up the differences. However, I really was surprised that the differences (whatever they might be) with the dbx XO in the signal path are small enough to be very difficult for me to locate and describe. "Notoriously bad sounding" wouldn't be an apt description at all.


The flexibility is great, but I'll probably do "the right thing :rolleyes: " and build all the active XO's I need based on fixed L-R alignments with quality components. I suppose the dbx will make a great tool in the meantime as I play with active XO settings, biamplification, and bass managemet to find the particular XO points and configurations that I'll need for a DIY solution.
 

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If money is not an issue, you should also consider the TacT 2.2x that offers crossover (up to 10th order), delays (millimetric adjustment), room correction and a state of the art digital preamp. If your source is digital it makes even more sense.


Michel
 

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Discussion Starter · #17 ·
Money is always an issue.
 

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Quote:
That's what I've heard, and that's what I expected to hear, but to be honest I don't think I could say the sound was worse based on my listening. Perhaps in an A/B comparison where I could switch it in and out of the signal chain quick enough I could pick up the differences. However, I really was surprised that the differences (whatever they might be) with the dbx XO in the signal path are small enough to be very difficult for me to locate and describe. "Notoriously bad sounding" wouldn't be an apt description at all.
VCAs were popular in the earlier days of receivers that had electronic volume control. But they were considered bad enough that even low-fi mfgs moved away from them.
 
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