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What do you guys think of this crossover?


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12 replies to this topic

#1 of 13 OFFLINE   RichardHOS

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Posted April 26 2003 - 02:24 PM

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?

#2 of 13 OFFLINE   Dave Milne

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Posted April 26 2003 - 05:05 PM

Plusses: Good price - way less than even a used Bryston 10B (my favorite). Looks very flexible. 24dB L-R slopes is nice. It accepts unbalanced TR connectors --so is should work with phono adaptors.

Minuses: 92-94 dB S/N is not great... would like to see something above 100. THD+N is respectable, but it should be spec'd from 20 to 20KHz. State variable filters are not my favorite... would prefer good ol' Sallen-Key, but these are difficult to do with variable frequencies.

Bottom line: Should be a nice XO in a three-way if you're not pushing the state of the art. Have you looked at the Marchand line? Another option is to build your own crossover along the lines of one of Rod Elliott's designs...

#3 of 13 OFFLINE   RichardHOS

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Posted April 26 2003 - 05:13 PM

$750 for two channels in kit form? Ouch. That's like $3000 for what I need. $680 for the dbx alternative sounds a lot better! Posted Image

I'll keep looking though... heading to the behringer site now to see what they offer...

#4 of 13 OFFLINE   RichardHOS

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Posted April 26 2003 - 05:46 PM

Hmm... this behringer XO has similar functionality to the three way dbx (pretty much identical, except that the behringer always sums the low frequeny channel to mono between the stereo inputs. 91db to 93db S/N ratios... and is only $80 street price. Hard to argue with those prices.

And the search goes on...

#5 of 13 OFFLINE   RichardHOS

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Posted April 27 2003 - 04:23 AM

Just checked out the Rane equivalent XO, the AC 23. At a street of nearly $400, it doesn't offer any more flexibility. Also, the S/N is again listed as around ~92db. I'm thinking that might just be a characteristic of state-variable designs that allow ultra-flexible XO point selection.

Anything I've seen listed with a S/N of 100db or better has had very limited XO points (i.e., spacings of 20Hz or even 40Hz, with limited minimum and maximum frequencies).

#6 of 13 OFFLINE   RichardHOS

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Posted April 27 2003 - 03:53 PM

Guess you guys don't think too much of them! Posted Image

#7 of 13 OFFLINE   Dave Milne

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Posted April 28 2003 - 01:46 AM

'Don't know much about Rane. I'm always leery about prosound gear, because its usually optimized more for electrical and mechanical ruggedness and in a small, lightweight package than sound quality. I'm sure there's some fine stuff out there, though... hopefully you can arrange an audition before purchase.

Ya know... I popped over to Bryston's website, and the S/N for the 10B is only listed as 90dB :b . I guess you shouldn't get too wrapped up in this spec. I have heard the 10B and thought it sounded very clean.

I thought that Parasound had a crossover, but I didn't see anything on their website. And I wonder if there is a high-end autosound unit that might be worthwhile --those guys use multi-amp systems almost exclusively. A little 12V power supply and you're in business.

Of course, there's the new Pass Labs unit... but I imagine it's big bucks. You might try posting in the DIY forum, even though you don't plan on building an XO. Many of the DIY speaker designers have at least experimented with bi-amp/tri-amp setups.

#8 of 13 OFFLINE   RichardHOS

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Posted April 28 2003 - 07:06 AM

Thanks for the input.

I think it's Paradigm that makes a crossover, not Parasound. The X30 or some such I believe.

I noticed that as well about the Bryston's S/N ratio. A member of a home recording forum strongly warned me to NOT use gear designed exclusively for +4dBu equipment with -10dBv equipment. Serious level matching problems, he said. Posted Image

Well, for the modest price, I ordered a dbx crossover. I'll play with it, see how the level matching goes (it does have adjustable input gain, so that might help), see if I can hear the noise introduced. If it's a flop I'll sell it on ebay for a 25% loss... not too high of a price IMO to find out whether I would need $700 or $3000 worth of XO's.

I've thought about the carsound stuff... I do have a powerful 12VDC power supply lying around. They tend to have relatively inflexible XO points though (just like the Paridgm and Marchand options), and I've yet to find one that has 24dB/oct slopes - they're all 12dB or 18dB. Posted Image

#9 of 13 OFFLINE   Brett DiMichele

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Posted April 28 2003 - 07:26 AM

Rich,

That guy wasn't BSing about the level matching issue. I
have a Behringer Tube Ultra-Q 4 band parametric with
adjustable octave from .3 to 2 full, plus notching and
shelving functions, dual channel. It has VU meters and I
can not get the things to move.. If I run a CD Player
directly into the unit I can get them to start moving but
it's just not the right levels.. Perhaps inline attenuators
could correct the issue but I don't want more gainstages
than I already have.

I have decided to just take the Behringer out of the loop
alltogether now that I have a fantastic pre amp and run
directly into my amps. I am tired of trying to get the
level matching right.. (And that's even going into the
Behringer true balanced.. I thought there was a +6Db boost
when using true balanced but I didn't see any change)

The unit is well built and it does function but you can tell
there are level issues.
Brett DiMichele
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#10 of 13 OFFLINE   Wayne A. Pflughaupt

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Posted April 28 2003 - 08:54 AM

Richard,

If you are only looking for low pass operation, any of these crossovers will work fine.

However, I’m very leery of using budget pro gear for full-range operation in a hi-fi system. High-end pro gear (especially studio gear) should be excellent stuff, but generally I agree with Dave that sonics are not the primary consideration with most affordable pro gear. I used a Carvin model for a while several years ago, and it noticeably degraded the sound. It added some prominence to the upper bass frequencies, and the sibilants became raspy and “spitty”-sounding.

If you want a excellent crossover for a low price, look on eBay for an Audio Control Phase Coupled Activator Series III. You should be able to get one for $125 or less. It has 24dB/octave Linkwitz-Riley filters and an excellent S/N ratio spec of 110dB and distortion 0.007%. You’d have to pay a couple grand for a pro crossover that could match those specs.

Regards,
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#11 of 13 OFFLINE   Stephen Dodds

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Posted April 28 2003 - 09:53 AM

I've used the Behringer and Rane gear full range without any problems.

Another good audio sub crossover is the Mirage LFX3 which is a three channel crossover allowing you to use up to 3 subs, with control over slope and crossover point.


Steve

#12 of 13 OFFLINE   RichardHOS

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Posted April 28 2003 - 10:59 AM

Thanks for the comments. I'll try out the dbx and see what I think about it. I'm open minded, but if it sounds like crap I'll just sell it... no harm done.

I'll check out the other options mentioned.

#13 of 13 OFFLINE   RichardHOS

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Posted May 02 2003 - 05:38 PM

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.