DBX DriveRack PX

[JCJR]

http://dbxpro.com/en-US/products/driverack-px



Had an ancient RTA. I used the RTA to check the flatness of the monitoring environment. Well, initially bought it to ring PA systems, and used it to ring lots of PA systems over the years.

When I quit that foolishness, would use the RTA for mixing as a reality-check-- Fer instance I was familiar with the typical spectral distribution of R&B. So if I happened to be working on an R&B tune and it might happen that my song's spectral distribution looked way different from R&B, then that would be a strong hint that not only was I barking up the wrong tree, but that wrong tree was not even in the right woods.

Kinda got a hankering for an RTA display in my scaled down recreational home rig. In theory the behringer UltraCurve Pro ought to be a fun box, except lots of folks don't like the sound and apparently many people who like the sound have numerous complaints about the UltraCurve's durability.

Happened across the DBX line of PA-oriented speaker controllers. Wish they had made these back in the good old days. Anyway, the price of the PX model designed for powered speakers ain't bad, and the published specs look like they ought to be good enough for tired old ears, even in a half-fast studio situation.

It has several tricks that might do me some good at home, though unfortunately this model doesn't have an "always on" eye candy RTA display mode. You only get to see the RTA display when ringing a room. Youtube has LOTS of demos of this box.

But here are some perceived benefits-- You can tell I'm trying to talk myself into spending money--

When I remodeled the basement apartment and moved some of the old studio into the apt living room-- I'm NOT going to fill the room with Sonex and bass traps. Forget about it. Luckily, the room accidentally doesn't sound that bad. There are several windows in the room with wood blinds. The wood blinds and other furniture suffice as not-too-shabby diffusors. The room has two about equal-spaced hallways in the back wall (opposite the monitor speakers). One hallway leads to bathroom and a bedroom, and the other hallway leads to kitchen, dinette, and out to the basement. So bass buildup is not oppressive in the living room. The bass energy leaks out into a much bigger space than the apartment living room, serving the function of a bass trap.

The "untreated" room doesn't have noticeable flutter or mid-high resonances. Low bass has some modalities but have heard worse.

**** Anyway, it MIGHT be possible to slightly even out my monitors and subwoofer, in the lows and low-mids, using modest tweaks of the graphic EQ and parametric EQ, because the room isn't real bad to begin with.

**** All my gear is ancient, but still works OK. 12" powered subwoofer, JBL-Urie amp driving JBL 8" monitors. They are hooked up lazy. The monitors get driven full-range off my mixer main output, and the subwoofer level gets set by the mixer headphone output knob. The subwoofer crossover is set to avoid overlap with the monitor speakers' bass rolloff. Works close enough for rock'n'roll.

**** However, that DBX has crossovers and peak limiters (and compressors though I'd not use the compressors). Unless the DBX crossovers and limiters suck, it might be possible to get a much better blending of the monitors with the sub, calibrated by measurement mic, protected from random accidental high volume blasts by the limiters.

**** The thang has some parametric bands, which might be useful to minimize the most obnoxious room modes. I haven't yet measured to find bass modes. I usually do that with slow sine sweeps. Maybe the parametric wouldn't make much diff, but would be an interesting experiment.

So, though it is a live oriented box, that DriveRack might have some applicability in a half fast residential sound room. Wish it had a "full time RTA display mode". Which would be the icing on the cake.

Anybody used one?

[camsr]

Yeah I though about using it as a 3-way stereo crossover for a tri-amped speaker design. I think what put me off of it was the 48khz sampling rate, which most likely would stuff the filters under nyquist in my design (mid/tweeter). Plus I work with 96khz ITB so I wouldn't want to downsample either.

[JCJR]

The question I'd have would more involve, does the gadget sound good, within the limits of my aged hearing, rather than its internal sample rate. DBX ought to be able to hire engineers who know sheets from shinola, and if they needed higher sample rate to get performance from some of the modules, could oversample those modules, just as is commonly done with puter plugins. But not having used the box, haven't the foggiest whether it works good enough to sound transparent on speakers two feet from one's face. Sound reinforcement is a much more forgiving environment.

Some of the fancier dbx speaker controllers may have digital input, but this box is just analog balanced in/out on xlr connectors, so regardless of the samplerate of the upstream signal, once it is converted to analog and sent to this box, it will either sound good or not.

I'm not an authority and do not have golden ears, but have seen some converters which sound very good on 24 bit 44.1k or 48k. Or even 16 bit. Whether that DBX px is among that subset, dunno.

[camsr]

I don't doubt the convertors sound good, but maybe there is a bias towards PA usage in it's design, IDK never having heard one. Whether oversampling is happening or not is unknown. I would think you would want to go digital throughout (for a daw), so having analog ins is only useful for analog equipment. There are a variety of these kinds of units out there. The behringer dcx2496 for instance, said to be plagued with noise problems and costly to mod them out. BBS also makes a few, pretty similar to Driveracks. Digital crossovers can get pretty expensive when you start including amplification, Ashly has a few units in this category, the NX and Pema models.

[JCJR]

Thanks for the good ideas camsr.

Yes, that is the rub, if it so happens that the DBX box is good enough for a live venue full of screaming drunk college chicks, but with noticeable warts monitoring in a relatively quiet room with the speakers in one's face.

Spent too much time reading text complaints and watching youtube complaints about the behringer ultracurve pro. Appears that if you get lucky and get a box that works and continues to work, it might be a fun box for what it is, but I don't want to chance it. Have not been able to turn up many irate user complaints about the DBX.

Didn't know about the BBS boxes, thanks will look em up.

I am ignorant enough of DSP, that when I have programmed filters running at 44.1K or 48K, if I was concerned with providing accurate performance of filter curves above the midband, I would resort to oversampling. But presumably someone smart enough to be hired by DBX might be able to figure it out better.

For instance, one possible way to skin the cat without being too cpu expensive, might be-- Every time the user adjusts an EQ band, the box flash-converts the new settings into an FIR kernel, and the third octave EQ just always runs as a single FIR filter rather than a bank of discrete filters. Similarly, it should be possible to mathematically factor all the parametric bands into the same FIR kernel. If implemented properly, such approach MIGHT have proper filter shapes without resorting to oversampling. And in a stereo third octave EQ + parametric bands, it might be more cpu efficient to do it thataway. Dunno.

I'm not real concerned about dropping into analog for the monitor chain. I don't plan to print the output of the box. Assuming it works and sounds good. I have analog subwoofer, analog power amp and analog speakers, and they work good enough and I'm cheap enough that none of that will change EVER unless the bought-and-paid-for gadgets burn up.

On the computer interface front, my little firewire Focusrite saffire 24 seems to sound purt good at 24 bit, 44.1 or 48. Can't recall if I've ever run it at 96K, but there is that possibility. If ever get to the point of needing more than four analog inputs, my old MOTU 2408 has real good converters for the era of the device. I was too cheap to buy a new PCI 424 card for the 2408 when puter pci specs changed, but it can pipe 8 "pretty good quality" extra channels into the saffire via optical. Making 12 inputs total.

Another fairly "budget sensitive" gadget, should I ever abandon my analog mixer, is that Presonus 16.0.2 digital mixer. Digital mixer, EQ and compression on 16 channels and masters, plus 16 input firewire computer interface for $1000. Haven't read anyone bitching about the reliability or audio quality.

At that price, it would be real hard to justify a high dollar multi-input audio interface unless one's ears are so pristine that nothing but 24 bit, 96K will do without hurting one's ears.

Lemme see, which would I rather do-- Pay MOTU $400+ for a new 424 card so I can use the ancient 2408 with an ancient analog mixer, or pay $1000 for a 16.0.2 and ditch the old mixer and the old audio interfaces?

The only "significant drawback" to that 16.0.2 is that it will only run 44.1K or 48K. Which wouldn't prevent me from getting something done, assuming I ever get around to doing anything.

[camsr]

woops, meant to say BSS, not bbs.

Are you after a sub/mains crossover? Room correction EQ? Limiter? Those units should be able to do it quite nicely. But if you are trying to get advanced into multi-amp monitors, prepare to sail the ship and every dollar on it lol.

MiniDSP may be worth looking into. I don't know if they have compressors/limiters, but they will do EQ and crossover, and delay.

[camsr]

Here's a promising looking box, discontinued unfortunately.
http://bssaudio.com/en-US/products/fds-366t

[JCJR]

Are you after a sub/mains crossover? Room correction EQ? Limiter? Those units should be able to do it quite nicely. But if you are trying to get advanced into multi-amp monitors, prepare to sail the ship and every dollar on it lol.

Thanks camsr.

Yep, rather simple, though somewhat nebulous objectives.

<in no particular priority>
-- Use linkwitz riley crossovers to add more precision to the interaction between studio monitors and sub.

-- Use the auto-eq and provided reference mic to ring my room and take a gander at the room response.

-- Polish the EQ if auto-eq gets it all wrong

-- Use sine wave sweeps to identify low freq room modes (using the puter), then experiment to discover whether slight parametric dips would help more than it hurts. This might not be feasible. Long ago in the old studio which was conditioned almost anechoic, I tried using an analog parametric on residual room modes, and it didn't seem to improve matters very much, but luckily the room resonances were not real obnoxious.

-- Set the peak limiters on monitors and subs to avoid accidental damage to speakers and/or ears. For instance I don't monitor at real high SPL, but if the sub gets beyond a certain point it begins to rattle around objects in the room, which is obnoxious. So on bass-heavy program material temporarily set too loud, I wouldn't mind the inaccuracy of occasional limiting on the sub, if it keeps the furniture from rattling.

[camsr]

Doesn't sound impossible at all. But you keep mentioning room acoustical issues, and the room is the first place to start in treating them. Low frequency modes are especially difficult to reign in. What's even worse than modes is low frequency SBIR (http://www.wsdg.com/dynamic_print.asp?i ... ndamentals), a non-resonant reflection that is essentially a slapback delay, causing comb filtering. SBIR reflections cannot be EQed away, and neither can modes, but the difference is modes are resonant and mesh with equalization in a more controlled way. You can cut into a modal room peak quite successfully with EQ, but attempting to boost a modal dip will make the speakers work much harder at that frequency, possibly saturating and/or distorting, and eventually damaging them.

Although if you are nearfield monitoring, the room should have far less influence, but it still reverberates and interferes, just to a lesser degree. What is your speaker setup like?

[JCJR]

Doesn't sound impossible at all. But you keep mentioning room acoustical issues, and the room is the first place to start in treating them. Low frequency modes are especially difficult to reign in. What's even worse than modes is low frequency SBIR (http://www.wsdg.com/dynamic_print.asp?i ... ndamentals), a non-resonant reflection that is essentially a slapback delay, causing comb filtering. SBIR reflections cannot be EQed away, and neither can modes, but the difference is modes are resonant and mesh with equalization in a more controlled way. You can cut into a modal room peak quite successfully with EQ, but attempting to boost a modal dip will make the speakers work much harder at that frequency, possibly saturating and/or distorting, and eventually damaging them.

Although if you are nearfield monitoring, the room should have far less influence, but it still reverberates and interferes, just to a lesser degree. What is your speaker setup like?

Thanks camsr

The old studio was heavily conditioned, to the point of sounding unnaturally dead to people unaccustomed to it. For better or worse, I will not condition the new office. After staring at sonex for years, have decided that sonex is rather ugly. Also, if I start tacking up sonex and bass traps then the wife will be less than amused and send me slinking back to the studio building.

Luckily, due to no planning on my part, it sounds not bad. No noticeable reverb, flutter, or mid/high resonances. Bass is about the right level, neither too much nor too little. As explained earlier in a long-winded boring description, the wall opposite the speakers has two hall openings which exit into multiple room volumes, allowing excess bass to escape without stupid-high reinforcement or cancellation.

However there are almost always room resonances. I just would prefer to minimize them if possible. However the sound isn't un-livable the way it is right now. In the picture, the sub is the box to the right of the keyboard/speaker stand. The little box that is. The big box to the far right is a toolchest for gadget storage. Nor the box to the right of the rack, which is a roland KC-500 I sometimes like to play thru, rather than the monitors.

[camsr]

Having the subwoofer that close to the toolbox will surely limit it's amplitude before it begins rattling. Everything else looks reasonably decoupled/damped, at a glance.

But one problem that immediately stands out is the subwoofer being too far from the center of the stereo triangle. This could skew the crossover and result in it not summing per it's design. Even a LR crossover would have this problem. Are all 3 speakers equidistant from the listening position? If so, it may be fine, but there could be a skewed Left/Right frequency response compared to having the sub dead center. The lower the crossover frequency, the less this is a concern.

If you are opposed to installing bass traps, the least you could do is some mid/high range diffusers on the upper walls. Something like these are unobtrusive and work well for small rooms (http://store.acousticfrontiers.com/cart ... _list&v=21)
Stylish and lightweight. Point being is you should attempt to eliminate flutter echo from parallel walls.

[JCJR]

Having the subwoofer that close to the toolbox will surely limit it's amplitude before it begins rattling. Everything else looks reasonably decoupled/damped, at a glance

Thanks camsr. Astute observations.

Surpringly it gets loud enough for my usual comfort before the toolchest rattles, but go a little louder and the toolchest gets going purt good. Also need to move that apc ups that is sitting on the sub. It starts dancing sooner than the chest. There is no other place to put the chest except another room

But one problem that immediately stands out is the subwoofer being too far from the center of the stereo triangle. This could skew the crossover and result in it not summing per it's design. Even a LR crossover would have this problem. Are all 3 speakers equidistant from the listening position? If so, it may be fine, but there could be a skewed Left/Right frequency response compared to having the sub dead center. The lower the crossover frequency, the less this is a concern.

Nope, the preferred listening position is facing the keys and speakers, so the monitors are equidistant but not the sub. Yer right that it might mess up crossover behavior. Hadn't considered it.

The sub would need to occupy the space used by the keyboard sustain pedals to be equidistant and would also displace my legs when playing keys.

One option would be to move everything another couple of feet away from the wall and place the sub behind the keyboard stand. Bass isn't directional and that is a down firing sub. Do you think putting it behind the keyboard box would invite problems of time delay of the bass waves "spreading around" the labyrinth formed by the keyboard box, or making a problem of yet another resonant sub cavity with the sub sitting between keyboard box and wall? The key box back is 3/4" baltic birch, so it would acoustically behave about the same as "part of a pa cabinet".

If I was nuts, might consider building a sub into the keyboard box. Perhaps cut a hole in the key box back, mount an 18" speaker firing into the wall, put a shallow sealed box stuffed with fiberglass over the rear of the speaker. Sealed acoustic suspension with undersized cab, but an 18 ought to overcome that for such a small room and modest spl.

If you are opposed to installing bass traps, the least you could do is some mid/high range diffusers on the upper walls. Something like these are unobtrusive and work well for small rooms (http://store.acousticfrontiers.com/cart ... _list&v=21)
Stylish and lightweight. Point being is you should attempt to eliminate flutter echo from parallel walls.

Thanks. If it turns out necessary, I can make nice looking wood diffusors like that quick and near free. Storms knocked out several trees a couple years ago and already ripped most of em into boards, stacked in the old studio drying. The old studio is still good for something! A drying shed!

The two windows behind the speakers, a window on the left wall, door on the right wall, vinyl double pane with wood slat blinds over windows and door. What do you think of my theory that the wood slat blinds act as diffusors? Additionally there is a three drawer cab with melamine mdf table top to the rear left as laser printer stand and a floor to ceiling four foot wide mdf shelf box in the left rear corner, filled with books, hard drives assorted crap. And in the rear right corner of the room is a six foot tall four foot wide wire shelf unit with ribbed rubber shelf covers, quickly filling with assorted old electronics salvaged from the studio. Am guessing all that junk does some diffusing, though very little bass trapping?

[camsr]

Yeah it does add "diffusion" in the sense of breaking flutter echo paths. My room is similar like that, sounds fine. It may cause asymmetry but I don't think there's a reason to worry about it.

I would use a desk without panels for legs. It will form a resonant cavity. With more openness there is less resonance from the desk itself, possibly more from the room.

Remember by equidistant, I mean the sub might be 3ft away and the monitors are also 3ft away, but it might not be symmetric. This is actually a problem that needs fine tuning, which the digital crossover might help with. You'd have to adjust all speakers positioning, delay, and the crossover in tandem to find the best and most balanced setup.

[JCJR]

Yup, need to do some testing and see the acoustic situation. Then decide what needs fixing or is fixable. The old rta may not work anymore, haven't tested it yet. Which loops back to getting that driverack or a bss box or whatever.

The keyboard box has a long history. For a long time would stack onstage keyboards atop a wurlie, rhodes, hammond or later a helpinstill piano. All solid feeling. Then going to sampler for stage piano, used ultimate support a frame for some years, strong but hopelessly bouncy. Then ultimate support apex for a few years, less bouncy but not completely solid feeling, and it was hard to use with sustain and volume pedals- Weird footroom issues.

So got a local speaker builder to make me that box, feels solid as playing a grand piano. It didn't have the speaker shelf, added the speaker shelf only recently.

Another advantage to the box, some places I'd play, managers with nothing better to do would bitch about pedals and wire clutter because as we all know, in the Elvis movies-- Elvis never had a rats nest of wires and boxes strewn all over the stage when he would spontaneously burst into song and wow the pretty girl.

So the box was painted black back then, and kept my eyesore pedals and such away from the vindictive eye of managers with nothing better to do. How could any civilized individual stand to swill booze and eat a steak if he has to look at a bunch of nasty wires and pedals!

[camsr]

Well they were most likely worried of a tripping hazard and getting sued. Musicians drink too

You could probably easily modify the thing as is by affixing 2x2 or 4x4 wood to the 4 supporting edges and cutting out everything that doesn't need to be there. The new beams acting as legs obviously. With support braces cut from the panels. It's your choice I highly recommend it, the one time I had a sub under the desk it was one note bass.