DBX DriveRack PX

[JCJR]

Camsr, will remember your idea re keyboard stand modification.

I'm a bit slow-witted. Just now "got" what you explained re "equidistant". If each monitor is 3 feet from my head and the sub is 3 feet from my head then there oughtn't be a problem with the crossover, because time of flight from all speakers would be the same-- Even if the sub is on one side rather than in the center?

Estimating by eye, there can't be more than a foot difference between the distance from the near side of the sub to my head, versus the distance from either monitor to my head. Probably less than a one foot difference. Will measure later.

The near side of the subwoofer at the floor ought to be a decent reference point? With the down-firing woofer, presumably sound from the near side will arrive first and loudest. First reflections from closest obstacles might smear the sub signal an additional foot or two with near-reflection multi-path.

These cheap JBL monitor speakers are spec'd flat +/- 2 dB 60 Hz to 20 KHz (38 Hz at -10 dB). The plot doesn't look horrible. The plot looks less than +/- 1 db between about 100 and 800 Hz.

First approximation guesswork-- Pick a crossover frequency of 60 Hz-- If the path to the sub would be one foot longer than the path to a monitor, then that would be about 1 ms subwoofer delay. The wavelength of 60 Hz is 16.67 ms.

Therefore the subwoofer phase lag due to a 1 ms delay, at a crossover frequency of 60 Hz, ought to be in the ballpark of (1ms / 16.67ms) * 360 degrees = about 21.6 degrees subwoofer phase lag due to the delay? At first glance that doesn't seem a real bad delay phase shift?

Of course some higher or lower crossover freq might work out better. The DBX driverack allows overlapping hipass and lopass frequencies. A lower crossover frequency with an overlap MIGHT be useful, would have to think about it.

[camsr]

One thing the DCX2496 has going for it is asymmetric crossovers. You could use different filters for the upper and lower bands. IDK if the DBX units do that, but they do have a variety of useful filters still. The band delay is the most important feature.

Just looked to be sure, the unit you linked to does NOT have a delay feature. You will want this, trust me.
http://dbxpro.com/en-US/products/driverack-pa
This one does, and seems to add more features. Do not get one without a delay!

1ms of delay from the sub as you described should have very little impact. Maybe a max ripple of 1dB. This is why that delay is so important.

[JCJR]

Thanks camsr

That driverack pa plus (in addition to three-way possible) has the delay feature plus an always-on display mode for the RTA.

As far as I can tell reading the manual of the less expensive driverack PX, and watching several PX demo videos-- It doesn't have an always-on RTA display mode. Apparently the PX RTA is only visible when using auto-eq. Or maybe the PX does have a way to make it display RTA during normal operation, but not mentioned. Dunno.

Apparently for both units, there is no line input switch to tell the RTA to use the line input rather than the calibration mic input. That is a shame. Most old RTA's I knew about, could select either mic or line inputs for RTA display. I could probably make up a cable for padded stereo-to-mono, to watch line levels by plugging a padded mux from the mixer into the analysis mic input. Maybe an added line switch to the new DBX models would have raised the price by another $100 or whatever.

The extra-charge-but-currently-free analysis mic that comes with the PA+ is probably better than the mic always-included with the half-price PX.

But both devices list the same samplerate, noise and distortion specs. So I should decide whether always-on RTA display and delay are worth $400 versus the $200 of the PX, to me, for a home toy. For $200 savings, maybe I could figure out how to get the subwoofer a few inches closer to the listening position!

[AusDisciple]

I've never used one of these in a studio setting but I used to work desgining and installing sound systems in live venues and night clubs and we did some pretty big, high profile jobs. One of the most high profile was Heat nightclub in Crown Casino in Melbourne and we installed Nexo speakers and DBX Driveracks with Camco amps. The system sounded amazing and was known as one of the cleanest sounding live venues in Melbourne at the time.
We topped that one though with a HUGE install in Billboard nightclub also in Melbourne. That was at the time, the biggest and most expensive Nexo installation in the southern hemisphere. It was used for everything from international touring bands to DJ's and everyone commented on the quality and punch of that system at the time. Once again, we used DBX Driveracks for the processing (system tuning, peak limiting, crossovers and delay stack timing). They were clean, flexible and reliable.

As I said though, I've never used one in studio use so I don't know how it would perform for critical monitoring but they sounded clean and transparent in our venue installations.

[AusDisciple]

Just out of curiosity, I did a Google search to see if there was anything still on the web from any of our installations and I just found a review of our Heat Nightclub installation. The review only mentions the Nexo speakers we used but, as I mentioned, we also used DBX Driveracks and Camco amps with that install.
Something you might find interesting is that we initially installed the Nexo speakers with their own Nexo controllers but the Nexo controllers we later replaced with the DBX Driveracks. The Nexo processors sounded amazing but the DBX Driveracks were just as good but more flexible.
Here's the review.... http://www.gtaust.com/filter/03/03.shtml

[AusDisciple]

Ooops. clicked quote instead of edit... deleting double post.

[JCJR]

Thanks for the good info, AusDisciple. The box will probably work good for my aged ears, even on studio monitors.

By the way, I like your music. Very well written, performed and recorded. Listened to all your instrumentals. They sound great. As I get older, have lost interest in vocals.

In my old age have become an impatient music listener, but it was very easy to pay attention to your instrumentals. Will probably give the vocals a listen sometime as well, considering the above proviso.

[AusDisciple]

Thanks heaps for the feedback on my tunes JCJR. Much appreciated.
I'm planning to really dig in and write a whole lot more instrumentals over the coming months. Now that I have my new RME Fireface UFX, I am even more inspired. The preamps and converters in it are superb.
I'm keen to hear your feedback on the tracks with vocals when you get time too. The lyrics are somewhat controversial to most but I've never been one to take the easy road!!

[camsr]

I think it will be okay to not use a delay, if you have the subwoofer right against the front wall. Testing the room with a program like Room EQ Wizard and a measurement microphone will reveal the truth. RTA isn't as informative as a frequency response graph or a waterfall graph.

[JCJR]

Thanks camsr. Will add to the to do list, investigate room eq wizard.

I realize that all the room adjustment, and even crossovers could be done in the computer if one were workstation centric enough. If one always listens via computer spdif -> studio monitor, or computer analog -> amp -> speaker, or whatnot.

But I have the monitors driven from an "output mixer" which can select from multiple computers, the hardware synth input mixer, or whatever junk I might happen to plug in and want to hear. Sometimes the computers are not even powered-on or not even running audio software. So in my case doing the actual room adjustment inside one computer would be infeasible, except perhaps dedicating a computer to that task.

One thing I routinely do when testing freq response and aliasing in dsp code (haven't done that for a couple of years, lately more mundane but needed tasks)-- I made several long sine wave sweep test files. The longest sweep file is 40 seconds. It starts at 20 Hz, and takes 4 seconds to sweep thru each octave. So the 4 second mark is 40 Hz, the 8 second mark is 80 Hz, etc.

So when testing a dsp algorithm, I have a shell that processes the sweep file (or any other file) thru the code to an output file. Then I can listen, measure, diagnose using cooledit pro or whatever. I put a little template in my calculator that will convert a play time to frequency or vice versa. So if I see a curious squiggle in cooledit at 12.671 seconds or whatever, I can tap into the calculator and find out the frequency.

The method is somewat precise for what it is capable of measuring. My rationale for very slow sweeps, is to avoid passing thru a problem area so fast, that the disturbance continues to ring at higher frequencies where a problem may not exist.

Was planning to hook up an omni mic and record my sweep from the speakers one of these days. Study it in cooledit. Could also record pink noise from the speakers and use cooledit spectral analysis features.

The room eq wizard probably has more/better tools. Will look into it.

[AusDisciple]

JCJR,
You might want to check out TrueRTA if you haven't already. I use it for testing room response, mic response and speaker response and it is very responsive and accurate. Room EQ Wizard has a lot more tools but TrueRTA is a lot more responsive.
I'm currently designing some custom microphones designed around the PZM principle and geared towards accurately recording accoustic instruments and I've been using TrueRTA for all the test and measurement duties.

They have four versions available and Level 1 is free but quite basic. I purchased the Level 4 version which is their flagship one ($99.95) and it is worth every cent.

Here's a link..... https://www.trueaudio.com/rta_abt1.htm

[AusDisciple]

Here's a pic of TrueRTA set up measuring one of my mic prototypes. The bottom curve is the initial mic response and the top curve is after some tweaking of the electronics and mic capsule adjustment.

[camsr]

AusDisciple that is interesting, making your own microphone, but the testing method looks a bit skewed. Any insight as to what you are doing there?

[camsr]

...

The method is somewat precise for what it is capable of measuring. My rationale for very slow sweeps, is to avoid passing thru a problem area so fast, that the disturbance continues to ring at higher frequencies where a problem may not exist.

...

The room eq wizard probably has more/better tools. Will look into it.

The waterfall graph and the spectrogram graph are far easier to analyze than a waveform, I have tried this before. The FFT process in REQ does very good IF you use the right settings (not too long or short of an FFT window). It's worth it if you need it. You don't need to use the computer for corrective EQ with the driverack, since it will have an EQ for this, maybe only limited by filter type and number of bands available.

If you shoot your room, post the results and I would be happy to look them over.

[AusDisciple]

AusDisciple that is interesting, making your own microphone, but the testing method looks a bit skewed. Any insight as to what you are doing there?

Ha! Yeah, I should've made mention that that image was NOT showing the setup as it was configured for testing!! That was simply an arranged photo designed to show the rig.
The speaker in the shot is a Tannoy dual concentric driver that I have running a slow sweep into the mic which I place actually FACING the driver contrary to what is shown in that photo! I run a number of sweeps at varying distances between the mic and speaker and take an average of the result. The foam around the driver is to limit standing wave reflections between the baffle and the mic plate from skewing the results.

I have a measurement microphone that I used to calibrate the mic pre/converters/speaker response and use that to generate a calibration file to use for my custom mic tests. Calibration files were made for each testing position.