DCX2496 and 4 Subs

[counsil]

I have 4 subs that aren't placed symmetrically in my basement. I got a DCX2496 for cheap and want to use it to set individual delays/phase/distances for each sub individually prior to running Audyssey.

I am rather proficient with REW v5 in regards to running frequency response graphs and waterfall charts, but I've never used it to set delays/phase/distances, let alone with an outboard EQ.

I don't think I want to take advantage of any of the EQ features of the DCX because I don't want to double EQ (Audyssey and DCX2496). Thoughts on that?

What's the easiest way to set the delays for each sub? I think I can connect a mic directly up to the DCX (according to the manual) and have it automagically set the delays right? Or can REW do this as well... and should I use REW to do it instead?

Any help/comments would be appreciated.

[JohnM]

Acoustic measurement of delay for subwoofers is generally a lot less accurate than using a tape measure, the limited bandwidth of the sub is the main difficulty. I would measure the distances from the main listening position and use those figures, you need to delay each of the 3 closer subs to match the distance of the furthest, delaying them by 0.9ms for each foot they are closer to the LP.

[Wayne A. Pflughaupt]

counsil wrote:

I don't think I want to take advantage of any of the EQ features of the DCX because I don't want to double EQ. Thoughts on that?

Double EQ? How do you figure that? Or are you already using subwoofer EQ?

After setting the distances / delays, it’s usually easiest to just EQ all the subs as a single entity. The experiences of some here indicate that even if you painstakingly EQing each sub for good response, when you fire them all up together response is then whacked.

Regards,
Wayne

[jtalden]

counsil wrote:

What's the easiest way to set the delays for each sub? I think I can connect a mic directly up to the DCX (according to the manual) and have it automagically set the delays right? Or can REW do this as well... and should I use REW to do it instead?

I had some variability when I tried to use the DCX internal utility to set speaker delays so I have more confidence using REW measurements to set the delays in my system.

I see from JohnM’s comment that using the physical distance is pretty easy and reliable. If I am thinking correctly, a measurement error of 6" with an 80 Hz XO is only about 13° phase error so that is very good.

Some of us enjoy using REW to tune our system however so I will share how I set the delay up acoustically using REW.

I have 2 SWs at about 11' and 24' from the LP and. Instead of a 13' delay (per the physical measurements) I found a 14.9' delay using REW. The procedure was:

> Set the REW preferences for loopback timing reference.
> Measure each SW separately with the mic at the LP.
> Overlay the 2 IR’s and find the offset to the initial (or the largest) peaks.
> Set the delay of the closer SW per the offset and then re-measure it.
> The IR’s should now overlay closely, but one can zoom in and fine tune the timing if desired.

That setting should work well for those 2 SW positions (you can do additional SWs similarly).


Here are my 2 SW IR’s without any delay.



Here they with a 14.9’ delay on the closer speaker.




It is then tempting to then offset the final IR measurements by the same amount to place the 2 individual IRs near 0 ms. In that way the relative phase can be compared in the overlay window. In practice it can be difficult to interpret the phase correctly due to multipath interference, but with some experience it is possible. That discussion is beyond the scope here and is not really needed for good results.

With JohnM’s comment I just tried a 13’ delay per the physical distance and also got good results. I would not be able to clearly show in the measurements that one was better than the other. I just decided to stay with the original 14.9 ft delay as the IR overlay and the phase chart seemed to be slightly better and my physical distance measurements are a little questionable.

counsil wrote:

I don't think I want to take advantage of any of the EQ features of the DCX because I don't want to double EQ. Thoughts on that?

I have had issues trying to use Audyssey MultEQ XT on top of my REW / DCX EQ setup. In that case Audyssey usually applies a 9 dB boost around my normal cutoff frequency, but it does not always do it. Subsonic is not place where I want or need excessive boost! I believe this result may be very dependent on my particular setup, i.e., SWs, room acoustics, and mic positions. I sometimes obtained more reasonable results with XT however! Audyssey XT32 may be more reliable, but I have no experience with it.

My experience suggests that it may be better to use either Audyssey or manual EQ, but not run Audyssey on top of a Manual EQ. Others may have different experience, but I am much more confident using REW and manual EQ. Also, I can also experiment with different house curves and XO timing.

[counsil]

Thanks jtalden... your post will help me tremendously.

Do you happen to have any experience using REW to set individual gains in the DCX? The trims on my sub amps are changed in wide increments. They're not variable like most amp gain knobs.

Also, what's the easiest way to accomplish all of this? By using a computer or via the DCX faceplate buttons?

I've read the manual a couple of times and it doesn't really help all that much. It will probably make much more sense once I actually hook up the DCX (I haven't even opened the box!).

[counsil]

I forgot to mention that I really like what Audyssey does for all my speakers. I just needed a *cheap* way to set individual gains and delays for my subs. Therefore I don't want to use the EQ in the DCX cause I want Audyssey to EQ all my other speakers and I don't want my subs to be double-EQ'd (via DCX and Audyssey).

Keep the recommendations coming because I will be working on integrating the DCX in my setup tomorrow after work.

[jtalden]

No problem using Audyssey and the DCX just as you intend.

I find using the PC interface to setup the DCX much more convenient than working from the front panel. Just download the Behringer DCX remote software from their website. You need a serial cable and probably a USB to Serial adaptor. Be sure you have a serial extension cable and not a crossover (null modem cable). The only other trick is to set the correct COM port in the remote software. It shouldn’t be a problem. You can open and use the remote interface without a DCX connected if you want to get familiar to the GUI and all the controls. Since you plan to just delays and levels for the SW’s just using the front panel is not too bad, but it is easier to see what is going on with the PC interface.

You could set the DCX to its Mono 6-way mode and then plug the SW preamp signal into input channel A and use any 4 of the 6 outputs to attach the 4 SWs (you can also buy 2 more SWs for the other 2 channels ). You will be able to set levels and delays differently for each output. [You will have to activate the delay feature (check box) before any delay setting will actually take effect. The long delay and short delay are additive so the total delay is the sum of the 2 settings.]

With 4 SWs it sounds like capacity (headroom) will not be problem for you no matter what you do with the levels. I will mention that in my case I decided not to boost the more distant SW to achieve the same SP level at the LP. It is 3 or 4 dB lower than the nearer SW. My reasoning is, that since they are identical SWs driven with identical Amps, they have identical capacity and I didn’t want one working harder than the other. If they ever get pushed to the limit there is no use overdriving one while the other still has a little capacity left.

Enjoy!

[counsil]

Thanks again jtalden... your posts helped me out tremendously.

I was easily able to set all the delays by using the Impulse Response graphs (by overlaying them). I even used a loopback cable (which I never do for frequency response sweeps) like you suggested (loopback timing reference).

I was also easily able to set the gains using REW's tone generator and SPL meter. I used the time-average equivalent sound level (Leq) setting and Pink Noise (using the sub cal option) which makes determining the SPL very easy.

The results were astounding after making these tweaks. My in-room frequency response was very flat even before running Audyssey XT32 in my Denon 4311.

So essentially the DCX is taking care of the time-alignment (delays) between my subs, as well as, level-matching them. Then Audyssey XT32 is EQ'ing my subs (as a single sub) and setting a single delay.

I wish someone would have mentioned the DCX2496 to me a long time ago. Sure $200 - 300 is a lot of money for my simple needs but this device can do SO much more. It even has dynamic EQ capabilities. Amazing. On top of that REW v5 now supports the DCX. So for the folks that use the parametric EQ capabilites they don't have to manually enter the values.

If I ever have the time (yeah right!), I'm going to see how well REW and the DCX can EQ my subs (compared to Audyssey).

BTW, the difference between the results with Audyssey alone and using the DCX before Audyssey is night and day. I wish I would have saved some of my previous REW sweeps. I'll post some sweeps later.

[jtalden]

It sounds like everything went smoothly. I'm glad it worked out well.

Happy Listening!

[jtalden]

counsil,
I meant to ask about the delays you determined. I assume they agreed closely with the physical distance as well?