Using RTA mic for dbx driverack

[mr_hankey20]

We use a dbx driverack with the RTA mic in the band i am in. I have always wondered what exactly it is that the RTA mic does for our system. For the most part, I understand what it means to "pink" a room but does it actually do aything? I can never tell the difference after, mostly just makes it worse. Is there any benefit? Is there a right way and a wrong way to use it?

kevin

[yeahforbes]

Is there a right way and a wrong way? Absolutely. In fact the way they implemented the system is pretty misleading. Have you ever played a high pitched tone (say, 10 kHz) through a sound system and walked around a bit? Even turning your head creates the phenomenon -- the level you hear varies considerably for every inch you move. Same thing happens with that RTA mic: it might be in a location where it hears 10k way quieter than most other locations, and so it boosts 10k (and keeps boosting it because it barely notices the increase in level, being in a node) which is not the right thing to do. Do this experiment and you'll see: have it run the pink with highest precision just so it runs it for a long time; then every so often move the mic a few inches and watch the right half of the bar graph change dramatically!

Short version: discard (manually set to 0dB) anything it does above the 630 Hz band because of that node effect I described, and probably anything below 50 or 60 Hz too just for subsonic reasons. This is actually recommended by dbx themselves in some whitepapers available on their site. It may seem counterintuitive to only use a third of the corrective EQ, but that low-midrange band is where all the most noticeable unevenness happens, and which the RTA EQ helps to solve.

Of course, you don't need to leave everything else at 0. Feel free to EQ to taste, or if you have plenty of time you could figure out what the AVERAGE values are after pinking it 10+ times with the RTA mic in a different place each time.

[DAS]

Have you ever played a high pitched tone (say, 10 kHz) through a sound system and walked around a bit? Even turning your head creates the phenomenon -- the level you hear varies considerably for every inch you move.

Keep in mind that much of this is due to the way your ears hear and not something a good omnidirectional mic would "hear" in the same way. Nevertheless I agree it is good to take a few readings to get an average of the HF response of the system.

[mr_hankey20]

i'm just thinking crazy on this but what would happen if you used multiple RTA mics (2 or 3) and ran them simultaneously through a mixer and then out into the driverack. this way you could cover the whole room. it's probably a recipe for a disaster and chaos but the thought just came to me.

[DAS]

Neat idea, but it would suffer from massive phase problems and therefore give a terrible result.

[yeahforbes]

If each mic was delayed by a significant amount, like a few seconds each to be safe, it might work. Think of a flanger: the farther apart the two signals drift in time, the lower the pitch of the effect. Once that pitch is below the frequency response of the system you don't hear comb filtering anymore. It essentially un-correlates the pink noise signals. Hopefully the RTA controller doesn't get confused when its EQ modifications don't seem to cause immediate changes.