Sign up for ProSoundWeb newsletters
Subscribe today!

Church Sound: A Step-By-Step Process For Optimizing Stage Monitors
+- Print Email Share RSS RSS

This article is provided by ChurchTechArts.

 

A few weeks ago I was having a discussion about the sound quality of our monitors with our sax player.

He’s a very discriminating guy who really knows sound. If he says he needs 185 cut 3 dB, he needs 185 cut 3 dB.

As we listened to his wedge, it was clear that the sound he was putting out of his horn was not being faithfully reproduced by the wedge.

I knew it would take a while to remedy this, but I set aside a day to go through and fix the wedges.

First, here is our signal chain: Each mic gets plugged into a splitter (it’s passive, not transformer isolated, which was a bad choice, but not mine).

One split goes to an M7 in monitor world. The M7 mixes up to seven wedge mixes.

The omni outs of the M7 go to two Klark Teknik 9848 4x8 processors set up in 4x-biamp mode. The KT 9848s feed a rack of QSC amplifiers, which in turn feed EAW SM12 monitors.

Aside from the split, it’s a decent system. It took me a little bit, but I finally got my Mac talking to the 9848s (using Parallels, XP and a RS232-USB converter). I should mention that KT’s tech support was very helpful and quick in getting this running.

Once I had that going, I had a nice, graphical interface with which to adjust the settings. I positioned a wedge in the middle of the stage, and placed our Earthworks M-30 measurement mic right about where a musician would stand.

I took the following approach: When EQ’ing monitors, you really aren’t worried much about the room as it’s really a near-field monitor.

The only real boundary is the stage itself, and my goal was a pretty linear system; that is, flat and set up so that what goes into the board comes out of the monitors.

In the past, I would have started running pink noise through the system and looking at the response on an RTA. But that amount of noise (I measured at 94 dB SPL-A) gets annoying really fast.

I’ve been learning more about more modern forms of measurement including swept tone and FFT, so that’s how I went about this process. I’ve found swept tone gets me a lot closer a lot faster than pink noise, without the grating noise.

I started off with a great little program I found called FuzzMeasure Pro 3 (from SuperMegaUltraGroovy Software, the best software company name ever). FuzzMeasure uses swept sine wave deconvolution to report frequency response.

If that sounds complicated, don’t worry. All you need to do is hook the mic up to a USB interface and press measure.

The software emits a quick click that is used for impulse measurements (great for setting delay, but that’s another post), then a swept sine wave from 20 Hz to 20 kHz (or in my case, 50-17 kHz; it’s user-adjustable).

The resultant frequency response is shown on a graph. Here’s where we started:

(click to enlarge)

Keep in mind that each light grid line is 1 dB. So we started off with the low end some 13 dB below the mid- and upper-range; not so good. I made a 12 dB adjustment on the gain for the low channel (actually I cut 6 off the top and added 6 to the low).

(click to enlarge)

Now we start getting a little closer. But it’s still way off. After spending some time with the parametric EQs built into the KTs, I ended up with a sweep that looked like this:

(click to enlarge)

It might look a bit wonky, but realize that this time, the heavy grid lines are 1 dB. So the response could be called flat, ±1 dB from 80 Hz-17 kHz (the right edge of the graph is 17 kHz, as set in my prefs)—that’s not too shabby.


Commenting is not available in this weblog entry.