The increasingly exact science of delaying mains to match the sound coming off a stage is a great way to go. Some good answers to Alex Keatinge’s basic question about the process.

Posted by Alex Keatinge on August 19, 2001

Some of the odd-shaped rooms (small 150-400 people size) we play enforce some distance from the mains to the drums and bass rig (say, 15-20'). I haven't done this before, but I was thinking of trying to delay the mains to the kit at the back of the stage.
I know (or at least I think that I do) that I can measure this distance and then find a chart to convert this to the necessary delay in milli-seconds. (please correct me if I'm wrong)

Aside from any comments on technique, what basic equipment would you recommend. I do not plan on getting anything fancy as we are just a local cover band running a basic tri-amped mono PA.

Thanks in advance for your help,
Alex Keatinge


Reply posted by Tom Young on August 19, 2001

Delaying backline to mains can yield a very audible improvement in definition and clarity and especially in smaller venues.

Here's what I would do in lieu of using Smaart to measure the exact delay:

Start with the theoretical formula that 1 foot equals 1 millisecond and get the delay set accordingly.

Next, have the drummer do repetitive snare hits (1 per second, +/-) and bring up the snare mic/PA to match the acoustic level of his hits. Now move the delay setting back&forth until you hear that it has locked-in. This should not be very hard to hear but will take a few passes to get.

You may need to lower or raise the PA in order to hear the two sources in a way that allows you to aurally detect syncronization.

I recommend that you get a DSP device that has delay, EQ and limiting. Almost all DSP devices made these days do these three functions (very few, if any, are delay only). The eq and limiting are just as useful as the delay function is for system optimization, which is best done w/ a measurement system and professional operator/user.

Whether you need one channel or more depends but keep in mind that you may eventually want to look into delaying (and processing) your subs separately than the fullrange boxes, so a 2 or 4 input device may make sense.

Tom Young
Electroacoustic Design Services


Reply posted by Tucci on August 19, 2001

Tom's advice is practical and as usual, on the money. The key to what he suggests is bringing the PA level up to and EQUAL to the sound pressure level off the stage. In order to maximize hearing the effect when it "locks in", it is imperative to have them combine equally. This is for the testing period only. We're not saying you need to mix it that way for the show. There's other issues in play also.

Polarity of the speaker system compared to the sound off the stage is important. Equal levels that are in time but out of polarity combine destructively. This would not do you any good. So to add to what Tom suggests, I would say try flipping polarity of the snare channel when you do the test. If it gets louder one way, leave it there. If it gets significantly quieter, flip it the other way.

PT


Reply posted by Tom Young on August 19, 2001

Paul's points are a very good addition to my post (also as usual..... he's right on the money). Especially the point about polarity which reminds me to point out that your loudspeaker system needs to be in correct polarity (to begin with) for you to hear (or measure) the delay required for alignment to the backline AND for the system to then work "in harmony" with itself and the backline.

So prior to backline alignment I would ensure that everything is polarity-aligned. This should include all mic cables, mic's, line-level cables, loudspeaker cables, loudspeakers and crossover/processors.

Tom Young
Electroacoustic Design Services