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4. Verification

#24 Timothy: Polarity issues

Hi Timothy, so I don’t know exactly what your polarity issues are, but polarity is a very important step in our verification process and it is pretty easy to do. Just change the delay locator in your audio analyzer to automatically update continuously, in SATlive it’s called Auto adjust delay and you can find it in the pop-up menu of the delay- display in the lower menu bar and in Smaart it’s call delay tracking and you can start it by hitting the d key. Then, take a solo measurement of each speaker and/or driver in the near field to verify that everyone’s polarity matches.

5. Placement

#24 Eric: Is a spread out speaker array better than brute force towers blasting from the stage?

So Eric, it’s hard for me to know what kind of system you are imagining in your head, but like everything, it’s a balance, right? So speakers from the stage might have a better sonic image, but a more distributed approach might give you less variance across the frequency response. But in audio, brute force is almost never a good thing. When you say brute force towers I’m imagining just a pile of speakers on stage trying to cover a giant range ratio. The people in the front rows are getting blasted and those in the back can barely hear. I’m definitely not in favor of that. The best solution is going to deliver a similar result to everyone in the audience with a minimum of complexity.

#25 Jim: How do you avoid microphone feedback?

So Jim, I would like to do another webinar training on microphone feedback, but I’ll start by telling you this: don’t focus on ringing out the monitors and ringing out the system. That’s our last line of defense in guerilla audio.
The way that you avoid microphone feedback is by improving the headroom of your sound system. And that isn’t improved at one place. It’s improved at every step in the chain.

So if I were to make one suggestion to you, Jim, it would be to not assume you need to ring out the system. In fact, don’t assume anything. Look at every step in the signal chain and see where you can make improvements.

This is what I did a few years ago and it made people kind of nervous. My colleague would say, “Did you ring out the system?” And I would say, “No, but here’s what I did instead.”

I listened to it. I placed and aimed my speakers for best GBF and after everything was set up, I did some tests to see if I was getting enough microphone gain before taking any kind of action. And 9 times out of 10, I was already. And I realized that I had only done the ringing out step out of fear that I hadn’t set things up properly.

But I didn’t just go cold turkey pushed the system into feedback and made note of those frequencies on my equalizer so that if anything started to ring during the sound check or the event I would be able to quickly put in a filter. That also put people at ease since they had no way of knowing if I knew what I was talking about.

Here’s a quick and easy test to see how effective your ringing out is. Ring out your system, as you normally would. Then, bypass whatever EQ you inserted and move the microphone a foot. If you get different results, then your EQ is not going be effective because you know that that microphone is going to move as soon as it has to interact with a performer or the ambient conditions change. So Jim, I hope that answers part of your question.

#26 Marcelino: Como hacer y poner los monitores en escenario y el retardo.

So Marcelino, my 3 best tips on monitor placement and delay are 1) get the monitor as close to the performer’s head as possible, 2) aim it at the null point of the microphone, and 3) don’t use delay. If I understand what you are asking, it’s kind of an unproven feedback fighting tip, which is to try adding delay to a microphone or stage monitor output for better GBF. My experience is that that does not work, it only moves the feedback to different frequencies. If you have had success with that strategy, let me know how you did it.

#27 Black: How do you avoid phase issues with microphone placement?

First, isolation. We use directional microphones, close miking, and gating to try to avoid as much bleed as possible. The signals might be out of phase, but if there is a 20 dB difference in level, we win by isolation. And if you can’t beat-em, join-em. That’s why I like a coincident pair for my drum overheads. Everything arrives in time.
Second, is polarity inversion and delay. Everybody knows that if you have your top snare mic and your bottom snare mic 1″ away from the head on each side, then one of those mics is going to need a polarity inversion. Then, if you want to fine-tune every other mic on the kit, you can pick a reference point, like the OH, and delay every other mic back to those.

#28 Mark: How do I place speakers for least reflections off of walls?

In the horizontal plane, start by using the right coverage shape and placing it at the center of its coverage area. That way you make it to the extents of the coverage area without overlap onto the wall.

Another strategy is to sharpen the edges of your coverage shape using subdivision. So if you would normally use a single 100º speaker, use two 50º speakers. Or better, yet, use three 30º speakers.

In the vertical plane, make sure that you are aiming at the edge of coverage and not at the back wall. If you’re stuck with speakers on sticks, you can get a speaker tilt adapter from K&M.

#29 Greg: Fast measurement/adjustment in a portable church setup where we have 45 minutes to setup and start soundcheck

So Greg, what I’m wondering about this is whether you are setting up in a new location every time or the same location? But here’s my thought, even if you are setting up in a new location because you can’t be at a new location every time, unless you are on tour, and I’m guessing that you’re not. So what I’m thinking is that you could come up with a streamlined verification and optimization process where all you have to do is basically check each step against the last known good data. So you always have your reference traces stored in your analyzer and all you have to do is compare today’s setup against them. You would have your speaker positions mapped out along with aim and splay angles and measurement microphone positions. So you would take a measurement at location A1 and compare it to reference trace A1 and I know you don’t have much time, but this should be really fast if you are doing it the same way every time, just verifying that things are as they should be.

#30 Robert: Best placement for Sub hung or ground stack

Hey Robert, so two things for you to think about: 1) If your goal is even coverage, getting the sub up in the air is going to improve your front-to-back distance ratio. 2) If your goal is power, ground stacked is going to give you half-space loading of +6 dB for free.

#31 Samuel: Where and how to place multiple speakers?

So Samuel, I want to call you Samwise Gamgi from Lord of the Rings, but my wife said you might not get the reference, so I definitely won’t do that. We talked a bit about how to estimate placement for multiple speakers in the last podcast, but this gives me the opportunity to approach it from a different angle. The reason to use more than one speaker is that one speaker will not cover the entire audience either because it’s too big or the shape won’t allow it. In either case, we need to find those points in the audience where the main isn’t cutting it anymore and bring in another speaker to restore the sound back to its original glory, as it was on-axis with the main speaker. And two of the most useful tools to do that are range ratio and forward and lateral aspect ratio.

#32 Mark: How to arrange 2 subs so they are useful?

So Mark, my question to you is: what do you mean by useful?

Does useful mean more power? If so, put those subs together and get 6 dB from their coupling. Push them into a corner for even more power.

Does useful mean more even coverage? If so, get’em up in the air for an improved distance ratio.

Does useful mean directional? If so, setup either an inline gradient or inverted stack for up to 20 dB of broadband cancellation in the rear.

#33 Alexander: How do LF radiation patterns change when you place subwoofers under the stage or close to boundaries?

So Alexander, as long as that boundary is long enough, like a wall, a floor, or a stage, it will change the LF radiation pattern in much the same way as another speaker. For example, if you have a speaker on the ground, that’s just like having two speakers stacked one on top of each other. Think of the boundary as a mirror, with another speaker on the other side.

This is why you can’t put a cardioid sub array below a stage. The stage acts as a mirror and ruins the coverage pattern.

#34 Ricky: Can you talk about determining the distance between speakers as it relates to comb filtering where the speakers combine?

So Ricky, I’m going to assume you are thinking about the low end since that is the hardest to control with aim. First of all, if possible, put the speakers right next to each other for the smallest contrast in path length at all positions. Problem solved.

If you can’t do that, keep in mind that you are always going to have some amount of subtraction when two frequencies meet beyond 120º of phase offset. So one thing you can do is make sure that your speakers are within 2/3 wavelength of the highest frequency at which they are going to combine. Imagine a subwoofer whose operational range goes up to 120Hz. 120Hz has a wavelength of 9.4ft, so we’ll want to keep those subs within 2/3 of that, which is 6.3. As long as those subs are within 6.3 ft of each other, we will have some amount of summation at all positions through the operational range.

#35 Bigman: Does phase cancellation occur when two point source speakers are placed side by side? mostly when they are connected in parallel

So Bigman, the coupled point source array, when properly splayed, is one of the most efficient and stable arrays because we are close enough that we get summation in the low end, but splayed in a way that we get isolation in the high end. And as long as they are symmetrical, meaning same make and model, you can run them in parallel.

#36 Carmine: How to compensate for phase problems caused by reflected waves in a live room?

So Carmine, if room reflections are negatively affecting your show, my first thought is to try to remove the reflections. Can you do anything about the architecture? Ideal knock out a wall. If not, add absorption.

If not, your next line of defense is speaker position and aim. I’m not sure what your situation is like, but maybe you can aim those speakers away from the wall for fewer reflections. Maybe you can move your subs closer to whatever is causing the reflection to reduce path length differences and minimize their destructive interaction.

One thing is for sure: it is impossible to counteract acoustic problems with electronic solutions. Once you have a 12dB cut from comb filtering, you can’t put that back with EQ.