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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.

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I just completed the fourth presentation of a live webinar training on sound system tuning. The webinars went well, but there just wasn’t enough time to answer all of the question that the 535 attendees sent in. But I don’t want to leave those people out in the cold so I have gathered all of the questions and I am going to answer all of here on the podcast.

I have organized them into sections, so today we are going to continue to part 3 and talk about how to design our sound system for maximum results.

#13 Godswill: What are the factors to consider before designing a sound system?

Godswill, I love that you’re asking this question because there’s a big difference between people who do their work in a purely reactive manner and just wait for people to ask them for things or something to break or something to go wrong before they take action. I was a mostly reactive sound engineer for a long time because I got burned out at the place I was working so I just got lazy and bored. And it was only after working with other sound engineers who were a lot more successful and happier in their work that I noticed how proactive they were with their service. The more you can anticipate the needs of your client and your show, the more time you’ll save and the more taken care of your client will feel.

The answer to this question could take us all day. My suggestion to you is that you sit down and right down all of the factors that you have determined to be most important in the success of a show and its sound system in the past. Turn that into a checklist and use it before every event that you work on.

Probably some of the most important questions to start with are:

• What is the program material?
• What is the size and location of the audience?
• What resources do we have in terms of speakers and power?

#14 Megan: What is the best DIY acoustic treatment for a room?

Hey Megan, so I have worked in two music venues that are small shoe boxes and that were really difficult to work in. Then, due to someone’s suggestion, they covered their ceiling and back wall with absorption panels that just screwed right into the wall and it made a huge difference. I reached out to them to find out exactly what the material was called, but I haven’t heard back. But my guess is that if you reach out to your local building supply store and told them what you were working on they would be able to guide you better than I can.

Obviously this is a permanent solution. It would be great if we could fill a room with temporary free standing movable panels, but you would need a whole lot of them to make a difference in a typical event space. So what most people do is start by trying to control the loudest things on the stage, the drums and amps. So you might try a drum shield or guitar amp isolation box.

#15 Andrey: How to deal with room modes in small rooms?

Similar to the last question, your first line of attack is acoustical. Can we change the architecture of the room? Can we put absorption on the walls? If not, what can we do with speaker positioning? Come up with a bunch of tests to try. Are you using multiple mains? Trying turning one off. Move it around. Use your audio analyzer to record everything you do to help make a decision.

#16 Martin: How do you maintain a clear and cohesive balanced sound throughout a venue?

Martin, you do that by adhering to the principles of minimum variance that we talked about in part 1. Do what you can so that the level and frequency response are as consistent as possible and that the sonic image matches what the eyes see. Who knows, maybe it has nothing to do with you? Maybe, at the end of the day, the noisy HVAC system is the biggest barrier to clear sound, so what can you do to improve that?

#17 David: How to determine where to place speakers in your space and how many speakers to use to get even coverage?

So David, I think one thing you can do is start looking at everything in terms of doubling of distance. Since we know that every doubling of distance cuts our sound level in half, we can look around our room, find which parts of the audience are more than double the distance to a speaker compared the nearest seat to that speaker, and know that we’ll probably need another speaker to start its coverage there.

Another idea that can help you is to start thinking about your speaker’s coverage in terms of length and width. For example, if your main speaker has a horizontal coverage of 100º and is 10ft from the front row, then you can calculate that its coverage of that front row will extend for 16ft. This is something that we discuss in Pro Audio Workshop: Seeing Sound, but you also just open up Bob McCarthy’s book and search for the sections on forward aspect ratio and lateral aspect ratio.

#18 Fernando: How do I choose the right speaker for the space?

So Fernando, in terms of coverage, on a basic level, you should choose narrow coverage loudspeakers for narrow shapes and wide coverage loudspeakers to fill wide shapes. And half the time, that’s the best we can do with a limited inventory. But if you can pick any speaker, then divide the depth by the width of the coverage area, including the speaker. That number is the forward aspect ratio, which you can convert to a coverage angle.

In terms of power, it depends on the program material and you really have to experience it to know if it’s right, but having too much is never a problem.

#19 Jennifer: How to determine how many speakers you may need to fill (x) amount of space?

So Jennifer, of course this depends on what kinds of speakers, what kind of array you are going to deploy, and the idiosyncrasies of the space itself, but let’s take the simple example of a single room covered by a point source array. Since we know that a single speaker can only cover a maximum range ratio of 1:2, then we estimate that a range ratio of 1:2-1:3 will require at least 2 elements in our coupled point source array. And a range ratio of 1:3-:14 will require at least 3 elements, etc. So range ratio can help you quickly estimate how many speakers you will need to fill a space.

#20 Micah: When to use an array versus standard speakers flown?

So Micah, I think the question you’re asking here is when to sub-divide and we need to do that any time we have a distance ratio of more than 1:2, our angular coverage does not match the space, or if we need more power.

#21 Rob: What is the weakest link in most small music venues? Amps, Speakers, poor tuning, Etc?

The weakest link in most small music venues is the architecture. It’s the acoustics. It’s the reflections turning out carefully crafted mix into mush. And as I mentioned earlier, I have worked at two music venues that put up a bunch of absorption, which helped, but this isn’t going to help you on the event that you’re working on today.

So if I had to pick the next most common weakest link in small music venues, it would be speaker position and aim. Since we are in these small reflective rooms it’s very important to position and aim for more control. One of the most common things I see is long narrow rooms with LR mains, which are playing half into the wall because people just default to stereo in most situations when what might work better is a mono main and a relay speaker further down the room. Another thing I have seen a lot is asymmetrical rooms with symmetrical sound systems. You probably know what I’m talking about because you’ve been in a long narrow room that has a bar sticking out of one side, so the speaker on that side is only good for a few feet until it hits the bar, yet we’re playing both speakers as though they are both covering the entire room.

#22 Rune: How to set up endfire sub system?

Here’s what you need:

• 3 or more subs
• Processing channel for each.

Position them in a line, all facing the direction that you want their sound to sum. Then, with your measurement microphone in the front, measure each sub solo, phase aligning it with the sub in the rear. Because what you want is for them to all arrive in time in the front. A couple of verification notes: make sure you are not adding more than 3ms of delay to the speaker closest to the rear, 6ms to the second closest, and so on. If you are, you need to go back and reduce the spacing in between them. Lastly, you’ll want to verify that, with all of them on, summation is maximized in the front.

#23 R: How to maintain frequency and volume/all coverage with budget audio system?

The three things that come to mind when I think about working with cheaper speaker models are:

1. The don’t sound the same when you drive them at low level and high level. So I try to get them distributed well so that I don’t need to drive them any harder than necessary.
2. The don’t have a very smooth axial response. And what I mean by that is when I stand on-axis with the speaker and then move left or right, it doesn’t just get quieter, the frequency response changes. So I have to keep that in mind during placement, maybe trying to keep the audience within the smoothest coverage area.
3. I’ll probably need to spend more time on EQ on a cheaper speaker to tame its response anamolies.