When organizing an event which produces more than 85 decibels of sound, you're obligated to monitor the decibel levels. But how exactly do you do that? Which matters require your attention? Kevin asks these questions to an expert in the field: Marcel Kok.
12-01-2015 - by Kevin Van der Straeten
When organizing an event which produces more than 85 decibels of sound, you're obligated to monitor the decibel levels. But how exactly do you do that? Which matters require your attention? I ask these questions to an expert in the field: Marcel Kok.
Hi Kevin, goodday.
Thank you for coming over to our studio. Today we're going to talk about decibels and how to measure them. But if you have to measure decibels on an event, where would you start?
I would start with reading the license carefully. And by reading what maximum level is allowed, for instance 95 dB(A) or 100 dB(A) or maybe something else.
I see you brought a lot of devices over here. What's the difference between them? Well, for example: you have the quite affordable Class 2 sound level meters, of a few hundred euros. You can find them on the internet. They give a quick detail of the sound level. You can measure it everywhere for not too much money. The second one, the most expensive one, is the official Class 1 sound level meter with a lot of options. Those are for the official investigations in acoustics. And the third one, widely used at events, mostly at front-of-house is the notebook version with sound level meter.
And if you organize an event, which version do you absolutely need? Is the cheapest enough or do you need something else?
That's not enough because the law says you need a log file of the results and therefore you need a computer.
Or this one, but this display is not very bright and large. And it's very easy if you're at the sound-desk to follow what's happening? And from your experience: what do you see most? Is it the sound technician himself or is it some expert you need on the event to follow-up?
Well, if you have a quite small event with for instance one area, you can ask the PA-rental company to take a company with them, or rent a computer for a few hundred euros a day. And you can watch the results yourself or a sound engineer. When you have five or seven areas; a much more complicated festival, you can still rent the measurement computers but you need a person who is installing the systems in time, and who takes the systems at the end of the show and who keeps the logging files.
But also someone who can react to things that happen at the event, I suppose?
Yeah, you need a consultant when the problems are bigger. When you have problems with the license, or problems with the neighbor, problems with the government, problems with management of artists, discussions; then you need a consultant.
And that's something you need to decide up-front? You can't decide that on the moment of the event itself; then it's too late to call somebody.
Yes that's true, but promoters who are producing a festival; five to seven areas... They do that the whole year, every year. And that is business as normal; they hire a tax consultant, a security consultant and for the decibel problems an acoustic consultant.
The next question then is of course: where do you put the microphones to measure the decibel levels?
The law says it's to protect the audience from too much noise, so you have to place the microphone in the middle of the audience. It's more convenient to do it at the front-of-house position. Unless the front-of-house position is not somewhere in the middle, but for instance up or under a balcony.Which is a quite wrong position, by the way.
But then you have a difference with what you measure in the center of the audience?
Yes, and you can correct the difference in the computer program. Quite simple: you measure 100 dB(A) on the middle of the floor, and you go to the front-of-house and you have 97 or 92 dB(A). And you can watch the difference. You know the difference and you add or subtract it, okay.
But isn't there a difference... You say: the law is to protect the people at your event, but I can imagine that if you are close to the speakers and not in the center of your event, that the decibel levels are higher over there.
Well, with larger events: with the barriers and the modern line arrays, you always have a distance of a few meters to the first loudspeaker. And the line array takes care of an equal sound-pressure level from the front to the back of the audience area.
So you don't have that problem over there?
No, you can have that problem in small venues, for instance bars, youth centers, where loudspeakers are stacked just on the stage or in front of the stage, and then sometimes you have a very minimal distance between the audience and the loudspeakers. You should take care of one to two meters.
You also hear some technicians talk about measuring at multiple spots. Why should you do that?
Well, you can do that, but let's keep it simple: one measurement point and one number to watch.
Okay, that's easy to follow and to react on.
Yes, you shouldn't measure peak-levels because that makes it more complicated. And music is dynamic, so don't cut up the peak-levels. It's very simple: an average over 15 minutes.
Okay, so if we go loud, we don't see: "now it goes up for just a second", but we see an average over a certain time?
Yeah, you can see it here: it goes up, it goes down, and that's very difficult to watch, so we monitor the equivalent noise level, that's the average noise level over 15 minutes.
Okay Marcel, thank you for all the advice.
And you at home; thank you for watching our show. I hope to see you next week.