The Acoustics of Noise: How Bass and Bleed Effect Live Music
Brad Ferguson, Freelance Production Manager / Sound Engineer
As more and more live events develop, we consistently find ourselves in different fields, parks, parking lots and with small venues cropping up (or being encircled) in residential areas, the challenge is ever there to do what we can to limit the amount of sound reaching our neighbour’s homes..
Noise issues usually stem from bass. Bass frequencies will travel farther to the outside perimeter of your venue, and penetrate buildings more effectively. Too often, an issue called “comb-filtering” can compound the problem by creating bass “power-alleys” in some areas, and nulls in others.
This phenomenon can affect the overall level of the mix dramatically, depending on where the sound engineer is mixing from within these zones. If they’re in the power-alley, they’ll likely mix quieter on the bottom end (as they are hearing it more), whereas if they’re in an area where there is a null they’ll mix very bass heavy to make up for what they’re not hearing. This bass heavy mix can contribute to an increase of noise complaints if you’re in a densely populated area or one that has surrounding residential buildings.
Comb-filtering most noticeably occurs when you have subwoofers in 2 separate setups (the most typical is one big subwoofer stack on each side of the stage), which are far enough apart that their waves either cancel each other out or add to each other, based on where you are listening from, and what frequency is being produced.
An experienced PA system technician sound be able to accurately predict how a system would behave within any space and these issues can be mitigated with a change in configuration of the system, as long as the venue has the flexibility to place the speakers differently.
On a small scale, this could mean putting all subwoofers in one position within the venue instead of two, to give you more even coverage around the venue. On a larger scale, for a festival or outdoor site, a proper PA system designer can help focus the PA system to cover the only appropriate area, and can deploy different types of subwoofer arrays (such as a cardioid configuration) to control bass behind the stage, or off to the sides. This is more difficult to do and isn’t always logistically possible due to space requirements, but if there are known areas of complaint, there are things you can do to aim the bass away from them.
Another practice that can improve sound in your venue is to have a sound engineer visit and use an acoustic measurement system such as Smaartlive. It allows you to see on the screen what is happening in a venue acoustically and will allow you to find and remove frequencies that are overwhelming in a room, be it through better equalization or other tweaks of your system, or the addition of sound baffling to help absorb resonant frequencies in the room. All top level PA system engineers use Smaartlive (or similar) to tune their PA system every time it is set up.
It’s important to note that most sound issues, regardless of scale, can usually be identified and solved by working on them early in any planning stages. It is always best to hire a qualified and experienced acoustician or PA system engineer (depending on your needs) to help determine the best configurations of speakers and acoustic treatment for your purposes, which could save you from an expensive renovation later down the line, or minimize the potential for complaints in the area.