Ask the Expert – Controlling volume overspill in an old church building
Carolina Labbé from Switzerland emails:
“I belong to a relatively small church that has evolved from worshiping with just voices and piano to worshiping with a full band and PA system over the last couple of years. Naturally, this means that the sound level has increased dramatically and because we are located in a historical building in the old town, our neighbors are not too happy about this shift. I don’t know what materials they made churches out of in 1834 but they’re certainly not soundproof and we’re struggling to come up with solutions to this.
So the question is, how do you soundproof a building or bring down the general volume when there are drums involved in a situation like this?”
So much has been written about controlling the sound levels inside the building that I won’t go over old ground.
Being able to control how much sound gets outside of the building is very difficult, fraught with complexity and, of course can be exceedingly expensive!
Typically the sound outside of a building is very muffled and unclear. The walls of a building will stop all of the high frequency energy getting outside, but because the wavelength of the low frequencies are so big (100Hz is 3.4m, for example) the walls need to be substantially thick to do anything. It is this bass content that will be most frustrating to the neighbours.
If you want to get serious about reducing the spill to the outside world then you should talk to a local acoustic consultant. But if you know that you haven’t got considerable sums to spend on acoustic consultants and any subsequent remedies then I honestly wouldn’t start that ball rolling.
When we are doing our big events like the Soul Survivor summer festivals, a lot of time goes into the placement and design of the speaker system; especially the sub-woofers. For these larger events, we are able to array the subs in a particular pattern, and then tune them so we only fire the low-frequency sound towards the people. The neighbours behind the stage are then in a cancellation zone behind everything which stops them getting swamped with bass noise. For the geeks out there (like me) we use Cardioid Sub Arrays to achieve this – perhaps a blog post for another time…
This is great for a big event, but in a local Church these kind of speaker system designs cannot be implemented. Therefore I suggest the most appropriate solution is a practical one, not technical: speak to your neighbours. Get them on your side, and come to agreements with them about when and how loud things will happen. If you are able to get your hands on an SPL meter (Sound Pressure Level) it would be worth walking outside and taking some readings (don’t forget to adjust the meter to a “C weighting” so that you include the bass content in your measurements too). That way you will be able to inform your thinking and discussions with the neighbours.
Often local councils or events organisers will specify a volume limit for concerts or whatever; usually for the audience’s sake. But this can sometimes be implemented for those outside the venue too. Again, using Soul Survivor as an example; one of our team will get on his bicycle and pedal around the countryside to take SPL readings during the main sessions. This information is passed back to the main system engineer who can compensate accordingly if things get too much. When the local authorities ask us what’s happening then, we can show them the data collected and show that we are operating within the guidelines and what actions have been taken to ensure this remains so.
I realise this is not necessarily answering your question directly.
Concentrate on getting the sound inside the Church as good as you can, and employ measures to reduce stage noise as appropriate. If you can get the stage noise down, you will be able to reduce the main PA sound and hopefully reduce problems with spill into the locality. As I’ve already said, talking to the neighbours will definitely help, not least because by showing a personal interest will help to build bridges.