Outdoor Church Service Sound

Work a real example. A 250 seat sanctuary in the model this site uses is about 35 feet wide and 53 feet long, with a throw of 45 feet to the furthest seat. To hold 88 dBA for a blended service with 12 dB of peak headroom, from a loudspeaker with 96 dB sensitivity, that room needs about 473 watts per box across two boxes.

Put the same pair of boxes on a lawn and ask them to cover a congregation 80 feet deep. The requirement rises to about 1,494 watts per box, so call it 1,500. That is 3.16 times the power for 1.78 times the distance, which is exactly what the inverse square law predicts: 20 times the base-10 logarithm of 1.78 is 5.0 dB, and 5 dB is a factor of 3.16 in watts.

This is the honest answer to the question churches actually ask, which is whether the sanctuary system will do for the outdoor service. It will, up to roughly the distance it already covers indoors, and no further. Past that you are adding power on a curve that gets steep very quickly.

Find your furthest listener, read across to your service style, and note that the contemporary column stops being a purchasing answer somewhere around 80 feet. That is not a limitation of the table, it is the physics telling you to change approach.

Look at the contemporary column above. At 100 feet it asks for 11,696 watts per side. The largest amplifier in normal church use is 4,000 watts, so the table has already left the world of things you can buy. When the answer exceeds the largest sensible amplifier, the real answer is more loudspeakers in more places, not a bigger amplifier in one place.

There are three practical moves, in order of cost.

Move the loudspeakers closer to the people. Distance is the expensive variable, so halving it saves 6.02 dB, which is three quarters of the power. Two boxes at the front edge of the seating beat two boxes behind a platform twenty feet further back, every time.

Add a delay position. A second pair partway back, delayed to the main system, lets both pairs work over a short distance instead of one pair working over a long one. Set the delay to the path difference multiplied by 0.889 milliseconds per foot, then add 10 to 15 milliseconds of Haas offset so the rear system stays invisible and the sound still appears to come from the platform. The delay speaker timing calculator does the arithmetic.

Use a narrower pattern. A 60 by 40 degree box puts more of its energy down the length of the field instead of into the grass on either side. Coverage pattern is free power, and outdoors it is the most under-used tool there is. A column array such as the QSC KC12 is built around exactly this idea.

Indoors, walls attenuate distant transmitters and your own signal has a short path. Outdoors, both of those change. Your range improves because there is nothing in the way, and so does everybody else's, so a scan on a field will show transmitters you have never seen in the building.

Scan on the day, on site, with every one of your transmitters switched off so the receiver sees only outside signals. Then assign frequencies, switch your transmitters on, and walk the whole congregation area listening for dropouts. Keep receiver antennas in line of sight of the transmitters and up off the ground, because a ground plane absorbs far more than people expect.

One legal point that matters more when buying or borrowing gear for an outdoor event. In the United States the working band is 470 to 608 MHz. TV channel 37, which is 608 to 614 MHz, is prohibited. The 614 to 616 MHz guard band is legal at 20 milliwatts. The bands 617 to 652 MHz and 663 to 698 MHz are illegal to operate, and 698 to 806 MHz has been prohibited since 2010. Borrowed or secondhand gear tuned to a prohibited band is worthless and must not be switched on. The full method is in how to coordinate wireless microphone frequencies.

Wind on the vocal microphone. A bare grille outdoors produces a low-frequency roar on every gust. Foam windscreens on everything, and a proper windjammer on any microphone that will face into wind. This is not optional at a lakeside baptism.

The system sounds fine empty and thin when full. A congregation absorbs sound and blocks the path at ear height. Aim over the first rows into the back, and expect to add level once seats fill.

Temperature changes the delay times. Sound travels at about 1,125 feet per second at 68 degrees Fahrenheit and faster when it is hotter, so a delay position set at a cool morning rehearsal will be slightly wrong by a hot afternoon. For speech distances the error is small, but it is real.

The neighbours. Outdoors your sound goes everywhere, and the complaint that follows an outdoor service is almost always about a subwoofer pointed at housing. Check local noise ordinances, aim deliberately, and consider a cardioid subwoofer arrangement if low frequency spill is a genuine issue.

Nobody planned the pack-down. An outdoor service ends with tired volunteers, damp cable and fading light. Budget the same time for pack-down as for setup, and count the microphones back into the case before anybody leaves. For the reusable version of this whole exercise, see portable church AV setup and the options in portable PA systems for churches.