How big a PA system do I need?

Why wattage is only part of the picture

A power figure does not describe how sound reaches the audience. Loudspeakers differ in sensitivity, output capability and coverage. Manufacturer ratings can also describe different things, so comparing two large numbers without the specifications is not a sound-system design.

The aim is usable coverage at an appropriate level. More output at the front does not necessarily solve poor intelligibility at the back, and maximum speaker output is not a recommended audience listening level.

Explain the shape of the job

Imagine two events with the same attendance: a seated presentation in a long room and a band playing to a wider standing audience outdoors. The number of people is identical; the listening area, programme and conditions are not. The supplier needs that context before suggesting a system.

• Room or site dimensions and audience layout.
• Stage position, obstructions and separate listening areas.
• Speech, recorded music, live performance or a mixture.
• Existing equipment and the microphones or sources required.
• Venue sound restrictions and who will operate the system.

Ask for coverage, not just a bigger box

Tell the supplier where clear speech or music is essential. If people also need sound in another room, mention it explicitly. Distributed or additional coverage requires planning and should not be improvised by plugging in whatever extra speakers happen to be available.

Ask for setup and a listening check if you do not have the technical team to specify and operate the system. A walk around the audience area with the actual programme material is a more useful test than judging the sound from one place beside the stage.