Delay tower

Past a certain distance a main system runs out of useful level, and the answer is a second set of loudspeakers closer to the back of the audience. On a field they go on towers; indoors they go on stands or fly points. Either way the problem is the same and it is one of time, not volume.

Sound travels at roughly 1,130 feet per second, which works out close to one millisecond per foot. A loudspeaker two hundred feet from the stage is therefore about one hundred and eighty milliseconds ahead of the main system for anyone standing beside it — early enough to be heard as a separate, slapping echo, and early enough that the audience turns to look at the tower instead of the stage.

So the delay position is held back electronically by its distance from the main system, then given a further ten or fifteen milliseconds on top. That small extra lateness means the main system arrives first and the brain locates the sound at the stage, while the tower supplies the level. Done properly it is inaudible as a separate source.

This is why delay positions are surveyed and measured rather than estimated, and why moving a tower twenty feet on the day means re-timing it before doors.

Concert and festival production — owned inventory, our own crew, and a site survey before anything is specified.

• Line array A column of loudspeakers hung in a curve so the sound reaches the back row without flattening the front — the standard answer for any room or field deeper than it is wide.
• Subwoofer The cabinet that carries the bottom two octaves — and the one whose placement, not quantity, decides whether the room has even bass or a map of loud and dead spots.
• Front of house (FOH) The mix position out in the room where the engineer sits, and the audio the audience actually hears — not a department, and not a place a venue should treat as spare seating.