Today's Lesson

Any time you place loudspeakers at different distances from the audience, either vertically or horizontally, you will need to delay the loudspeakers that are closer to the audience so that their arrival time at the listener is consistent with the sound coming from the main loudspeakers. If you don’t, the audio from the closer loudspeakers will arrive at the audience’s ears before the main loudspeakers, causing a distinct lack of clarity and intelligibility for the people listening to those loudspeakers at the back.

The formula to calculate such delay time is:

Ds = M/C x 1000

To break it down:

• Ds is the delay in milliseconds
• M is the distance from the main loudspeakers in meters
• C is the speed of sound of 344 m/s (20 degrees), which does depend on altitude and humidity.

However, there is more to it. For instance, after the initial delay is calculated, fill loudspeakers are often delayed by a few extra milliseconds taking advantage of what’s known as the ‘Haas Effect’, to create the illusion that all of the sound is coming from the main loudspeakers.

The main thing to know is that properly delaying your fill loudspeakers will dramatically improve the clarity of your overall PA and allow for proper localization of each musician and sound source. All this will greatly enhance the experience for the audience. 

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