Delay Stack / Fill
Definition
A delay stack, or delay fill, is a loudspeaker placed further from the stage to restore level for distant listeners without raising the main system. Its signal is delayed so that it arrives slightly after the sound of the main system, and listeners continue to localise the sound towards the stage because of the precedence effect (Haas effect). The base delay equals the distance to the main system divided by the speed of sound, about 343 m/s at 20 °C, and a small additional offset is commonly added to it.
In the field
Common practice adds an offset of roughly 10 to 20 ms to the calculated delay, so that the main system arrives first and keeps the localisation. According to the precedence effect, the delayed source can be up to about 10 dB louder than the first arrival and still be heard as coming from the direction of the first. Because the speed of sound rises by about 0.6 m/s per degree Celsius, delay times set during a cold morning setup can need adjusting for a warm evening.
Related lessons
Sources
- Precedence effect (Wikipedia) : localisation dominée par la première arrivée · en.wikipedia.org
- ProSoundTraining, « It's About Time... The Effective Haas Effect » : effet Haas marqué entre 5 et 25 ms environ ; arrivée tardive jusqu'à 10 dB plus forte · prosoundtraining.com
- Gear Supply, « Speaker Delay: What You Need to Know » : calcul du retard d'une enceinte de delay à partir de la distance et de la vitesse du son · gearsupply.com
- QSC, « What is Haas Effect and how to take advantage of it » : retard de propagation augmenté d'environ 10 à 20 ms ; source retardée jusqu'à 10 dB plus forte · blogs.qsc.com
- Speed of sound, formule c ≈ 331,3 + 0,606 × T : environ 343 m/s à 20 °C, +0,6 m/s par °C · redcrab-software.com