need of delaying sound over area

[StuRobson]

I can remember something from my education (years ago) about having to delay signal to speakers if the distance between speakers is greater than .... that's what I can't remember. Any help would be great...

[Stuart91]

A very rough rule of thuumb is that sound takes 1ms to travel a foot. The distance at which the average punter can distinguish between two distinct sounds is around 15ms. At 20, it's often blatantly obvious. Of course, there are other factors at play, such as reflections from the room etc. so your mileage may vary. (in terms of the perception of the distinct sounds, obviously the speed of sound stays constant) ;)

 

We use delays a lot in installations. The longest distance I've ever had between speakers without a delay line was 11 feet, and that was for a budget installation in low-ceilinged hall with dreadful acoustics.

[Seano]

The distance at which the average punter can distinguish between two distinct sounds is around 15ms. At 20, it's often blatantly obvious.

I think that depends on the sound. With a click, or something clicky (like a drummer playing snare+hihat) yes. With something more complicated (like speech) I'd say those times are a bit short and its more like 30-35ms before people notice.

 

The speed of sound in the average room at 20degreesC is about 350m/s, so that millisecond per foot is pretty good. 20ms equates to about 7m before you really need some delay.

 

Just to add confusion, let me mention the Haas effect. If you have two sound sources, and the wavefront from the first arrives before the wavefront from the second, the sound will appear to be coming from the first even if the second source is a bit louder. (Within limits. The effect is strongest at about 30ms if I remember right, and at that delay the second source can be 15dB louder than the first before they appear to be at the same volume.)

 

The upshot of all that is that if you're reinforcing sound in a subtle kind of a way, you can improve the imaging by having delay times set slightly longer than your tape measure tells you. To take advantage of that though, you need to delay everything, not just the delays IYSWIM. Touring theatrical systems usually have delay lines inline with every bit of the system, front-fills and prosc speakers included. Concert (rock&roll) systems don't, there wouldn't be much point.

 

hth

Sean

x

[Stuart91]

Concert (rock&roll) systems don't, there wouldn't be much point.

 

It can be very useful to delay your main speakers against the backline and/or drumkit, even on a fairly large rock'n'roll stage. It means that your PA is working in tandem with the acoustic sound, rather than having to battle to get above it.

 

(Also for smaller, more intimate shows, delaying FOH slightly further back - Haas effect again - can give people the impression that they are hearing the live drumkit, rather than the reproduced sound etc. You can give the impression that the event is more "acoustic" than it really is)