What is Pre Delay (in system setup)?

[david.elsbury]

Hi

I am "system tech" as such this week for a conference in at a venue I work at - another tech is engineering it.

 

He asked this morning about pre-delay - and I realised I wasn't actually aware of what this was. Below is a sketch of the setup we have - subs behind a drapeline at rear of stage, flown FOH and delay line, and some speakers on stands as infills. It's mainly playback with lapel mics (typical conference stuff)

 

Is someone able to fill me in please? I'm using a DBX Driverack 480 for processing, I do have output delay on every output, and each group of speakers is on it's own output (or stereo pair as appropriate).

 

Thanks :)

 

David

 

http://i42.tinypic.com/2vrwr55.jpg

[Doug Siddons]

I would assume he's getting his jerds wumbled, unless of course you have a two second delay on each mic to veto stupid comments. Never heard of Pre delay in a delayed system, have of course heard of it with reverb and effects of course but the consequences of that in this set up would be horrendouse .

[BlueShift]

Pre-Delay is a function of a reverb processor. It refers to a delay thats applied to the incoming signal before it gets fed to the reverberation.

 

In a system like this, essentially everything is going to be delayed to the subs, which are the furthest element back - or more correctly, have the latest arrival time (assuming all other things are equal, etc...)

 

My approach would be to start by aligning everything back to the infill, and then once you have all the tops aligned, go ahead and align the main hangs to the subs at your desired position, but making sure when you do, you delay all the top boxes together to keep the alignment between them intact

[Bobbsy]

Pre delay is normally taken as the timing difference between the direct sound and the first onset of early reflections in terms of reverb. Getting the pre-delay right (i.e. delaying the direct sound to be much closer to the reverb (either electronic or just the natural room reverb) can greatly improve intelligibility and clarity.

 

That said, I can't be entirely sure of what your tech is asking about but I would hazard a guess that, with the subs back behind the drape line, he's suggesting delaying the main PA to match the subs (then, of course, more delay on the delay line).

 

As I say, that's only a guess but...

[Oldradiohand]

Pre delay is on the four inputs and is used as an overall delay to, for example, sync sound and pictures. The transducer alignment delay is on the outputs and lets you time align the HF and LF units. I agree that "pre delay" is a term usually associated with reverb units but, manufacturers, what can you do?

[Electrolytic]

maybe he was talking about pre delaying the whole system in regard to the Haas effect / precedence effect. So when the person speaking talks the audience things the sound is emanating from their mouth not the PA. Up to around 30millisec before the brain can define the two signals.

[Oldradiohand]

Yeah - some output delay to sync up the subs with the main PA line then some predelay in the other input fed to the forward speakers to sync them up to the main PA line (roughly 1ft per millisecond). Get it right with a minimum of PA level and a decent speaker who can project properly and you won't hear the PA unless you turn it off.....

Of course, if you're just putting speech on the PA you might as well not use the subs.

[TimmyP1955]

Having the subs behind the mains is a bad idea. Subs are behind the tops time/phase wise even when right against them. The tops are delayed to match the subs, which often has the side benefit of delaying them to the backline. With the subs where you have them, the system cannot be properly aligned without causing big problems.