PA Audio Delay lines

[Simon Lewis]

OK - I'll concede graciously! A small delay between the two arrival times does give rise to comb filtering, but my understanding was that this is not as apparent above 5ms. The additional delay is not arbitrary per se - it's well documented and can incorporate use of the Kutruff Effect. However, the applicaion of delay is a compromise depending upon the reference position chosen.

Looks like an afternoon with a laser measure, Smaart, and a standoff between messrs McCarthy and Whittaker is needed...!

[DrummerJonny]

Could any of you suggest some background reading for me so I can try and grasp the concepts being discussed? This thread is going way over my head, but seems to me to be something useful to know :)

[mackerr]

Though I will give MacKerrs method a go sometime.

 

It was developed before the days of the Disto. These days I measure acoustically, but if I had a Disto back then, I could have saved some time. Listening to clicks is still the cheap way.

 

Mac

[Bobbsy]

Re: the Haas/precedence effect, may I dive in and add an "it depends on the type of job" comment.

 

I've used the precedence effect with great success when doing drama in venues small enough that everyone gets a bit of direct sound from the stage. In those circumstances the amount of sound from the various speaker cabinets is relatively low and delaying these so the "live" sound arrives slightly before them really does make the amplification disappear for the audience. They just think they can hear clearly. When adjusting this, I do a calculation based on 1ms per foot (i.e. deliberately getting a low number) then do the final adjustment by ear. There is a dramatic "suddenly it sounds like the sound is coming from the stage" moment that is easy to detect.

 

However, for louder shows where the amplification IS the sound, I agree that using the Haas effect just muddies things. You don't want to fool the audience into thinking everything is coming from the front speaker stacks--you just want to time align things for maximum clarity. For this sort of show I'll do calculations as accurate as I can get them and just use the ears as a final check.

[addoaddo]

This has gone way more complicated that I expected. However it is very interesting to read.

 

As most of the presentation is just voice I would rather go for clarity than trying to “foil” the audience in to thinking the sound is coming from the stage.

 

As I do not have accurate sound measuring equipment or analysers I think the best way is to measure the two paths and work out the delay like that.

 

If time allows I may play with extra setting and see what effect it has as it will be very interesting to put in practice some of the comments on here. I am worried that if I optimise it to much for one location it might affect the sound in other locations. We can not have everyone sitting in the “sweet” spot.

 

I will let my ears decide.

[Doug Siddons]

From a practical point of view in this type of situation, my approach has always been 1ms per foot as a starting point then listen and use ears for best results. Knowing the theory is great and as proved in this thread there is a lot of it to know, and a lot of people who know it and it always good to hear opinions from people who really know there stuff.

 

Now this is not meant as a criticism of anyone, but did we help the OP by diving into a very detailed discussion of delay systems temperature humidity ect interesting as it was?

 

(Sorry woke up with my keep it simple head on today!)

[Simon Lewis]

Could any of you suggest some background reading for me so I can try and grasp the concepts being discussed?

 

Acoustics and Psychoacoustics is a good general read. A Google for Haas Effect, Precedence Effect, Law of the First Wavefront, Interaural Intensity Difference, Interaural Time Difference. Binaural Hearing and - if you want to delve deeper, Head Related Transfer Functions should do the trick...

 

Simon

[Bobbsy]

 

If time allows I may play with extra setting and see what effect it has as it will be very interesting to put in practice some of the comments on here. I am worried that if I optimise it to much for one location it might affect the sound in other locations. We can not have everyone sitting in the “sweet” spot.

 

I will let my ears decide.

 

This is exactly the issue. Once you start with the calculations, you'll find that the delays are slightly different in every seat--you eventually have to use your ears for the best compromise (and remember to do a lot of walking!).

 

This is also why I suggest you try to find speakers with appropriate coverage to use fewer speakers--if you could get it down to mains at the front and only a pair of delays half way (or a bit more) back, it simplifies things and probably improves your intelligibility. So would suspending the delays a bit more centrally rather than wall mounting--if this is possible it changes the angles to make the distances more consistent.

[Sam Jelfs]

Couple of things that are worth a read if you really want to understand what is going on at a psychoacoustical level:

 

"Spatial hearing - the psychophysics of human sound localization" by Jens Blauert (MIT Press)- A good book Chapter 3 being the main relevant one here (spatial hearing with Multiple Sound Sources and in Enclosed spaces)

 

Any number of papers by Ruth Litovsky and colleagues, though "The precedence effect" by Ruth Y. Litovsky, H. Steven Colburn, William A. Yost, and Sandra J. Guzman (J. Acoust. Soc. Am. Volume 106, Issue 4, pp. 1633-1654 (1999)) is probably a good place to start.