# What is Delay? (AMPS)



## MikeyHP (Apr 5, 2009)

Ok... this might be a stupid question.... (Im a LD) On my HS's Sound rack there is a Amp that is labled Left and Right delay? There are also 2 amps for the stage moneters one for the subs, one for the lobby, one for backstage and one for the house mains.


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## 2mojo2 (Apr 5, 2009)

Delay is used in audio primarily to ensure that sound coming from two different sources arrives at the listeners' ears at the same moment.
Suppose you have a main house group of speakers and fill speakers in an overflow area,far from the stage. Using the speed of sound, you calculate the time it takes sound to travel from the mains to the fill speakers. You then dial in that delay time to the controller for the fill speakers.
The mains sound and the fill sound arrive at the patrons' ears at the same time. Through the magic of human sound perception, the patron accepts the sound as originating on stage.
This is the basic idea (see the Yamaha Sound Reinforcement manual). Like everything in audio, it gets more complicated as you look into it further.


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## Eboy87 (Apr 5, 2009)

2mojo2 has it correct. Many times, the mains cannot cover the entire seating area on their own, either because their coverage pattern doesn't include the entire audience, or there are obstructions in the way, like a balcony. Other times, like an outdoors concert, the mains simply cannot provide the sound pressure levels (inverse square law, in an ideal world, a doubling of distance results in a 6 dB loss for a point source radiating with no reflections, that's the simple definition). 

So, to work around this, we hang speakers to provide "fill" for these areas. In my theatre, we have two Apogee AE-5's mounted stage left, and stage right against the wall, and about fifteen feet off the floor. If I'm standing under the balcony, the horns providing the high's don't make it under the balcony, so we have a ring of JBL Control 5's as under balcony fill. We use the delay on the outputs of the console to not only align the Apogees to the stage, but to align the JBL's to the Apogees as well so that the signals from the stage, the signal from the Apogees, and the signal from the JBL's arrive at the same time (well, we have them a bit behind each other, which is another discussion). Like Mojo said, our brain perceives these as a single acoustic event.


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## rwhealey (Apr 5, 2009)

That being explained, you should go out and find each speaker, just to further your education. The house cluster should be obvious. The delayed speakers (which are often referred to as "delays") should be in the audience area somewhere. Grab a flashlight and look around.


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## howlingwolf487 (Apr 6, 2009)

If your venue has a balcony, check underneath the overhang and/or on the ceiling above the balcony seating. If the room is very long (or wide, potentially), there may be clusters hung from the ceiling in the areas that are outside the coverage pattern(s) of the main speakers.

There is also something (which you should read into because it's pretty cool) called the Haas Effect - which is what 2mojo2 alluded to.


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## museav (Apr 6, 2009)

A bit redundant to what has already been offered, but the delay speakers do indeed likely refer to some balcony or under balcony fill speakers. Hopefully, someone there has some drawings and other documentation of the system, that could help you tremendously in understanding how the systems is configured.

Getting way beyond the initial question, there was recently a rather intense discussion regarding delay Haas effect on one pro sound forum. Reader's Digest version, or at least my take on it, is that while the practical application can be quite effective, both delay and Haas effect are often somewhat misunderstood and/or misapplied. One point brought up is that since the sources, be they natural or from speakers, cover areas rather than discrete points, then the physical relationships to the two or more sources differ throughout those areas, and thus the relative delay between them also varies. In larger venues one has to be careful that the delay applied works for the all areas involved and this often involves compromises. I have seen people base the delay on the center of the coverage area and then add 10-15ms of additional delay for Haas or precedence effect and in doing so cause the sound from the delays to be an echo for some listeners at the front edge of the delay coverage. Other issues regarded some of the details of Haas, such as it applying primarily to lateral relationships versus vertical relationships and that factors such as frequency response are also involved.


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## MikeyHP (Apr 7, 2009)

Thanks for all the help.... I guess I will turn the House Mains amp off and see where the sound comes from. We have two rows of Speakers... One is driectly above the procenium ( nicely hidden behind mesh ) and a second row about 25 ft away under the catwalk... So im assuming the the second row is the delay... Would it hurt anything to turn the house mains amp off and run sound?


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## waynehoskins (Apr 8, 2009)

Yes, the boxes at your catwalk are the delay ring. They cover the upper orchestra, while the main array covers the lower orchestra. As noted, the delay ring is delayed so it's in time alignment with the main array (which may itself be delayed back to the stage) where they overlap. There's no reason you couldn't only use the delay ring, though I don't know why you'd want to, since the lower orchestra wouldn't be covered at all. A danger you might run into is trying to push the delay ring too hard since you don't have the main array in there as well. Delay rings and other fill systems are primarily intended to provide intelligibility in the speech (and up) rang, while the main array still likely does provide some lower-frequency (like low-mid) coverage in the "fill" areas. And your subs, of course, provide low-frequency extension for the entire place.

The PA is designed to be operated as a complete system, not in parts.

As to documentation, that's a relatively new facility. Whoever did the system design and/or install should have provided some sort of documentation there, and if they're still around they would probably have some documentation themselves, and might be a good resource for explaining why they chose to do it how they did (which it isn't that out-of-the-ordinary a design). Electro Acoustics and Ford Audio are likely candidates, as might be Sound Reinforcements, though SRI is gone now. Could be Accent, who are gone now too, but EA and Ford would be my guesses. EA and SRI at least used to like to put their name on installs, to there's likely a power sequencer panel in there with the installer's, and possibly designer's, name and phone number on it.


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## dafunkmonster (Apr 10, 2009)

MikeyHP said:


> Thanks for all the help.... I guess I will turn the House Mains amp off and see where the sound comes from. We have two rows of Speakers... One is driectly above the procenium ( nicely hidden behind mesh ) and a second row about 25 ft away under the catwalk... So im assuming the the second row is the delay... Would it hurt anything to turn the house mains amp off and run sound?



If you're just trying to identify the delays, then no, it wouldn't hurt anything to turn the mains off. Just don't push the delays. If you're unfamiliar with the system, I wouldn't touch the amp levels either.


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