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Audio delay, how distant before needed?

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Audio delay, how distant before needed?

Postby funky54 » Tue Oct 22, 2019 5:54 pm

Do I check this by the “time” it takes for the natural tail of a reflected sound....OR by the distance?

I’ve read too many different opinions. If it’s distance, how much distance before it matters?

I know some overlap of another thread... but thought I’d clear this up to help me decide on the right approach for another thread.


If I place a second set of pa speakers deeper into the FOH using the Bryston formula shows 22.16 milliseconds of delay (setting the second pair 25’ deeper in the room)

35.55 at 40’ apart.

53.32 at 60’ apart

Room is 125’ deep. Is it worth doing?
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Re: Audio delay, how distant before needed?

Postby Sam Spoons » Tue Oct 22, 2019 6:16 pm

Delayed satellites need a delay of roughly 1ms.ft (you calculate it more accurately in your OP), it's nowt to do with reverb times AFAIK. It's down to time aligning the sound coming from the satellite with the direct sound from the main FOH (so that kick/snare drum arrives at the ear at same time from both speakers).

It's definitely worth doing in a room that size and, if you can adjust on an iPad from down the room you'll hear the bass clean up as the time alignment becomes correct. The effect can be dramatic.
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Re: Audio delay, how distant before needed?

Postby Hugh Robjohns » Tue Oct 22, 2019 6:44 pm

I usually start with a calculation of 1ms per foot of distance (or 3.4ms per meter) between the main PA and the delay speakers... and then tweak that delay time up or down (usually up) a few milliseconds around that value just to bring the sound into focus -- most especially the low end. As Sam says, it can be quite a dramatic effect, depending on the room acoustics.

H
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Re: Audio delay, how distant before needed?

Postby funky54 » Tue Oct 22, 2019 7:34 pm

Sam Spoons wrote:Delayed satellites need a delay of roughly 1ms.ft (you calculate it more accurately in your OP), it's nowt to do with reverb times AFAIK. It's down to time aligning the sound coming from the satellite with the direct sound from the main FOH (so that kick/snare drum arrives at the ear at same time from both speakers).

It's definitely worth doing in a room that size and, if you can adjust on an iPad from down the room you'll hear the bass clean up as the time alignment becomes correct. The effect can be dramatic.
Thanks guys! That sounds pretty easy. It’s a 125’ long or deep room. I only have 50’ cables but I have a nice 1000’ spool of sheilded 12/4 so I think I’m gonna make 2X 100’ Cables, set the furthest first and wind up the left over for the one nearest the PA. Probably end up around 60-70’ into the room from the front FOH mains.
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Re: Audio delay, how distant before needed?

Postby Wonks » Tue Oct 22, 2019 7:43 pm

Sam Spoons wrote: it's nowt to do with reverb times AFAIK.

Well, it can be down to reverb levels, but that's a bit of a guess to calculate, so it's really down to empiric measurements in the space. Once you get to the critical distance, where the reverb level is 100% or more of the direct level at that point, then you'd certainly want supplementary speakers to help out by producing more direct sound.

You can have a go at calculating the critical distance - here's a calculator http://www.mcsquared.com/critical.htm - but you need to know the reverb time for the space and the room/hall dimensions (which may not be rectangular) and you may well have a mixture of soft and hard walls/furnishings that vary the reverb level at different points in the room.

You are probably best setting up the main FOH speakers, walking backwards until it all starts to get a bit mushy, and then siting the repeater speakers slightly forwards of that, and then setting the delay time based on distance. But even then, the reverb time will be very different once you've got a room full of people.
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Re: Audio delay, how distant before needed?

Postby Sam Spoons » Tue Oct 22, 2019 9:27 pm

Wonks wrote:You are probably best setting up the main FOH speakers, walking backwards until it all starts to get a bit mushy, and then siting the repeater speakers slightly forwards of that, and then setting the delay time based on distance.

That's how I would do it.

But even then, the reverb time will be very different once you've got a room full of people.

:thumbup:
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Re: Audio delay, how distant before needed?

Postby resistorman » Tue Oct 22, 2019 10:40 pm

I personally prefer using a post fader aux bus for delay mixes... it will still track your mix but you can offset the levels of the individual instruments.
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Re: Audio delay, how distant before needed?

Postby funky54 » Wed Oct 23, 2019 4:31 am

Thanks guys! Some pretty great info.
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Re: Audio delay, how distant before needed?

Postby Mike Monte » Wed Oct 23, 2019 2:27 pm

I usually don't use audio delay, however, when I do, I use my ears to align delay speakers.
What I do:
Power up mains and delay speakers. Using a wireless mic, leave the stage and stand in front of the delay speakers (10-20 feet). "Click my tongue" into the mic (sounds like a snare drum rim shot) and align by ear.

It's not quite scientific but it works.

I tend to trust my ears.....
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Re: Audio delay, how distant before needed?

Postby Sam Spoons » Wed Oct 23, 2019 5:32 pm

I prefer to use sound with bass content to time align delayed satellites, you can hear the bass (to use Hugh's words) 'come into focus' but I'm sure your method works fine too. Measuring the distance and starting with a delay time of 1ms/ft saves a little time but ears are essential to fine tune the delay.
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Re: Audio delay, how distant before needed?

Postby shufflebeat » Fri Oct 25, 2019 12:04 pm

Wonks wrote:
Sam Spoons wrote: it's nowt to do with reverb times AFAIK.

Well, it can be down to reverb levels, but that's a bit of a guess to calculate, so it's really down to empiric measurements in the space. Once you get to the critical distance, where the reverb level is 100% or more of the direct level at that point, then you'd certainly want supplementary speakers to help out by producing more direct sound.

There are two questions being answered here:

1) where do I put my satellites?
2) how do I calculate the delay?

The reverb is relevant to the first one and folks are generally concentrating on the second.

Getting the timing right can make the satellites "disappear" in the picture, it's extremely satisfying for those of us who care about these things.

I also use clicks to align where I can. It's true to say that it has a significant positive effect on lower frequencies but the actual alignment I find quicker to do and easier to judge with rim shots or acoustic guitar muted strings. When set optimally this will, of course, coincide with the numbers on the calculator, as is always the way with physics.

Slight aside - tiny changes sometimes make big differences and I now usually delay the main FOH to align the acoustic kit with the mains. This has also solved a whole lot of onstage low frequency resonances.
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Re: Audio delay, how distant before needed?

Postby Sam Spoons » Fri Oct 25, 2019 12:43 pm

shufflebeat wrote:Slight aside - tiny changes sometimes make big differences and I now usually delay the main FOH to align the acoustic kit with the mains. This has also solved a whole lot of onstage low frequency resonances.

Not something I've done but have often considered, will try it on the next gig.
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Re: Audio delay, how distant before needed?

Postby MarkPAman » Fri Oct 25, 2019 1:53 pm

You've got to give it a try Sam!

If you slowly increase the delay from 0 while listening to the drums there comes a moment when the PA seems to just disappear. It's really rather wonderful.
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Re: Audio delay, how distant before needed?

Postby Sam Spoons » Fri Oct 25, 2019 1:58 pm

Will do :thumbup:
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Re: Audio delay, how distant before needed?

Postby Wonks » Fri Oct 25, 2019 2:02 pm

Note that you can achieve the same effect by turning off the PA. HTH. :D
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Re: Audio delay, how distant before needed?

Postby MarkPAman » Fri Oct 25, 2019 2:04 pm

I do some of my best work like that!
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