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[Keith Humphrey]

My band played an outdoor benefit last year at Duke University and provided the PA. I have been asked to provide the PA again this year (for pay).

Last year the PA worked fine for music across the area but I received some complaints about speeches and announcements  not being heard in the back. To remedy this I plan to use some delay speakers about 2/3 of the way back when someone is speaking. I have never done this before and was wondering if there is something I can read to learn how to set up the delay, etc.

Thanks.

[g'bye, Dick Rees]

My band played an outdoor benefit last year at Duke University and provided the PA. I have been asked to provide the PA again this year (for pay).

Last year the PA worked fine for music across the area but I received some complaints about speeches and announcements  not being heard in the back. To remedy this I plan to use some delay speakers about 2/3 of the way back when someone is speaking. I have never done this before and was wondering if there is something I can read to learn how to set up the delay, etc.

Thanks.

1.  How deep is the sound field?
2.  How high did you (can you) position your mains?
3.  Did the speakers actually speak directly and strongly into the mic?

Delay speakers won't help someone who is mic shy.  And you need to have your speakers at least 7' in the air, more depending on conditions/layout.

That said, sound travels at 1,126 ft/sec @ 68 degrees F.  Simple math will give you your delay in milliseconds.  75' / 1126 fps = .0666 sec 

But delay can only be set perfectly for one position.  As you go off axis the values will change.  But it's a LOT better than no delay at all.

[Dave Dermont]

1.  How deep is the sound field?
2.  How high did you (can you) position your mains?
3.  Did the speakers actually speak directly and strongly into the mic?

Delay speakers won't help someone who is mic shy.  And you need to have your speakers at least 7' in the air, more depending on conditions/layout.

That said, sound travels at 1,126 ft/sec @ 68 degrees F.  Simple math will give you your delay in milliseconds.  1126 fps / 75' = approx 15 Msec. 

But delay can only be set perfectly for one position.  As you go off axis the values will change.  But it's a LOT better than no delay at all.

Check your math

If sound travels over 1ms per foot, how do you get 15ms for 75 feet?

The main speakers and the delays are fixed points. You are setting the delay for time-of-flight between those points.

If you set the delay speakers so they lag the mains, precedence will remain with the main speakers. I believe the magic number where the ear/brain detects two distinct sounds is around 30ms, so if you keep the arrival time below that, your good.

1ms/ft is a reasonable starting point, and the math is really easy.

[g'bye, Dick Rees]

1.  How deep is the sound field?
2.  How high did you (can you) position your mains?
3.  Did the speakers actually speak directly and strongly into the mic?

Delay speakers won't help someone who is mic shy.  And you need to have your speakers at least 7' in the air, more depending on conditions/layout.

That said, sound travels at 1,126 ft/sec @ 68 degrees F.  Simple math will give you your delay in milliseconds.  1126 fps / 75' = approx 15 Msec. 

But delay can only be set perfectly for one position.  As you go off axis the values will change.  But it's a LOT better than no delay at all.

Check your math

If sound travels over 1ms per foot, how do you get 15ms for 75 feet?

The main speakers and the delays are fixed points. You are setting the delay for time-of-flight between those points.

If you set the delay speakers so they lag the mains, precedence will remain with the main speakers. I believe the magic number where the ear/brain detects two distinct sounds is around 30ms, so if you keep the arrival time below that, your good.

1ms/ft is a reasonable starting point, and the math is really easy.

Oopsie.  I did the math in my head in a hurry.  It's actually 66 Msec for 75'. 

Time to go back and edit my shameful misinformation.

Edit:

Actually it takes sound .888 seconds/ft @ 68 degrees, so 75 ft x .888 = 66.6 Msec.  If you figure it a 1 sec/ft you'll get enough extra delay to let the sound from the mains take pscho-acoustic precedence.

You state that delay becomes audible for the average listener at around 30 Msec, but to me it starts sounding noticeably like an effect at 11 Msec.  30 Msec would be quite noticeable and a bit disconcerting.  I usually just add 3-6 Msec to the exact figure to let the initial sound wave take precedence.

  Thanks, Dave.  Maybe now I've said it right.

[Keith Humphrey]

Thank you for the responses. This is what I was looking to read up on (not just the math but fudge factors as well).

I am aware that much can't be done with a soft speaker. Basically with my PA I end up with a loud area near the stage, an area that requires somewhat elevate conversation around the mid-point and then normal conversation/background music at the back. This works out well for the musical portions of the program but not so much for the speeches/announcements. This was why I thought the delay speakers would be the best way to resolve the situation. Again thanks for the assistance. 

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