The hall was long and narrow.
A wedding, two hundred guests,
tables all the way
to the back wall.
Our speakers
stood either side of the stage.
The venue had its own speakers too,
halfway down the room
and at the back,
so the far tables could hear the speeches.
We plugged into the house system
and sent our mix
to both.
At the front
it sounded fine.
At the back
the guests said
the singer sounded strange.
Doubled.
Smeared.
And coming from the wrong place.
She was on the stage.
To them
she was in the ceiling
above table twenty.
Sound is slow.
About three hundred and forty metres
a second,
roughly three milliseconds
for every metre.
The back tables were thirty metres
from the stage.
The signal in the cable
reached the speaker above them
almost instantly.
The sound from the stage
arrived nearly a tenth of a second later.
The ear has a rule for this.
When the same sound arrives twice,
close together,
you hear one sound,
and you place it
where the first copy came from.
It is called the precedence effect,
and in 1951 Helmut Haas showed
that within a short window
the later copy can be noticeably louder
and still not move it.
Leave too long a gap, though,
and the later copy breaks away
into an echo.
That was our night.
The nearby speaker won,
and the stage arrived as a slap
behind it.
The fix is a delay
on the fill speakers.
Measure the distance
from the main speakers
to the fills.
Divide by three hundred and forty
to get the time.
Then add a little more,
ten milliseconds or so,
so the stage sound arrives first
and the fill only adds level.
Then the back of the room
hears the singer
where she is standing,
just louder.
Most digital desks
and many house processors
have the delay built in.
Nobody sets it,
because nobody stands
at the back.
Walk the room before the first song.
Stand at the far table
and close your eyes.
If the voice
does not come from the stage,
the delay is wrong.
The sound that arrives first
decides where the music is.
– Serguey Asael Shinder
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