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- Yes! Speaker placement is very important.
First, let's look at natural sounds we hear each day. Say you're
taking a walk in the morning and are about to cross an intersection
when you hear a loud noise. You look to your left and see a car
coming--apparently it doesn't have a muffler. The car stops, and
then proceedes to cross the intersection. As it passes in front
of you, the noise is right in front of you for an instant, and
then it's off to your right.
Now, why did you look to the left when you heard the noise? Well,
it's because the sound got to your left ear a little sooner than
it got to your right ear--your brain processed this information,
and told your head to turn to the left. When the car was in front
of you the noise got to both ears at the same time, and so you
looked straight forward. As the car passed and went off to your
right, the sound reached your right ear first which told your
brain that the car was on your right.
OK, yeah, you could have just LOOKED to your left and seen the
car--and followed it with your eyes as it passed. But your eyes
and ears work together. Your ears tell you there is sound, and
you'r eyes help you identify what's making the sound.
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Is this important to our understanding of speaker placement?
It sure is! Look at figure 1. It shows a typical speaker
setup where there are two speakers--one on each side of
the room (shown as black squares). We call this a "Left-Right"
speaker system.
A listener at point "A" will be looking to the
right at the person speaking (the oval on the platform),
and yet the sound will be coming from directly in front
of them or even a little off to their left. This causes
the brain to work overtime trying to match up the two events--the
ears say the source of the sound is a little off to the
left, while the eyes say the source is to the right. This
is one cause of listeners fatigue which results in a short
attention span. |
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The listener at point "B" is looking just just about straight
ahead, and is hearing sound from both speakers. The sound waves
of the two speakers interact with eachother and they will either
add up to twice the sound level, or they'll cancel each other out!
This doesn't happen at all frequencies (pitches) of sound, but at
specific ones based on the distances of the listener to the speakers
and their position relative to the two. If the person moves just
a few inches to the right or left, the sound will change.
| The other choice is to use a point-source speaker system.
This can be in the form of a single speaker, a single speaker
with fill speakers for the front sides, or a large array
of speakers to cover a very large or wide room. The main
difference between a Left-Right system and a point-source
system is that in a point-source system the sound comes
from only one location, not two like the left-right system.
Take a look at figure 2. As you can see, the sound waves
come only from one place, so there's no sound wave interaction
of the direct sound. (Now, there will always be some sound
wave interaction between the direct sound and the reflected
sound waves--this can't be totally eliminated. Besides,
the goal is to cover the congregation with DIRECT sound--not
reflected sound.) |
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What about the height of the speaker? Does that matter too? Glad
you asked! Figure 3 shows the situation when a speaker is mounted
low to the ground. The first few rows get a blast of volume, absorb
a lot of the sound, and leave very little for those in back. Another
volume problem deals with the inverse-square law. This law states
that if you double the distance from a sound source, the volume
will be half. Thus, if the front row of people in figure three are
10 feet from the speaker, the people at the back (who are 40 feet
away) hear one-fourth the volume. (half the volume at 20 feet, double
the distance again to 40 feet, and it's half the volume again.)
(Keep in mind this doesn't take into account the reflections heard
in the room--there are times when the reflected sound can be louder
than the direct sound).
Figure 4 shows the solution--mounted high, the front row is now
20 feet from the speaker, and the back row is about 45 feet away.
There's only half the volume at the rear--this is acceptable. Speaker
placement is VERY important--we've only talked about the very basics.
We havn't even touched on speaker angles or placement in the sweetspot.
Call us for more information! |
