| Part 3
- How to find the sweetspot
Blake A. Engel, All Church Sound
This section is in two parts. The first part discusses finding
the sweetspot using a few people and your ears and mouth, while
the second part is an overview of how to find it using test equipment.
How to find the sweetspot using your mouth, ears,
and a few friends
Have your friends sit out in the congregational seating area in
random locations (some close, some far, some in the center, others
off to the sides). The listeners should be instructed to close
their eyes. Tell them you’re going to repeat a word or short
phrase over and over. When the sound seems to be clearer to them,
they should raise their hand. When the sound is no longer as clear,
they should put their hand down. To find a good starting point
for the person speaking, take the length of the room, divide it
by 4, and subtract 10 feet. This is the distance from the front
wall (behind the platform) where the person talking should begin.
The person speaking should stand this distance from the front
wall, centered between the two side walls. Begin repeating a word
or short phrase over and over as you slowly walk forward (toward
your listeners) (A simple word such as “sound-check”
works well.). You should only move about 6 inches between words
or phrases. (If there’s a modesty rail or other obstructions
in the way, move them if you can or simply work around them.)
At some point (usually close to ¼ the length of the room)
most if not all of your listeners will hear a change in the sound.
Most will describe it as being louder and clearer; as if you raised
your voice. When you’ve identified the sweetspot, try the
test a second and third time with a different word or phrase (use
the same talker). If everyone raises their hand to indicate they
hear a change in the sound, continue moving forward and repeating
the word or phrase. You should see all hands go down. Then start
walking backwards and back into the sweetspot. The hands should
go up. When you continue walking backward, hands should go down
again. Walking in and out of the sweetspot and speaking different
words or phrases should prove the location of the sweetspot. If
you’re still not totally convinced, try a different person
as the talker or a different group of listeners and repeat the
entire test.
In most churches, the sweetspot is very easy to find using this
method. In other churches, the sweetspot is a very large area
(thus harder to determine if you’re in it or not) or is
off to one side or the other, depending on the shape of the room.
How to find the sweetspot using test equipment
To do this test properly, you need a test system such as MLSSA,
TEF, SMAART, or similar which will allow you to make intelligibility
measurements. In addition to this hardware/software, you also
need a test microphone and preamp (or mixer) to interface with
the acoustical hardware/software measurement system. Also, you
need a test speaker and a speaker stand that’s 9 to 13 feet
tall (or taller). The test speaker can be self powered or interfaced
with the test system with an outboard amplifier.
Before making any measurements of the room, be sure to test your
measurement system (with the test microphone a few feet from the
test mic). This measurement should then be compared to a previous
measurement which is known to be good. This process ensures your
test system is set up properly and that you’ve not made
any mistakes. It also ensures that your test speaker and microphone
are operating correctly and have not been damaged at some point
without your knowledge. Not taking this step can result in false
measurements which are meaningless.
Begin with the test speaker near the estimated sweetspot (using
the formula previously mentioned, or ¼ the length of the
room from the front wall (behind the platform)). The speaker should
be at the full height the speaker stand allows and should be aimed
straight back toward the rear of the room. Next, place the test
microphone within the main seating area (within 90-degrees of
the test speaker), and about ½ to ¾ of the way back.
Be sure the room is quiet when making these measurements. If
the HVAC system is noisy or if the ceiling lights have noisy filaments,
you should be sure to turn these systems off. Be sure to watch
out for the intrusion of road noise, aircraft noise, or noises
from within the building (but outside the worship sanctuary).
Take your first measurement and write down the measured intelligibility
(%ALcons). Be sure to note the location of the test speaker. This
can be done by measuring the speaker location from a stationary
location (such as the back wall or front pew). Now, move the test
speaker ahead (toward the back of the sanctuary) about a foot.
Take another measurement and write down the result. Continue this
process several times. (To ensure you’re not exciting the
room based on equally spaced locations of the test speaker, move
the speaker between 10 and 24 inches between each measurement.)
Once you’ve taken a number of measurements moving toward
the rear of the room, work toward the front wall of the room (from
the original test speaker location). Continue these measurements
several times. The entire process should result in moving the
test speaker 5 to 10 feet both in front of and behind the original
test speaker location.
At this point you should have two columns; one should contain
the location of the test speaker, the other should be the intelligibility
measured at that location. If done right, you should see one location
where the intelligibility is 1/2 to 2 percent higher (better score)
than the locations either side of it. This will be an indication
of the sweetspot.
Next, pick another random location for the test mic, and repeat
the entire process. If done correctly, you should see that the
best intelligibility score in this second test is the same location
(or near the same location) as in the first test. Be sure to put
the test speaker in the same locations for the second test as
you did for the first test.
To further confirm your findings, repeat the test with the test
mic in two more random locations. (A good way to locate a totally
random location is to toss small, square, cardboard coasters (like
those found at some restaurants) out from the pulpit location
into the congregation seating area. Simply flying them like a
Frisbee works very well.)
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