| This article is in three parts. The
first part is a basic introduction to the theory, including the
definition, how it was discovered, and application. Part two is
an example of how the sweetspot was found in one church sanctuary
(testing), and in part three a description of how to find the
sweetspot yourself is discussed.
Part 1 - The Theory
(This portion copied in part from The
Church Sound Network, hosted by JdB
Sound, Acoustics. Click here
to be directed to the same article on the original web site.)
Written by Joseph De Buglio
Updated June 2000.
Updated May, 1999
Originally written June 1991
Preface
It’s no secret that the success of a good sounding church
sound system begins with proper speaker placement in a sanctuary.
The better church sound systems use central clusters when the
worship space permits. Some clusters are positioned better than
others. What if there was a way to ensure better cluster performance?
Imagine for a moment for smaller churches (under 1500 seating)
to have a quick and simple method of starting the design of their
sound systems beginning with the speaker system. Imagine some
rules and simple formulas that help beginners to church sound
to design as good a sound system as possible without high priced
professional help. Imagine using these rules to help determine,
for the average lay person, how to assess a sound system proposal
and to know who will most likely design the better sound system
for their church. Imagine also these same rules showing the exceptions
to the rules which suggest when you need professional help. Imagine
a church on a very limited budget - determined to do their own
installation, to have some rules that are helpful enough that
no matter what, they’ll have a reasonable sound system to
start with. It’s my hope that the idea of a Sweetspot for
church sound systems can make a difference for the church community.
Introduction
Fact or fiction, myth, new discovery or rediscovering old science
- you decide. The term “sweetspot” for churches is
not new, but what is new is whether it makes a difference in sound
system designing and room acoustics. What’s presented here
isn’t an absolute theory, but rather a part of sound system
designing that may have been over looked for the past 50 years.
While testing done by myself and others does show that this effect
exists in most large rooms, a professional study needs to be done
by someone more qualified. Knowing about this sweetspot theory
as I have experienced it, how to use it, and what to do when you
can't use it has made an impact on how the overall performance
of a church sound system ultimately worked.
What is a Sweetspot
The sweetspot of a room is an important attribute of a house of
worship. It’s a spot in the room where people naturally
gravitate to for special music or special presentations of sound.
You know - where the choir sounds best for special music and where
the string quartet likes to play for concerts. For years people
have known about the sweetspot of a room and they’ve used
it many times. All I’m trying to do is explain why it’s
used and perhaps why it matters in church sound system design.
The idea of a room having a sweetspot dates back to when monks
where using tuning forks to tune church pillars 600 years ago.
Until recently it was ignored for the designing of a sound system
for a church. My limited research has shown that knowing how to
use it can make a large improvement in the performance of some
sound systems. I also believe that it can help architects to better
plan new sanctuaries.
In general, your could say that it’s the spot where a person’s
voice projects the furthest into a room before reflections from
walls and other surfaces interfere with the original sound. To
the person talking or performing, the sounds that are projected
back most often gives the ideal picture of how well their sound
is covering the room un-amplified or amplified. If there’s
a string quartet, they often gather around the sweetspot so they
will be able to play together with less effort while having an
excellent level of being able to hear each other.
Can a person hear the sweetspot without test equipment? What
does the sweetspot sound like? For the average listener (and depending
on the room), stepping into the sweetspot is often subtle. Much
like a near sighted person putting on glasses to make out the
hymn numbers on an overhead at the front of a church. In some
churches, it can be very dramatic. In many of the tests that I’ve
done with my MLSSA, it has shown as high as a 2% difference between
standing in the sweetspot and stepping out of it by a few feet.
The question is, does this matter for church sound system designs
or can we just ignore the effect all together?
First Contact
I first noticed the effects of sound getting clearer in 1985 while
installing an active speaker on top of a 30-foot scaffold. Someone
on the floor noticed the speaker sounding better when it was a
few feet further back. We cleared the planks and moved the speaker
around and the 15 people around the room noticed the effect. As
far as those church members were concerned, they made it very
clear to me that the sound from the loudspeaker was better in
one position over another and they asked me to put the speaker
in the better position. As it happens, we were able to move the
speaker and the results were as I had hoped with good gain before
feedback, coverage and so on.
From that point on, on many installations, I would set up a temporary
bracket at the top of the scaffold and slide the speaker back
and forth until there was a spot where I or a church volunteer
would notice that extra bit of clarity in the sound. I would use
a prerecorded tape of a person speaking. That was how I would
find the idea position to install the speaker. Then, I tried the
same thing on the ground. The results were almost the same, but
less dramatic. After doing this at about 40 churches, I had found
that as long as the ceiling was symmetrical, the "sweetspot"
remained constant on the vertical axis down to the floor. I’ve
done such testing on over 100 other churches too. With my MLSSA
(and on a few occasions - I use a friend of mine's TEF), these
toys confirmed what I was hearing without test equipment - and
it gave a quantified test result.
All of this work was done only in churches. Before installing
the speaker or cluster system, I would ask 20 to 30 people to
listen to a person speaking into a mic down below and listen to
some music. These people could hear a definite difference of sound
quality, even with just a movement of the speaker of only 6 inches.
These experiences have led me to marking this position as the
sweetspot.
Some of the Facts
The sweetspot is a mathematical calculation that as of now hasn’t
been written in scientific terms yet. Ray tracing programs show
the effect through trial and error. That is, by moving the speaker
back and forth of a 3D ray trace, you can see one position as
better than another. The ray trace matches what people hear. From
these ray tracings, it should be possible to create an equation
to explain the sweetspot just as a scientist did for calculating
a knot. That is, for thousands of years people have been making
knots and recently it was finally written as an equation to explain
it. In every room there are two sweetspots, one at the front and
the other at the back of a church. The one that concerns us is
the one at the front of a church. Regrettably, this doesn’t
apply to round or square rooms much. Nor can it be applied to
churches with low ceilings. Again, while the sweetspot exists,
you can't always use it and these are just three of the exceptions.
First of all, you can find the sweetspot without test equipment
or doing any calculation. With two people, a listener and a talker,
you can find the sweetspot in many existing church buildings.
The best way to describe the effect is like this. The moment a
person steps into the sweetspot while talking, that persons voice
with get just a little clearer. Under some acoustical conditions,
it’s very apparent. In other rooms, you have to really listen
closely. Sometimes you’ll have to turn off the air or heating
system, the lights and other noises in the sanctuary, and you
should be able to hear it. Once you’ve found it, have the
listener go to another location. The sweetspot should be the same
spot. If the church isn’t symmetrical on either side, the
then sweetspot may be off center. If your church is over 1500
seating, then you may need test equipment, as it was from our
experiences in larger rooms.
With A TEF or MLSSA or JBL SMAART system, you can find it too.
Just place a microphone in the center of the left or right side
of the seating area. Next, use your test speaker on a stand of
8 to 10 feet high and move it around. Do the STI (speech transmission
index) or %ALcons (percent articulation loss of consonants) test
as you move the speaker from spot to spot. When you see the intelligibility
of the test increase by half a percent or more, that’s generally
the sweetspot. In some churches, this change was found to be up
to 2% in intelligibility. To confirm the spot, you move the microphone
to another location forward and do the test again moving the speaker
around. You should find the sweetspot in the same place.
I’ve attempted this calculation. As a simplified calculation,
it looks like this:
(L - W) / 2 + W
L is the length of the room
W is the width of the room
This is the distance from the back of the church to the front
for its location. In short, the results show a position between
one-third and one-quarter from the front and center of left to
right. The formula doesn't always apply.
What’s most interesting is that since humans are better
at locating sounds on a horizontal plain, the sweetspot remains
constant from the floor to the roof. Now, if there are near by
physical structures near the sweetspot on the roof, it can change
the amount of improvement that is hoped to be gained as shown
on the floor. However, it’s still the better location from
which to start to build your speaker system from, even with a
variety of ceiling types. If these obstacles are in the line of
sight of the speaker system, common sense would force you to move
the speaker system if you can't raise or lower the speaker system
to clear the obstacle.
OK, then what does this spot mean?
Well, for existing churches, there are many issues you can overcome
when designing your speaker system and it’ll also explain
why even with your best efforts in the system design, it creates
feed back problems at the pulpit and nowhere else in the church.
This isn’t about sound lobbing down under large and wide
clusters. I’ve checked for that.
As mentioned earlier, the sweetspot represents a point in the
room where if a person speaks or sings from it, their sound will
penetrate further into the room without any amplification before
reflections from the walls and other surfaces interfere with the
original sound. Choir leaders and those doing special music often
will want to perform from that position. In a church that is well
diffused, the sweetspot area can be larger and harder to find.
For us in the sound and acoustics business, this is a spot from
which we can take advantage of the rooms' design. When designing
a system in an existing church, you may not be able to put the
speaker system in the sweetspot, but if you can, it should get
you a little more gain before feedback. In almost ever case, you
should get an extra 1/2 to 2% in speech intelligibility.
Better Sound System Planning
But there are other items you have to consider. If the pulpit
is in the sweetspot and can’t be relocated, then your gain
will most likely be lower and you’ll also have excessive
feedback problems. If the minister stands where the sweetspot
is, the omni wireless microphone will most likely have less gain
and feedback excessively. It’s a paradox many people in
sound are often getting stumped with, but don't know how to explain
or what to do about it. If the speaker system and pulpit are in
the sweetspot, it just limits the gain all the more which in turn
is excessive feedback.
Better Feedback Control
However, since as stated earlier that the sweetspot is also the
place where you can also hear yourself the best, it would stand
to reason that putting a microphone there will also lower your
gain before feedback. While there are other factors that cause
feedback, this is an element that testing has shown to support
the sweetspot working in reverse as part of the audio chain. Knowing
this can allow the sound system design to anticipate these problems.
Furthermore, when installing a cluster, even when it’s
not in the sweetspot, if the pulpit mic is there, you will most
likely have limited gain and a lot of feedback problems.
Ray tracing programs, the EASE program and other audio simulation
programs do show the improvements when a speaker system is placed
in the sweetspot verses when it’s not. However, none of
the programs are designed to help you find the sweetspot. You’ll
have to try several speaker locations to see the improvements.
This is very time consuming.
People have laughed at the idea of a sweetspot in the past. Today,
when I have a chance to demonstrate to other experts, they become
aware of its existence and find that it really can make for a
better system, even though their other systems were already working
very well. Overall, the improvement can vary from church to church
and in some churches, it can be dramatic.
It should also be pointed out, as we discovered, is that a speaker
system, slightly in front of the sweetspot can also pass the HIS
System test. Moving the speaker back only makes it better. However,
in some cases, the cost was too high to make the effort for that
extra percentage or two.
New Churches
For new churches, this opens a whole new dimension of church designing.
If an architect is aware of a sweetspot, he can design platforms
to take advantage of it. It means hanging points for the speaker
system can be designed in the early planning stages. This also
impacts the seating arrangements, placement of the piano, organ
pipes or organ speakers, the pulpit, the choir loft seating and
much, much more.
This also means that for the first time, an architect can look
at how to design the widows or place walls with artwork and work
around the speaker system. The light system has to also work around
the sound system. Currently, the artwork or windows or crosses
are already designed before the sound system is even considered.
This equation changes that.
The Bigger Picture
However, there is a bigger picture here. Until now, when a church
asks the question, "where does the speaker system go?"
you had to go through a very long explanation. Then a church board
member asks, "how come the other 3 contractors want to place
speakers in different places? Why should we believe you?"
Again, you have a long song and dance ahead of you to prove that
you have the better system.
Since 1989, I’ve been promoting the idea of a sweetspot
and in 1994 a math professor tried to explain it to me with ray
tracing. Later, the (L - W) / 2 + W formula was worked out. It
quickly has shown many in the church community that there’s
a science to church sound and ignoring it means the sound system
will most likely have a slightly or dramatically lower level of
performance and higher feedback problems.
Furthermore, in most churches, the sweetspot is easy to demonstrate
to a church board. Once this message is understood, a church will
no long consider what the other contractor says or does, no matter
how good of a reputation they may have. In a few cases where other
contractors used simulation programs to prove they were the best,
taking the church board into the sanctuary and having them hear
the sweetspot changed that opinion fast. It proved that the person
using the program didn't consider if one speaker position was
better than another. Oversights like that can cost a person a
contract.
Sure, it isn’t always possible to place the speaker system
in the sweetspot, but knowing what the sweetspot is and does means
you can compensate with alternate speaker choices, or different
mics at the pulpit. You can better tell the church that because
of this or that, they will need to re-angle the slope of the book
board of the pulpit or you’ll need a better pulpit mic with
a processor on it. The sweetspot is just another tool in making
church sound better. It’s not a panacea or a magic bullet.
If anything, the sweetspot does give the best starting point
for designing a church sound system. This also applies to churches
that have LCR system too. If the acoustics, physical barriers
or existing seating arrangement won’t let you use the sweetspot,
it’s still a reference point and good audio experts should
be trained to know how to compensate accordingly. Furthermore,
it’s also a place where you don't want a pulpit or a standing
position for the minister regardless of where the speaker system
is.
This is just a brief summary of what the sweetspot is and how
to use it. Audio contractors who are looking for that extra edge
in their system designs are already finding this to be very helpful.
Architects are already realizing that this is really helpful in
their efforts of designing better churches. As a church, knowing
about it will assist you in your future decisions. Ignoring it
doesn't mean you’ll get a bad sound system, but by using
it or knowing how to work around it means you can make your sound
systems than much better.
For the Thomas's out there
Finally, there are those who are experts in the field of audio
who seem unsure of what to make of all this. For them, I can only
say the following. If your systems work as good as a HIS System
or better, chances are, you’ve already been placing the
speaker system in or around the sweetspot. I’m positive
that if you test your own systems, you’ll find this to be
true. The idea of stating that the sweetspot is the best location
for the speakers system helps the layman to better understand
a part of sound system designing. We can’t ignore the fact
that the term sweetspot, as a non-scientific term, has been used
in home HI-FI and in recording studios for years and is accepted
by the industry. Since the live sound reinforcement system is
a HI-FI system in reverse, shouldn’t it be logical that
a sweetspot exists in a church setting and is just as important
for the listener in the pews.
The sweetspot should only be looked at as a tool to sound system
designing. Some may see it as a short cut to hard work in system
designing. What if this shortcut was always there? What if, somewhere
along the line, the exercise of doing all of the math for system
designing was less important that just getting to the results
faster? What if, for the layman, who doesn't have an engineering
degree, who may get the math wrong without knowing it, the sweetspot
guides him to getting the math right? What if getting to the answers
faster also means the smaller churches could be paying less for
sound system designing and more on equipment? How much do sound
system designers really know about room acoustics?
As stated earlier, the sweetspot isn’t an absolute, but
if it saves time and money, it’s valid. If it means the
average guy in the music store who gets the call to install a
church sound system understands the sweetspot and designs a better
sound system, it’s valid. If it means more smaller churches
will get better sounding sound systems they can afford that can
perform as good as systems costing thousands more in the larger
churches, it’s valid.
Click here for Part 2 |
