Theory For Better
by Joseph De Buglio
|Written by Joseph De Buglio
A Theory - The Sweetspot of a Room
What is presented here is just theory about a part of sound system designing that may have been over looked. It has made an impact on how the overall performance of many church sound systems ultimately worked.
What is a Sweetspot
Many professionals in the audio trade use the term sweetspot for HIFI and Studio Recording systems. It is referred to the spot where the stereo image is in focus for every sound that is in the mix. The idea behind the sweetspot theory in a sound reinforcement system for large rooms is the focal point to broadcast mono/live sounds to many people in a large room. Since people can see where the live sounds are coming from and you don't have to be between two speakers to locate a sound on the stage, reinforcement of live sound become like a HIFI system in reverse.
The idea of the stereo system is to be positioned between two speakers and the audio recording is manipulated to create room effects or the impression of sounds coming from more that one place between the speakers. In a stereo system the sweetspot is the focal point of sounds for just one person between two speakers.
For live sound, the opposite is required. No matter where you are sitting, you are expected to hear the same sounds everywhere less any room effects on the listening position. This required a position from where a single focused sound can broadcast into a room that is affected only by the room effects just as the natural sounds from the stage or performance area. Is there such a position? If there is such an area, do you put the speaker system in that spot or do you keep away from it?
For years people have been using a sweetspot of sorts and they have used it many times. It is 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. Where the string quartet likes to play for concerts.
In general, your could say that it is the spot where a person's voice projects the furthest into a room before reflections from walls and other surfaces interferes with the original sound. Just about every church I go to, I ask the music director or minister if there is an ideal performance spot where people sound their best when performing. Just about every church has such a spot and it is most often center stage and anywhere between 6 feet behind the front of the stage to about 5ft. ahead of the front of stage. Center stage is the most common but where along that center line – it changes from room to room.
You can't always
hear the sweetspot. Standing waves and strong early reflections
can mask the spot. To the person talking or performing, what
sounds heard is most often the ideal picture of how well their
sound is covering the room un-amplified or amplified. If there
is a string quartet, they often gather around the sweetspot so
that they will be able to play together with less effort.
I first notice 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 that the planned hookup point. 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.
Here are two
Some of the Facts
The sweetspot is only a theory. Just as diffusion is almost impossible to calculate, the sweetspot seems to be the same.
In every room there are two sweetspots, one at the front area 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 does not 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 here are just 3 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 person's voice with get just a little clearer. Under some
acoustical conditions, it is very apparent. In other rooms, you have to
really listen closely. Sometimes you will 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 have found it, have the listener go to another
location. The sweetspot should be the same spot. If the church is not symmetrical
on either side, then the 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.
Better Sound System Planning
But there are other items you have to consider. If the pulpit is in the sweetspot and can not be relocated, then your gain will most likely be lower and you will also have excessive feedback problems. If the minister stands were the sweetspot is, the omni wireless microphone will most likely have less gain and feedback excessively. It is 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 is in the sweetspot, it just limits the gain all the more.
Better Feedback Control
However, since, as stated earlier that the sweetspot is also the place
were you can also hear yourself the best, it would stand to reason that
putting a microphone there will also decrease your gain before feedback. It is the place you don't want your microphone to be. While there are
other factors that cause feedback, this is an element that testing has
shown to support the effect of the sweetspot in the audio chain. Knowing
this can allow the sound system design to anticipate these problems. The sweetspot is the best place to start the speaker system design but
the worship place for minister with hand mics, wireless mics or pulpit
mics. The feedback problems was rather consistant no matter where you put
the test speaker. This is not a loobing problem. It happens with Left Right
The Bigger Picture
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 3 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.
In a few cases where other contractors used simulation programs to prove they were the best, all I needed to do was take the church board into the sanctuary and having them hear the sweetspot and that changed their opinions really fast. It proved that the person using the program didn't consider if one speaker position was better than another nor the impact it can have is system designing.
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 church sound standard or better, chances are, you have already been placing the speaker system in or around the sweetspot. I am positive that if you test your own systems, you will 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 not ignore
the fact that the term sweetspot is a non-scientific term, but
it has been used in Home HI-FI and in recording studios for
years and it is accepted by the industry. Since the live sound
reinforcement system is a HI-FI system in reverse, should it not
be logic that a sweetspot exists in a church/ live sound setting
be just as important for the listener in the pews.
By Joseph De
Buglio (c) JdB Sound, Acoustics, Canada Jan. 1999-2006
Copyright © Jan, 1992-2002 -2006
This Page was created by JdB Sound, Acoustics