A Theory For Better
Church Speaker System Installations

Written by Joseph De Buglio
Comments of the author are not necessarily those of the Audio Community.

A Theory - The Sweetspot of a Room

Introduction

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.

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. In some churches, it can be very dramatic. In many of the tests that I have done with my MLSSA (Maximum Length Sequence System Analyzer), 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 design or can we just ignore the effect all together.

First Contact

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.

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 noticed that extra bit of clarity in the sound. If I was by myself I would use a prerecorded tape of a person speaking to 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 have done such testing on over 100 other churches too. With my MLSSA and on a few occasion - 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 to 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 lead me to marking this position as the sweetspot.

Here are two examples.

In both examples, the speaker cluster can be moved forwards and backwards. First, the speaker location was tested with a test speaker on a pole about 10 feet high. To see if the location carried up to the ceiling, a custom bracket was installed. Next, using the same technique as on the floor, the new speaker system for the churchis moved back and forth to see if one location is better over another. When that location is found, it is then tested for coverage and gain before feedback. This has been tested in many church and churches of many different shapes and acoustical condition. .


** Note - There has been a standing invitation for anyone interested to got to one of these two churches and test the sweetspot concept themselves or to have a demonstration of the sweetspot in their own church. There is also an invitation to go to any of the projects design by Joseph De Buglio or Blake Engel to experience the results of the sweetspot theory and to do independent testing. This invitation is open to all including AES, NSCA, SAC and NAS. The Sweetspot Theory has been demonstrated and tested at various Bible Colleges and audio experts representing various churches around the world. Many churches and individuals have tested this theory and most of them have used it to design their sound system or the room would not allow the sweetspot to be implemented due to Architectural limitation.

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.

With A TEF or MLSSA or JBL SMARTT system, you can find it too. Just place a microphone in the center of the left or right side of the seating area. Next, using your test speaker on a stand of 8 to 10 feet high and moving it around. Do the RASTI or %Alcons 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 is 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. In short, the results show a position between 1/3rd to ¼er from the front and center of left to right. No one has been able to create a calculation for the sweetspot. From what I have been told, there isn't one for setting up stereo speaker so I imagine that such a formula will be as elusive as the formula for diffusion is.

What is most interesting is that since human 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 is 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. You may have to raise or lower the speaker system to clear the obstacle.

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 systems too.

Many audio experts 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 it's 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.

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.

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. It's not. It just cuts down on the guesswork.

As stated earlier, the sweetspot is not an absolute and sometimes I question it until it shows up on the next job. Here is a challenge for you. Try to find the sweetspot in your church. Test it for yourself. Get someone to help you find it. Then post your results on the CSN discussion group. Your results, good or bad will be posted. If you have any other questions or comments about the sweetspot, please e-mail me or post your comments on the discussion group. Thank you.

By Joseph De Buglio (c) JdB Sound, Acoustics, Canada Jan. 1999-2006

The following are comment written from others about the sweetspot. These comments are posted as is.


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