Understanding the difference between a PA (public address) system
and a Cathedral Sound System

We all have experiences with sound systems as end users or listeners. Our research and experience shows that more church ministries are unhappy with their sound systems than those that are satisfied with very few that are thrilled. This article explores one of the major reasons church ministry struggles with poor performing sound systems.

Music directors and those involved in music and drama ministries are more likely to be  frustrated with the inability to hear the words of the choir and drama, especially of children. Now, there=s no problem with peeling the paint off of the rear walls with music tracks from CD=s or tapes! There=s no problem hearing the pastor or vocalists. But, getting basic speech clarity out of the choir and drama without hitting the ceiling of dreaded feedback is exasperating. No matter how loud the choir sings, how well diction is practiced, how coached the kids are, you just can=t hear the words clearly enough to get the message of the song or the story line of the drama production. Often, this problem persists even when a new sound system is purchased! 

Listeners of all ages strain to hear what is being said during a special music piece or drama production. Those sitting near the front of the church may not have a problem in hearing the smallest voices, but those seated in the back two thirds of the church hear glimpses of what was said. But, they sit in quiet desperation and politely say how much they enjoyed the production afterwards. Loving grandparents long to hear their grand kids and often suffer in silence. 

Why is this an on going problem? Why can=t you hear the words of the choir and drama without feedback? Simple. There=s a huge difference between a PA system and a Cathedral Sound system! 

Most tend to think of a sound system as nothing more than a few microphones, an amplifier, a mixer, and some speakers. The sound equipment you see in music stores and catalogues are PA or public address systems. Systems installed, dare I say it, by a lot of Asound system contractors@ are PA systems. Public Address systems are nothing more than a few microphones, an amplifier or mixer, and some speakers! PA systems simply amplify sound. Nothing new there. But, notice where you have to hold the microphone to be heard. Right! Very near the microphone. Notice where the sound is the loudest in these types of systems; near the speakers! This is why when a PA system is installed in a church there is usually no problem with hearing the pastor and vocalists. The pastor and vocalists usually have well trained voices and the microphones are always within inches from the mouth. This means you don=t have to turn up the volume very high to amplify their voices. They already have strong voices. It makes it very easy to amplify strong voices with any Asound system@ with a mic just inches from the source of sound.

Think about where the sound is the loudest in this type of installation. It=s always near the front of the church because most installs of this type place a speaker in the side chambers or organ lofts on each side of the church. This always results in the complaints of the sound being too loud in the front of the church and too soft in the back. This will always be true because if you sit near the source of sound, it will be louder. There=s no way to avoid this fact.  

A variance on this type of install is where a central speaker is located over the pulpit. Often the wrong speaker for the application is selected (the ceiling may be too low to use a central speaker effectively) and you still have the same problems. Too loud in the front, can=t hear in the back, and we can=t understand the voices of the choir or kids, with constant problems with feedback.

Again, understand that we are not saying that you can=t hear the sound system. Playing music from CD=s or tapes through the system can make the hardest rock and roller head for the doors! No problem with loudness. It=s clarity or articulation that we are after! Where does that come from? How do we get it? 

Despite what some salespersons will tell you, it has very little to do with name brands as compared to the design of the system! It has everything to do with how the system is installed! Quality products are important. There are definitely differences in sound quality between brands and price ranges of components. But, the application of the chosen equipment is the key in getting a high articulation sound system. Here is a simple analogy.  

If you wanted to haul some rocks, which would be better, a truck of some sort or a car? Obviously a truck would be the better choice. A truck is more suited for the application. How large of a truck would depend upon how much of a load you wanted to carry or how many times you wanted to carry a load. A pickup would be fine for short small loads. But if you are going to start a gravel business you will need heavy duty trucks to take the day in and day out abuse to ensure dependability of delivering on time.  

Notice that the first selection in the above example was to choose what type of vehicle we needed, not name brand! It wouldn’t matter if we picked the most expensive Mercedes car on the planet, it wouldn’t serve our need to haul rocks as effectively and efficiently as a cheap used pick up. Once you have decided what type of truck you need, then you can start thinking about the features, benefits, and what you are willing to pay for the performance of each brand. 

The same concept is true in sound systems. Often the buyer and salespersons alike will jump straight to step two and buy name brand and price. How the equipment is going to perform in the given sanctuary or acoustical environment is never considered in the slightest detail. Why? Because no one knows there=s a reason to think about such things. After all, all we need is a few microphones, an amplifier or mixer, and some speakers! All we want to do is make the sound louder so we can hear it better.  

Will the sound be louder? Yes. Will we be able to hear the words of the choir and drama clearly?  The overwhelming odds against success is a resounding no.

 

A crash course on engineered sound

Back to our need to haul gravel example. What was the first thing we had do decide? What type of vehicle to buy. 

If you want to hear the words of the choir and kids clearly at every seat in your sanctuary without worrying about feedback, you must understand how being able to turn up microphones before feedback works in the first place.  

System gain is the difference between the sound system being turned off and the maximum volume setting just before feedback. In very simple terms, start with a pulpit mic on channel 1 on your mixer with the volume control set to A0" or at the very lowest setting (don=t get confused by some mixers having A0 db@ near the 75% travel of the slider - we=re using relative terms here). Then advance the control until the sound system starts to ring and back off slightly. That range from the system being off to just before the point of feedback is called system gain. Let=s assume, again in relative terms, that this difference on your mixer was A10" units. Your system gain would be 10. That is your usable range of operation.  Let's also assume that you can hear the pastor, CD's, and soloists just fine without feedback problems with any setting between 6 and 10.

But, what if you needed to get more gain so you could pick up the words of the choir? Every time you attempt to turn up the system past 10 to hear more of the choir, you run into feedback. How do we turn the system up past this point if we want to pick up the small voices of children? What would you do or need to get more gain from your system? Understanding more about how feedback occurs is in order. 

Feedback - what is it?

There are many good books written on the technical aspects of feedback. But, for the sake of discussion and to present a simple example, feedback occurs when a microphone Ahears@ itself in the speaker system and attempts to amplify itself all over again. This starts a vicious circle, feeds on itself over and over, and we hear this noise as feedback or also known as Aoscillation@. The pitch of the feedback is called the feedback frequency. Sometimes the system will feedback at low notes or frequencies, high frequencies, or any seemingly random frequency. What determines the frequency where the system will feedback is often dependent upon the acoustic environment that includes how sound behaves in the sanctuary, microphone characteristics and placement, and speaker characteristics and placement.  

Here=s an experiment with mirrors if you want to get a sense of what=s happening. 

Take two mirrors (the larger the mirrors the more pronounced and easier to see the effect) like a hand held mirror and your bathroom mirror, and face them so they can see each other. Now, look down the axis of the mirror you=re hold into the wall mirror and you will see an infinity of mirrors inside of mirrors. They seem to go on forever. This same idea is what happens when a sound system Aavalanches@ into feedback by a microphone re-amplifying itself hundreds of times over.

The acoustic environment is anything that can change a sound wave. That means the type of  microphone and it=s placement relative to the loudspeakers, the tone control settings on the offending mixer channel, equalizer settings, characteristics of the amplifier (rare but possible), the type and placement of the loudspeakers in the room, and here=s the key - how sound will behave in the sanctuary under consideration (type of construction, wall coverings, furniture, style of seating layout, number of people seated, and anything that can bend, reflect, or absorb sound). Anything amiss in this pipeline of sound from the microphone (including the diction and resonance of the person speaking) through the sound system components, through the air to the audience can place a strangle hold on system gain.  

If you want to get the maximum system gain before feedback, here is what must be done.

 

Step 1) Decide what type of loudspeaker(s) are required to match the acoustic space

 

There are literally thousands of speakers on the market with a matching number of different sanctuary acoustic spaces to put them in. So how do we determine what speakers fit in what acoustics space? That=s what sound system engineering is all about. If you want to learn how to design sound systems or just learn more about the process, pick up the book ASound System Engineering@ second edition by Davis and Davis ISBN:0-672-21857-7 Howard W Sams, Publisher for around $39. It=s the best place to start. 

A detailed example of selecting the correct speaker system for a space is beyond the scope of this article and is best presented in the book mentioned above. However, a summary of the process is as follows. 

First, a detailed acoustic analysis of the sanctuary is made. This study will determine how much echo and reverb present plus other acoustical properties of the space that will directly affect speech intelligibility. The acoustical study can be made directly with test equipment in an existing building or the sanctuary can be constructed in Avirtual space@ within computer software and analyzed. The object is to determine the best type of speaker (remember the gravel truck example?) and the placement of that speaker or speakers to provide the highest gain before feedback, articulate speech, and even coverage of the audience or listening areas.  

The type of speaker system refers to how a speaker disperses sound. They range from a wide coverage Aflood light@ style of sound coverage all the way to a very direct focused Aspotlight@ style of sound coverage. Just as you would pick different types of light sources to evenly light a floor, speaker systems are chosen in much the same way. A mixture of different types of speakers are usually required to give the desired results. If you want to throw sound a long way, you will need a Aspotlight@ type of speaker system. If you want to Awash@ an area of seats, you would use a Afloodlight@ type of speaker system. This is why you will see central speaker Aclusters@ used in some places, overhead distributed systems, and variations of each in some applications. Again, what determines the type of speakers used is directly related to how sound will behave in that particular sanctuary. There is no such thing as one speaker system to fit all sanctuaries.

Don=t let the sentence above  A . . .the placement of that speaker or speakers to provide the highest gain before feedback,. . .@ slide by! You mean that the speaker system type and placement determine the maximum gain before feedback?! Yes!!!!!!!!  

If you want maximum system gain before feedback and high articulation, you MUST  have the correct speaker system to fit your sanctuary acoustics! No exceptions. No shortcuts. No way to fix it later with an add on Aelectronic gadget@, budget or not.

 

Step 2) Determine the best speaker or speakers to fit the acoustical environment

 

Every speaker system on the market can be classified as some type of Afloodlight@ or Aspotlight@ in terms of the way it projects sound. The parameter that describes the coverage angle or the area that speakers project sound is called AQ@ or another term often used is directivity index. A AQ@ of 1 would be an omni-radiating sound source. This source would radiate sound in all directions equally. This is a theorectical concept. In the real world there are few true omni-radiating sources. A Q of 7 is roughly the radiating pattern of the human mouth a Afloodlight@ type of sound source. A Q of 27 is getting closer to projecting sound much like a high school cheer leader=s megaphone or a Aspotlight@ type of source of sound. All true pro speaker systems publish complete acoustical data to allow sound system engineers to predict how each speaker will behave in certain acoustical environments.  

Once the acoustical environment is known from test analysis we know what type of speaker or speakers we need to install to provide maximum gain before feedback and cover the audience with clear, clean sound. We must also understand the style of ministry of the church to know whether to concentrate on speech only or a contemporary music and drama style of worship. This determines how much horsepower we need to fill the space with sound. With all this considered, then we look at different brands of equipment to find the products that best fit the application. Again, pick the type of equipment we need first, brand second.  

Once the speakers have been selected and calculated to best fit the acoustical space most of the work has been done to get maximum gain before feedback. There are only a couple of more areas were we can get a pinch more microphone gain.

 

Step 3) Choose the correct microphones

 Remember that a microphone used with a typical PA system must be held very close to the mouth to be heard. Not a problem for pastors and vocalists with trained voices. But what about choir mics? What about mics placed out front for picking up the voices of drama and kids choirs? And to a lesser extent, what about lapel mics? How far are these mics from the mouth? From several inches in the case of lapel mics to several feet for choir and drama mics! When you move a mic away from a sound source the mic becomes less sensitive meaning you have to turn up the gain or volume to restore the amplifying ability of the system. When you turn up the volume you are in essence forcing the mic to Areach out@ to pick up the sound. What if your mic can=t Areach out@ far enough before you run into feedback? What causes feedback? The mic hearing itself in the speaker system. How do we stop a mic from hearing itself in a microphone? You can=t! You can only minimize the problem by carefully engineering your speaker system for the acoustical environment and by careful selection and placement of microphones. Keep in mind that every sound system on the planet will feedback at some point if turned up loud enough. Sound system engineers just know how to get the most gain so that you can turn up your system loud enough to pick up the choir or drama before you ever get to the point of feedback.

Keep in mind that designing a sound system is a combination of technical expertise and art. It takes years of practice to blend technicals with art to master the art of sound system engineering. The phrase "acoustically engineered" has become the latest buzz among salespeople. Often, this only means that they have some sort of software program that purports the best speaker system design thereby is a guarantee that their system design is infallible. Garbage.

The fact is we have all of the latest tools also. And they are just that. Tools. Tools are necessary to help round out the designers technical toolbox. But, it does NOT mean that those tools will show you how to automatically design a successful sound system no more than a mechanic owning the finest tools on the market will show him how to fix your engine! Learning to be a successful mechanic takes years of practice. So does the art of sound system design.

Now you know why our systems sound so good and why you will sound your very best.