As its size is increased the loudspeaker becomes more directional. Directivity control is mandatory in all audio systems, and the more control that is needed, the larger the loudspeaker must be. That’s just how it works.
Another reason for large loudspeakers is low frequency efficiency. Systems in many houses of worship are expected to produce very high sound pressure levels at very low frequencies.
This means that lots of air must move, which in turn requires a lot of piston surface area. There is simply no way to get high sound pressure levels in large rooms at low frequencies without a large loudspeakers—often used in multiples.
Each successively lower octave requires more radiating surface area. If you really do expect to reproduce thunder claps during the Easter musical, or the lowest pedals on an electronic organ, you had better plan on a very beefy low frequency loudspeaker system. It has to be big, and it has to be in the room.
Sound Problems
Many of the typical sound system ailments – lack of definition, muddiness, dullness and poor localization can be caused by reflected sound. Many of these detrimental reflections result from efforts made to disguise the loudspeaker.
Reflected sound is a part of life. We expect it, we use it, we need it. But not all reflections are good. The two types of reflections that sound designers try to avoid are those that come from objects very near the loudspeaker, and those that come from objects very distant from it.
The former produce colorations of the sound, the latter produce echoes that can garble the clarity of music and speech. Any attempt to disguise a loudspeaker invariably produces early reflections that change the loudspeaker’s response. This includes grills, fabric coverings, and cavities that were carefully designed to be aesthetically pleasing. In short, what makes a loudspeaker look better potentially makes it sound worse.
A careful and thoughtful design process is required to allow loudspeakers to be covered yet still perform acceptably.Unlike light waves, sound waves can cancel each other if the timing is appropriate. This is not always a bad thing.
Sound system designers use constructive and destructive interference to achieve the desired radiation pattern from a loudspeaker array. Good sound designers understand interference and how to use it to enhance the performance of a system.
Let’s look at some methods used to reduce the visual impact of loudspeakers.
Coverings—Grills always obstruct sound. The only questions are “How much?” and “Will it be audible?”
I have seen system designers go to great expense to extend the frequency response of the sound system to beyond 20 kHz, only to hide the whole thing behind a grill that is acoustically opaque to this part of the spectrum.
But even without the grill, there is little chance of sound energy above 16 kHz making it to anyone in the audience due to air absorption alone, so we can live with some fabric in front of the loudspeaker.
The fabric, of course, will require a frame. The frame is potentially more obstructive than the fabric that it supports. Frame members should be made as small as possible, and ideally not placed in the main path of the system’s high frequency drivers.
Cavity Placement—The worst place to put a loudspeaker is in a cavity. The loudspeaker itself is a carefully tuned resonant system. It’s size, volume, and openings are carefully selected to produce a desired response.