Home   |    About Us   |    Projects   |    Services   |    Contact   |    Links   |    Articles    |    JSBP

"Helping You Sound Your Best"

Jordan Audio Consultants
THE CENTRAL CLUSTER: A Single Source Of Sound

    This audio revolution began in the late 1800's with Thomas Edison's phonograph. It used a needle and diaphragm to record and reproduce sound. All of that sound was amplified by using one horn. This is an excellent approach for audio systems -- monaural reproduction from one point of origin.
 

   Because the early compression drivers and horns had a very limited power handling capacity and volume level, churches and auditoriums strayed away from the ideal and began placing multiple eight or twelve inch speakers around the seating areas. In order for sound to reach all the seats in a large room, speakers had to be placed closer to the audience. The result was a louder system, but this one major advantage left many minor disadvantages.

    As improvements were made in loudspeaker design and manufacturing, both cone speakers and compression drivers developed to the point of being able to reproduce very high volume levels. Many different combinations of speakers were tried and marketed including a variety of column arrays, "tuned" enclosures, and some very interesting horns (some of these designs are still in use). For some applications the simple distributed eight inch speakers still remains the standard approach for sound reinforcement.

    When stereo "HiFi" systems arrived in the late fifties and early sixties, dramatic changes took place in how sound reinforcement systems were designed. Well intentioned but unknowing people reasoned:
"If I have two speakers on either side of my living room, and that sounds good, then two speakers on either side of a stage should sound good for an entire auditorium."

    This would at first appear to be true, except that all audio is bound to the basic laws of physics and these laws can not be compromised. In order for a sound reinforcement system to function at its optimum levels, it must present a uniform wave form in the listening environment. This means that all sound being reproduced, must be in sync.

    When two loudspeakers are placed on either side of the platform, there will always be an area or several areas (usually more than one third of the room) where the soundwaves arrive at different times. This difference of time is only a matter of milliseconds but it is enough to cause detrimental coloration of the sound, and cancellation at some frequencies. This is not true in home stereos because stereo is the reproduction of two separate signals, whereas sound reinforcement is reproduction of a single, or monaural signal.

    This time difference with its coloration and cancellation results in reduced levels of speech intelligibility, compromised music clarity, unusual tonal response, increased premature feedback and elevated listener fatigue. It is always disappointing and sometimes uncomfortable to listen to a program when in these effected seats. Since the split speaker type of system is so obviously the wrong approach, it raises the question of "Why do they do it?" especially when there are better solutions. The answer to this question may never be known (in this world.)

    A more proper approach to system design is -- one point of origin. For sound reinforcement in an auditorium, this would be an aligned central overhead cluster. This places the necessary loudspeakers together in one location and uses digital delay devices to compensate for the microsecond differences between the multiple speakers in their assigned listening areas. This type of system can more easily present a coherent wave front. This is important for the shorter (higher pitched) wavelengths where the difference is most noticeable and detrimental (as listed above.)

    When this type of speaker system is properly designed and installed with the correct speaker directivity, coverage and gain, the results are excellent for speech intelligibility, music clarity, tonality, and potential volume before feedback.

    It is also advantageous for the speaker cluster to be located overhead. The fields of physiology and psychology provide the reasoning for this advantage.   The human head, with two ears in a horizontal plane, most easily assimilates sights and sounds which are in different vertical planes. At the same time sights and sounds which are in different horizontal planes are not assimilated without constant effort both consciously and subconsciously. (This is what helps to induce listener fatigue.)

    In a sound system, the fact that all the sound for the room originates (or appears to originate) from the overhead central cluster means the properly controlled sound system will not be responsible for inducing unnecessary listener fatigue (depending on the mix prepared by the operator.)

    This results in the message being communicated better, and the audience not going away tired or disappointed in the artist or presenter because of the audio system.

        disclaimer:  Jordan Audio does design and endorse some other approaches to speaker placement for some applications and given situations, we consider the overhead central cluster an ideal to which other systems are properly compared.

© 1992, 2000,  2005 Jordan Audio Consultants