Beaming Up

Loudspeaker technology has followed a long and steady evolution since the days of Western Electric. Most of the commonly used transducers do not look very different from those early designs. What has changed dramatically is the level of control we can now exert over the signals that reach each transducer in a loudspeaker array. That control may be the defining change in sound reinforcement, as we near the end of the first century of its development.

The underlying development of transducers has primarily been the changes in materials that are used to create and manufacturer the devices. However, the physical constraints that control their acoustical behavior remain far more restrictive. While there has been some excellent work in horn design over the past two decades, the combination of multiple devices to form a single loudspeaker array have remained a compromise. Even when the high frequencies were carefully controlled, the low-frequency energy was prone to destructive interference due to the inevitable physical offset that results from the size of the transducers, themselves.

Enter the very versatile DSP-based loudspeaker processor. Where budgets allow, this flexible signal manipulator can alter the timing and spectrum of the signal for each transducer to create a far more homogeneous acoustical output from a complex array of devices. As I have discussed in previous columns, this provides a method to develop pattern control even at very low frequencies. Taken even further, this approach can create broadband pattern control that may offer solutions in venues that were out of reach for conventional loudspeaker approaches.

There are sports facilities and churches that fall outside of the capability for even the largest horns (should the owner even allow such highly visible loudspeakers) to achieve good speech intelligibility and adequate coverage of all the listening areas. The rooms are too large and reverberant to make reinforced speech clearly understood in every seat. These spaces have had to make do with compromises, and in many cases a long series of "new" sound systems have tried to address their needs. Extraordinary measures are required to reach these listeners from a sound system. This calls for an array that may only have a few degrees of vertical dispersion. Just enough to graze the ears of the listeners, while it refrains from sending any direct sound to the floors or ceilings of the room.

This is an area where the imagination of the array designer may be as limiting as the transducer technology. The laws of physics will still apply, but creative application of basic principles can yield surprising results. Developments of this type are likely to force more of the loudspeaker manufacturers to take an interest in manufacturing everything from the line level input to the component's cabinetry. They need to be able to control the audio signal and the relationship of the loudspeaker components if they want to exert the full power of this design approach. There are a number of manufacturers that will be exhibiting forms of "shaded arrays," ranging from vertical line-arrays to beam steering in touring-style formats.

Significant developments have been taking place in Europe, as well as in North America, which deserve a good audition. We have read of completely new transducer technologies, such as ultrasonic sound projection, but it may be in the careful control over signal (sent to more conventional loudspeaker drivers) that we finally hear profound clarity in even harsh acoustical environments. The 105th AES convention, in San Francisco, should provide an excellent opportunity to see (and perhaps even hear) some of the latest developments in this marriage of signal processing and loudspeaker technology.

United Entertainment Media Inc.
460 Park Avenue South, 9th Floor
New York, NY, 10016
Ph. 212-378-0400
FAX 212-378-2160

page construction