Table 182 Bandwidth of Various Loudspeakers

Type of Loudspeaker

Bandwidth (Hz)

1" Compression Driver 1.5" Compression Driver 2" Compression Driver 1" Dome Tweeter

1200-16 k 1000-12 k 850 -10 k 2000 - 20 k 700 -10 k 500 - 7 k 350 - 6 k 250 - 5 k 200 - 4k 150 - 2k 80 -1250 70 -1000

3" Cone Driver 4" Cone Driver 5" Cone Driver 8" Cone Driver 10" Cone Driver 12" Cone Driver 15" Cone Driver 18" Cone Driver

Low-Frequency Loudspeakers

When separate subwoofers are used as part of a sound system, the loudspeakers are most efficient if they are coupled to one or more reflecting surfaces no more than one-sixth of a wavelength away. Coupling can increase the efficiency and overall output. A bass loudspeaker is most efficient when placed on a solid floor near a wall or in the corner of a room. From a corner location the loudspeaker can excite all room modes since they all have pressure maxima at the corner.

If low-frequency drivers are located away from a wall and grouped together in a cluster, additional support for the bass cabinets can be obtained by constructing a baffle wall around them. To be effective the wall must be large enough to reflect all frequencies of interest and heavy enough to minimize diaphragmatic absorption.

It is particularly important in the construction of baffle walls to seal any openings between the wall and the loudspeaker cabinets. An opening around the face of the loudspeaker, along with the cavity behind, forms a Helmholtz resonator, which will selectively absorb sound at its resonant frequency. Thus if the baffle is not properly sealed, it can do more harm than good by creating notch filters in the frequency response.

Loudspeaker Systems

A range of reinforcement systems is shown in Fig. 18.4 and includes single and multiple clusters, overhead or column-mounted distributed loudspeakers, and pewback systems. In some cases a combination of clusters, point-source and distributed loudspeakers, can be used. The choice is strongly influenced by the architecture of the space. The main design considerations include adequate signal-to-noise, maintenance of the correct image, sufficient gain before feedback, and architectural sensitivity.

Distributed Loudspeaker Systems

A distributed loudspeaker system is one in which the loudspeakers are located more or less evenly throughout the space, most often in the ceiling. The direct-field coverage can be

Figure 18.4 Types of Sound Systems (Klepper, 1999)

Figure 18.4 Types of Sound Systems (Klepper, 1999)

Cluster

Cluster

Fewback Distributed System

Split Cluster

Split Cluster

Distributed Horn System

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