For sound reproduction in large halls or in the open, you need loudspeakers with a high efficiency rating. This means that the electrical input has to be converted to sound output with the minimum possible loss. Since the mid- and high-range sound is dampened more than the bass sound as the distance from the loudspeaker increases, the frequency response of a speaker designed for this application has to rise as you move up the frequency scale. Otherwise, the speaker will sound dull at a distance.
The MB 212/H musician's P.A. system has the required characteristics and is therefore well suited to use in discos, as an outside small-volume P.A., or as a vocals and instrument speaker. The two powerful 30-cm musician's subwoofers run parallel up to around 4,000 Hz, at which point the robust, but neutral-sounding HTH 8.7 8 Ohm high-range flare takes over.
The following calculation shows how important it is to have the right efficiency rating for professional P.A. speakers: the MB 212/H speaker generates a mean sound pressure of 98 dB at 1 watt and at 1 metre from the speaker. At the maximum permanent load of 300 W, the maximum achievable at 1 metre is 123 dB. In the open, measured at 60 metres from the speaker, the level is merely 87 dB.
Suppose we were to use a normal hi-fi speaker with a high efficiency rating of 90 dB/1 W/1 m, it would take 1,900 watts (!) to achieve 87 dB at a distance of 60 metres. As you can see, no normal hi-fi speaker is in a position to achieve anything like the required compression-free sound output.
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