712 Chapter 24
Of these, the latter two are important, practical forms that have to be lived with. They
can in any event be made relatively quite effi cient by making the enclosure big. To some
extent, Colloms ’ law holds here: “ Loudness ( per watt or volt ) is inversely proportional to
bandwidth and smoothness. ”
This is fi ne until we come to consider the refi ned horn speakers, which do not attempt
50% effi ciency, and where a minimum of three types are needed to cover the audio band.
While at least 10 times more effi cient, there is little or no bandwidth narrowing over
ordinary speakers.
Compression and piezo drivers are those usually coupled to horns (fl ares) and may
need no other boxing or at least not any specifi c enclosure, as their rear chamber is
usually already sealed. Sound radiation is then mainly defi ned by the horn, subject to
mounting.
Ribbon drive-units may be also horn mounted or, if “ planar ” types, then along with ESLs,
they may be simply mounted in a frame that has little effect on the sound radiation, which
isdipolic , that is, two sided, like a harp’s.
The other two types of drive-units—the cone and soft dome—are usually mounted in
closed ( “ infi nite baffl e ” or “ sealed box ” ) enclosures or, in the case of cone drivers alone,
in ported ( “ Thiele-small, ” “ vented, ” or “ refl ex ” ) enclosures.
Cone drivers are also used “ coupled to ” horns—either midrange, or bass ( “ bins ” ). In
practice, as the rear of the cone’s basket mounting frame is open, and the fragile magnet
is also unprotected, cone drivers in bins and horns are almost always mounted inside the
overall enclosure.
Horns, transmission lines, sealed and vented boxes, and other loading types may form
complete loudspeakers in free permutation. Of these, only combinations of horns or
sealed boxes can cover the full audio frequency and dynamic range within their own
family, that is, without involving each other or the other types.
24.1.4 Loudspeaker Confi gurations: A Résumé
Few or no single loudspeaker drive-units offer overall, high-performance audio
reproduction. The nearest contender is an ESL or ribbon type panel, which can work as
the sole drive-unit for the kinds of music that have no loud, low bass content. But to listen