Dunlavy Audio Laboratories SC-IV loudspeaker Singer's Corner
The term "loudspeaker" is something of a misnomer. Literally, it refers to the amplification of speech (footnote 1), and only at high levels. However, a high-fidelity "loudspeaker" is used mostly for the reproduction of music, and at levels that vary from soft to loud. Rather than functioning like a "speaker," the device is more like a "singer." In fact, I think the analogy between singing and music reproduction by loudspeakers has some interesting implications.
A trained singer (footnote 2) has to have a range that encompasses all music written for that voice category (eg, soprano). Similarly, a loudspeaker has to have a range wide enough to reproduce all types of music. Other things being equal, singers with wider ranges are "better," in the sense that they're able to handle wider ranges of music—a bass singer who can't sing anything below a G is handicapped when it comes to much of the repertoire.
Similarly, a loudspeaker that has a weak frequency response at the bottom end is not suitable for reproducing organ music. A singer may practice vocal exercises that are aimed specifically at extending the top or bottom of the range, but it's well-known among singers that if you work a lot at the top, the bottom of your voice tends to get weaker, and vice versa. It's rare to find a bass-baritone with an impressive top who has an equally impressive bottom, just as it's rare to find a speaker with equally strong performance at bottom and top.
Assuming that the singer has a wide range, we can then ask questions about the character of the sound in different parts of the range. Good singers and good loudspeakers must first have a pleasing quality in the midrange, a quality that both singers and loudspeaker designers try to extend up and down the range. The singing voice has different "registers" (ie, chest vs head); ideally, the transition between registers should be so smooth as to be undetectable.
A loudspeaker, too, has different "registers": woofer, midrange, and tweeter. These also have to be blended so that the listener is not aware that different sounds are being produced by different drivers. For the singer, one of the most difficult areas is the passagio, the transition between registers. For the loudspeaker designer, one of the most difficult areas is the crossover, the transition between drivers.
Then there's the matter of loudness. A singer must be able to sing loud enough to be heard properly by every member of the audience in the hall; the loudspeaker must produce sound that listeners judge as sufficiently loud. Some singers can sing very loud without sounding strained; others have a much more restricted maximum volume. Ditto for loudspeakers. Typically, a singer with a big sound will have difficulty singing softly, may have a narrower range, or can't negotiate the fast vocal turns required in some music.
Loudspeakers capable of producing very high volumes usually lack finesse at low levels, may be restricted in range (eg, deep bass is missing), and their ability to follow the music's quick dynamic turns is usually not optimal.
There are singers who have great beauty of tone and vocal agility, but not much power—much like the best minimonitors of the loudspeaker world. It takes a rare singer—eg, a Joan Sutherland—to offer tonal beauty, range, agility, and power. It's just as rare to find a wide-ranging loudspeaker that well communicates rhythm/pace, and can play loud.
Footnote 1: Of course, the term is derived from the early use of these devices to do exactly that.—Robert Deutsch
Footnote 2: I'm talking about classical singing, although many of these principles also apply to pop, folk, jazz, and rock singing.—Robert Deutsch