Getting "bigger" sound especially bass tones, from petite speakers enclosures has become something of an ongoing contest among many hi-fi companies. Right now the undisputed title-holder of the bantam-box-with-big-bass has to be the KLH-3.
Each speaker system in this stereo pair measures only 8 1/2 by 12 1/2 by 6 inches, and containes a 6-inch woofer and a 1-inch tweeter. Yet it can produce bass responsed to below 35 Hz, and its overall sound output level tops the 100-dB mark. In plain English, this is the kind of sound you might normally expect from a speaker system considerably larger than the KHL-3. It is well suited for stero coverage in rooms that themselves are larger than what might be thought suitable for really compact speakers.
KLH's "secret weapon" in this system is separate third box called an "analog Bass Computer." About the size of a cigar box, the "ABC" monitors the bass signal and automatically controls the vibrations of the woofer diaphragm in each system so that the in-and-out movement or "excursion" is ample for the response but not excessive to the point of distortion. In this way, the response of the woofer is said to be optimised in terms of its physical characteristics down to its designed low-frequency limit. The limit, in this case, is 30 Hz, below which the response is sharply reduced by a built-in filter. The ABC also provides some equalizaton of the bass, and it can compensate for "heaviness" above the bass when the speakers are located too close to large reflecting surfaces.
As might be expected, the KLH-3 cost more than most other small speaker systems, and its hookup into a stereo system entails a little more effort. The price of $450 gets you the two speaker systems plus the computer and a power-supply adapter. The ABC is patched into the stereo system between preamplifier and power amplifier, or via the tape-monitor faciltiy provided on integrated amplifiers or receivers. It also is connected to the outputs of the amplifier or receiver along with the speakers. Power for operating the Abc comes through its own line cord which is fitted with an adapter that gets plugged into an AC outlet.
The amplifier or receiver used in this setup should be capable of providing at least 40 watts power output per channel. Hooked up and adjusted as per instructions, the KLH-3 system does work "as claimed" -- it provides what is likely the best sound-to-size ratio on today's hi-fi market. Note, incidentally, that this petite prodigy also is fairly exclusive: once the KLH-3 system is running, you cannot at the same time operate other kinds of speakers from the same amplifier.