.
A "Mighty Midget" Is Smart, Too
-----
POSITION: WALL/FREE-STANDING
MONITOR (SOURCE/TAPE) "COMPUTER" IN/OUT
KLH-3 loudspeaker system
ANECHOIC RESPONSE CHARACTERISTICS (0-dBW input) HZ 20 50 100 200 500 1K 2K boundary-dependent region average omnidirectional response average front hemispheric response -- on-axis response
AVERAGE OMNIDIRECTIONAL OUTPUT (250 Hz to 6 kHz) 80 dB SPL for 0 dBW (1 watt) input 5K 10K 20K
CONTINUOUS ON-AXIS OUTPUT (at 300 Hz) 102 3/4 dB SPL for 17 3/4 dBW (59 1/2 watts) input
PULSED OUTPUT (at 300 Hz) 114.5 dB SPL for 29 1/2 dBW (893 watts) peak
"NOMINAL" IMPEDANCE 6.3 ohms
-----------------
KLH Model 3 loudspeaker system, in wood veneer cabinet; sold in pairs with Analog Bass Computer unit. Dimensions: 8 3/8 by 12 1/16 inches (front), 6 inches deep; computer, 2 1/2 by 10 1/2 inches (front), 6 inches deep plus clearance for connections. Price: $450. Warranty: "limited," five years parts and labor. Manufacturer: KLH Research and Development Corp., 145 University Ave., Westwood, Mass. 02090, USA.
A true bookshelf-sized loudspeaker, barely larger than the familiar mini format, the Model 3 is the smallest in KLH's computer-controlled line. A vented, two-way design, it incorporates a 6-inch combination woofer/midrange and a 1-inch soft-dome tweeter surrounded by acoustically absorbent foam to reduce high-frequency diffraction effects. The real story with this speaker, however, lies in the separate Analog Bass Computer that comes with each pair. Although speaker systems equipped with equalizer modules are not new (Electro-Voice and Bose have offered them for years), KLH's approach takes that concept a step further. Aside from its equalization function (completing the speakers' bass alignment, so to speak), the KLH "computer" acts as a sort of electronic motional feedback device, preventing high-level bass signals from driving the woofer's diaphragm beyond its excursion limits, thereby keeping distortion low.
The computer module is inserted either in the tape monitor loop or at the pre-out/main-in connections. (Tape monitor jacks are duplicated on the back of the module, and a TAPE button on the front panel restores monitor switching.) Wires marked LOUDSPEAKER MONITOR on the back must be connected in parallel with the loudspeaker outputs of the receiver or power amp. AC power for the computer is derived via a small transformer that plugs into a jack on the module's back panel. An IN/OUT button on the front panel bypasses the circuitry when speakers other than Model 3s are to be used. (KLH strongly advises against use of the computer with "standard" speakers, warning of possible damage to them. Therefore, running Model 3s simultaneously with a dissimilar pair of rear or remote speakers is ruled out.) There are no controls on the speakers themselves, and connection to the amplifier is accomplished with screw posts.
In operation, the computer accomplishes several things. First, it provides an equalized signal to the amplifier in accordance with the speaker's own performance characteristics. Second, it acts as a sharp high-pass filter, effectively cutting response below 30 Hz. Third, it provides low-frequency compensation for placement either against a wall or free standing. And, fourth, it suppresses signal elements that would represent woofer overdrive. When too great a low-frequency signal is present, the pre-programmed analog circuitry automatically modifies the response of the equalizer so that maximum displacement of the woofer is not exceeded, whatever the unequalized (preamp-out) signal. Awakening of the processor logic can be monitored visually on the module's front panel via two lights above the IN/OUT button.
A primary objective of this scheme is, of course, to wring as much bass as possible from a small enclosure. Judging from the measurements made in the CBS Technology Center anechoic chamber, the Model 3 proves that it has muscle as well as brains. With the POSITION control set for free-standing placement (away from bass-reinforcing walls), low-frequency output is strong and response quite flat and smooth above the characteristic bass hump. The alternate placement setting reduces bass output by around 5 dB below 60 Hz and progressively less as frequency increases. This reasonably efficient speaker handles power to hefty sound pressure levels (above 102 dB on continuous tones and 114 dB on tone bursts) before distortion becomes excessive. While these levels show that the Model 3 can be "played loud," the actual dynamic range does not extend to the super-loud peak capability of many contemporary speakers. Second and third harmonic distortion figures are low over most of the audible spectrum, averaging out to 1/2% from 100 Hz to 10 kHz at moderate listening levels (0 dBW). At high listening levels (100 dB), third harmonic distortion remains around the 1/2% figure, and the "softer" second harmonic rises a bit, to an average of some 2%.
In at-home use, the Model 3 acquitted itself nicely indeed. The sound is remarkably uncolored for such a small speaker. A polypropylene formulation (developed by the BBC) was used in the fabrication of the driver cones, and the sound in the critical midrange reflects KLH's claims that the material has superior anti-coloration qualities. Bass is also remarkably extended in these small speakers, and, try as we might, we could not hear the "attack" of the computer as it limited the low-frequency input. If anything, we found the quantity of bass difficult to balance against the upper range. KLH makes much of the necessity of good room placement to extract the best possible sound from the system, but shelf mounting seems mandated by the format. Even with the POSITION button pressed in (for back-to-the-wall placement), we encountered bass-heavy reproduction until we touched up the balance by trimming down the bass at our preamp.
Overall, the Model 3s are impressive performers. Stereo imaging is well defined and stable. The un-boxy sound combined with some midrange warmth makes them easy to live with. If you are short of space and seeking a superior small speaker, the KLH certainly should be on your audition list.
(High Fidelity, Jan. 1980)
Also see: