KEF Reference Series 103/4 loudspeaker Specifications

Sidebar 3: Specifications

Description: four-driver, three-way, floorstanding loudspeaker with "Conjugate Load Matching," "Coupled-Cavity" bass loading, and optional, line-level equalizer. Drive-units: two 6.5" (160mm) fiberglass-reinforced, pulp-cone woofers, one 6.5" (160mm) "Uni-Q" midrange/tweeter with concentric 1" (25mm) soft-dome tweeter. Crossover frequencies: 3rd-order at 160Hz, 5th-order at 2.5kHz. Frequency response: 50Hz–20kHz, ±2.5dB, –6dB at 38Hz (measured at 2m on reference axis). Sensitivity: 91dB/W/m (2.83V RMS input, band-limited 50Hz–20kHz, anechoic conditions). Nominal Impedance: 4 ohms. Amplifier requirements: 50–200W into 4 ohms.
Dimensions: 35.5" (900mm) H by 8.5" (215mm) W by 12" (305mm) D. Weight: 40 lbs (18.1kg).
Serial numbers of units tested: 002693 A&B.
Price: $1800/pair in walnut, black ash, or rosewood veneers.

KEF Kube 200: Active Equalizer providing fixed/variable EQ. LF contour: continuously variable shelf control, +4 to –6dB, centered at 160Hz. HF contour: continuously variable shelf control, +4 to –6dB, centered at 1kHz. Input impedance: 51k ohms. Maximum input voltage: greater than 1.9V RMS above 20Hz, greater than 8V above 50Hz. Maximum output voltage: greater than 5V RMS. Output impedance: 100 ohms. S/N ratio: greater than 104dBA ref 1V RMS. Distortion: <0.005% for 1V RMS input at 1kHz.
Dimensions: 2.6" (65mm) H by 5.6" (152mm) D by 9.2" (234mm) D. Weight: 2.87 lbs (1.30kg).
Serial number of unit tested: 002739.
Price: $400.

For both products: Approximate number of dealers: 300.
Manufacturer: GP Acoustics (UK) Ltd., Eccleston Road, Tovil, Maidstone, Kent ME15 6QP, England, UK. US distributor: KEF Electronics of America, Inc., Colonial Heights, VA 23834 (1992); GP Acoustics (US) Inc., 10 Timber Lane, Marlboro, NJ 07746. Tel: (732) 683-2356. Fax: (732) 683-2358. Web:

US distributor: GP Acoustics (US) Inc.
10 Timber Lane
Marlboro, NJ 07746
(732) 683-2356

kensargent's picture

I think what you mean is something other than that the woofers in the KEF 103/4 operate IN phase. For there to be any pressure generated in the central chamber, and thereby generation of any velocity at the port, the drivers must be OUT of phase, both electrically and mechanically. That is to say that as one of them moves away from its' frame, the other moves toward its' frame. As a result, the pressure in the central chamber is increased in one half of a cycle, and decreased in the other half of a cycle. This is the actual arrangement that would create the situation you describe: when the pressure is at maximum in the central cavity, it will be at minimum in the opposing cavities at the ends of the enclosure.

The rod connects the woofers' frames, surely, as this arrangement would, in fact, reduce vibration as the manufacturer states, but only if the cones were moving opposite each other. If the woofers were moving in phase, the rod would serve only to equalize, or average, the vibration, but not reduce it.

There are some arrangements in professional loudspeakers that put the woofers out of phase both mechanically and electrically, on an ordinary baffle, with one facing into the cabinet (front-loaded) and one facing out (rear-loaded.) In this arrangement, the advantage is said to be a cancellation of nonlinearities caused by the woofers' suspension, with the result reportedly being measurably lower distortion.