Equipment Reviews ,..: • a • •,• • • 1 ....

Manufacturer: Rola Celestion Ltd., Ditton Works, Foxhall Road, Ipswich, Suffolk IP3 8JP. Price: £250 per pair.

THE development engineers at Celestion have been living a double life for the past couple of years. On one level they have been maintaining, and adding to, their popular Ditton range of loudspeakers. The most recent models under this heading are the Ditton 100 and Ditton 110 (£69.90 and £89.90 per pair respectively). These low-priced compacts are nevertheless of decent sensitivity and can be seen as pursuing the policy adopted by all the other major UK loudspeaker manufacturers of producing attractive alternatives to the usual run-of-the-mill speakers offered as part of the music-centre or rack system package.

At the same time, however, the Celestion laboratories have been busily applying their laser interferometer/computer techniques to a fundamental reappraisal of loudspeaker design. My colleagues JG and GH and I have been keeping an eye on these developments (see report of our visit to Ipswich in the November 1980 issue, page 764). By scanning the vibrating diaphragm with a laser beam, Celestion have been able to derive a continuously moving high-definition image in three dimensions. This has provided evidence of all sorts of shortcomings in conventional speaker design, including irregularities in the cone/ surround glue joint, lead-out wire colorations, dust-cap distortions and coil/cone junctions. Countless investigations in each of these areas have enabled the engineers to diminish the sources of error, and almost always led to a simpler, rather than more complex, construction.

The SL6 loudspeaker is the first product to put all this research together and, though we were asked to keep mum about it, we did already hint that something special was coming from this company in our reports of the 1981 Chicago and Harrogate exhibitions where prototype SL6s were demonstrated privately. Though it is of not much more than mini proportions, at 370 x 200 x 255mm, the SL6 has a superior specification under every heading and seems certain to attract critical acclaim on both sides of the Atlantic.

Everything about the SL6 is new. The drive units are Celestion designed and built—other manufacturers often buy in from some other source.

SPECIFICATION AND TEST RESULTS CELESTION SL6 LOUDSPEAKER

The 32mm metal alloy dome tweeter is made by a process which ensures uniform diaphragm thickness, symmetry and mass. The voice-coil is actually wound directly on to the dome, avoiding former aberrations, achieving more closely coupled drive and, incidentally, causing the dome itself to act as a heat-sink and give higher power „ 32 Al All ig 18 1161E111 MO1111111111111111111111 ,2 5111111•11111111111111112M 0E 50 100 200 500 1k 2k 5k 10k 20k Frequency (Hz I

Fig. 1. Impedance/frequency curve handling capacity. The dome surround is ultrathin. The 165mm bass driver is equally unusual. Instead of a dust-cap attached at the cone centre, there is a moulded 'terminator' and this, together with the non-glued long-throw cone/surround construction, produces a unified piston-like motion up to large amplitudes. Using a one-point connection for coil, cone, suspension and lead-out wires has avoided decoupling problems, and the total design is claimed to handle up to 100 watts without the need for built-in protection devices. The simple four-element crossover network operates at 2.3kHz.

The cabinet is beautifully veneered on four sides. The back panel has a deep recess for the connecting posts which can accept rugged spade terminals or 4mm plugs (two pairs of each are supplied, along with self-adhesive rubber feet). The enclosure panels are of 20mm thick board and there is substantial internal damping. The cabinet has a sealed back and each driver is mounted on a black, ribbed metal panel for maximum rigidity and sensible scattering of diffracted sound. The instruction booklet has helpful hints on speaker positioning on shelves, wall brackets or (preferably) 38cm high floor-stands. Removing the stout-framed brown grilles is recommended for serious listening, and amplifiers rated at between 35 and 100 watts rms are suggested. Individual frequency plots of the two speakers are supplied, and a list of recommended recordings.

Coupled to a high-quality disc and tape system, and compared scrupulously with other loudspeakers having the highest credentials, the Celestion SL6 never failed to please. My first impressions were of a quite unique clarity and top-end smoothness. This had a beneficial effect on practically every type of sound source—strings, brass and percussion—and the voices of BBC announcers were surprisingly free of the spitting and booming effects heard on many loudspeakers. Indeed naturalness was a recurring characteristic, with the advantage of good articulation and—a related effect when everything else is right— precise stereo imaging.

Tests with white noise confirmed the good basstreble balance with only a barely detectable restriction in the lower-middle register. Thirdoctave response plots in normal room conditions agreed with the specification of only 6dB down at 60Hz, and showed otherwise the gentle downward slope on axis from middle to high frequencies which I recognise as consistent with the most realistic-sounding loudspeakers. The impedance plot (Fig. 1) shows that amplifier matching at 8 ohms will present no problems. Sensitivity is only a little below average and of no significance if an amplifier rating at the recommended 35 watts-perchannel or over is available. High sound levels are achieved without distortion—up to reasonable limits.

This is a compact loudspeaker which does not sound small. It easily out-performs many other loudspeakers at around the same price— regardless of size—and so the price of £250 per pair, which at first looks a little uncompetitive, suddenly turns out to be very good value indeed. How nice it is, when digital sound is soon to be a reality, to find a loudspeaker development that is ready for anything that the 1980s can bring in the way of source improvements. JOHN BORW1CK.