Specifications: Four-way, six-driver loudspeaker system with coupled-cavity bass loading. Drive-units: 1" (25mm) soft-dome tweeter, 6.5" (160mm) polypropylene-cone midrange unit, 2x6.5" (160mm) polypropylene-cone lower midrange units, 2x10" (250mm) pulp-cone woofers. Crossover frequencies: 2.8kHz, 500Hz, 160Hz. Frequency response: 35Hz-20kHz ±3dB, -6dB at 32Hz. Nominal impedance: 4 ohms. Maximum spl: 118dB. Sensitivity: 92dB/W/m. Amplifier requirements: 50-400W.
Dimensions: 47.8" (1266mm) H by 11.8" (300mm) W by 15.3" (390mm) D. Weight: 108 lbs (49kg).
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Sidebar 1: Description
Sidebar 2: Measurements
JA measured the KEF Model Four using the DRA Labs MLSSA system and a calibrated B&K 4006 microphone and provided me with the results after I had completed my listening tests.
The KEF's calculated sensitivity measured a very respectable 90dB/W/m. Though this is slightly below specification, the fact that this figure is B-weighted might explain the difference. Its impedance characteristic is shown in fig.1. With a minimum impedance of 3.2 ohms at about 70Hz, and a notable increase in the phase angle below 20Hz, this is a relatively demanding load. The…
The impulse response on the tweeter axis is plotted in fig.6, the step response in fig.7. The Model Four's drivers are all connected with the same acoustic polarity, though the speaker is not time-coherent. The cumulative spectral-decay or "waterfall" plot is shown in fig.8. This is a very clean result, with noticeably less decay hash apparent across the spectrum than is usually seen. The only significant mode is associated with the on-axis rise above 10kHz.
Fig.6 KEF Reference 4, impulse response on tweeter axis at 50" (5ms time window, 30kHz bandwidth).
Fig.7…
Wood is not an engineering material. It might look pretty, but it's inconsistent and therefore unpredictable. So we smash cheap wood into sawdust and then glue it all together again to create something that can be machined. This is called medium-density fiberboard, or MDF. We then thinly slice some classy hardwood—hopefully harvested from sustainable sources—and use it to cover the ugly MDF. This might have made sense back when Chippendale was making furniture, but it seems strangely old-fashioned in our age of plastics and composites. I haven't seen wood trim on a TV set for more than a…
The tweeter is arguably the most interesting of the drivers. An original and creative variation on the dipole and tube-loaded themes, the whole assembly is roughly 9" deep and features a fat metal rod behind the diaphragm that's perforated by a logarithmic spiral of thin, differentially tuned pipes. The purpose is to create a flat acoustic impedance at the rear of the tweeter dome while also allowing through some noncoherent treble output to add air and spaciousness. The elegantly tapered rod is located within a rubber decoupling jacket and pokes some inches out through a hole in the back of…
Sidebar 1: Specifications
Description: Three-way, port-loaded, floorstanding, magnetically shielded, triwirable loudspeaker. Drive-units 1" Aspirated Tweeter Technology, aluminum-dome tweeter, 4" continuous-profile aluminum-cone midrange driver, two 6.5" continuous-profile aluminum-cone woofers. Crossover frequencies: 350Hz, 3kHz, damped second-order filters. Frequency range: 35Hz–32kHz. Sensitivity: 89dB/2.83V/m. Impedance: 4–8 ohms. Power rating: 15–250W.
Dimensions: 48" H by 9.5" W by 17.5" D. Weight: 66 lbs.
Finishes: Brilliant Silver, Granite Gray.
Serial numbers of units…
Sidebar 2: Associated Equipment
Analog Sources: Linn Sondek LP12 turntable, Rega RB1000 tonearm, Linn Akiva cartridge; Magnum Dynalab MD 102 tuner.
Digital Sources: Naim CDS 3, Burmester 001 CD players.
Preamplifier: Naim NAC552.
Power amplifiers: Naim NAP500, Yamaha MX-D1, Leak Stereo 20 (restored).
Loudspeakers: B&W N802D, Tannoy Kensington.
Cables: Naim Audio interconnects; Vertex AQ Moncayo, Chord Signature, speaker cables.
Accessories: Mana, Naim support furniture; Vertex AQ platforms.—Paul Messenger
Sidebar 3: Measurements
I estimated the Performance 6's voltage sensitivity at 88dB(B)/2.83V/m, which is slightly but inconsequentially below the specified 89dB. The speaker's impedance (fig.1) mostly ranges between 4 and 8 ohms, with a minimum value of 3.6 ohms at 33.5Hz. Probably the point hardest to drive lies at 27Hz, where a fairly low 5.2 ohms is combined with a –39.4° capacitive phase angle; fortunately, with the exception of classical organ recordings and some techno, music has very little energy in this region.
Fig.1 Mordaunt-Short Performance 6, electrical…
Going from being an audio hobbyist to a professional reviewer is like passing kidney stones in an emergency room staffed with Playboy bunnies: Not only can you not have what you want, but you don't even want it anymore. In fact, you begin to consciously associate desire with a blinding pain in your crotch.
And if you think I shouldn't whine about this cushy, cushy job, think again: There's nothing more brutally sadistic than to tease a man by dangling a never-ending stream of desirable but unobtainable worldly goods before him, only to snatch them away three months later and…
Again, where the Thortofon combo had trouble keeping up was in getting very subtle sonic details across. The timbral differences between, say, different kinds of electric bass guitars were much clearer and easier to hear on the Linn rig. So was the sense of air in a recording—not to mention bumps, groans, crashes, and other noises in the studios.
And, yes, because bass notes were clearer in their attack/sustain/decay entireties, the pacing of some music was snappier with the Linn—although the Thortofon was hardly terrible by comparison, and was certainly less ponderous than, say, your…