We wanted an enclosure large enough to deliver realistic low frequencies and scale but was small enough to be relatively discreet. It had to be low enough to sit below windows and work well close to walls.
Enclosure
The sculptured front baffle of KIM reducing in width from 300mm to 205mm around the AMT is to aid high-frequency directivity and minimise diffraction. Multi-layers of MDF panels glued together with a new unique damping adhesive form the front baffle, which is then precision CNC routed. The sides and rear of the enclosure utilise a similar technique, but the panels are only a single sandwich.
Bracing is one-dimensional to avoid the unnecessary spread of panel resonances common in modern loudspeaker designs. Designing for the lowest radiated energy is almost impossible without the benefits of laser interferometry and FEA.
Strunk absorbers are used inside the enclosure to remove standing waves. These Helmholtz resonators in anti-phase to the standing waves cancelling them without the deleterious use of masses of absorbent material.
Mid-Bass Driver
The trend since the 80s has been for slim loudspeakers, which has necessitated the use of smaller mid/bass drive units. The classic two-way loudspeaker went from being an eight-inch with a 19mm tweeter to a six and a half to a five or even four-inch mid/bass, and at the same time, tweeters generally moved to 25 or 29mm.
Materials technology and better adhesives have allowed massive changes to power handling, maximum excursion, and reliability, encouraging smaller drive-unit systems.
With KIM, we wanted to design a speaker we would use ourselves, forcing us in the direction of an 8inch mid-bass driver.
Similarly, as we said with the 10.25inch driver unit of Borg, a great 8inch will not beat a great 10.25 incher, but it can deliver a full range performance with only a small compromise on maximum SPL.
Unlike our previous bass and mid-bass drivers, we needed a sizeable half-roll surround to allow the excursion due to the smaller pulp paper cone. The softer rubber half-roll surround also terminates the cone correctly to eliminate colouration caused by energy returned to the cone from the cone surround.
From our learnings from Borg development, the mid/bass has an oversized magnet. This ensures a Q that is too low and which alone would reduce the low-frequency performance. Combined with the higher than convention resistance of the primary inductor feeding the driver, the Q is corrected, enabling the system to deliver clean, accurate in-room bass to 32Hz—a clever solution to using an air-core inductor for the lowest distortion.
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