Introduction and Overview
The KEF Reference Series 209 subwoofer is a ‘state of the art’ subwoofer for use in the very best home theatre and stereo systems. Every component is critically designed to give optimum acoustic performance in a compact, elegant enclosure. The key components in the 209 subwoofer are the drive unit, the amplifier and the enclosure – all three of these contain innovations that make this model a class leader.
The 18” (450mm) drive unit is designed to give 60mm (peak to peak) of linear excursion. The magnetic field, which powers the motion, is constant over that region.
The magnet system is a radically different design from that found in conventional loudspeaker drivers, it has been designed by KEF from the ground up using advanced
computer modelling techniques to predict the behaviour and orientation of the internal magnetic field. Unlike conventional drivers the Reference 209 magnet system uses a series of 24 neodymium magnets radially arranged around the voice coil of the driver. This unusual topology allows the unit to have a remarkably long range of motion while maintaining a very strong magnetic field around the voice coil. Together with a double suspension and massive roll surround this allows high levels of bass to be reproduced with very low distortion - giving a sense of power and clarity not normally found in high end subwoofers.
The amplifier section is custom designed to get the very best out of the new drive unit. A 1000W class D power amplifier with switched mode power supply allows top end performance in a neat and tidy package. In addition, the front end incorporates Digital Signal Processing (DSP) which is used to provide comprehensive equalization options and an innovative room acoustic correction system (see page 9 for an overview and page 23 for operation guide).
The enclosure is beautiful on the outside and highly technical on the inside. Attached to the inner surface are 30 ‘ACE’ modules - tubes of activated carbon which increase the effective internal acoustic volume by a factor of 2. ACE technology
(see page 8) is KEF’s solution to the oldest catch 22 in loudspeaker design – that to get good bass extension with good efficiency you need a large enclosure. The Reference Series 209 subwoofer gives the kind of bass extension normally found in subwoofers twice the size.
This subwoofer is specifically designed with bass speed and articulation in mind, because of this we chose to make the subwoofer a closed box design. A closed box design does not rely on the resonance of port or passive radiator for output. All sound radiation is from the 18” driver the motion of which is carefully controlled and damped by the amplifier and large magnet system, there are no port resonances to continue ringing after a sudden bass event. Additionally it is not possible to recreate extreme low bass output with a ported system,
which cannot radiate below the port tuning frequency.
All this technology is neatly packaged in an elegant enclosure with straightforward connection options and an easy to use remote controlled user interface.
You can run the Reference Series 209 subwoofer with the default ‘switch on’ settings or experiment with the DSP based equalisation options to fine tune it to your particular system setup.
Line level or high level speaker inputs are available to allow flexibility in
For ease of use and installation the subwoofer is equipped with an IR remote control allowing for easy adjustment of subwoofer level, cut off frequency and phase from your listening position. A microphone is also included to allow the subwoofer to measure the sound produced within your room and compensate for abnormalities using integrated room correction algorithms.
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