KEF R&D KC62
CONTENTS 2 Introduction 2 Philosophy 2 KC62 2 Compact Subwoofers 2 Hofmann’s Iron Law 3 3 Technology Uni-Core Driver Array 3 Force Cancelling/Dual Voice Coils 4 Matching Driver Behaviour 5 Inductance 6 P-Flex Surround 7 Smart Distor�on Control Technology 7 8 Hybrid Control Systems Aluminium Cabinet 8 Vibra�on Control 8 Thermal Management 8 Frequency Response 9 Conclusion 9 References 10 Specifications
KC62 front (Mineral White finish, top) and side (Carbon Black finish, bo�om) ₁
Introduc�on Designing a small, high-performance subwoofer is difficult. There are compromises to be made in regards to output and extension. With the KC62 Uni-Core subwoofer, KEF engineers have developed three new patent-pending technologies that work together to deliver a higher level of performance in all aspects at the form factor. This paper discusses these new technologies, and other features, as well as giving insight into KEF’s philosophy on subwoofer and loudspeaker design.
Consider the modern string family of musical instruments - the violin, viola, cello and double bass. Table 1 shows the lowest notes that these instruments will play in their standard tuning, along with the frequency of that note - the violin being the highest pitch, through to the double bass as the lowest. It should also be no�ced that the size of the instrument increases as the frequency of the lowest note it can reproduce decreases (Figure 1).
Force cancelling provides two major benefits - firstly, as driver mo�on exhibits Newton’s Third Law -every ac�on has an equal and opposite reac�on - the driver’s mo�on To achieve force cancelling, one voice coil in the UniCore arrangement has been wired in inverse polarity due to the shared magne�c flux direc�on. causes mechanical vibra�on in the cabinet. Having an iden�cally performing driver placed in opposi�on cancels out the reac�on force of each driver - hence the term ‘force cancelling.
BL is the product of the magne�c flux density in the voice coil gap (B) and the length of wire in the gap (L). In Uni-Core, the larger diameter voice coil has a larger amount of wire in the gap. However, the structure of Uni-Core naturally accounts for this. In the single motor system design of Uni-Core, both sides have approximately the same magne�c flux passing radially through the motor gap. However, due to the different coil diameters, the area through which the flux passes is different.
The red curve shows the inductance of a pair of parallelconnected back-to-back conven�onal drivers with a simple ring ferrite motor and no aluminium or copper conduc�ve rings, and with the coil held at the rest posi�on. The inductance is plo�ed against frequency and is maximum at low frequencies, then reduces as frequency increases due to the effect of eddy currents flowing in the motor steelwork.
Smart Distor�on Control Technology There are numerous mechanisms whereby distor�on is introduced into the radiated sound. An ideal loudspeaker would exhibit the following: • BL(x) stays the same at all coil posi�ons • The s�ffness of the suspension is consistent across the excursion • The s�ffness of the internal air volume does not change as the driver moves back and forth • Voice coil inductance should not modulate with coil posi�on Figure 9.
The DSP por�on of the system uses an inverted numerical model of the loudspeaker, pre-programmed with the driver parameters, which pre-corrects the DSP output signal such that the added distor�on counteracts distor�on generated by the drivers. Simultaneously the instantaneous cone mo�on is indirectly sensed from the electrical current in the driver coils, and this signal is used in a feedback loop within the amplifier electronics.
Conclusion Through significant References new technological advancements and considered engineering, KC62 delivers an unprecedented combina�on of depth, detail and output from an ultracompact form. By pushing the boundaries of what has been considered [1] J. Wright, ‘Finite Element Analysis as a Loudspeaker Design Tool’, presented at the Audio Engineering Society UK 13th Conference; Microphones and Loudspeakers, Mar. 1998. [Online] Available: h�p:// www.aes.org/e-lib/browse.
Specifica�on Model KC62 Design Uni-Core Force Cancella�on Drive units 2 x 6.5 in. Frequency response 11Hz - 200Hz Max output 105dB Amplifier type Built-in Class-D Amplifier power 1000W RMS (2 x 500W RMS) Variable low pass filter 40Hz - 140Hz, LFE Input RCA Phono sockets Speaker level inputs Line output RCA phono sockets Line output high pass filter 40Hz - 120Hz, Bypass Power requirements 100 - 240V ~50/60Hz Power consump�on 1000W Weight 14kg (30.
Control panel of KC62 KC62, Carbon Black ₁₁
