KEF R&D LS50 Meta LS50 Wireless II
CONTENTS CONT’D CONTENTS 1 Introduction 17 LS50 Wireless II 1 Philosophy 18 Overview 1 LS50 Meta 18 Inputs 1 Tweeter 18 Connection between Primary and Secondary 2 Metamaterials 19 Streaming support 2 Tweeter Metamaterial Absorption Technology 20 DSP Processing 4 Coupling the Absorber to the Tweeter Dome 21 EQ Settings 4 Tangerine Waveguide 20 Desk & Wall Modes 5 Tweeter Gap Damper 21 Treble Trim 6 Motor Design 21 Phase correction 7 Bass/Midrange 23 Bass Extension
Introduction “If I have seen further, it is because I stand on the shoulders of Giants.” This famous quotation, attributed to Sir Isaac Newton, illustrates how progress is made in virtually all scientific disciplines - progress is evolutionary, rather than revolutionary. So it is in the development of speakers and techniques developed for one model are carried through to subsequent designs and added to.
The most important innovation in this loudspeaker is the near-perfect absorption of the unwanted rear sound generated by the tweeter dome. One might legitimately ask, “Why is this important?” It’s true that, if the tweeter is listened to on its own without the contribution of the bass/midrange driver - and here we are talking of frequencies above about 3kHz - very little seems to come out of it. More revealing is to listen to any loudspeaker system without the tweeter connected.
Coupling the Absorber to the Tweeter Dome The absorber sits at the rear of the Uni-Q™ driver and is coupled to the tweeter dome by a slightly tapered conical duct, which acts as a waveguide. This waveguide passes through the centre poles of both the tweeter and bass/midrange drivers and has involved a complete redesign of the tweeter magnet assembly to accommodate the wider diameter required for the duct to work properly. The difference in the motor assemblies is shown in figure 9.
the back of the dome is directed into the metamaterial absorber. but also reduces non-linear distortions caused by air pressure changes behind the tweeter. As a tweeter moves in and out, it compresses and decompresses the air behind it. This negatively affects the excursion characteristics and linearity of the tweeter The larger the air volume, the lesser the effect. Also notable is the increased saturation of the steel components of the motor system.
the HF filter is on a separate board, placed well away from the LF filter. Crossover The topology of the crossover of the LS50 Meta is shown in figure 24. The smoother response of the new tweeter has resulted in fewer components in the HF filter and the remaining series capacitor (C1) is of higher quality. Figure 19 Bass/midrange blocked voice coil inductance against frequency. Figure 20b Bass/midrange voice coil inductance against displacement at 200Hz (figure 20a) and 2kHz (figure 20b).
Specification - LS50 Meta Appendix 1 - Cabinet Description Bookshelf Loudspeakers The cabinet construction follows closely that of the original LS50. Drive Units Uni-Q™ Driver Array LF/MF: Nominal dia. 130mm (5.25 in) magnesium/aluminium alloy cone HF: Nominal dia. 25mm (1 in) aluminium alloy dome vented with Metamaterial Absorption Technology (MAT) Frequency Range (-6dB) 47Hz - 45kHz Frequency Response (±3dB) 79Hz - 28kHz Sensitivity (2.
• There is more freedom on the rear panel compared to the front in positioning the port so it is placed close to nodes (nulls) of the resonances, so less energy is transmitted through the port. To illustrate this last point, figure 29 shows the difference in output when the port is placed at an antinode and at a node of an internal resonance. For the first of these measurements there is no wadding inside the cabinet, so the effect is made clearer. The resonance can clearly be seen in the total response.
The optimum dome shape for waveguide loading is a spherical cross-section, but the optimal shape for stiffness is an elliptical cross-section. Both were combined into the patented KEF Stiffened Dome. A one-piece elliptical dome and voice coil former is deep drawn and the centre removed. This is capped by a spherical dome and a very stiff triangular section is formed where the two parts join. Being within the human audio range, the breakup has to be tamed, rather than putting it out of hearing range.
References [1] M. Yang, S. Chen, C. Fu and P. Sheng, “Optimal sound-absorbing structures,” Mater. Horiz., vol. 4, pp. 673-680, 2017. [2] S. Degraeve and J. Oclee-Brown, “Metamaterial Absorber for Loudspeaker Enclosures,” 148th Audio Eng. Soc. Convention, 2020. LS50 Wireless II [3] KEF Research and Development, “R Series White Paper,” 2018. [4] KEF Research and Development, “The Reference White Paper,” 2013. [5] M. Dodd and J.
The following music streaming services are also supported (dependent on territory): Overview 4. Analogue stereo - Aux 3.5mm stereo jack socket Streaming support The active LS50 Wireless II incorporates all the technology described for the passive LS50 Meta, plus a few extras that either add to the presentation of the music - making it even more accurate - or add to the functionality. 5. Network - Wireless (2.
DSP Processing Phase correction Figures 44 & 45 show block diagrams of the electronics in the Primary and Secondary speakers respectively. All settings are controlled from the smartphone app and applied equally to both speakers. As stated before, the basic crossover introduces an allpass into the speaker’s response.
The result is that any phase correction in the crossover is only valid directly on axis. In fact, any blending at all of the two drivers suffers phase distortion off axis. This is how the output of the speaker would look with the phase correction switched OFF: Not so with a Uni-Q combination; the two drivers remain at the same point in space and have the same distance to the microphone, whatever the angle of measurement.
Should the subwoofer have an inverting amplifier (rare) or be sited well away from the LS50 Wireless II such that the output is not in-phase with that of the LS50 Wireless II at crossover, there is the option to invert the signal to the subwoofer. In this case the appropriate toggle should be set to ON. More usually it is set to OFF. The correct setting will provide a fuller sound.
Specification - LS50 Wireless II Description Wireless HiFi Speakers Drive Units Uni-Q™ Driver Array LF/MF: Nominal dia. 130mm (5.25 in) magnesium/aluminium alloy cone HF: Nominal dia.
