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Magic TRIck

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Multichannel active loudspeaker system

Main loudspeakers of the Magic TRIck ver. 3. These were controlled directivity speakers with a 20” midwoofer and a ring radiator in a waveguide. They were designed as fairly big bookshelf loudspeakers and equalized for such a type of operation.


Magic TRIck revision 3 front panel. First beats of Haendel's Messiah creates a display bar for controlling volume and other adjustments.


Analog Signal Processor boards (the set of active filters and equalization circuits well known from Linkwitz’ projects) driving eight LM3886 power amplifiers. Every loudspeaker in this system is directly driven by its own power amplifier. Tweeters and midwoofers are helped by four subwoofers (multisub system a ’la Geddes style). Such an active multichannel system can sound really well. Not quite magic, but close.


Magic TRIck will soon change into 3 main channel system for stereo program reproduction. Michael's Gerzon 3x2 Optimal Reproduction Matrix for multispeaker stereo is to be implemented in the Analog Devices ADAU1701 DSP chip. Pretty sophisticated project made fairly easy:


Trifield decoder implementation in the Analog Devices’ Sigma Studio software. No special programming skill is necessary, as the decoder is built of predefined blocks and connections among them. Some blocks, however, will have their parameters set up by a microcontroller.


Vifa XT25TG30 ring radiator tweeter has a fairy low open-air resonance frequency and therefore is a good candidate for a big waveguide. This is the circular waveguide with a conical main section and a gentle flare of a circular radius to blend the conical section to the baffle and to avoid nasty wave diffractions. The Vifa driver was to operate above 1000 Hz and the waveguide equalization was made actively in the ASP board (Magic TRIck v3).

Nearfield measurement of the Peerless SLS-213 driver in a 24-litre sealed cabinet. This woofer speaker is a part of the Magic TRIck v4 multi-sub configuration.

Magic TRIck v4 woofer cabinets under construction.

The crossover frequency between the Peerless 20” midwoofer and Vifa ring radiator built into a waveguide was set to 1 kHz. This was rather a daring idea to set this point in the middle of the critical mid-frequency range, but many well-regarded waveguide designs encouraged me to try such a solution. Indeed it sounded quite well and also measured well. The midwoofer was working in a sealed 22 litre enclosure and was actively equalized to achieve Qtc=0.5 and bottom frequency of 25 Hz (-3 dB).

Vifa XT25TG30 ring radiator and the inner side of its waveguide. Thanks to low resonance frequency of the tweeter and big diameter of the waveguide the driver is capable to radiate effectively from roughly 1 kHz.