Introduction

Mirror Xover is digitally controlled analogic filter for subwoofer and two main channels. Device is designed to meet high quality standards. It is easy to use and nice to watch. Every function can be remote controlled.

Filter was done as a project work at Electronics design course. Project team was Kari Hakanen, Petri Keski-Opas, Arto Kolinummi and Jussi Mikkonen.

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Filter Functions

Filter is mainly designed for stereo use so there is two main channels and one LFE channel which can be summed from main channels or use separate channel. LFE channel has two outputs with differential output and phase control.

Main channels have second order Bessel highpass with crossover frequency adjustable from 30 to 140 Hz. LFE Butterworth lowpass has same range. LFE-channel has also level control, subsonic and boost. Level can be controlled from -10 to +10 dB. Boost at 20 Hz affects 6dB at its maximum. Subsonic is fixed third order Butterworth at 16 Hz.

Enclosure and Interface

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Filter enclosure is mainly made of proncemirror and copper. Front plate as well as wheel and buttons are copper. Internal structure is made of aluminium. Filter is inside another aluminium box to diminish EMI disturbances from digital control electronics.

Interface is made very easy and logical to use. All changeable parameters are easily available in menu and can be selected using wheel or remote control. Setting new values is done with pressing wheel once and rotating the wheel clockwise or counterclockwise. Value as well as parameter name are showed in the display. Remote teaching menu can be selected with leftmost button behind a hole in front plate. Settings can be saved to memory keeping memorybutton pressed over 4 seconds. Similar procedures are used in car audio equipment.

Filter Protection and tolerances

Filter has heavy ESD-protection, overcurrent and overvoltage protections both at inputs and at outputs. Filter is excessively shielded from EMI with two layer aluminium box. Interference with digital card is no problem because digital signals are used only when settings are chanced. Power supply has 55VA toroidal transformer with separate secondaty wounding and regulators for digital and analog parts.

All the adjustments have about 256 steps and are software compensated so that measured and displayed value are close to each other. Tolerance in cross-over is about plusminus 2 Hz.

Filter was measured with appropriate measurement equipment and parameters are attached at the technical data.

Remote control

Mirror Xover was made remote-controllable for easy chance of predefined settings. Unique in Xover is that receiver can be teached rather than transmitter like usual. That is why there can be used any confortable transmitter. IR-receiver works fine with all remote controllers tested so far. Remote control makes it easier to tune system correctly from listening point. Display has large letters so that text can be read from some distance. All the Xover controls can be teached and it is made very easy.

Confortable way of using this teach ability is to use random buttons from transmitter while tuning the system. When satisfied, settings are saved to memory places 1-3. After that channel selection buttons of pre-amp remote control are teached to Xover memory selection buttons, so that every time you switch for example from CD to video, Xover settings are updated too. So you can have different crossover settings for different music materials without any extra keys to be pressed.

Technical data

Operating voltage 230Vac, 50Hz
Power consumption typ 10W, max 30W
Size (H x W x D) 11 x 30 x 30 cm
Weight 5,5 kg

Line connections:

Input impedance 50 kohm
Output impedance 470 ohm
Frequency response (± 0,5dB) 15Hz - 60kHz
THD @ 1 kHz < 0.002 %
Signal to noise ratio (0 - 20kHz, 3V) 105 dB

Functions:

Lowpass cut-off (4th order Butterworth) 30Hz - 140Hz
Highpass cut-off (2nd order Bessel) 30Hz - 140Hz
Subsonic (3rd order) 15Hz
Subwoofer level ± 10dB
Subwoofer boost (@ 20Hz) 0dB - 6dB
Phase shift (LFE B) 0°/180°