Crossover Network for Centre Channel Loudspeaker
Description of this page
This is a co-operative effort with my mate Bill from Subwoofer Builder to create a high accuracy centre speaker for his sound system. I built and tested the crossover network.
After looking at speaker specs, Bill settled on a pair of 165mm Polypropylene coned Woofers crossing over to a Jaycar 25mm Dome Tweeter through a fourth order Linkwitz network at 3.0 kHz. He designed the crossover from a calculator found at www.ajdesigner.com/crossover/crossoverfourth.php. The following drawing was emailed to me with a request to source the components with exact values. I measured the capacitance values in store with a hand held meter and re-checked all component values later against a Hewlett Packard 4262A LCR meter.
Capacitors were individually measured to bring the installed values within 1% of the calculated values. Inductors were unwound one turn at a time and measured. They are accurate within half a turn when measured on the LCR meter. When the Tweeter was measured, the samples I had showed an inductance between 30 and 35 uH at 10kHz, so a Voice Coil Inductance correction circuit of a 6.8 ohm resistor and a 0.82 uF capacitor was added across the tweeter output. Woofer Equalisation consists of a 3.4 ohm resistor in series with a 20.5 uF capacitor. The complete circuit was assembled on a piece of veroboard with the components close mounted onto vero pins. This allows the components to be glued down to prevent microphonics. Input/output cables of 45cm length were attached to complete the job.
Testing now evinced a sweeter sound with a suprisingly wide dispersion angle. The bass/midrange response will improve tremendously when the woofers are mounted in the enclosure. I expect the cabinet to be a tilted fascia floor mounted d'Appolito design (Woofer-Tweeter-Woofer) capable of supporting a TV. If this works out as planned, I might consider building a set for myself. This is my first experience with a fourth order Linkwitz crossover and I am impressed. The total cost for the crossover worked out at just over $110.00 for all the parts.
Circuit for the Crossover Network