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High Fidelity

Centre Crossover

A. Design
B. Listen
C. Specs
D. Crossover
E. Components


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Worthingtons Workshop

High Fidelity

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.

The completed Circuit Board

Testing the Crossover

A. Design of the Speaker

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.

B. Listening to the Speaker

The project is still not complete as my mate has not yet built the enclosures. When the crossover is delivered, the enclosures should be complete and the results ready to post on the web site. Initial listening tests in the workshop with a set of similar Jaycar 5" Polypropylene drivers demonstrated a seamless crossover to the tweeter, although the woofers sounded a little harsh. This was corrected when the Voice Coil Inductance equalising network was introduced across the woofer output.

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.

C. Specifications of the Speaker

Specifications : Two Way d'Apollito design Bass Reflex
Enclosure : 52 Litre Braced and Lined
Frequency Response : 35hz-20khz at -3dB
Efficiency : 90dB at 1W at 1 metre
Impedence : 3.5ohms typical
Power Handling : 160W rms
Crossover : 3.0kHz 4th Order Linkwitz Network
Impedence Correction : Woofer and Tweeter - Voice Coil Inductance
Bass Driver : 2 off Response 165mm Polypropylene Cone (Jaycar CW-2135)
Tweeter Driver : Response 25mm Dome Tweeter (Jaycar CT-2010)

D. Crossover Network

Circuit for the Crossover Network

E. Components for the Crossover Network

Circuit Part No. Calculated Value Off The Shelf Actual Value Installed Value
C1 4.328uF 3.3uF 3.28uF
1.0uF 1.01uF 4.29uF
C2 8.656uF 4.7uF 4.73uF
3.3uF 3.37uF
0.33uF 0.33uF
0.22uF 0.22uF 8.65uF
C3 24.47uF 10uF 10.34uF
10uF 10.30uF
2.2uF 2.24uF
1.5uF 1.60uF 24.48uF
C4 5.439uF 2.2uF 2.32uF
2.2uF 2.29uF
0.56uF 0.53uF
0.33uF 0.33uF 5.47uF
L1 0.217mH 0.22mH 0.216mH 0.216mH
L2 0.975mH 1.00mH 0.974mH 0.974mH
L3 0.345mH 0.39mH 0.346mH 0.346mH
L4 0.1725mH 0.22mH 0.1724mH 0.1724mH