Crossover Altec 414A - 802D
This two way crossover it was made for ALTEC 414-A woofer and 802-8D compression driver with 811B sectorial horn .
As first step we measured the Thiele and Small parameters of loudspeakers with CLIO System of Audiomatica italian company. It is important know the impedance module of the woofer, in fact a Zobel network were calculated for compensate the inductive raising Z module.
LOW PASS FILTER
The Low pass filter for the woofer is a 12 dB/oct with Zobel network. A interesting features of the low pass filter is a variable slope from 6 to 12 db/oct. his is a great feature that can give a variable phase shift and consequently it easy obtain a good integration with the tweeter emission.
Free air impedance and phase of the woofer 414-A
The inductor in the low pass filter have a very low DC resistance . The resistive losses is very dangerous because disperse power and worsen the quality and the damping of the bass register. So it is primary keep it to the lower value is possible.
The high pass filter have a slope of 12 dB/oct. For the compression drivers , and tweeter, a high slope is reccomended to preserve the diaphram from the low frequency that could be broken it. A notch filer is centred to the resonance frequency of the diaphram: at this frequency the Z module of the have a peak, ant this is a big problem when this frequency is too near to the frequency crossover: the crossover don't work correctly. The notch filter is costitued from Resistance, capacitor and a coil in series connection. For a perfectly coupling of the notch filter with the diaphram a Clio System measure was essential. In this high frequency network , the driver attenuation is not made with resistive losses. The L-PAD give not a natural sound; a expensive inductive control it has been placed. We made a custom coil with 5 taps for attenuation, with 2 dB each from other. A two way rotary commuator drive the taps of the coil and a resistive load that allow to the crossover to see a costant load.
impedance module of the compression driver with and without the Notch filter
Electrical response of the two way, loading on respective drivers
- woofer Altec 414 A
- Low pass filter with variable sloping between 6 e 12 dB/oct.
- Frecuency crossover 1 KHz.
- Zobel network for rising copensation of the impedance module
- Custom coil wiring an heptalitz cable ( 7 isolated cables) around a high permeabilty core, for minimize DC resistance
- Driver Altec 802-8D
- High pass filter with 12 dB/oct
- Crosso over frequency 1 KHz.
- Notch filter on the resonance frequency of the driver + horn system.
- Inductive volume control , made with custom Clinamen coil with 5 attenuation taps