The Home-Constructed Cross-over Network

There are many hi-fi hobbyists who find pleasure in building as much of their own equipments as they possibly can. For these, we will now offer a simple but concise method of building a workable crossover network.

            The design of a crossover network is based on the three factors: (a) speaker circuit impedance; (b) crossover frequency; and (c) attenuation at the crossover point. The factors determine the electrical size of the capacitors and inductors that make up the various branch circuits. The chart in fig.1 provides a simple means of selecting the proper value of components for a chosen crossover frequency between any two speakers whose frequency ranges overlap. The chart also presents values for either a 6db or 12db per octave attenuation rate. It is not limited in any way to the number of branch circuits that may be used in the system. It may be applied to a two, three, four or even five – way system, if desired.

Fig. 1

This versatility is accomplished by taking the speakers one by one,, starting from the lowest frequency range and selecting the proper constants to cross that speaker with the next adjacent speaker circuit in the frequency rang. Then, in a like manner, the constants are chosen to cross this second speaker with the third speaker

Sample Network Design

            Let us design a network for a three-way system, such as shown in Fig.2, with crossover frequency at 350 Hz and at 5000 Hz, for speakers of 8 Ohms impedance, and to have a 6 db per octave roll-off. We first concerned with the woofer and the speaker adjacent to it, the midrange speaker. The crossover frequency is to be 350 Hz. Locate 350 Hz on the frequency scale. Extend a horizontal line to the right until it intersects the proper C/L line, which gives the electrical constants necessary for the low frequency speaker circuit – 3.7mH for the inductor coil and 58uF for the capacitor in the lead to midrange speaker.

Fig. 2

Incidentally, if we were concerned only with a two way system to cross over at 350 Hz, these two values would give us the complete design of the network. However since we are building a three-way network, we must now deal with second crossover point.

            To select the constants for the upper crossover frequency of 5000 Hz, we regard the midrange speakers as the lower speaker circuit. Entering the chart from 5000 Hz mark, we again proceed to 8 Ohms C/L line and find the value of the choke 0.28 mH to be put into the lower speaker circuit circuit, and the value of the capacitor 4.2uF to be put into the upper speaker circuit. The network design for a system to crossover at 350 Hz and 5000 Hz with 6-db attenuation is now complete.