Patent GB-1351842-A (GB)
Title: Transducer assemblies
IPC: H04R1/32
Filed: 1971-03-15
Abstract: 1351842 Loud-speakers; crossover networks RANK ORGANISATION Ltd 15 March 1972 [15 March 1971] 6868/71 Headings H4J and H4X The radiation response of an acoustic transducer assembly including a crossover network is adjustable above a transition frequency to selectively control the directional distribution of the frequency components of the overall radiation pattern. The invention is applied to a loud-speaker assembly comprising a cabinet 11 (Fig. 1) having an upwardly facing bass loudspeaker LS5, front and rear treble loud-speakers LS1 and LS2, and side loud-speakers LS3 and LS4. Preferably a parasitic diaphragm 15 in the base of the cabinet is air coupled with the bass loud-speaker LS5 in the low frequency range. The cabinet stands on legs 13. An alternative cabinet (Fig. 9, not shown) is barrel shaped, has an upwardly facing bass loud-speaker LS5 and four treble loud-speakers LS1, LS2, LS3 and LS4 located in the curved surface near the top of the barrel so as to have an upward tilt. A simple circuit (Fig. 4) includes a reactive bridge C1, C2, L1, L2 acting as a crossover network, known per se. The bass loud-speaker LS5 is connected across capacitor C2 and receives signals below about 1 KHz. Loudspeakers LS1, LS2, LS3, LS4 receive signals above about 1 KHz. An inductance L3 and a capacitor C3 have the same reactance at a transition frequency above 1 KHz. Above this transition frequency the signal to loud-speakers LS3 and LS4 is attenuated by inductance L3 and the signal to loud-speaker LS2 is attenuated by capacitor C3 by movement of a slide of a potentiometer R 1  to position D. The signal input to loud-speaker LS1 increases, however, to a corresponding extent so that the system total acoustic power generated is independent of the radiation pattern. In order to compensate for the different acoustic properties of rooms, potentiometer R 1  may be adjusted so that slide is at position 0 whereby the effects of the elements C3, L3 are substantially eliminated. By suitable adjustment of the potentiometer slide to intermediate positions different degrees of directionality of the high frequency pattern generated by the assembly can be obtained. An elaboration of Fig. 4 shows the resistor R1 (Fig. 5), three different capacitors C3a, C3b, C3c and three different inductances L3a, L3b, L3c, together with two ganged switches 16, 17. The values of capacitance and inductance are so chosen that the three switch positions provide transition frequencies of 3À5 KHz, 5 KHz, and 7 KHz. Another variation of the radiation pattern is obtained by a switch S1 (Fig. 6) provided on one side of capacitor C3 so that the capacitor can be connected across loud-speaker LS2 or loud-speaker LS1 or can be disconnected. A second switch enables inductance L3 to be short-circuited. Various radiation patterns (Fig. 8, not shown) are obtained by various formulations of positions of switches S1 and S2. The switches S1 S2 may be replaced by potentiometers (R2, R3) Fig. 7 (not shown) so that continuous variation of the radiation pattern can be obtained. The capacitors C3a, C3b, C3c (see Fig. 5) together with corresponding inductances L3a, L3b, L3c and switches 16, 17 may be introduced into the circuits of Figs. 6 and 7 so that, apart from a choice of different radiation patterns, the frequency above which the choice of radiation patterns is available can be varied. (For Figures see next page.)