GB2126455A

GB2126455A - Loudspeaker crossover networks

Info

Publication number: GB2126455A
Application number: GB08307469A
Authority: GB
Inventors: William George Richardson
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-08-13
Filing date: 1983-03-17
Publication date: 1984-03-21
Also published as: GB8307469D0; GB2126455B

Abstract

Crossovers employing three- pole filters and a bandpass filter to linearise their input impedance combine a fast filtering action with a range of possible responses and tolerance to variations in component values. The bandpass filter to linearise the input impedance may be constructed using reactances whose values are the same as some of those used in the crossover filters. The network of figure (4) is designed to have a crossover frequency of approximately 3.2 kHz for load resistances, R, of 7.5 OMEGA . Either air-cored or ferrite cored inductors may be used. The extra circuit components to linearise the input impedances of the loudspeaker drive units have not been shown. <IMAGE>

Description

SPECIFICATION Voltage-sharing loudspeaker crossovers employing three-pole filters British Patent application number 2 095 073 A described crossover networks which shared voltage between the two loudspeaaker drive units and employed an additional bandpass filter to linearise the input impedance in the region of the crossover frequency. In common with the majority of loudspeaker crossovers, these employed either single or twin pole filters. Unfortunately, these were particularly shallow in their action, demanding the drive units to work over a relatively wide frequency range. They are also sensitive to variations caused by component tolerances.

Crossovers employing three-pole filters and the necessary band pass filter to linearise their input impedance have subsequently been developed. These combine a faster filtering action with a range of possible responses and tolerance to variations in component values. It is these developments which cre the subject of this patent application.

Fig. (1) shows the low-pass filter. The values of all reactances (X) will be quoted at the crossover frequency, unless otherwise stated. The values of X2 and X3 are made equal and opposite, to simplify construction of the complimentary high-pass filter. Satisfactory voltage-sharing crossovers can result if X2 and X3 have magnitudes between R and R 2 (R = loudspeaker input resistance). At the higher values there is a dip in response at each side of the crossover frequency, while the lower values show a rise in these regions.

The value for X, can be calculated by letting the input conductance G 4R at the crossover frequency.

A solution of particular interest occurs where X2 and X3 have magnitude approxi mately equal to 0.69R. Here the values for X1, X2 and X3 coincide with those needed to realise the bandpass filter necessary to linear ise the input impedance in the region of the crossover frequency (Fig. 3). This obviously brings considerable benefits in the ease and cost of manufacture, while the solution aiso exhibits good amplitude linearity. However, even if this solution is not chosen, the values of X1, X2 and X3 may be utilised in the bandpass filter to give approximate impedance linearisation.

The realisation of the high-pass filter follows standard practice and is illustrated in Fig. (2).

The loudspeader input resistances may be linearised using CR, LR or resistive networks.

Alternatively the loudspeaker reactance may form part of X3 or X'3, giving the designer considerable control over the acoustic output.

EMBODIMENT This is illustrated in Fig. (4) and is designed to have a crossover frequency of approximately 3.2kHz for load resistances, R, of 7.5S1. It uses values such that, within component tolerances, X3 = - X2 = 0,88R and X = 1.98R. Either air-cored or suitable ferrite cored inductors may be used. The extra circuit components to linearise the input impedances of the loudspeaker drive units have not been shown.

CLAIM

The theory behind single and twin pole voltage-sharing crossovers was described in British Patent Application GB 2095 073 A, as were the band pass filters used to linearise their input impedance.

Subsequent research has shown how these concepts may be extended to the design of crossovers employing three-pole filters. As a result of this, the applicant claims the monopoly on all voltage-sharing crossovers employing three-pole filters which are characterised by the inclusion of an L.C.R. circuit to linearise their input impedance.

Because it is envisaged that the loudspeaker reactances may form part of the crossover circuit, the voltage sharing crossover is taken to include any which approximately halve the total power dissipated by the drive units at the crossover frequency.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

SPECIFICATION Voltage-sharing loudspeaker crossovers employing three-pole filters British Patent application number 2 095 073 A described crossover networks which shared voltage between the two loudspeaaker drive units and employed an additional bandpass filter to linearise the input impedance in the region of the crossover frequency. In common with the majority of loudspeaker crossovers, these employed either single or twin pole filters. Unfortunately, these were particularly shallow in their action, demanding the drive units to work over a relatively wide frequency range. They are also sensitive to variations caused by component tolerances.

Crossovers employing three-pole filters and the necessary band pass filter to linearise their input impedance have subsequently been developed. These combine a faster filtering action with a range of possible responses and tolerance to variations in component values. It is these developments which cre the subject of this patent application.

Fig. (1) shows the low-pass filter. The values of all reactances (X) will be quoted at the crossover frequency, unless otherwise stated. The values of X2 and X3 are made equal and opposite, to simplify construction of the complimentary high-pass filter. Satisfactory voltage-sharing crossovers can result if X2 and X3 have magnitudes between R and R

2 (R = loudspeaker input resistance). At the higher values there is a dip in response at each side of the crossover frequency, while the lower values show a rise in these regions.

The value for X, can be calculated by letting the input conductance G 4R at the crossover frequency.

A solution of particular interest occurs where X2 and X3 have magnitude approxi mately equal to 0.69R. Here the values for X1, X2 and X3 coincide with those needed to realise the bandpass filter necessary to linear ise the input impedance in the region of the crossover frequency (Fig. 3). This obviously brings considerable benefits in the ease and cost of manufacture, while the solution aiso exhibits good amplitude linearity. However, even if this solution is not chosen, the values of X1, X2 and X3 may be utilised in the bandpass filter to give approximate impedance linearisation.

The realisation of the high-pass filter follows standard practice and is illustrated in Fig. (2).

The loudspeader input resistances may be linearised using CR, LR or resistive networks.

Alternatively the loudspeaker reactance may form part of X3 or X'3, giving the designer considerable control over the acoustic output.

EMBODIMENT This is illustrated in Fig. (4) and is designed to have a crossover frequency of approximately 3.2kHz for load resistances, R, of 7.5S1. It uses values such that, within component tolerances, X3 = - X2 = 0,88R and X = 1.98R. Either air-cored or suitable ferrite cored inductors may be used. The extra circuit components to linearise the input impedances of the loudspeaker drive units have not been shown.

CLAIM

The theory behind single and twin pole voltage-sharing crossovers was described in British Patent Application GB 2095 073 A, as were the band pass filters used to linearise their input impedance.

Subsequent research has shown how these concepts may be extended to the design of crossovers employing three-pole filters. As a result of this, the applicant claims the monopoly on all voltage-sharing crossovers employing three-pole filters which are characterised by the inclusion of an L.C.R. circuit to linearise their input impedance.

Because it is envisaged that the loudspeaker reactances may form part of the crossover circuit, the voltage sharing crossover is taken to include any which approximately halve the total power dissipated by the drive units at the crossover frequency.