GB2145904A

GB2145904A - Loudspeaker crossover networks

Info

Publication number: GB2145904A
Application number: GB08323135A
Authority: GB
Inventors: William George Richardson
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-08-27
Filing date: 1983-08-27
Publication date: 1985-04-03
Also published as: GB8323135D0

Abstract

In a network comprising a pair of simple-pole filter limbs and a bandpass filter all connected across the input of the network, at least one of the filter limbs is such that part or all of its essential reactance is provided by the loudspeaker in that limb.The bandpass filter renders the input impedance substantially constant in the region of the crossover frequency. <IMAGE>

Description

SPECIFICATION Low-cost constant impedance loudspeaker cros- sovers British Patent Application UK 2095 073A described loudspeaker crossover networks which shared voltage bstween the units and incorporated a bandpass filterto linearise their input impedance at the crossoverfrequency. These incorporated either single or twin-pole filters.

Subsequent systems based on three-pole filters were described in patent applications GB 8307469 and PCT/GB 83/00199. While developing thisthree-pole system it was realised that the inductance of the moving-coil low-freqency unit might forum part of the low-frequencyfilter. This is generally true for anyT section filter of odd order, a result which has now been applied to the design of constant input impedance crossovers employing single pole filters. These require relatively few components and are the subject of this patent application.

Forvoltage-sharing crossover employing singlepole filters each element has a reactance of magnitude R V at the crossover frequency, where R is the resistance of the loudspeaker forming the load. In patent application UK 2095073 A it was envisaged that the reactance, particularly of the low-frequency unit, would be compensated by additional CR networks so as to present a constant resistive load to the crossover in the frequency region in which it operates.

If the acoustic output of the low4requency unit falls smoothly at the top if itsfrequency range, its inductance mayform all, or part, ofthe inductance required for a single-pole low-pass filter. The principal advantage being that no CR correction network is required across the input to the bass driver and thus the total number of components is greatly reduced.

Where the inductance ofthe bass driverforms all that required forthe filter, it will have a reactance equal to R < ; atthe crossoverfrequency, so the modulus of impedance, IZI, will equal 2R at that frequency. The voltage-sharing crossover will then consistofonlya capacitor forming the high-pass filter, with reactance equal to - R aatthe crossover frequency.

Crossing over a pair of drive units with just a capacitor in series with the H.F. unit is not new.

However, if this is done in the way described, a L.C.R.

band-pass filter may be connected in parallel across the inputto give a constant input impedance in the region ofthe crossoverfrequency, as shown in the embodimentto this application. A resistive network may be added to attenuate the high frequency unit if this is required, while the sign indicates that the H.F.

unit is phase reversed. The bandpass filter contains R R resistance = 2 Rand reactances of + - and - 2 2 V atthe crossover frequency, as described in patent application U.K. 2095 073A.

Fig. (1) shoves the circuit required to produce a constant input impedance crossoverat approximately 3.7kHz for loudspeakers of 7.5D resistance. The bass driver has a modulus ofimpedance of 15R atthe crossover frequency.

C1 = 6.6 F, R1=15D, L1=O.3m11 C2 = 3.3,u

CLAIM 1. A loudspeaker system having a crossover network comprising a pair ofsingle-polefilter limbs and a bandpassfilter, all connected across the inputofthe network, the two filter limbs each including a loudspeaker, the reactance of which may form part ofthe filter limb, wherebythetotal electrical power dissipated by the loudspeakers is approximately halved at the crossover frequency and the bandpass filter renders the input impedance substantially constant in the region ofthe crossover frequency.

The claims were filed later than the filing date within the period prescribed by Rule 25(1) of the Patents Rules 1982.

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

Claims

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

SPECIFICATION Low-cost constant impedance loudspeaker cros- sovers British Patent Application UK 2095 073A described loudspeaker crossover networks which shared voltage bstween the units and incorporated a bandpass filterto linearise their input impedance at the crossoverfrequency. These incorporated either single or twin-pole filters.

Subsequent systems based on three-pole filters were described in patent applications GB 8307469 and PCT/GB 83/00199. While developing thisthree-pole system it was realised that the inductance of the moving-coil low-freqency unit might forum part of the low-frequencyfilter. This is generally true for anyT section filter of odd order, a result which has now been applied to the design of constant input impedance crossovers employing single pole filters. These require relatively few components and are the subject of this patent application.

Forvoltage-sharing crossover employing singlepole filters each element has a reactance of magnitude R V at the crossover frequency, where R is the resistance of the loudspeaker forming the load. In patent application UK 2095073 A it was envisaged that the reactance, particularly of the low-frequency unit, would be compensated by additional CR networks so as to present a constant resistive load to the crossover in the frequency region in which it operates.

If the acoustic output of the low4requency unit falls smoothly at the top if itsfrequency range, its inductance mayform all, or part, ofthe inductance required for a single-pole low-pass filter. The principal advantage being that no CR correction network is required across the input to the bass driver and thus the total number of components is greatly reduced.

Where the inductance ofthe bass driverforms all that required forthe filter, it will have a reactance equal to R < ; atthe crossoverfrequency, so the modulus of impedance, IZI, will equal 2R at that frequency. The voltage-sharing crossover will then consistofonlya capacitor forming the high-pass filter, with reactance equal to - R aatthe crossover frequency.

Crossing over a pair of drive units with just a capacitor in series with the H.F. unit is not new.

However, if this is done in the way described, a L.C.R.

band-pass filter may be connected in parallel across the inputto give a constant input impedance in the region ofthe crossoverfrequency, as shown in the embodimentto this application. A resistive network may be added to attenuate the high frequency unit if this is required, while the sign indicates that the H.F.

unit is phase reversed. The bandpass filter contains R R resistance = 2 Rand reactances of + - and -

2 2 V atthe crossover frequency, as described in patent application U.K. 2095 073A.

Fig. (1) shoves the circuit required to produce a constant input impedance crossoverat approximately 3.7kHz for loudspeakers of 7.5D resistance. The bass driver has a modulus ofimpedance of 15R atthe crossover frequency.

C1 = 6.6 F, R1=15D, L1=O.3m11 C2 = 3.3,u

CLAIM 1. A loudspeaker system having a crossover network comprising a pair ofsingle-polefilter limbs and a bandpassfilter, all connected across the inputofthe network, the two filter limbs each including a loudspeaker, the reactance of which may form part ofthe filter limb, wherebythetotal electrical power dissipated by the loudspeakers is approximately halved at the crossover frequency and the bandpass filter renders the input impedance substantially constant in the region ofthe crossover frequency.

The claims were filed later than the filing date within the period prescribed by Rule 25(1) of the Patents Rules 1982.