GB2282022A

GB2282022A - Loudspeaker cross-overs

Info

Publication number: GB2282022A
Application number: GB9418961A
Authority: GB
Inventors: Mohammed Akhtar
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-09-21
Filing date: 1994-09-21
Publication date: 1995-03-22
Anticipated expiration: 2014-09-21
Also published as: GB9418961D0; GB9319433D0; GB2282022B

Abstract

Filter units 11, 12, 13 are provided for dividing an audio signal produced at an amplifier output into one or more frequency ranges and the filter units are connected to a negative terminal of loud speaker drivers 2, 3, 4 and interposed between that negative terminal and a return terminal of an amplifier output. By providing the filter unit in this particular configuration, it is found that distortion is alleviated as compared with conventional arrangements, giving audio signals a more pleasant tone. <IMAGE>

Description

FILTERS The invention relates to filters and, particularly, to cross-over assemblies for loudspeakers.

In many conventional arrangements, loudspeaker crossover assemblies are positioned between the "positive" output terminal of an audio amplifier and the "positive" terminal of the loudspeaker driver assembly. In other arrangements, due to phase reversals in the cross-over, the cross-over is positioned between the "positive" output terminal of the amplifier and the "negative" terminal of the driver assembly.

However, such conventional cross-over arrangements tend to de-grade audio signals passing through them to some extent. Examples of cross-over distortion include ringing and, particularly in higher order cross-overs, phase reversal.

Accordingly, an aspect of the invention provides a cross-over arrangement for connection between feed and return terminals of an audio amplifier output, the crossover arrangement comprising: one or more filter units for dividing an audio signal produced at the amplifier output into one or more frequency ranges and conveying the divided signal to one or more loudspeaker driver units, the or each driver having first and second terminals; wherein, each first terminal is connected to the feed terminal of the amplifier and each second terminal is connected to a respective one of the filter units.

Preferably, each said first terminal is a "positive" driver terminal and each second terminal is a "negative" driver terminal.

Preferably, the, or each, filter unit is connected between the return terminal of the amplifier and the second terminal of its respective driver.

Preferably, the return terminal is a ground terminal.

The or each filter unit may comprise low-pass and/or band pass and/or high pass filters.

Preferably, the or each filter unit comprises at least a resistive element disposed between the return terminal of the amplifier, and other components of the filter unit.

The or each filter unit may be series circuits or alternatively, the filters may be parallel circuits.

The or each filter unit may comprise active and/or passive components.

The or each filter unit may comprise a first part connected across the first and second terminals and a second part interposed between the second terminal and the return terminal.

The first part may comprise a capacitor.

The invention includes amplifiers and loud speakers incorporating cross-over arrangements in accordance with the first aspect.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which: Figure 1 is a schematic diagram showing a first exemplary embodiment; and Figure 2 is a schematic diagram showing an alternative embodiment.

Figure 1 shows, in schematic form, the output of an audio amplifier 1 which is connected to three driver units a woofer 2, mid-range 3, and tweeter unit 4 for the reproduction of bass, mid-range and high frequency audio signals respectively.

The positive output from the amplifier is connected directly to the positive terminal of each driver unit and the negative unit of each driver connects with a first terminal, 5, 6, 7 of one of three series filter units 8, 9, 10. A second terminal 11, 12, 13 of each filter unit is, in turn, connected to the return or ground terminal of the amplifier 1.

The filters 8 to 10 are low-pass, band-pass and highpass filters respectively.

By way of example, sample filter arrangements will now be described. In each of these examples, each of the driver units 2, 3, 4 will be assumed to have an impedance of 8 ohms.

Low-pass filter 8 comprises a resistor R1 and an inductor L1. Exemplary component values to give an effective cross-over frequency of 600 hertz are: L1 = 0.002 Henrys (or 2 millihenrys) and R1 = 2 ohms.

Band-pass filter 9 comprises a resistor R2, capacitor C1 and inductor L2. To give an effective frequency band of 600 to 5,000 hertz, typical component values are: R2 = 2 ohms, L2 = 0.25 millihenrys and C1 = 33 microfarads.

High-pass filter 10 comprises a resistor R3 and capacitor C2. Typical values for a cross-over frequency of 5,000 hertz are R3 = 2 ohms and C2 = 3.9 microfarads.

As explained previously, in many conventional crossover arrangements each filter unit is disposed between the feed terminal of the amplifier and the first or "positive" terminal of its respective driver. In those arrangements, the cross-over filter units are presented with an impedance element on each side, i.e. amplifier on one side, driver on the other. In my inventive arrangement, each of the filter units 8, 9, 10 is positioned between the second or "negative" terminal side of the driver 2, 3, 4 and the return terminal of the amplifier and, it is preferred that the resistive element R1, R2, R3 of each filter unit 8, 9, 10 is positioned as shown so as to connect directly with the amplifier return terminal and provide an impedance on both sides of the cross-over. In this manner, the filters are presented with the driver impedance on one side and a resistance R1, R2 or R3 on the other.

Each of the filters shown have a roll off rate of 6dbs per octave. The component values given are exemplary only and alternative values may be selected. For instance, a steeper roll-off rate may be achieved by adding a second inductor in series with L1 in the low pass filter, so as to give an initial attenuation of 12dB per octave at the cross-over frequency and this arrangement has been found to be particularly advantageous. Of course, other alternative values may be used so as to tailor the frequency response of the cross-over according to particular requirements.

In use, positioning the filters 8, 9, 10 between the negative terminals of the drivers 2, 3, 4 and the return, or ground terminal, of the amplifier 1 performs the necessary cross-over function, whilst alleviating some of the problems of the conventional arrangement.

In other words, cross-over distortion, ringing and phase reversal effects appear to be alleviated to some extent. It appears that these undesirable effects do actually still occur in the cross-over shown in the figure but changing the position of the filter elements to the opposite side of the driver unit to that which is normal, has the beneficial effect of rendering them largely inaudible to the human ear.

Figure 2 is a schematic diagram showing an alternative embodiment in which for the woofer 2, a capacitor is placed across the input terminals of the woofer so as to be in parallel with it and a resistor having a value of 2 Ohms is placed in series between the negative terminal of the woofer and the ground terminal of the amplifier.

For a cross-over frequency of 2,000 Hz, we can use the following equation to calculate the value of capacitor required.

1 I 2N fo Z where F0 cross over frequency, Z = impedance of resistor and C = capacitor value.

Putting the relevant values into the equation gives a capacitor value of 40 microfarads.

Referring to Figure 2, it can be seen that low frequency signals would be blocked from entering the capacitor but, as 2,000 Hz is approached, the impedance level of the capacitor drops and more and more signals will be shunted across the woofer to bypass it. Above 2,000 Hz, the capacitor impedance drops further and audio signals will tend to take the lower impedance path through the capacitor, rather than through the woofer, so as to attenuate the woofers frequency response with the rise in audio signal frequency.

By virtue of the fact that there are no components in series with the positive terminal of the woofer, no additional distortion or signal changes are introduced and a very pure tone may be achieved.

It will be evident to the man skilled in the art, that the mid-range 3 and tweeter 4 may be connected in any way in accordance with the present invention.

Although the filter units shown are single order series filters, other types of filter may be used to perform the low-pass, band-pass and high-pass functions.

Although the cross-over shown is for a three-way loudspeaker unit, the invention may be employed in systems utilising any number of driver units per channel.

Furthermore, passive components may be replaced by active components. The term "ground potential" (or like terms such as "ground voltage" or "earth" potential or voltage) is used conveniently in this specification to denote a reference potential. As will be understood by those skilled in the art, although such reference potential may typically be zero potential, it is not essential that it is so, and may be a reference potential other than zero.

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAINS

1. A cross-over arrangement for connection between feed and return terminals of an audio amplifier output, the cross-over arrangement comprising: one or more filter units for dividing an audio signal produced at the amplifier output into one or more frequency ranges and conveying the divided signal to one or more loudspeaker driver units, the or each driver having first and second terminals; wherein, each first terminal is connected to the feed terminal of the amplifier and each second terminal is connected to a respective one of the filter units.

2. An arrangement according to claim 1, wherein each said first terminal is a "positive" driver terminal and each second terminal is a "negative" driver terminal.

3. An arrangement according to claim 1 or 2, wherein the or each filter unit is connected between the return terminal of the amplifier and the second terminal of its respective driver.

4. An arrangement according to any of the preceding claims, wherein the return terminal is a ground terminal.

5. An arrangement according to any of the preceding claims, wherein the or each filter unit comprises low-pass and/or band-pass and/or high-pass filters.

6. An arrangement according to any of the preceding claims, wherein the or each filter unit comprises at least a resistive element disposed between the return terminal of the amplifier and other components of the filter unit.

7. An arrangement according to any of the preceding claims, wherein the or each filter unit is a series unit.

8. An arrangement according to any of claims 1 to 6, wherein the or each filter unit is a parallel circuit.

9. An arrangement according to any of the preceding claims, wherein the or each filter unit comprises active and/or passive components.

10. An arrangement according to any of the preceding claims, wherein the or each filter unit comprises a first part connected across the first and second terminals and second part interposed between the second terminal and the return terminal.

11. An arrangement according to claim 10, wherein the first part comprises a compacitor.

12. An arrangement substantially as herein described with reference to Figure 1.

13. An arrangement substantially as herein described with reference to Figure 2.

14. An audio amplifier including an arrangement according to any of the preceding claims.

15. A speaker including an arrangement according to any of claims 1 to 13.