CA2358085C

CA2358085C - System for distributing a signal between loudspeaker drivers

Info

Publication number: CA2358085C
Application number: CA 2358085
Authority: CA
Inventors: Stefan R. Hlibowicki
Original assignee: Audio Products International Corp
Current assignee: Audio Products International Corp
Priority date: 2001-09-28
Filing date: 2001-09-28
Publication date: 2007-08-07
Anticipated expiration: 2021-09-28
Also published as: CA2358085A1

Abstract

A loudspeaker system includes a drive arrangement having an autotransformer. An input drive signal is supplied to a tap connection of the autotransformer. Two end connections of the autotransformer are then connected, directly or indirectly, to drivers or individual speakers. The individual drivers can then have filter networks or the like to provide desired cutoff characteristics. The filter networks can be capacitors around the drivers. More than one autotransformer can be provided, with the output of one transformer forming the input of another, to enable three or more drivers to be driven in this manner.

Description

. .1 SYSTEM FOR DISTRIBUTING A SIGNAL BETWEEN LOUDSPEAKER
DRIVERS
FIELD OF THE INVENTION
5[0001] This invention relates to loudspeakers, and more particularly is concerned with loudspeaker crossover topology for varying signals delivered to drivers or speakers in the same crossover section of a loudspeaker system.
BACKGROUND OF THE INVENTION

[0002] It is common to provide individual loudspeaker units or assemblies which include two or more individual speakers or drivers. To provide adequate frequency response, it is common to provide individual speakers covering different parts of the frequency spectrum, since large speakers for providing low frequencies cannot provide adequate response at higher frequencies. Such systems are commonly known as two or three way systems, depending upon whether there are two or three different frequency portions.

[0003] Moreover, in some designs where higher efficiency is a concern, multiple drivers can be provided in each crossover section or for each frequency band. It is not uncommon to have up to three drivers or speakers in a low pass section and even two drivers in a midrange section.

[0004] A disadvantage to having multiple drivers is that they occupy more space, and can narrow the spatial characteristics of the system, i.e., the sound from multiple speakers or drivers can appear to be more directional than from a single driver. This effect is more pronounced at higher frequencies.

[0005] Accordingly, to reduce this side effect of multiple drivers, it is known to differentiate the signals fed to the individual drivers in one section.
This is achieved by setting different low pass cutoff frequencies for each driver, and this is common practice where multiple drivers are provided. The effect of this is to reduce the number of drivers participating in sound reproduction, at higher frequencies, which improves sound dispersion.

[0006] However, this technique has a number of disadvantages. One of them is low efficiency, since at higher frequencies fewer drivers are radiating the sound. Another is that is difficult to achieve a flat frequency response, because of a complex phase relationship between drivers connected to different low pass filters. Even if one designs low pass filters which, by simple mathematical addition, should produce a flat frequency response, this may not be the case in practice. This is because each low pass filter may introduce unwanted and varying phase shifts. At higher frequencies, these phase shifts can be more pronounced, and, in effect, there is no simple straight addition of the different signals to provide a desired output signal, i.e., the phase shifts result in a reduced signal level.

SUMMARY OF THE INVENTION

[0007] Accordingly, the present inventor has realized that it is desirable to provide a cross over topology that will simply and efficiently divide an input signal between different drivers, and which will enable different low pass cut off frequencies to be set for the drivers, while enabling a flat, total frequency response to be provided.

[0008] According to the present invention, a system for distributing a source voltage from a signal source is provided. The system comprises:

[0009] a) at least one autotransformer for connection to the signal source; and

[0010] b) a plurality of drivers electrically connected to the at least one autotransformer;

[0011] wherein the at least one autotransformer is adapted to distribute said source voltage across each of the plurality of drivers.

[0012] The present invention is based on the realization that a tapped coil or autotransformer can be used for this purpose. While such tapped autotransformers are known, they have never been used for such a purpose.

i il I

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a better understanding of the present invention and to show more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings, which show a preferred embodiment of the present invention and in which:

[0014] Figure 1 shows the basic configuration of a center-tap autotransformer, and relationship between input and output voltages;

[0015] Figure 2 shows schematically the configuration of an autotransformer used to connect a signal source to two drivers;

[0016] Figure 3 shows the implementation of an autotransformer in accordance with the present invention with low pass crossover for one driver;

[0017] Figure 4 is a graph showing the frequency response of the drivers of the Figure 3 configuration;

[0018] Figure 5 shows a driver configuration similar to Figure 3, including a low pass filter;

[0019] Figure 6 shows a driver configuration including two autotransformers, for driving three drivers, including individual low pass cross over characteristics;

[0020] Figure 7 is a graph showing the frequency response of the driver configuration of Figure 6.

DETAILED DESCRIPTION OF THE INVENTION

[0021] Referring first to Figure 1, there is shown an autotransformer indicated at 10. As is known, an autotransformer is a single coil having end taps or connections indicated as a first end connection 12 and a second end connection 14. It also has a tap connection 16.

[0022] Here, the tap connection 16 is connected to signal source ul, the second end connection 14 is connected to ground and the first connection 12 has an output voltage U2. As is known, where the tap connection 16 is in the middle of the coil, then the voltages uland U2 are related, as follows:

[0023] u2 = 2u, (1)

[0024] In Figure 2, the autotransformer 10 has the same reference numerals and characteristics as in Figure 1. Here, two drivers, indicated at and 20, are shown between the end taps or connections 12 and 14 and ground. An input signal source 22 is connected between the tap connection 16 and ground, as shown. The input signal source generates a source voltage E, and the drivers 18, 20 have voltages across them of V1 and V2.
The drivers may be any suitable loudspeaker.

[0025] This relationship can be used to drive a pair of speakers or drivers. Here, the output voltages are indicated as V1 and V2. It can be shown that sum of the output voltages V1 and V2 remain constant, disregarding the load impedances. If the loads are identical, then the voltages are identical and equal to the input voltage. More specifically, if the input voltage is E, then the voltages are related by:

[0026] V1 + V2 = 2E (2)

[0027] This relationship between the input and output voltages remains constant, even if the loads are varied. Thus, if the impedance is varied so that one voltage, e.g., V1, decreases, then the other voltage V2 increases , to maintain the relationship indicated by the equation (2) above.

[0028] Referring now to Figure 3, this shows a configuration similar to Figure 2, and for simplicity and brevity, common components are given the same reference in Figure 3 as Figure 2, and their description is not repeated.

[0029] Here, the voltages (which are also referred to as signals) supplied to the first and second drivers 18,20 are indicated as V1, V2.
Additionally, the second driver 20 is provided with a capacitor 24 across it, with a value, for example, with 100 mircrofarads.

[0030] The effect of providing this capacitor 24 is to provide a cutoff frequency for the driver 20, lower than for the other driver 18. In effect, as the frequency increases, the combined impedance of the driver 20 and the capacitor 24 drops, and a greater proportion of the signal passes through the capacitor 24. In effect, this reduces the voltage across the driver 20. In accordance with equation 2 above, this requires that the voltage across driver 18 increase to compensate.

[0031] As the sound level generated by each speaker 18, 20 corresponds to the voltage across it, this means that the total sound level, as measured by the sound pressure, remains the same.

[0032] This is shown in Figure 4, which shows the frequency response for the arrangement of Figure 3. The same reference numerals are used in Figure 4 to indicate the frequency response of the separate drivers 18,20.
Thus, the second driver 20 has a frequency response of that falls off at higher frequencies. Correspondingly, the frequency response of the first driver 18 increases. The sum of both signals V1 and V2 remains constant and is represented by the straight line at + 6dB (6=20x1og(2)). This also means that the total efficiency of the system does not change as a function of frequency.

[0033] Referring to Figure 5, this shows a development of the configuration of Figure 3 generally indicated by the reference 28, and again for simplicity and brevity, like components are given the same reference numeral and the description is not repeated.

[0034] Here, in Figure 5, a low pass filter is provided comprising, in known manner, an inductor 30 and a capacitor 32 having values chosen to give a desired low cut off frequency. This configuration will work similarly to that of Figure 3. It is intended for driving a pair of drivers 18, 20 which are low frequency speakers or woofers. Thus, at a desired cutoff frequency the filter comprises the elements 30, 32 will cutoff or reduce power delivered to the drivers 18, 20. Otherwise, the drivers 18, 20 will behave as in Figure 3.

[0035] It is to be noted that while the low pass filter 30, 32 is shown before the transformer 10, it is possible to provide individual low pass filters for each driver 18, 20, after the transformer 10. This would have the advantage that, if desired, slightly different characteristics can be provided for each of the low pass filters, so as to achieve the desired and different cutoff characteristics.

[0036] It is also been noted that, while the capacitor 24 is shown in Figure 5 providing the cutoff frequency for the driver 20, various other elements can be included or substituted. In general, it is expected that passive elements will be provided, and in known manner, any suitable combination of resistors, inductors, and capacitors can be provided to achieve the desired frequency characteristics.

[0037] Turning to Figure 6, this shows an arrangement, which provides a further development of the configurations already described. As for earlier figures, for simplicity and brevity, common components are given the same reference numerals and the description of these components is not repeated.

[0038] In Figure 6, in addition to the first and second drivers 18, 20, there is a third driver 40. To split the power from the signal source 22 accordingly, a second transformer 42 with end taps or connections 44 and 46 is provided. The signal source 22 is now connected to a tap connection 48 of the second transformer 44. This tap connection 48 is provided so that the winding ratios between the two parts of the transformer 42 is in the ratio 2:1, i.e., the number of turns between the end connection 46 and tap connection 48 is the twice the number of turns between the end connection 44 and tap connection 48.

[0039] The three drivers or speakers 18,20, and 40 are then provided with signals or voltages V1, V2, and V3, and, due to the transformer configurations, these must then follow the equation:

[0040] V1+V2+V3=3E

[0041] The above equation may be expressed more generally as:
Vl+V2+V3+...Vn=nE, where n is the total number of drivers connected to signal source 22.

[0042] As before, the second driver 20 is provided with a capacitor 24, with a value of for example 50 microfarads, to give a low cutoff frequency.
The third driver 40 has a capacitor 50, with the value of for example 100 mircrofarads to give an even lower cutoff frequency.

[0043] The effect of this overall scheme is shown in Figure 7, where the characteristics of the three drivers are indicated by the reference numerals 18, 20, and 40. Thus, the third driver 40 has a relatively low cutoff frequency, as shown. The second driver 20 has a slightly higher cutoff frequency. As before, the balance of the signal is made up by the first driver 18, so that at higher frequencies a greater proportion of the signal is derived from the first driver 18. The total signal is indicated at 52 at a 9.54 dB level (9.54=20xlog(3)).

[0044] As noted, capacitors connected in parallel to the individual driers are not the only option for adjusting individual driver responses. Depending on particular requirements, more complex networks can be provided in parailel with the drivers. This could be in junction with networks before each transformer as desired.

[0045] The principal concept of the present invention is to use a tap coil or autotransformer. An input signal is provided to the tap terminal or connection, and the two end terminals or connections supply signals to the following networks. One of these output signals of a first transformer can be the input signal supplied to the tap terminal of another transformer, and so on.

Claims

Claims:

1. A system for distributing a source voltage from a signal source, the system comprising:
a) at least one autotransformer comprising:
i) a tap connection adapted for electrical connection to said signal source;
ii) a first end connection;
iii) a second end connection, wherein said tap connection is located between said first end connection and said second end connection; and b) a plurality of drivers electrically connected to said at least one autotransformer;
wherein said first end connection is electrically connected to a first one of said plurality of drivers and said second end connection is electrically connected to a second one of said plurality of drivers or a second of said at least one autotransformer, wherein said at least one autotransformer distributes said source voltage across each of said plurality of drivers.

2. The system of claim 1, wherein said at least one autotransformer produces an output voltage across each of said plurality of drivers, each of said plurality of drivers converting said corresponding output voltage to an acoustic signal, wherein the sum of said output voltages is substantially equal to said source voltage multiplied by the number of said plurality of drivers.

3. The system of claim 2, wherein said at least one autotransformer comprises a plurality of autotransformers, wherein the number of said plurality of autotransformers is one less than the number of said plurality of drivers.

4. The system of claim 3, wherein said first end connection of each of said plurality of autotransformers is electrically connected to a corresponding one of said plurality of drivers, said second end connection of a distally positioned one of said plurality of autotransformers being electrically connected to one of said plurality of drivers, said second end connection of a remaining portion of said plurality of autotransformers being connected to the tap connection of an adjacently positioned one of said plurality of autotransformers.

5. The system of claim 4, wherein each of said plurality of autotransformers has a turn ratio, each turn ratio being (n-x):1, where n is the number of said plurality of drivers and x is the position of a selected one of said plurality of autotransformers from said signal source.

6. The system of claim 5, wherein said plurality of autotransformers comprises a first and second autotransformer and said plurality of drivers comprises a first, second, and third driver, wherein said first end connection of said first autotransformer is electrically connected to said first driver and said second end connection of said first autotransformer is electrically connected to said second driver, wherein said first end connection of said second autotransformer is electrically connected to said third driver and said second end connection of said second autotransformer is electrically connected to said tap connection of said first autotransformer, wherein said tap connection of said second autotransformer is electrically connected to said signal source, said first autotransformer having a turn ratio of 1:1, said second autotransformer having a turn ratio of 2:1.

7. The system of claim 6, further comprising a first and second low pass filter, said first low pass filter being electrically connected between said first autotransformer and said second driver, said second low pass filter being electrically connected between said second autotransformer and said third driver, each of said first and second low pass filters reducing said corresponding output voltage at different cutoff frequencies.

8. The system of claim 2, further comprising at least one first filter means for reducing said output voltage at a predetermined frequency, said at least one filter means being electrically connected to at least one of said plurality of drivers.

9. The system of claim 8, wherein said filter means is connected in parallel to said at least one of said plurality of drivers.

10. The system of claim 9, wherein said at least one filter means comprises a low pass filter.

11. The system of claim 10, wherein said low pass filter comprises a capacitor electrically connected said at least one driver.

12. The system of claim 11, wherein said low pass filter further comprises an inductor in combination with said capacitor.

13. The system of claim 11, wherein said low pass filter comprises a resistor in combination with said capacitor.

14. The system of claim 9, further comprising a plurality of low pass filters, each of said plurality of low pass filters being electrically connected to a corresponding one of at least a portion of said plurality of drivers.

15. The system of claim 14, wherein at least a portion of said plurality of low pass filters have different cutoff frequencies.

16. A system for distributing a source voltage from a signal source, the system comprising:
a) a first autotransformer comprising:
i) a first end connection adapted to produce a first output voltage;
ii) a second end connection adapted to produce a second output voltage; and iii) a tap connection adapted for electrical connection to said signal source, wherein said tap connection is located between said first end connection and said second end connection;
b) a first driver electrically connected to said first end connection, wherein said first output voltage is received by said first driver solely from said first end connection; and c) a second driver electrically connected to said second end connection, wherein said second output voltage is received by said second driver solely from said second end connection.

17. The system of claim 16, further comprising a plurality of autotransformers and a plurality of drivers, wherein said plurality of autotransformers are adapted to produce an output voltage across each of said plurality of drivers, wherein the sum of said output voltages is equal to said source voltage multiplied by the number of said plurality of drivers.

18. The system of claim 17, wherein said plurality of autotransformers comprises said first autotransformer and a remaining portion of said plurality of autotransformers, wherein said first end connection of each of said remaining portion of said plurality of autotransformers is electrically connected to a corresponding one of said plurality of drivers, wherein said second end connection of said remaining portion of said plurality of autotransformers is electrically connected to said tap connection of an adjacently positioned one of said plurality of autotransformers.

19. The system of claim 18, wherein the turn ratio of each of said plurality of autotransformers is (n-x):1, where n is the number of said plurality of drivers and x is the position of a selected one of said plurality of autotransformers form said signal source.

20. The system of claim 19, wherein said plurality of autotransformers comprises said first autotransformer and a second autotransformer, wherein said plurality of drivers comprises said first driver, said second driver, and a third driver, wherein said first end connection of said second autotransformer is electrically connected to said third driver and said second end connection of said second autotransformer is electrically connected to said tap connection of said first autotransformer, wherein said tap connection of said second autotransformer is electrically connected to said signal source, wherein said first autotransformer has a turn ratio of 1:1 and said second autotransformer has a turn ratio of 2:1.