IMPROVEMENTS IN AND RELATING TO SPEAKER SYSTEMS This invention relates to speaker systems and, more particularly provides a speaker system that utilizes the audio output jack socket of audio equipment to power an auxiliary speaker without isolating the speakers of the equipment and that gives to a listener the impression of"surround sound"without relying on banks of large and expensive woofers and sub-woofers and other speakers.

BACKGROUND TO THE INVENTION Many pieces of audio equipment, such as CD players and computers and radios and television sets, are provided with audio output jack socket, which could be a headphone jack socket or an RCA jack socket. The headphone jack socket enables listeners to plug a headphone or a remote speaker and listen to the sound from the equipment. In order that other people in the room in which the equipment is located cannot hear the sound, the jack sockets have an internal switch that when a jack plug is inserted into the socket, it cuts off the sound from the speakers associated with the equipment. The volume is still controlled, however by the volume control of the equipment. Some slight different construction forms of headphone jack sockets are used by different equipment manufacturers. On the other hand, the RCA jack socket is used to pass audio signal to an audio amplifier. Standard RCA jack socket provides audio signal but the volume cannot be changed.

In most commercial audio equipment having built-in speakers, the speakers are responsive over the middle to high range of audio frequency but are not responsive over the low range, the so called"woofer and sub-woofer range".

Accordingly, in order to achieve high fidelity sound reproduction of the sound from such equipment, it is necessary to feed the sound from the jack socket to a separate amplifier and then to a bank of speakers responsive over the whole desired range of frequencies. In small rooms this is impractical and a method of using the existing speakers in a high fidelity sound reproduction system would be desirable. It would also be desirable to provide a system that does not require a plurality of remote controls for a plurality of speakers and amplifiers.

SUMMARY OF THE INVENTION This invention provides a speaker system for use with audio equipment having in- built speakers and plugs into the audio output socket of the equipment to provide a listener the impression that he is listening to full high fidelity audio equipment.

According to the invention, a speaker system comprises a jack plug input from the audio equipment, a pre-amplifier, preferably a pre-amplifier that automatically sets its volume to the volume of the item of audio equipment, a phase angle converter, preferably capable of converting the phase angle of the incoming signal through 0° to 180°, a low to middle pass active crossover filter to tune the band width of the signal to that of the speaker or speakers of the item of the item of audio equipment and a speaker responsive to frequencies in the 40 to 2000 Hz range.

When headphone jack socket is used, the jack is so shaped that when inserted into the headphone jack socket of an item of audio equipment it does not contact the speaker switch-off contacts and the jack plug is directly connected to the pre- amplifier.

When the RCA socket is used, the jack is connected to a microphone controlled volume adjustment circuit to monitor the speaker volume and adjust the audio signal volume before the pre-amplifier.

In operation, the speaker system of the invention generates a sound signal in the low frequency range at the same volume and matching band width as the signal from the speaker or speakers of the item of audio equipment and of such different phase angle that the listener perceives that the entire sound signal is produced from the speaker or speakers of the item of audio equipment.

The bandwidth control may be designed to adjust the bandwidth to compliment the existing speaker system and once that is adjusted, no further adjustment is necessary.

The phase angle may be adjusted manually and will only require further adjustment either if the speaker system is moved to a different item of audio equipment or the relative positions of the speaker of the system and the speaker or speakers of the item of audio equipment is changed.

Accordingly, once the position for the speaker of the system has been decided and the system tuned to produce the optimum sound quality it may be left untouched and therefore it can be located in a relatively inaccessible position, such as behind an item of furniture or the like, and thus be hidden from view.

The system therefore does not require to be encased in a fancy cabinet and since the components of the system are relatively cheap, the user can obtain high quality sound reproduction at a fraction of the cost of a full high fidelity sound system.

DESCRIPTION OF PREFERRED EMBODIMENTS The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which Fig. 1 is a schematic diagram of a speaker system according to the invention; Fig. 2 shows a conventional headphone jack plug ; Fig. 3 shows one form of headphone jack plug for use in the system of the invention; Fig. 4 shows a second form of headphone jack plug for use in the system of the invention;

Fig. 5 shows a fourth form of headphone jack plug for use in the system of the invention; Fig. 6 shows a fifth form of headphone jack plug for use in the system of the invention; and Fig. 7 shows a sixth form of headphone jack plug for use in the system of the invention; Fig. 8 is a schematic diagram of a speaker system according to the invention utilising the RCA jack; Fig. 9 shows a conventional RCA jack plug ; As shown in Fig. 1 the system of the invention comprises an input headphone jack 1 of a configuration as shown in one of Figs. 3 to 7, depending on the configuration of the headphone jack of the item of audio equipment with which the system is to be used.

Jack plug 1 leads to a preamplifier 2 the output of which is connected to an adjustable phase angle converter 3 capable of adjusting the phase of the signal by 0° to 180°. The output of adjustable phase angle converter 3 is connected to an adjustable low to middle pass active crossover filter 4, the output of which is connected to a power amplifier 5. A speaker 6 responsive to frequencies in the 40 Hz to 2000 Hz range is connected to the output from amplifier 5.

As shown in Fig 2, a conventional headphone jack plug 1 comprises a tip 11 with contacts for receiving a sound signal from the remote end of the jack socket 13 of an item of audio equipment 14 and a shaft 12 that when inserted in jack socket 13 activates a cut-off switch or switches inside the socket to isolate the speaker or speakers 16 of the item of audio equipment 14.

Figs. 3 to 7 show various configurations of tip 11 and shaft 12 such that when the jack plug 1 is inserted in jack socket 13 do not activate the switch or switches.

As shown in Fig. 3, the shaft 12 of jack plug 1 for use when a single switch is located along the length of the socket 13 has a cut out portion 17 in a position that ensures that when jack plug 1 is inserted in socket 13 and, if necessary rotated to a relevant position, the switch lies over cutout portion 17 so that it is not activated.

As shown in Fig. 4, the shaft 12 of jack plug 1 for use when two diametrically opposed switches are located along the length of the socket 13 has a pair of cut out portions 17 in a position that ensures that when jack plug 1 is inserted in socket 13 and, if necessary rotated to a relevant position, the switches each lie over a cut out portion 17 so that they are not activated.

As shown in Fig. 5, the tip 11 of jack plug 1 for use when two diametrically opposed switches are located towards the tip of socket 13 has a spade end 18 that ensures that when jack plug 1 is inserted in socket 13 and, if necessary rotated to a relevant position, the blade of spade end 18 passes between the switches so that they are not activated.

As shown in Fig 6, it is also possible to combine the arrangements of Figs. 3 and 4 so that the plug can be used with both forms of jack socket. Jack plug 1 has both a cut out portion 17 and a spade end 18.

Fig. 7 shows a further arrangement in which shaft 15 is shorter than usual so that it does not extend to the location of the switch or switches and the plug terminates in an insulated portion 19 of narrower diameter and a hook-shaped pick-up contact 20.

As shown in Fig. 8 the system of the invention comprises an input RCA jack 21 of a configuration as shown in Fig. 9. In this case the, the audio signal is taken from the RCA output socket 24 but since the audio output can not be adjusted in volume, a means is employed for enabling volume adjustment. The volume adjustment is achieved by attaching a microphone 23 to the audio equipment 14 and passing the signals to a microphone controlled volume adjustment circuit 22.

The adjusted audio signal leads to a preamplifier 2 which is connected to an adjustable phase angle converter 3 capable of adjusting the phase of the signal by 0° to 180°. The output of adjustable phase angle converter 3 is connected to an adjustable low to middle pass active crossover filter 4, the output of which is connected to a power amplifier 5. A speaker 6 responsive to frequencies in the 40 Hz to 2000 Hz range is connected to the output from amplifier 5.