Armour Group Plc v Leisuretech Electronics Pty Ltd

A patent is invalid for obviousness where the claimed combination would have been a technically obvious choice for the skilled person at the priority date. The assessment must identify the skilled person, common general knowledge, the inventive concept, the differences from the prior art and whether those differences required invention. Commercial obviousness is distinct from technical obviousness, although commercial considerations may shape the skilled person’s choice of technical solutions. Particular care is required to avoid hindsight, especially with simple inventions and allegations based on common general knowledge. A combination of familiar components may nevertheless be obvious where their selection and combination involve no inventive step. The court also accepted that a claim may be construed as inherently limited by the technical capability of the claimed cable arrangement.

Armour sought revocation of a patent for a distributed stereo audio system. LeisureTech brought infringement proceedings against Armour Home Electronics Ltd and QED Audio Products Ltd. Infringement was accepted if the patent was valid.

The patent claimed a remote amplifier connected to an audio source and mains power supply by a single Cat.5 four-pair twisted cable carrying both stereo audio signals and low-voltage DC power. The principal issues were construction, obviousness over common general knowledge and specified prior art, and insufficiency arising from the power limitations of Cat.5 cable.

1. Construction. Claim 1 was not limited to hi-fi sound quality or to any particular system size. It was, however, inherently limited to systems providing only the level of electrical power which a single pair of conductors in a Cat.5 cable could deliver. The insufficiency objection therefore fell away on the adopted construction.
2. Obviousness framework. The court applied the structured approach requiring identification of the skilled person and common general knowledge, the inventive concept, the differences between that concept and the state of the art, and whether those differences were obvious. The inventive concept was a distributed stereo system in which one Cat.5 cable carried two audio channels and DC power from the source to a remote amplifier.
3. The relevant skilled person was a designer of home audio systems, particularly multi-room systems, with appropriate electronics or electrical engineering knowledge and experience. The common general knowledge included local amplification with central power, suitable low-power integrated-circuit amplifiers, and the ability of Cat.5 cable to carry audio signals and low-voltage DC power.
4. The claimed combination involved three steps: selecting local amplification with central power; selecting a compact, inexpensive and low-heat IC amplifier; and using a single Cat.5 cable for both audio and power. Each step, and the combination as a whole, was technically obvious. The skilled person would not have been deterred by the lower power, interference or source-impedance issues because the claim could operate with reasonable domestic sound quality, tolerant IC amplifiers and suitable cable lengths.
5. The absence of an earlier marketed product, alleged long-felt want and Armour’s later commercial choices did not establish non-obviousness. The MRS system did not render the claim obvious because its distinctive 40-conductor cable would not have led the skilled person to the claimed arrangement; but it added nothing once common-general-knowledge obviousness was established.
6. The patent was invalid and had to be revoked.