Armour Group Plc v Leisuretech Electronics Pty Ltd

In action HC 2007 C01407 Armour Group plc seeks the revocation of European Patent (UK) No. 1 004 221 B1 (“the Patent”). In action HC 2007 C01673 LeisureTech Electronics Pty (“LeisureTech”) sues Armour Home Electronics Ltd and QED Audio Products Ltd for infringement of the Patent. There is no need to distinguish between the various Armour companies and I will refer to them collectively as “Armour”. There is no dispute that Armour’s system infringes the Patent if it is valid. Armour challenge the validity of the Patent on two grounds, obviousness and insufficiency. Insufficiency was deployed primarily as a squeeze. Armour’s principal attack is obviousness over common general knowledge. They also rely on two items of prior art known as Linn Knekt and MRS, but as discussed below these add little to the principal attack. A number of other issues fell by the wayside in the run up to, and during, the trial.

The Patent is for a distributed stereo audio system, that is, a system for providing stereo sound to several rooms or zones from a single source of audio signals. Distributed audio systems are often referred to as multi-room audio systems, and I shall use both expressions interchangeably. The Patent has a priority date of 15 August 1997. LeisureTech proposes to amend the Patent in the manner set out below. Armour do not object to the amendments. For reasons which it is unnecessary to go into, LeisureTech did not formally apply to make these amendments prior to the trial. It was agreed that the trial would be conducted on the basis of claim 1 as proposed to be amended and that, if the validity of that claim is upheld, directions will be given for the making of a formal application to amend. If claim 1 as proposed to be amended is invalid, LeisureTech does not contend that any of the subsidiary claims is valid.

Armour called as their expert William Miller. Mr Miller studied Electrical and Electronic Engineering at Glasgow University, and obtained his degree in 1977. After completing his degree, he worked for Hewlett Packard for four years as a design engineer. After leaving HP, he spent the next 25 years working for Linn Products Limited (“Linn”). During that period Linn became a well-known manufacturer of hi-fi components and systems, in particular “high end” products targeted at audiophiles. He was a member of the Management and Product Development Group at Linn and was thus involved in technical aspects of the design of a large number of audio systems and components. From 1981 to 1988 he was a design engineer. From 1988 to 2002 he was the Design Engineering Manager. As such, he was responsible for the development of Linn's multi-room audio system, the Linn Knekt. From 2002 to 2006 he was Chief Engineer.

LeisureTech accepted that Mr Miller’s oral evidence was completely honest and fair. They criticised his written reports as being inaccurate in two respects, but in my view these inaccuracies were merely the result of slightly careless wording. More importantly, LeisureTech submitted that Mr Miller was overqualified in that he was more skilled and experienced than the addressee of the Patent and was inventive. Mr Miller repeatedly emphasised in his evidence, however, that he had tried to view matters from the perspective of the ordinary skilled person, and I am satisfied that he did so as well as anyone in his position could. LeisureTech also made the valid point that, since Mr Miller had spent almost the entirety of his career at Linn, which was both a manufacturer of high end equipment and an innovative company, this was likely to have influenced his viewpoint. I have taken this into account in assessing his evidence. I have taken into account the fact that Mr Miller was slightly diffident in his manner, something that I attribute to his personality and his inexperience as an expert witness rather than to his technical ability or his belief in the opinions he expressed.

LeisureTech called as its expert Martin Colloms. Mr Colloms graduated from The Polytechnic (now the University of Westminster) in 1971 with a BSc in Electrical Engineering specialising in Electronics. Following graduation, he was employed as a design engineer in electronic instrumentation at the UK division of Tektronix Inc, a US company best known for its test and measurement equipment (e.g. oscilloscopes and logic analysers). In 1973, he co-founded Monitor Audio Limited, a company specialising in high fidelity loudspeaker designs. His role was as Technical Director of the company with responsibility for the design and quality control of its products. He left the company in 1975. In that year he founded an independent design and evaluation consultancy, Colloms Electroacoustics, through which he provides a range of services to the audio and electronics industry internationally. He has an impressive list of clients in this field. During his career Mr Colloms has designed or co-designed a large number of audio products, and has designed and installed sound distribution systems. He was admitted as a Chartered Engineer of the Institution of Electrical Engineers in 1981.

Mr Colloms is also a prolific author. He has been Contributing Technical Editor of Stereophile in the USA for 15 years and held an equivalent post at Hi Fi News and Record Review in the UK for 25 years. He is the publisher of a journal called HIFI CRITIC, which he founded in late 2006 to provide more serious coverage of stereo systems for enthusiasts and the audio industry. By 2007 he had published more than 3,900 product reviews and articles in a variety of publications. He has also written or contributed to three books, including High Performance Loudspeakers, which was first published in 1976 and is currently in its sixth edition.

An unusual aspect of Mr Colloms’ career is that he has had much more extensive experience with patents than most expert witnesses in patent actions. He is a named inventor on 200 patents worldwide. In addition, he has acted as a consultant intellectual property manager and patent analyst to NXT plc since 1995, in which capacity he has been responsible for advising on over 1,000 patent applications in 260 patent families. The activities which he lists in his CV as having been performed in this role include many activities of the kind normally undertaken by patent attorneys, including patent drafting, analysing prior art, responding to official actions, attending examiner interviews, helping attorneys prepare oppositions and responses to oppositions, revising patent claims and responding to patent queries by licensees. In addition, Mr Colloms has given expert evidence in several previous cases.

Armour submitted that Mr Colloms was focussed on the higher end of hi-fi. I do not accept this. If anything, Mr Colloms has more experience of the middle and lower ends of the hi-fi market than Mr Miller. More importantly, Armour submitted that Mr Colloms was a patent advocate par excellence. As I have said, I agree that Mr Colloms’ experience of patents was unusual and I have taken this into account in assessing his evidence. Armour did not suggest, however, that Mr Colloms had been partisan in his approach to this case. I have also taken into account the fact that Mr Colloms was more confident in his manner than Mr Miller, which I attribute to his greater experience in this field.

LeisureTech also adduced unchallenged evidence of fact from Paul Tam, the co-owner and director of The Listening Rooms, a home electronics retail business. I have taken this evidence into account, but in my judgment it is of little assistance on the key issues because, although Mr Tam evidently had considerable knowledge of the distributed audio system market at the relevant time, he was not representative of the addressee of the Patent since he did not possess the qualifications and experience of such a person as discussed below.

The Patent is a fairly short document. Paragraph [0001] defines the technical field. Paragraphs [0002]-[0008] describe the background art. This section includes an acknowledgement of the Linn Knekt system. Paragraphs [0009]-[0024] are headed “Summary of the invention”. The key paragraphs are as follows:

“[0009] The present invention is characterised in that the amplifier is connected to the signal source and power supply by means of a Cat. 5 four pair twisted cable which provides, in respective conductors of the twisted pairs, right channel audio signals from the signal source to the amplifier, left channel audio from the signal source to the amplifier, and DC power from the power supply to the amplifier.

[0010] The right channel audio, left channel audio and DC power may be provided in respective twisted pairs.

[0011] This system enables decentralisation of amplification, and permits the amplifier to be installed remote from the signal source and close to the speakers, reducing speaker cable loss and increasing total system damping factor. The remote amplifier does not need to be positioned close to a voltage source since it receives its power via the Cat. 5 four pair twisted cable.

[0012] The cabling is very simple and easy to install. One Cat. 5 cable connects the source of audio signals, to each room or zone. This cable carries audio signal system power, and if required, data and status. Digital systems can also carry video transmission. More of the cables can be laid in parallel if higher power or bi-amplification is required.

…

[0016] The remote amplifiers can be integrated circuit amplifiers. As a result of not requiring built-in power supplies they may be compact, and they may be constructed to fit into a standard electrical light switch housing or be incorporated into a speaker box or in-wall or in-ceiling speaker. A suitable example is the Silicon Monolithic Bipolar Linear Integrated Circuit, TA8216H, dual audio power amplifier.

…

[0021] The remote amplifiers may accept standard line level signals from the audio source components, or speaker outlet of a master amplifier which may be matched to the audio source, or sources, and may be located with them. In other words, the remote amplifiers may be driven by either a low impedance (4 to 16 ohm) speaker level signal, or high impedance (10k ohm) line level signal.

…

[0024] The output from the remote amplifiers is sufficient to drive a pair of hi-fi speakers, 4 to 16 ohm, at a reasonable sound level for most domestic requirements; typically 90-100dB unweighted. The remote amplifiers do not require fused output protection.”

The specification then describes two specific embodiments. The first, illustrated in Figure 1, comprises a source of audio signals consisting of several units and a power supply in one room connected by means of a Cat.5 cable to an amplifier and two speakers in another room. The second, illustrated in Figure 2, comprises a source of audio signals and a power supply in one room connected by means of two Cat.5 cables to an amplifier and two speakers in each of two other rooms.

The specification concludes with some more general description, including some technical details regarding Cat. 5 cable. It is explained that Cat. 5 is an abbreviation of category 5 in the Underwriters Labs Level classification system, which corresponds to a category in the American National Standards Institute’s Electronic Industry Association/Telecommunication Industry Association 568A standard.

As proposed to be amended, omitting reference numerals and broken down into integers, claim 1 is as follows:

As can be seen, the amendments explicitly limit the claim to systems in which the amplifier is connected to the source and power supply by means of a single Cat.5 cable. Thus systems with multiple parallel Cat.5 cables of the kind contemplated by the last sentence of paragraph [12] are excluded.

Although the subsidiary claims are not in issue, it is worth noting two features which are the subject of them. First, claim 5 adds the limitation that “the or each amplifier is based on an integrated circuit amplifier”. Secondly, claim 13 adds the limitation that “infrared signals received by the amplifier are transmitted to the source or source components through a fourth twisted pair in the Cat.5 cable”. These signals are control signals for e.g. source selection and/or volume control.

A patent specification is addressed to those likely to have a practical interest in the subject matter of the invention, and such persons are those with practical knowledge and experience of the kind of work in which the invention was intended to be used. The addressee comes to a reading of the specification with the common general knowledge of persons skilled in the relevant art, and he (or, once and for all, she) reads it knowing that its purpose is to describe and demarcate an invention. He is unimaginative and has no inventive capacity.

In the present case there is little, if any, dispute between the parties as to the identity and attributes of the person skilled in the art to whom the Patent is addressed. He is a designer of home audio systems, in particular distributed or multi-room systems. Such a person would have a degree in electronics or electrical engineering, or an equivalent qualification, and some post-qualification experience in designing audio systems. He would know not merely about multi-room audio systems, but about audio systems and components generally. Mr Colloms described the knowledge required of such a person in this way:

“At the Priority Date, specialist technical knowledge would have been required to develop a new technical design for a home sound distribution system. This would have included knowledge of loudspeakers, including ‘area coverage’, ‘impedance’, ‘frequency response’, ‘sound quality’, ‘sound pressure levels’, and ‘sensitivity’. In addition, detailed knowledge of the technical performance of speaker cables would have been needed, along with some over-arching system design skill. The skilled person would have needed to be able to design for multiple remote sound reproducing locations, multiple (generally two) channel music signal sources, customer-friendly remote control interfacing, and a central distribution unit to take care of the complex interfacing and logical control of the components. Such a skilled person would also have needed to understand the transmission of sensitive, low power audio signals over long distances in view of possible interference from, for example, electric power cables.”

Although Mr Colloms does not specifically refer to amplifiers in this passage, it is clear that the addressee would need to know about them too.

The correct approach to identifying the information which constitutes the common general knowledge of the addressee was explained by Aldous LJ in Beloit Technologies Inc v Valmet Paper Machinery Inc [1997] RPC 489 at 494-495. In the present case there was considerable ground between the parties and their respective experts as to the common general knowledge, but also some differences. I find that the common general knowledge included the following matters. For convenience I shall mainly use the present tense, but I am referring to the position in August 1997.

Home audio systems come in many shapes and sizes, but they all have three basic features. First, a source of music and other sounds. This might be a radio tuner, CD player, cassette player, record deck or a combination of some or all of these. Secondly, an amplifier to amplify the signals generated by the source. Thirdly, at least one loudspeaker, or in a stereo system at least two loudspeakers. For many years, these components have been available in various physical configurations. There are “all in one” products where source, amplifier and speaker(s) are all combined in a single unit. These include portable radios and “boomboxes” or “ghettoblasters”. There are also products, often referred to as “music centres”, where the source and amplifier are in one box with separate loudspeakers connected by cables. Then there are “separates”, where each item is contained in a separate box and connected by cables.

As with most kinds of consumer products, so with home audio equipment there are different kinds of product for different segments of the market. The car market has its sports cars, its family saloons and its small hatchbacks. The market for home audio is no different. There is a spectrum of products both in terms of sound quality and expense. Moreover, as discussed below, these are not the only variables. Although, as Mr Colloms pointed out, it is possible to achieve good sound quality on a moderate budget, there is a well-established distinction between two broad segments of the market.

First, there is an “audiophile” market populated by hi-fi buffs. Audiophiles are primarily interested in achieving good sound reproduction. They will generally purchase carefully selected separates with high specifications, often from different manufacturers, so that the CD player is made by A, the tuner by B, the amplifier by C, the loudspeaker by D and the cables by E. Some people with relatively modest budgets might count themselves as audiophiles, but many audiophiles will be prepared to spend hundreds, or even thousands, of pounds on individual components of a system. While audiophiles may be interested in the visual aesthetics of the products they buy, obtrusiveness is not generally a concern for them. Indeed, they may be proud of having a large pair of loudspeakers in their living room and be prepared to tolerate ugly runs of speaker cable being visible.

Secondly, there is a “mainstream” market in which sound quality is less of a priority. Portable radios, boomboxes, music centres and systems consisting of matched separates all of which are made by the same manufacturer primarily sell into this market. As a broad generalisation, consumers in this segment of the market are more concerned about both cost and obtrusiveness than audiophiles.

At this point it is necessary to say something about the term “hi-fi”. This is an abbreviation of “high fidelity”. The Oxford English Dictionary defines the term “hi-fi” as meaning:

“That part of acoustics and electronics that deals with the design, construction, and use of equipment for the recording and reproduction of sound to a fairly high standard. Also attrib. or as adj., esp. hi-fi equipment, set, system, equipment for the home designed to reproduce (and sometimes to record) sound to such a standard, consisting often of several distinct units. Also ellipt. for hi-fi equipment, etc.”

As this definition indicates, hi-fi is not a precise term. It does not denote any particular sound quality, although it is generally used to refer to reasonably good sound. Nor is it confined to systems consisting of separates, although it is more commonly used in relation to such systems.

Although some home audio equipment, such as a portable radio, produces mono sound, most produces stereo. For present purposes mono equipment can be disregarded, and in the remainder of this judgment it should be taken as read that I am considering stereo systems even if I do not say so.

Like home audio systems in general, there are different types of distributed audio systems which range in sophistication and cost. The simplest type, which has existed for many years, comprises systems in which the amplifier (or amplifier part of the unit) has connections for two sets of loudspeakers. One set would usually be placed in the same room, while the other could be placed elsewhere. This would enable the user to listen to music in a second room, but would not enable him to control the system (for example to adjust the volume) without returning to the first room. The same result could also be achieved by a switch box external to the amplifier. Then there are “satellite” systems, which have also been around for a considerable time. These systems comprise a central audio system with multiple connections from the amplifier to loudspeakers in various rooms. The desired source (e.g. CD player or tuner) can be selected and controlled from the rooms (e.g. by means of a wall-mounted control unit), but there is no facility to listen to different sources in different rooms. More recently, multi-room systems have emerged which enable the listener to select different audio sources for different rooms using a switching matrix controllable from each room. Such systems employ either a multi-channel amplifier or several amplifiers.

A common requirement of multi-room audio system customers is that the system should be unobtrusive. This often means concealing the amplifiers, the loudspeakers and the cabling. Compact amplifiers and flush-fitting, in-wall or in-ceiling loudspeakers serve this purpose. Such loudspeakers are necessarily of lower quality than separate free-standing or even shelf-mounted loudspeakers. Because these loudspeakers are embedded in the wall or ceiling they have to be quite small. Their size means that their low frequency, bass, performance is compromised. In addition, much of the sound generated is lost into the ceiling or wall cavity because there is no room to construct a speaker enclosure. They are visually unobtrusive, but as a result they give relatively poor sound quality. Nevertheless, there is a substantial market for such systems amongst customers who value unobtrusive aesthetics over sound quality.

The majority of multi-room audio systems are designed to be installed by professional installers. This market is known as the “custom install” market. Custom installers work with clients, for example householders, architects or developers, and their job is to join together a number of off-the-shelf products into a coherent and functional whole. A custom installation will often not only include entertainment systems (audio and video), but also the lighting system, heating and air conditioning and other aspects of home automation. The products in question are inevitably from different manufacturers, perform a wide range of different functions and use different control protocols. Assembling them into a seamless whole is a complex undertaking because it involves creating a user interface that can control all of the components of the system. This typically involves the use of a programmable control system that has to be programmed by the installer to recognise and control the system components. In addition, the aesthetic demands of customers who choose multi-room audio systems, including the need to hide wires and place loudspeakers discreetly about the home, means that practical skills are required to complement the programming skills. For these reasons, trained and experienced professional installers perform nearly all installation work.

Because most multi-room audio systems are installed by custom installers, any designer of such systems has to be well aware of the needs and views of the installers. Installers prefer systems that are easy to install, reliable, expandable and “open”, that is to say, interconnectable with other components.

Mr Miller’s evidence, which I accept, is that the market for multi-room audio systems started to take off in 1988 and that the custom install business grew from almost nothing in 1990 to substantially larger than the “high end” hi-fi retail business by the late 1990s.

Mr Miller gave evidence that the designer of a distributed audio system in 1997 would have to make a number of choices between various well-known options regarding different aspects of the system. These included the following:

It is clear from the evidence that there are, and the skilled person would be aware that there are, trade-offs between many of these choices in terms of functionality, sound quality, cost, unobtrusiveness, ease of installation and so on.

It is common ground that in August 1997 two basic architectures for distributed audio systems were common general knowledge. The first involves “central” amplification: the signal from the source is amplified by a central amplifier and then distributed to speakers in the various rooms at “speaker level”. The second involves “local” or “remote zone” amplification: the signal from the source is distributed to amplifiers situated in each of the rooms at “line level”. It is also common ground that at that time the large majority of systems were central amplification systems.

Although counsel for LeisureTech suggested to Mr Miller in cross-examination that the choice of central amplification was a “one way street” for a moderately priced, unobtrusive system, it was common ground between the experts that each architecture was known to have advantages and disadvantages. Indeed, in the common general knowledge section of his first report Mr Colloms listed no less than six classes of problems with central amplification, namely (i) cable issues, (ii) transformer-related losses, (iii) volume control issues, (iv) signal selection issues, (v) difficulties in automating and remote control and (vi) overall expense. Among the problems he highlighted were the need to use powerful, expensive amplifiers and bulky, expensive speaker cables. Mr Colloms went on:

“A number of years before the Priority Date, several manufacturers had identified remote-zone amplification as a means of overcoming some of the problems highlighted above.”

In a later section of his report he added:

“The sound quality advantages of remote zone amplification were known but up to the Priority Date remained expensive and inconvenient to implement.”

In the case of local amplification systems, it is common ground that all the distributed audio systems on the market of which the skilled person would be aware from his common general knowledge involved “local power”, that is to say, each amplifier was powered from a supply located in the same room as the amplifier. It is also common ground that there was one system on the market (namely the MRS system discussed below) involving “central power”, that is to say, power distributed to the amplifiers from the central location along the same cable as the audio signal; but the existence of that system was not common general knowledge. Armour contend that, even though he would not have known of any actual example on the market from his common general knowledge, the skilled person would also have been well aware that local amplification with central power was a possible option. LeisureTech disputes this.

In my judgment the evidence of the experts establishes that using local amplification with central power was part of the common general knowledge in the sense that the addressee would have been well aware that it was one option available. Thus Mr Colloms stated in the section of his first report dealing with common general knowledge:

“For systems with remote zone-located amplification, this gave rise to difficulties as to where this power would be supplied from. One option was to arrange local mains power to supply the amplifiers. An alternative approach was to use the multi-room system cable (i.e. the same one that transmitted the signals) to provide the amplifier power at a safe lower level voltage.”

When asked about this paragraph during cross-examination about common general knowledge, he said:

“Q. It is right, is it not, that the options that you identify are options that would have been available to the skilled person in 1997?

A. Yes, I think we are talking MRS at this stage for zone remote power.

Q. But even more generally, those would have been options that would have been in the skilled person's toolkit.

A.

Yes. It is certainly possible to design one, yes.”

Like the other parts of a home audio system, amplifiers range widely in their size, performance and cost. A key measure of amplifier performance is the output power expressed in Watts per channel.

LeisureTech contends that the general perception in the art in 1997 was that 30W per channel or so was the starting point for hi-fi sound quality; that it was regarded as desirable for amplifiers to have a certain amount of “headroom” in terms of power so as to be able to deal with sudden dynamic changes without clipping; that most amplifiers described as hi-fi were rated at 30W per channel or more, and in many cases significantly more; and that all of the multi-room audio systems available in 1997 had amplifiers rated at 30W per channel or more. By contrast, Armour contend that the person skilled in art was well aware that the power ordinarily required for normal domestic listening was much less than 30W per channel, with around 1W per channel being adequate; that systems rated at 30W per channel or more mostly operated at much lower power during ordinary use; that many domestic audio systems were rated at only a few Watts per channel; and that (as described in more detail below) integrated circuit amplifiers were available off the shelf which were rated at a few Watts per channel which were suitable for home audio applications.

In my judgment the evidence demonstrated that both parties’ contentions are well-founded, and there is no contradiction between them. LeisureTech’s focus here is upon the audiophile market. I am satisfied that in that market the general perception was as LeisureTech contends, notwithstanding the fact that it was known that normal domestic listening did not require anything like as much power as 30W. But as I have described above, the audiophile market was not the only market for home audio equipment. In the mainstream market the position was different. The person skilled in the art would have been aware of both. In particular, the skilled person would have been aware that, if one was prepared to compromise to some extent on sound quality, lower-powered amplifiers were not merely available, but also perfectly satisfactory.

So far as multi-room audio systems are concerned, it does appear to be the case that all the systems on the market used amplifiers rated at 30W per channel or more, but I do not accept that the skilled person would have thought that it was essential to employ such powerful amplifiers. As discussed above, many customers for such systems are more interested in visual appearance than in sound quality of the kind expected by audiophiles. Mr Colloms’ evidence was that consumers purchasing distributed audio systems “expected at least basic hi-fi quality [my emphasis]”. The skilled person would have been well aware that lower-powered amplifiers could deliver sound of that quality.

An important class of amplifiers for use in home audio systems is integrated circuit or IC amplifiers. These are amplifiers in which most of the components have been fitted into a single integrated circuit. Such amplifiers are referred to in the Patent at paragraph [0016]. It is common ground that such amplifiers were well known and widely available in 1997. Mr Colloms described them in this way:

“An example of a suitable commercial stereo power amplifier is given (which is a single integrated circuit chip) (see para [0063] of the Patent). This device was widely used for car stereo systems and moderate power home audio products, such as combination ‘Hi Fi’ sets. Data sheets, easily accessed from chip manufacturers and resellers, show a power output of 2x 10W for an 8 ohm load and 2x 15 W for a lower impedance 4 ohm load.”

“… the Patent clearly provides that the skilled person may readily use a typical, widely available and well known IC chip amplifier, familiar to the audio industry as a low power, relatively low voltage, two channel device used widely in compact domestic audio units and also built into car stereo head units on a grand scale. With a 10W to 15W power output for 8 to 4 Ohm loudspeakers, it is conveniently capable of operating from a single DC rail supply up of to 24 volts. … These IC amplifiers were intended for lower power, good performance applications and their manufacturers provided comprehensive engineering guidance on their trouble free application.”

“For mass production, the IC amplifier with its fewer parts has its attractions but some care was needed with its selection since some were of higher distortion, more intended for ‘boom boxes’ than high fidelity. Cheaper IC amplifiers were low on power and quality. They did not have good noise levels and experienced distortion that was so high, that for some amplifiers one could get only 1/3 to 1/2 of the claimed power on bench testing. There were a few, more expensive, IC amplifiers that came with more precise specifications and could deliver hi-fi quality at 10-15W; and even higher powers were available right up to 100W. The example given in the Patent was one of these off-the-shelf IC amplifiers, and is merely an example of a compact amplifier with a suitable audio performance, well specified for power, noise, frequency response and distortion.”

A considerable range of IC amplifiers was available in 1997. Specification sheets for a number of examples of IC amplifiers which were available then are in evidence, including several manufactured by Toshiba. These include the TA8211AH dual audio power amplifier, which provided an output power of 6W per channel, had a recommended supply voltage of 20V for an 8Ω load resistance and was described as “suitable for power amplifier of TV and home stereo”; and the TA8216H dual audio power amplifier, which provided an output power of 13W per channel, had a recommended supply voltage of 24V for a 4Ω load resistance, and was described as “suitable for power amplifier of music center”. In the case of the TA8216H the specification sheet includes a graph of total harmonic distortion (“THD”) against output power at three different frequencies, which shows that the device has a THD of less than 0.3% when output power is below 10W. Consistently with the third extract from his reports quoted above, Mr Colloms agreed in cross-examination that this was a hi-fi amplifier if used within its limits.

The evidence does not go so far as to establish that either the TA8211AH or the TA8216H was itself common general knowledge in 1997, but I am in no doubt that the existence and general characteristics of IC amplifiers of the type exemplified by the TA8211AH and the TA8216H were part of the common general knowledge of the addressee. Selecting a suitable IC amplifier for a given application from the manufacturers’ catalogues would have been a routine matter for a skilled person. Furthermore, the skilled person could quickly calculate the power requirements of such an amplifier from the information provided in the data sheet.

IC amplifiers of the kind exemplified by the TA8211AH and the TA8216H have a number of advantageous characteristics. First, they are very compact (less than an inch long), which makes them highly suitable for use in applications where space is at a premium. Secondly, they are inexpensive, which makes them highly suitable for use in applications involving a multiplicity of amplifiers. Thirdly, because they are low power devices they do not dissipate a great deal of heat. Fourthly, they are quite tolerant of variations in the power supply.

In order to connect the various parts of a distributed audio system together one needs cables. Cables are used for a number of purposes. If central amplification is used, long runs of cable are needed to take the speaker level signal from the central amplifier to the speakers in the various rooms. If local amplification is used, long runs of cable are needed to take the line level signal from the source to the remote amplifiers and much shorter runs to take the speaker level signal from each amplifier to its speakers. Cable that carries speaker level signals must carry a heavier load than cable that only carries line level signals. This presents a problem for long runs of cable, because resistance is proportional to length. Cable for both purposes should be good at signal transmission without interference.

Cable is also needed for the transmission of electrical power. If local amplification with local power is used, then the cable is likely to be carrying ordinary mains power (i.e. 240V AC) which is transformed in the amplifier. If local amplification with central power is used, then the cable only needs to carry relatively low voltage DC power (e.g. 24V DC).

Cat.5 is an industry standard for a certain type of cable which contains four sets of twisted pairs of thin conductors. Telephone systems have used twisted pair cables for many years. Twisted conductor pairs have two significant characteristics: (i) with appropriate circuitry at each end, they have a high immunity to electromagnetic interference; and (ii) they have a predictable and consistent characteristic impedance which, with appropriate circuitry at each end, yields good high frequency signal transmission. The former is particularly relevant for the distribution of audio signals; the latter is essential for the transmission of high speed computer networking signals. Because Cat.5 cable has four twisted pairs of conductors, it is inherently suitable for carrying up to four different signals, although in some circumstances it can carry eight.

Cat.5 has certain other advantages. It is inexpensive and widely available; it can be used with simple RJ45 connectors similar to those used to connect telephone cables to sockets; and it is tolerant to bending and abrasion, and so is relatively easy to thread through a building. Mr Miller gave unchallenged evidence that it would have been assumed to have been certified as flame retardant, although the evidence does not establish that it actually was certified in 1997. Certainly, it appears that by then it was being widely installed in newly-built houses as well used for custom installations in existing houses.

Cat.5 was originally developed for data transmission. Indeed, it is probably best known for its use in Ethernet networks. The first standard describing Cat.5 was published in 1991, but it is clear that it caught on quickly and not just in the computer industry. This is illustrated by what happened with the Linn Knekt system. Linn started developing this system in about 1987. To begin with, Linn used FCC68 eight-conductor flat cable terminated with RJ45 plugs. The product was launched in June 1993. Almost immediately after the launch, Linn was informed by custom installers that they wanted to use Cat.5 cable with the system instead of FCC68. Linn was able to achieve this simply by providing installers with a diagram showing how to connect the eight conductors in a Cat.5 cable to the eight terminals of an RJ45 plug for use with the Linn Knekt system. It was Mr Miller’s evidence that by 1993 it was clear that Cat.5 was the preferred cable for use in multi-room audio installations. Mr Colloms agreed that by 1997 it had become the most commonly used cable for wiring homes for communication and control purposes, but not for audio.

LeisureTech contends that the use of Cat.5 cable for transmission of audio signals, as opposed to digital data, was not common general knowledge by August 1997. In support of this contention it points out that the only system in which Cat.5 is known to have been used for audio signals by that date is the Linn Knekt. Against this, Armour contend that the Linn Knekt system was itself well known to skilled persons interested in multi-room systems and that that in itself was sufficient to make the use of Cat.5 for carrying audio signals common general knowledge. In my judgment the evidence supports this contention. In any event, however, I am satisfied that the skilled person would have been well aware of the existence and characteristics of Cat.5 cable, and in particular its suitability for carrying audio signals, particularly line level audio signals. Thus in his discussion of the common general knowledge in his first report Mr Colloms said:

“CAT-5 was a useful cable for carrying the audio signals for a multi room install as such cables need to carry the audio signal (and data signals for the remote commands and control) over long distances e.g. 100m or more.”

In cross-examination Mr Colloms agreed that by 1997 the addressee would have had a motivation to use Cat.5 cable to distribute audio signals in multi-room audio systems since it was so widely installed.

LeisureTech also contends that, even if the use of Cat.5 for the transmission of audio signals was common general knowledge, the use of Cat.5 for the transmission of electrical power, and in particular power together with audio, was not. In support of this contention it points to the fact that, even in the case of the Linn Knekt, Cat.5 cable was not used to carry power to the amplifiers, but only audio and bi-directional control signals. Indeed, although Linn Knekt was a local amplification system, it used local power for the amplifiers (although it did use Cat.5 cable to carry about 3W of power from the amplifier to the room control unit).

In my view one must be careful here to be precise about what one means by “power”. What matters is for present purposes is low level power of the order of 15W delivered by low voltage DC. It is common ground that Cat.5 cable is not in fact capable of carrying any higher power than about 15W over any significant distance, but it had been used in the telecommunications and computing fields for carrying low level power. I agree that the actual use of Cat.5 cable to carry power has not been shown to be common general knowledge in the audio field, but I am satisfied that the skilled person would have been aware that Cat.5 cable was suitable for carrying low level power. After all, it is an electrical cable. As Mr Colloms accepted during cross-examination, the skilled person would readily be able to calculate the power-carrying capabilities of a length of Cat.5 cable.

As for transmission of audio signals and low level power, again I am satisfied that the skilled person would have been aware that Cat.5 was suitable for carrying both. As can be seen from paragraph 35 above, it was Mr Colloms’ evidence that using the multi-room system cable to carry both audio signals and low voltage power was an option that was part of the common general knowledge. It was also his evidence that Cat.5 cable was well known to provide good immunity to electrical noise and interference.

Because custom installations usually include other systems in addition to audio systems, they are somewhat expensive. The evidence suggests that the cheapest custom installations in 1997 cost several thousand pounds. LeisureTech contends that this meant that cost saving was not a particular concern for a designer of a multi-room audio system, and in particular not cost saving on individual components such as amplifiers. I do not accept this. It was common ground between the experts that there was a market for moderately priced multi-room audio systems. Such systems could be sold both to those who only wanted a distributed audio system and to those who wanted a complete custom installation. In the former case, there were customers who could not afford, or did not want, to spend thousands of pounds. Satellite systems were among the products targeted at such customers. In the latter case, some customers might well prefer to spend more money on, say, the video and lighting systems than on the audio system. Furthermore, the designer of a multi-room audio system would appreciate that the cost of the system depended not merely on the cost of the components, but also on the cost of the cables and on the ease of installation.

A moderately priced distributed audio system dating from before August 1997 which was mentioned by both experts in their reports, and by Mr Tam in his statement, is the QED Systemline system. Mr Colloms described Systemline in this way:

“The QED Systemline distributed sound system (pre-1997) was an approach to remote zone amplification aimed to reduce cost. One part of this solution was to provide lower cost custom amplifiers. There was also a considerable simplification of the control system and versatility when compared with Linn Knekt (e.g. fewer sources and zones could be catered for, and more limited intelligence in the user interface). This reduced cost objective was not fully met because the remote amplifiers were at the time 30 + 30W and required the provision of local mains supply. The system also used a proprietary QED cable.”

It will be noted that Mr Colloms says that the objective of reduced cost was not fully met because the remote amplifiers delivered 30W per channel and required the provision of local mains supply, and that a defect of the system was the use of a proprietary cable. Similarly, Mr Tam said that the system was “quite bulky and expensive because each amplifier required an individual power supply”.

Systemline was promoted both as being “almost invisible” and as producing “real hi-fi sound”, but the evidence of both experts was that it did not deliver good sound quality. Thus Mr Colloms said:

“… the Systemline product produced by QED … was considered good value but it did not produce particularly good quality sound.”

Mr Tam’s evidence was that in about 1995-97 Systemline was developed into a central amplification system in which Cat.5 cable was used to carry control signals but not amplifier power. It is not entirely clear from his description whether or not the Cat.5 cable carried audio signals, but my understanding is that it did not.

Subsequently Systemline was developed into the system which is the subject of LeisureTech’s infringement action.

The task for the court when construing a patent claim is to determine what the person skilled in the art would have understood the patentee to have been using the language of the claim to mean: see Kirin Amgen Inc v Hoechst Marion Roussel Ltd [2004] UKHL 46, [2005] RPC 9 at [30]-[35]. In that case the list of principles to be found in the judgment of Jacob LJ in Technip France SA’s Patent [2004] EWCA Civ 381, [2004] RPC 46 at [41] was approved subject to one point.

Unusually, in the present case there is little dispute as to the construction of claim 1. Nevertheless, there are three points of construction which are of some significance. First, it is common ground that claim 1 is not limited to systems which deliver hi-fi sound quality or indeed any particular sound quality at all. Paragraph [0024] of the specification refers to “a reasonable sound level for most domestic requirements [emphasis added]”, which is not the same thing; but that is as far as the specification goes. This is not surprising given that sound quality has a considerable subjective element, although there are some objective measures.

Secondly, LeisureTech contends that claim 1 is inherently limited to systems which deliver the sort of electrical power, and hence the amplifier output power, that a single pair of conductors in a Cat.5 cable is capable of delivering. Armour pleaded as the basis for their insufficiency attack that claim 1 has no limit with regard to the power of the system. As I will discuss below, however, counsel for Armour did not press this attack, submitting instead that the insufficiency objection had done its job in forcing LeisureTech to limit its claim. Accordingly, I accept LeisureTech’s construction.

Thirdly, claim 1 is not limited to systems of any particular size, in particular in terms of either the number of rooms or the lengths of cable required.