FEATURE

BLUFFERS GUIDE TO TECHNOLOGY

CORDLESS HEADPHONES AND SPEAKERS

Cordless headphones and speakers, it sounds clever but what's the point?

No wires means freedom and flexibility. Headphones you can boogie around the room in, and rear-channel speakers for surround-sound systems, with no cables to trip over.

So how does it all work?

There's two ways. The majority of cordless headphones and speakers on sale at the moment use infra-red systems, but we're starting to see a few devices using radio frequency (RF) transmitters.

What’s this infra red stuff?

It's light, at the lower end of the visible spectrum, on the borderline between heat and light, and it's invisible to our eyes. In the transmitter unit audio signals from the source component are modulated onto one or two high frequency carriers -- depending whether it’s a mono or stereo system -- that are used to drive infra-red light emitting diodes.

It sounds complicated?

No, not really. Think of a light bulb being switched on and off many times each second; the change in the rate at which it’s switched is determined by the frequency or pitch of the audio signal. 

What happens at the other end?

The light, in this case invisible infra-red light is picked up by a sensor on the receiver unit, it’s de-modulated -- i.e. turned back into an audio signal -- and fed to an amplifier, that drives a pair of headphones or a loudspeaker. In the case of cordless headphones the amplifier is powered by a small battery; cordless speakers are normally mains powered.

How about RF systems?

They use high-frequency radio waves -- on or around 49Mhz which is at the low end of the VHF band -- to carry the audio information between the transmitter and receiver, almost everything else is the same.

What are the pros and cons?

IR technology has good immunity to interference, it's comparatively cheap and reasonably reliable. The downside is limited range -- the receiver has to be able to 'see' the transmitter, or at least be close enough able to pick up light beams reflected from walls and ceilings. Radio signals can penetrate walls, so there’s no need for the receiver to be in the same room as the transmitter; range is typically 30 to 50 metres. That can be an advantage for cordless headphones  -- it means you can move around the house and garden with them on -- but it’s not quite so important for cordless speakers, which will normally be located close to and in the same room as the source components. RF systems are however prone to interference, from other nearby transmitters, and they can also cause interference to others -- in theory it would be possible for a neighbour with a similar set of headphones to pick up your signal. RF is also inherently noisier than IR, though with careful design it needn't be a problem

Why aren't there more RF cordless headphones around?

In fact RF cordless headphones are relatively common in other countries, including much of Europe but the Radio Regulatory Department of the Department of the Environment has tended to frown on such things.

What have they got to do with it?

They're the Government department in charge of radio waves. In this country the RF spectrum is very highly regulated and all radio transmitters -- even titchy ones like those used on cordless headphones --  have to operate within a very tight specification before they’re allowed to be used. The rest of Europe uses 433 MHz for this kind of thing but that band has been allocated for ham radio use in the UK. Thus far few companies have been moved to go to the time and expense of designing equipment capable of getting type approval just for the British market.

What’s the quality like?

It varies between quite good and bloody awful, needless to say you get what you pay for!

Which is best?

There are no RF cordless speakers at the moment, so that’s not an issue. At the top end of the market there’s not a lot to choose between  RF and IR headphones, the main reason for choosing RF would be for the extra freedom. The cheapest IR phones start at around £30, but you should be thinking in terms of at least £50 to get anything worthwhile. The first RF phones -- Vivanco CyberWave -- have just gone on sale for £80. Cordless speakers are only just coming onto the market, reckon on at least £150 for anything worth listening to.

2. GETTING STARTED

LASERDISCS

INTRO

All the hype surrounding the imminent launch of DVD has tended to overshadow the fact that movies with broadcast quality pictures and sound have been available for more than a decade, on Laserdisc

COPY

Laserdisc is one of the great survivors of the entertainment industry. The format has been written off many times, yet it continues to thrive within a sizeable niche of the home cinema market. In fact it has been a modest success in some countries, notably the US, Japan and parts of Europe, where quality often takes precedence over price, as a key buying consideration.

The format got off to a fairly shaky start, back in the early 1980’s. At the time rival video disc formats from JVC and Hitachi were about to be launched, and the VHS versus Beta battle was in full swing, all of which caused a good deal of confusion amongst the buying public. Nevertheless it did well in the crucially important American and Japanese markets, achieving the necessary critical-mass needed to ensure support from software companies. The format received a much-needed boost in 1986 when there was a change from analogue to digital soundtracks on discs. It was the same system as CD, which allowed manufacturers to develop more versatile multi-role players, that could play both video and audio discs.

The European market remained sluggish, most people settled for a VCR, for movie playback. In spite of inferior picture and sound quality VCRs have the all-important recording facility. At the last count there were over 9,000 NTSC laserdisc titles in the States, with around the same again in Japan and the Far East. Hardware sales in Europe are still way behind the US, consequently fewer PAL coded movies are released. Currently there are around 500 PAL titles, selling for between £10 and £40, with maybe 500 more available from specialist dealers in Europe.

That relatively narrow choice of material clearly hasn’t helped sales, though most of laserdisc players sold in this country can also replay NTSC coded discs, in some cases on ordinary PAL televisions, others can only be used with multi-standard sets. That facility to play NTSC coded discs has resulted in a small market in imported discs, catered for by a number of specialist retailers. However, recent changes to way the BBFC (British Board of Film Censors) certify movies is now preventing the sale of many imported discs, though they can continue to be purchased by mail order, direct from the US.

Laserdisc owes its current run of popularity to the fact that many US discs have THX soundtracks, recorded using the Dolby AC-3 six-channel digital recording system. This combination of technologies is proving very popular with home theatre purists, seeking to recreate the cinema experience in their own homes.

Including recently deleted machines, clones and imports there’s around ten laserdisc players on sale in this country at any one time, almost all them made by Pioneer. Their current range is headed by the CLD-D925, a highly specified dual-standard deck with an AC-3 output, two-side replay, advanced digital replay facilities and a price tag of £800. Pioneer also market cheaper single-standard players, prices start at below £400; more versatile multi-standard mid-range machines are in the £500 to £600 price bracket. Philips, who developed the laserdisc system stopped production around three years ago to concentrate on CDi. The only other major player is Sony, who have one model, the MDP 850, a dual standard deck selling for £750.

DVD will provide laserdisc with its biggest challenge to date, and if the bean-counters have got their sums right, it could eventually spell the death-knell for the format. However, it’s far too early to be writing eulogies, Laserdisc has a habit of defying the odds. Players are sensibly priced, there’s a good supply of software, with new titles being released all the time. It’s still worth considering if you care about quality.

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Ó R. Maybury 1996 0511