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.
Whatís 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 itís 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 itís 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, itís 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 thereís 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 itís 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 theyíre 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
Whatís 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 thatís
not an issue. At the top end of the market thereís 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
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
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 1980ís. 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 hasnít
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
Including recently deleted machines, clones and imports thereís
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, itís far too early to be writing
eulogies, Laserdisc has a habit of defying the odds. Players are sensibly
priced, thereís a good supply of software, with new titles being released all
the time. Itís still worth considering if you care about quality.
R. Maybury 1996 0511