This week my life has been dominated by writing a new review of nanotoxicology. Not that the world needs another review – far from it, as there are a number of excellent ones out there (I’ve even contributed to some). But in a moment of abject weakness, I agreed to help a good colleague out on a paper he’d committed to. And now here I am, two slipped deadlines later and an absolute drop-dead date just around the corner, struggling to find something new to say about stuff that has already been covered ad nauseam.
Not that I’m not making progress – I have a great title! That just leaves 11,991 words to go before Monday morning…
However, enough of nanotoxicology – what I was really looking for was a few minutes’ distraction from reinventing the nano-wheel before I have to get down to business again. So I thought I would post a few words about an old technology that still has the capacity to surprise – electrostatic loudspeakers!
I’ve been a bit of an audio nut for almost as long as I can remember – slowly building up my hi-fi kit over the years in the pursuit of a sound that at least pretends to be something resembling live music. But there’s always been that mythical land just beyond my reach of esoteric amps, hand-crafted components and mega-speakers that fringe (or extremely rich) audiophiles dabble in. And somewhere in this mythical land resided the Quad Electrostatic Speakers – supposedly the ultimate in audio nirvana for the discerning listener!
Over the years I’ve had a tantalizing distance-relationship with these loudspeakers. I grew up for a time a few mules from where they were designed and made in Huntingdon in the UK. While at high school, I remember my physics teacher talking about them with awe as we played around with aluminum-coated Mylar (the speakers use a Mylar diaphragm). We were graced with their presence in Physics of Music lectures at Birmingham University. And I remember being bowled over by a pair at a Hi-Fi show in London years ago.
But I never thought I would ever own a pair.
Well, things change, and with the move to Ann Arbor we eventually ended up with a house big enough to house a pair of Quads. So this last week I took delivery of two rather large Quad ESL 2805 speakers – and haven’t been disappointed.
But rather than write about realizing a childhood dream, I wanted to talk about the technology that these speakers use. Because it’s a great example how sometimes we need to look to the past to find the best technological solutions to problems.
- Quad electrostatic speakers – the route to audio Nirvana? (Don’t even ask about domestic bliss!)
First a bit of physics though. Loudspeakers convert an electrical signal into an audio signal by physically moving something back and forth at the same frequency of the sound they produce. Most speakers do this using a large coil of wire that slots inside a magnet, and which is attached to a stiff cone. As an electrical signal passes through the wire, the induced magnetic field pushes against the field from the magnet, and causes the cone to vibrates – sound is produced. But it’s a lousy way of producing a clean sound – the cone has it’s own resonances that add to the sound, and the weight of the coil in the magnet means that the thing never starts and stops precisely when you want it to, smearing the sound out a little. And when you put all this inside a box – as manufacturers tend to do – suddenly you have all sorts of other bits that start vibrating in sympathy with the music or whatever is being played, and generally messing it up.
But cone speakers are cheap and easy to produce – which is why we spend our lives listening to distorted, muddy music so much of the time.
- The Quad electrostatic concept (Source: Quad)
But this isn’t the only way to make a loudspeaker. Over half a century ago, engineers realized that there was a more elegant alternative to the compromises presented by cone speakers. If you placed a thin, light sheet of charged material between two electrodes, and fed an alternating electrical signal to the electrodes, you could get every point on the sheet to move simultaneously in sympathy with the signal – producing oodles of distortion-free music that started and stopped when you wanted it to. What you had was an electrostatic speaker – a beautifully elegant solution to high quality music production. The only problem was, ideal electrostatic speakers ran at voltages high enough to fry the unwary (typically up to 10,000 volts). And they were difficult and expensive to make.
But Peter Walker – the engineer and brains behind Quad – cracked most of the problems, and started work on his first commercial electrostatic loudspeaker back in 1957. The result was the legendary ESL57 – there are still people who believe this to be one of the most accurate speakers of all time!
But it’s the innovation behind the second incarnation of the Quad electrostatic speaker that particularly interests me. Walker realized that, using this thin charged sheet (which was later made of Mylar), sound could be made to ripple out from its center – much like the ripples created by a stone dropped into a still pond. The beauty of this is that the ripples can be made to emulate a perfect point source of sound placed around 30 cm behind the speaker (imagine the sound radiating from a single point moving through a flat surface places a few centimeters in front of it – if you could see the movement of the surface, it would look like concentric ripples moving out from the center.) The result was a loudspeaker where the whole surface radiated sound coherently at all audio frequencies, where the sound appeared to come from a perfect point source, where the diaphragm was so light that it started and stopped when the music demanded it, and where there were negligible bits and pieces (like enclosures) to mess around with the sound.
It was something approaching the perfect speaker – and it was designed in 1963.
The speakers I took delivery of this week – Quad ESL 2805′s – use pretty much the same technology. The enclosure and electronics have been tweaked a bit over the years. But the basic operation is the same as it was back when they were conceived in the 1960′s. And the sound? I must admit, it’s possibly the closest thing I’ve heard to being at a live performance.
The point here (apart from me finding an excuse to put off writing about nanotoxicology) is that the technologies we rely on now aren’t always the best ones. And sometimes it’s worth revisiting old ideas rather than re-invent new ones to get the best out of life.
But talking about revisiting the past, I hear the cackle of the nanotoxicology review calling. Now that’s one past I’d rather not be going back to, but you know what they say about academics and publishing…
Back to the grindstone!
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{ 2 comments… read them below or add one }
Nice kit. And one of those technologies I always thought I understood how it worked – but didn’t. So thanks for the education.
But until we trade the London flat for the Scottish mansion, I’ll be sticking to my little square boxes
Nothing wrong with little square boxes
But it’s nice to be out of the box, so to speak!