My almost certain-to-be longest-running sound design ever is not in a theatre or an exhibition. It sits in a gallery in one of London’s most popular historic house museums, The Wallace Collection, in Manchester Square, a stone’s throw away from the busy shopping area that is Oxford Street. The show runs for just under a minute every hour, 24 hours a day, 365 days a year, year in, year out and, as you’ve probably guessed by now, is located inside a clock. This is not just any old clock, but an 18th-century French mantel clock, worth many thousands of dollars. How I came to be involved in this particular project is one of those long, rambling stories, involving my wife, her cello pupil, his father, and a German furniture conservator and Bauhaus houseboat builder living in London.

When I learned that said pupil’s father, Jeremy Warren, was a director at The Wallace Collection, I mentioned that I’d recorded some of the chiming clocks there many years ago and what an amazing collection I thought they had. Warren, in turn, told me that they’d been investigating the possibility of replicating the failing carillon (or musical box) mechanisms of two of these clocks by electronic means but were having little success. It was then that I uttered the fateful words, "That shouldn’t be too difficult. I should be able to sort something out." Almost two years, a couple of conservation award shortlists, and one "highly commended" later, I think I can now safely say that I was a tad over-optimistic.

I met Jürgen Huber, the chief furniture restorer at The Wallace Collection, and he introduced me to the clocks: two ornate 18th-century French mantle-clocks, both with complex musical chiming mechanisms capable of playing over a dozen tunes just before the hour chime. Then Huber explained what he needed: first, the recording had to be indistinguishable from the real thing; we had to be able to convince both the director of the collection and the general public that they were listening to the actual chime mechanism. Next, the playback had to be triggered by the clock mechanism, so that it was always in sync with the clock itself, which ruled out the use of a standalone system running to a wireless time-check signal. Then, the whole thing had to be powered by a rechargeable battery, lasting a week between battery changes. Finally, it all had to fit inside the clock, but nothing could be physically attached to the clock case or to the carillon trigger.

Huber mentioned that he’d been in contact with a number of people, that no one had yet come up with a practical solution that fulfilled all the necessary criteria, and that he was currently in contact with someone in the Swedish military who thought he had the answer. A couple of ideas were already sloshing around in my mind, so I told him that I needed a couple of days to think about it and went off to do just that.

Working in theatre and exhibitions is good training for things like this, and in a few hours, I had the basis of a system and a rough cost mapped out. I would need a high-quality stereo playback system, working at the highest sample rate and bit depth possible in something small enough to fit inside the clock. Luckily, I’d met Doug Mobley of Gilderfluke at a number of trade shows in the US and knew that his SD-10 playback module would do the trick. I used my Metric Halo ULN-8 rig to make the recording of the 13 carillon tunes, making sure to capture all the mechanical sounds along with the music to help with the verisimilitude of the playback. These were loaded as 48K WAV files onto an SD card.

Previous attempts at producing a suitable system had always involved MP3 players, but the wealth of high-frequency content present in the clock recordings was badly affected by the lossy compression, making the recordings seem lifeless and dull. By making the original recordings at as high a resolution as possible and keeping them in an uncompressed format, I was able to maintain the realism of the carillon movement. Next, I needed to find a suitable amplifier, small enough to fit in the space, powerful enough to drive the speakers, and able to be battery-powered without drawing too much current. That came in the form of the now-defunct Tripath digital amplifier, of which there are a number available through various outlets in the Far East. The amazing Tony Robinson, chief technical guru at Autograph Sound, had designed a circuit board for use in practical sound props, which is a mere 2cm (0.787") square and runs from a 12V DC source, as does Mobley’s SD-10.

Finally, the dual-timing circuit, which would keep the whole system on a low current-drain standby, switching it to full power only when triggered by an as-yet-undecided mechanism, allowing the audio to pre-load and then, ten seconds later, triggering the playback, had to be devised.

I drew up the specifications and another show-control stalwart, Jerry Durand, conceived a beautifully small unit that would do the business. Then came the real problem: how to trigger the carillon sound without having any physical contact with the clock mechanism. First experiments involved a cheat—using conservation-grade removable adhesive and a mercury tilt switch on the carillon actuator arm—but although this was useful as a proof-of-concept mechanism, it was inevitably too inaccurate and unwieldy to be used in the long term. The problem was exacerbated by the fact that the second clock’s trigger movement was miniscule, just half a millimeter (0.019").

A response to a query on Charlie Richmond’s Show Control mailing list pointed me in the right direction toward the field of industrial control systems, and I finally found an infrared LED-based optical switch with the same operating window, half a millimeter, meant for use in systems for counting electronic components. Durand produced a second set of timer boards as the circuitry needed to be slightly different, and, in terms of the playback system, we were there.

Initially, I had been concerned that the clock movement would be damaged by the proximity of the magnets in conventional loudspeakers and experimented with small flat-panel models, but these were deficient both in power and fidelity. However, this problem quickly went away when I ascertained that all the clock components were brass and therefore unaffected by magnetism. I quickly sourced a pair of high-quality 3" mid- to high-frequency loudspeakers with a shallow profile that allowed them to fit neatly inside the casing of the clock, held in place with foam rubber wedges, and the whole system was mounted to a wooden platform that sits neatly over the top of the musical box movement. A rechargeable battery pack provides the power and is changed once a week when the main clock mechanism is wound.

Before officially unveiling the system to the museum’s director, Huber and I returned the first clock to its rightful place in the gallery, set the time correctly, and waited for the hour to strike. A small crowd gathered as the time approached, and, at one minute and ten seconds to the hour, an almost inaudible click confirmed that system had turned on, and ten seconds later, the chime began to play for the minute leading up to the stroke of the hour. As it finished, the real bells inside the clock struck the hour, and we’d completed our first public trial. No one listening in the room realized that they’d listened to a recording, and we knew that we had a winner.

With the public convinced, the museum director was next, and she was equally happy with the result, so we carried out a similar conversion on the second clock, which is also back in place in the museum. Each system can be removed from the clock in minutes, leaving it in its original condition, and the replacement of a small pin is all that’s required to return the carillon movement to full working order, should it be required. We’ve been shortlisted for two conservation awards and won a highly commended designation from one of them, no mean achievement when we were up against the heavyweight conservation departments of the UK’s leading museums.

So next time you’re in London, take a tour of The Wallace Collection. Get the timing right, and you’ll probably hear the result of a collaboration between an 18th-century French clockmaker, a German conservator, two American show-control experts, and a British sound designer. We’re there on the hour, every hour, seven days a week, 365 days a year (assuming someone’s remembered to change the batteries).

John Leonard is an award-winning designer who has been working in theatre sound for more than 30 years. In his spare time, he records anything that makes an interesting noise in high-definition surround sound.Live Design readers can get his sound effects collections at a 50% discount by using discount code BSMC50 at