Magnetophonic Chess-Set

They looked across at each other, their eyes glinting in the candlelit gloom of the library.
"Check!" announced Quartermain, his voice only just audible over the eerily discordant sound emanating from the object between them.
"Damn you Quartermain." Dr Moreaux leaned forwards, his brooding face obscured by thick pipe smoke.
"Why must you insist we play on this infernal thing?"
"It helps me relax, not to mention it having certain...associations."
Dr Moreaux sighed, leaned forwards, and toppled his King. The sound from the board changed subtly, as if a voice had been silenced from a choir. The King rolled, describing a gentle arc on the board before reaching the edge and smashing onto the tiled floor. Pieces of china scattered revealing the strange and intricate mechanism within.
Close inspection showed a short triangular loop of magnetic-ribbon, one side of which was stretched across the base, and driven round by a tiny voltaic-engine, apparently receiving its power directly from the board via the two metallic contacts in the base of the chess-piece. The engine, now divorced from the board, was visibly slowing down to a halt. Moreaux, raised an eyebrow and thought of the strange tingling sensation he’d felt earlier on touching the board. It was one of the many things about it he found deeply disturbing.
"Good God Man! What is this trickery?!" Moreaux exclaimed.
"I had hoped not to have to reveal this to anyone," began Quartermain, "but I fear I must offer you some explanation.
"You see, this device is what I call my Reverberating Feline Memorial Magnetophonic Chess-Set. While a piece is on the board, it draws its power from a grid of charged wires, which provide the power to turn the voltaic-engine. The engine drives the ribbon, which has had a regular, but invisible arrangement of magnetised and un-magnetised stripes infused along its surface. A sensitive voltao-magnet hidden beneath each square of the board is stimulated into generating a weak oscillating voltaic current. This current is amplified and transmitted into the motion of a stiffened board of velum hidden within, the oscillation of which produces sound. Allow me to demonstrate."
One by one, Quartermain took the remaining pieces from the board and laid them back into their box. Each time he removed one, the sound from the board became quieter, less discordant. Until, with one piece left, there was only a single, distinct tone, wavering ever-so slightly.
He lifted the bishop from the board and everything was quiet.
"Each piece has its ribbon patterned with different spacings between the magnetised and de-magnetised stripes."
"However, it is not only regularly varying widths and gaps between stripes of magnetism that can be used."
He lifted a knight from a separate velvet-lined box and placed it on the board. A tone, of an altogether different quality and higher pitch, wafted from the machine. Moreaux couldn't believe his ears,
"Smiffles?"
"Yes. In reversing the mechanism, I was able to infuse the pattern of a sound directly into the magnetic ribbon, thus capturing it forever. I was able to entice Smiffles into meowing into the machine using a saucer of milk. It is unfortunate that milk is such a good conductor of voltaic current."
"Yes, I had wondered what had happened to him."
Quatermain, placing the original piece back on the board, blew wistfully into his handkerchief.
"I know. I do miss him so."
He then added a third piece and immediately the two notes and the echo of the deceased cat swelled into a deep melancholic chord.
With a sniff, Quatermain removed the knight, gently returning it to its special box. He continued,
"In addition, since the amplification modules are of different attenuations for each square on the board," he moved a piece,
"it is not only the pattern of stripes on the magnetic ribbon in each piece that defines the pitch and quality of the sound you hear, but also the position."
As Quatermain moved the piece, the quality of the sound and the pitch altered once more. He began setting the pieces up on the board, but this time in a configuration Moreaux had not previously seen, the noise building as he did so like that of an orchestra tuning before a performance. A second later, with a flurry of movement, he began shifting each piece around in a frantic dance, accompanied by an intensifying fountain of sound. Dr Moreaux's jaw dropped as Quartermain built up to a frantic crescendo.
"Oh my, that's...incredible!" Moreaux exclaimed.
Quartermain, breathing heavily, slowed, and taking each piece off between motions, caused the sounds to die away until finally all was silent.