New discovery: really good violins make hidden, subtle sounds

What makes a good violin sound so good? According to new research, published in The Journal of the Acoustical Society of America, at least part of the reason is extremely subtle extra notes the best instruments sounds out.

When two musical notes are played, listeners can sometimes hear “combination tones”: an additional, subjective note that comes from the way the cochlea processes the two sound waves in the inner ear.

Some musical instruments can also make combination tones themselves: called “objective combination tones.” These subtle notes are produced in the instrument, rather than the ear.

Not all instruments can make these objective combination tones – but this new research shows the surprising news that violins can.

“Up to now, the combination tones generated by the violin were considered too small to be heard, and therefore, of no importance in music,” says study co-author Giovanni Cecchi, of the Università di Firenze, Italy.

“Our results change this view by showing that combination tones generated by violins of good quality can be easily heard, affecting the perception of the intervals.”

More on combination tones: What are ‘binaural beats’ and do they affect our brain?

The researchers got a professional violinist to stand in the centre of a musical auditorium and play a series of dyads: two notes played simultaneously.

The violinist played dyads on five different violins, all of different ages and qualities, and the researchers recorded the tones.

Each violin produced combination tones in all of the dyads. The strongest of these notes was at a slightly lower tone than those of the dyads.

Each instrument made the combination tones at different volumes (or amplitude), depending on the instrument’s air resonance.

Three views of a violin front, side and back, the violin made the best objective combination tones
This Totoni violin, made in Bologna in 1700, produced the strongest and most audible combination tones. Credit: Gabriele Caselli, Giovanni Cecchi, and Giulio Masetti

“We found that combination tones were much stronger and clearly audible in good violins,” says Cecchi.

“The strongest one was found in an old Italian violin, made in Bologna in 1700 by the famous luthier, Carlo Annibale Tononi.

“Combination tones were instead negligibly small in violins of poor quality.”

Next, the researchers are investigating more violins to see which part of the instrument causes these objective combination tones.

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