The violins of Antonio Stradivari (1644–1737) are a model for violin makers all over the world and a dream for collectors, who pay millions to own one. But do they really sound better than other violins? Previous experiments, in which blindfolded violinists played old and new instruments, found that players often preferred modern violins and could not tell old from new. When a violinist plays, however, the judgement depends also on how the instrument responds under the fingers and the bow, on its weight, on the habits of the player.

This page summarises a listening experiment, published in the Journal of the Acoustical Society of America^[1], in which seventy violin makers of Cremona did not play the violins: they only listened to them, and judged their timbre. Two of the five violins were made by Stradivari.

The experiment

The violins

The experiment compared five violins, whose identity was hidden from the listeners and from the experimenter:

• X, the reference violin: a Stradivari of the maker's late period;
• B: a Stradivari made at the end of the maker's so-called "golden period";
• A: a modern violin made in 1988, worth about 20 000 euros;
• C: a modern violin made in 1917, worth about 100 000 euros;
• D: an industrially made violin, worth about 300 euros.

The two Stradivari are each worth several million euros. Each violin had its own strings and all were tuned to A₄ = 440 Hz. They were all played by the same violinist, with his own bow.

The listeners

The 70 listeners were all experts: 36 students of the violin making school of Cremona and 34 professional violin makers, about a quarter of all the violin makers working in Cremona, perhaps the town with the largest community of violin makers in the world. The experiment took place on 7 May 2019 in the Auditorium Giovanni Arvedi of the Museo del Violino in Cremona, a concert hall with very good acoustics. A white curtain, which lets sound through, hid the violinist and the violins from the audience.

What the listeners heard

To make the listeners concentrate on the timbre alone, the violinist did not play a piece of music but a simple scale: a portion of a G major scale, from G₃ up to D₄ and back to G₃, played always in the same way: détaché, mezzo forte, without vibrato, at a steady 35 notes per minute.

In each trial the violinist played the scale first on the reference violin X, then on one of the test violins. An assistant handed him the second violin, so that only 6–7 seconds separated the two scales: comparing two sounds heard one right after the other is much easier than remembering the timbre of a sound heard some time before.

The listeners judged the second violin compared with the first one on a scale from −2 to +2 (0 meaning no difference), in four blocks of ten trials, each block devoted to one quality of the timbre. The four qualities were described with words familiar to the violin makers of Cremona:

• nasal (nasale), like the sound of an oboe;
• bright (chiaro), as the vowel A is brighter than the vowel O in the word "ciao";
• open (aperto), as an instrument sounds "closed" with the mute on and "open" without it (see the mute);
• pleasant (piacevole).

In each block the reference violin was compared twice with each test violin, and twice with itself, without telling the listeners. This allowed checking how reliable each listener was: a good listener gives a rating close to 0 when the same violin is played twice, and gives the same rating when the same comparison is repeated. 55 listeners out of 70 turned out to be clearly more reliable than someone answering at random, and the results below are theirs (including the other listeners does not change them).

The results

The ratings of the four test violins for openness, brightness, nasality and pleasantness, compared with the reference violin X (a rating of 0 means "same as X"). Each small circle is the rating of one listener; the diamonds are the averages; the boxes contain the central half of the ratings.^[1]

The listeners heard clear differences between the violins, along all four qualities:

• the Stradivari B was judged the most pleasant: 43 listeners out of 55 gave it their highest pleasantness rating (each listener could give the highest rating to more than one violin). The modern violin C got the highest rating from 19 listeners, the modern violin A from 3, the industrial violin D from 2;
• compared with the reference X, the order of pleasantness was B, then C, then A, then D;
• the ratings of violin C were mostly close to 0: to the listeners, the modern violin of 1917 sounded very much like the Stradivari X;
• the industrial violin D was judged the least pleasant, more nasal and less open than the reference.

So the preference of the listeners converged on one particular violin, the Stradivari B, which was preferred even to the other Stradivari, X.

After the experiment, many of the listeners were asked what a good timbre should be like. They agreed that a violin should be bright, but with enough bass to avoid sounding harsh, and as little nasal as possible. The same "recipe" comes out of the ratings: the pleasantness of a violin can be predicted, in two cases out of three, from a combination of its openness (which counts most), its brightness and its nasality (which counts against it).

Listening to the body of the violin

Frequency response of the five violins, struck on the bridge by a small hammer with the strings muted. Thin lines: the measured response; thick coloured lines: the response averaged over bands about as wide as the critical bands of the ear. Bottom: the averaged responses of the five violins superimposed.^[1]

The sound of a violin starts from the vibration of the strings, but it is the body of the instrument that "filters" it and passes it on to the air (see the formation of timbre on the page about the violin). To look for a physical trace of the differences heard by the listeners, the authors measured the frequency response of each violin: with the strings muted, the bridge was struck with a small hammer that measures the force of the blow, and a microphone recorded the sound radiated by the violin. The ratio between the sound and the force, as a function of frequency, shows how readily the body of the violin turns a vibration of the bridge into sound at each frequency: its peaks are the natural frequencies of the body.

The responses of the five violins turned out to be quite different:

• the lowest peak is the A0 mode: the air inside the body resonating as in a Helmholtz resonator. Around 500 Hz there are the first resonances of the wooden body. The Stradivari B has the strongest response in both these regions, and therefore a particularly strong bass. It also has a strong response between 1.5 and 5 kHz, balanced by its strong bass;
• the response of the industrial violin D is concentrated between 0.8 and 1.4 kHz: its body behaves almost like a narrow band-pass filter centred around 1 kHz. This matches the judgement of the listeners, who found it more nasal and less open;
• violin A has the weakest A0 resonance;
• the responses of violins C and X are very similar to each other, just as their ratings were.

Sound level (RMS amplitude) of the five violins during the listening test, from the recording of the experiment.^[1]

Listeners are known to prefer louder violins (see perception of loudness). To check that no violin was preferred simply because it was played louder, the authors measured the sound level of every scale in the recording of the experiment: the violins were all played at a very similar level.

This kind of measurement cannot explain everything about the timbre of a violin: for instance, it ignores the attack of the notes and the direction in which the sound is radiated. But with a stimulus as simple as a slow scale without vibrato, the spectral differences between the violins are surely important.

Why are the Stradivari a myth?

The experiment shows that the experts did hear the differences between violins, and that their preferences converged on one instrument, a Stradivari. It does not show that all the violins of Stradivari are better than all the others: the other Stradivari, X, sounded very similar to a modern violin, C. The quality of the timbre of a violin can be judged only instrument by instrument, whoever made it.

Many factors that have nothing to do with sound contributed to the fame of Stradivari, such as the historical circumstances and the famous violinists who played his instruments, in the same way as Jimi Hendrix made the Fender Stratocaster guitar popular. At the end of the 18th century, when the violins of Stradivari were already well known, the most sought-after violins were those of Jakob Stainer. The authors suggest one more factor: a few tonally superior instruments, like violin B, may have created a favourable bias towards all the violins made by Stradivari.

In-depth study and links

• Exploring timbre of Stradivari violins, an episode (2023) of Across Acoustics, the podcast of the Acoustical Society of America, in which two of the authors, Carlo Andrea Rozzi and Massimo Grassi, talk about this experiment (in English).

References