The difficulty in defining the sound properties of Old Italian instruments is that there are at least two distinct groups of instruments based on their sound characteristics.
One group is characterized by a low, mellow tone apparently lacking
the higher end of the sound spectrum, and seemingly subdued volume.
The other group is marked by a highly intense sound with a penetrating ringing tone, but not without the low end.
We can only speculate about the reason for such difference.
Another aspect that confuses the issue is the fact that musical recordings have made by far the biggest impact on how the sound of Old Italian instruments is perceived.
The majority of distinguished classical recordings belong to an era when recording technology was inadequate to reflect the full spectrum of a violin, thus, creating the impression that Old Italian violins played by the old virtuosos had a very narrow tonal range.
Whole generations of musicians grew up listening to these recordings and consequently could not escape their influence.
Though the tonal spectrum of these two groups appears to be different from up close, there are certain sound properties that are common to both, setting them apart from all the rest of the violins.
One such property is referred to as projection of sound or just projection. This sound property belongs exclusively to the Old Italian instruments (all claims to the contrary confuse this unique property with simple loudness or volume of the sound)
Another exceptional quality of Old Italian instruments is their exceptional tone. As opposed to the sound of all other violins, which are basically an acoustically amplified sound of strings, these instruments respond to the touch of the bow with their own unique voice. This distinctive tone with unusually strong overtones (can be heard by an un-augmented ear from up close) helps Old Italian violins to stand out from the rest of the orchestra, and facilitates unique to these instruments playable characteristics such as treble sustain and slotting
Aesthetic components of the BelCanto sound:
The sound characteristics of a violin