The purpose of testing an instrument is to determine its actual sound properties.
The easiest way to accomplish this is by comparing it side by side to other instruments.
There are basically two main properties of an instrument that must be tested. First, the playable characteristics of an instrument, which can be accomplished in any room. Second is the quality of the sound, for which a bigger space is mandatory. Since violins are made to ‘work’ the acoustics of a hall to produce a full-bodied sound, it is essential to test a violin in a large concert hall.
It is very helpful to have at least one other instrument (preferably a good old Italian violin) as a point-of-reference to cut down on second-guessing yourself.

 

VIBRATO:
Vibrato is often used to alter the real sound quality of an instrument. Consciously or unconsciously, a musician will often use extensive vibrato to make the sound appear more ‘vivid’, ‘full’ and ‘free, or abandon it altogether on an instrument he/she doesn’t like. An extensive vibrato creates a false perception of ‘better projection'. In many cases it is used to mask the "wolf" notes, or even to make the weak base string to appear more resistant to bow pressure than it really is.
That's why, while comparing instruments, it is important to keep vibrato under control and always remember how it affects the perception of sound.

NOTE:
A really good violin will retain its distinctive, beautiful voice even if no vibrato is used. A lesser quality violin demands an extensive vibrato.

 

SKILL:
There is a difference between the actual sound properties of an instrument and the sound we hear when it’s played by a good musician.
A skillful performer can significantly alter our perception of the tone an instrument can produce. The same instrument played by different people may appear to sound better than it really is, or sound really ‘dull’.
Some of the ‘tools’ performers can use to modify the sound include vibrato, bow speed/pressure, the bows position on the string, etc. etc.

 

Concert HALLS:
Violin was never intended to be played outside.
As a matter of fact even the best of violins will sound pretty ‘thin’ and pitiful without enclosed area acoustics. Smaller rooms do not support violin's sound to its fullest extent. So when trying out a violin, it is essential to have access to a decent concert hall.

There are two types of concert halls. One is smaller – a chamber hall; the other is bigger – a concert hall. Despite variations along the line of interior decorations (i.e. balconies, columns, sculpture, light fixtures etc.) both concert halls are traditionally of the shoe box type.
Another type of hall is an amphitheater based conference hall. It has different acoustics and is not suited for music performance.

Process of listening in the hall:

  • Find a “sweet spot”
  • Compare sound from “fly-over” zone to the “sweet spot” sound (can you hear the difference?)

The Diagram of where the sweet spots are in different types of halls:

  • Chamber hall (box type)
  • Chamber hall (columns along the walls)
  • Big Concert Hall( shoe box type)

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Additional Material:

Another website about Hall Acoustics (in plain English):
        http://www.angelfire.com/music2/davidbundler/acoustics.html