My 1st prize awarded Amati model violin has some unconventional features some of which even the judges might not have been aware of!
Besides of being completely ebony-free and sustainable (fingerboard and nuts are made from Blackwood Tec), having a slab cut back (not quite common in violinmaking competitions because of it’s reputation of “poor sound”) and the tiny lead weights glued under the fingerboard and tailpiece in order to achieve a perfect mode match, it featured what Deena Spear calls a “Peresson-style” soundpost means a soundpost with rounded edges. I first came across this kind of soundpost reading the book by Chuck Traeger “The Setup and Repair of the Double Bass for Optimum Sound”. In his book Traeger writes about his experience with an Instrument he was working on. The instrument sounded well with a poorly fitted soundpost but with the new one, perfectly fit, it lost most of its sound. He learned the acoustical principle behind this phenomenon in a conversation with Carleen Hutchins and thus came up with his idea of rounding the edges to reduce the bearing area of the soundpost.
Most violinmakers are trained to cut the touching surfaces of the soundpost flat and with sharp edges but this often doesn’t give the best acoustical results. Also the sharp edges might damage the inner surfaces of the instrument when the soundpost is moved around during setup. The idea of rounding the edges is not new. I have found the oldest mention in Hans Johann Roedig’s book “Geigenbau in neuer Sicht” of 1962. Deena Spear writes about it in her book “The Ears of the Angels” where she tells us about her years working with the late Sergio Peresson and the already mentioned Chuck Traeger in his book about double basses.
The acoustical reason for rounding the soundpost edges is the following: You’ve probably seen some pictures of the vibrating modes in string instruments or at least are familiar with the Chladni figures. What they show are moving areas separated by so-called nodal lines. These vibrating modes vary with frequency and the higher the frequency the smaller get the vibrating areas. At frequencies around and over 5000Hz they will have an extension of only a few centimeters. With the introduction of the soundpost into the violin body we create a forced nodal line. As we firmly couple the top and the back of the instrument, we create a system with a great mass of inertia at this point so vibrations of high frequencies can only occur around this pivot.
Now imagine what happens at the touching surfaces of the soundpost. While large bearing surfaces of the soundpost will block lots of the micro-movements of the violin top, the smaller ones of the Peresson style soundpost will leave it more free to transmit the overtones in the brilliance region.
In making a Peresson style soundpost you just have to take care about a couole of things. You should first fit your it in the usual way and only round the edges after you’ve obtained a perfect fit and you should take care not to reduce the bearing surfaces too much. Before you insert the soundpost definitely you can add some chalk to the touching surfaces innorder to compensate for the reduced friction.
It’s something that might help with instruments that lack in brilliance but I just like its effect on the sound! So I do this on almost all my instruments.