Rosin

 

The QRS Virtuoso Violin works without rosin, but it sounds better with it.  Therefore a small wood tray of rosin is added to the right of the bow arm, at home position.  The location is based on the bow arm mechanism, which pivots down to the right of the bridge during a “bow up” command.  When the bow raises during a homing command, it contacts the rosin as it moves home.  This “swipe” of the horse hair against the rosin transfers enough rosin to ensure the proper bow/blade “stick/slip” interaction during subsequent performance.

 

Rosin is basically tree sap.  It is melted and poured into a carved-out wooden tray, and when dried forms the same rosin that musicians use on their violins.  The function of the rosin is the same for the orchestral musician as it is for the Virtuoso Violin – it causes the horse hair to stick better to the string, thus create more string motion:

 

     “When a bow is drawn across the string, the string appears to widen in a smooth ribbon of a lenticular shape [ie: like a lens]; but this is an optical illusion. To a first approximation, the string under the bow takes the form of a sharply bent straight line, a phenomenon noted by Helmholtz. A slow-motion camera would show this bend, or discontinuity, moving around the lenticular path extending between the ends of the string.

     The 'stick-slip' action of the bow on the string, though somewhat similar to the chattering of a piece of chalk on a blackboard or the squeaking of a chair leg across the floor, is more complicated. As the discontinuity, or kink, moving from nut to bridge, passes the bow it dislodges the string from the hair to which it has been clinging and reverses the string's motion. When the discontinuity returns from the bridge it restores the forward motion of the string, which again sticks to the hairs. The bow is thus freed from the string not as a result of the gradual increase in stress between the rosined hair and the rosined string, but because the kink has arrived to set it loose.

     During the time of sticking, motion is in one direction followed by a quick snap back in the other on release, thus giving the saw-tooth wave form. If this motion is produced by a downbow, the entire pattern will be reversed by an up-bow.”

 

The difference between a violin played in the orchestra an the QRS Virtuoso Violin is that a real violin will make no noise when an unrosined bow is pulled across its strings (because the horsehair has no stick) whereas the Virtuoso Violin will because it is the string driver that creates the string motion, not the bow.  In the case of the Virtuoso Violin the bow rather modifies this string motion, changing it from sinusoidal to saw-tooth in nature, and the rosin functions to  modify it even further.

 

This is the reason why the Virtuoso Violin sounds best with a properly rosined bow moves at an ideally matched speed to the string’s drive.  The speed is regulated by an Angle/Drive/Speed algorithm built into the software. 

 

The amount of rosin applied is regulated 2 ways.  First by the violin code which determines how far down the bow moves towards the rosin, and second mechanically by how high the rosin tray is manually adjusted.

 

Violin Rosin Code

 

The bow angle – which we have defined as controller 21 – is adjustable from 0 to 127 as defined by MIDI spec.  We have assigned the following bow positions:

 

Controller 21 #       Bow Position             On/Off String       Bow/Rosin Position

127                        Full up position          Off String            On Rosin – Fully Engaged

110                        Rosin                         Off String            On Rosin – Engaged

090                        Note Off                   Off String            Off Rosin – May be Engaged

055                        Note On                    On String             Off Rosin – Not Engaged

000 (not used)        Full Down Position    On String             Off Rosin – Not Engaged

 

[Note: The region between 000-049 is not used for our purposes.  The region from 050 to 127 gives us the needed speed and flexibility.  DO NOT OPERATE THE VIOLIN BOW BELOW 050 AS DAMAGE TO THE STRING DRIVER COULD RESULT.]

 

[Note: The bow/drive algorithm automatically moves the bow angle between 050 and 060 to vary bow pressure depending on bow speed and string drive.]

 

As the violin plays the bow angle changes depending on whether a note is playing or not, and whether the bow is going home or not.  When the violin is powered up, but a note is not playing, the bow is normally Off String in the Home position (bow frog above the sensor light, bow extended fully to the left of the violin).

 

In this position the bow angle is automatically set at 090, off rosin.  It is automatically set to this position when the violin powers up, and after a note has stopped playing for 2 seconds.  It’s the “automatic position of rest.”

 

 

When the violin receives a MIDI NOTE ON command, the bow automatically drops down to On String position 055, and begins moving.  At the same time the string driver starts driving the string blade and a note is sounded by the violin. So far the bow as not touched the rosin. 

 

 

When a note stops the bow is automatically raised back to Off String position 090, and the bow continues to move back and forth for up to 2 seconds.  In this position the bow may or may not have contact with the rosin, depending on the exact height of the rosin holder and how much rosin has been removed by previous bow rosining.

 

If a note begins playing again within the 2 second “waiting” period, the bow again automatically drops down to On String position 055, and the process begins again.

 

However, if the violin does not receive another note during the 2 second Off String “idling” period, it automatically lifts further to Off String position 110 and returns to the Home position.  It is this “return to home” position which lifts the bow enough to sufficiently drop the bow hair down against the rosin, and as the bow moves back to Home position, the bow hair is rosined.

 

 

 

 

Adjusting the Rosin Holder

 

The Wooden Rosin Tray (Part #700___) is attached to the Rosin Holder Bracket (Part #700____) using 3m double-sided foam tape.  The Rosin Holder is attached to the String Driver Frame (Part #700___) via two 4-40 allen cap screws and an elongated washer in such a way as to be adjustable up and down.

 

The Rosin Holder Bracket should be adjusted so that the rosin is about 1/32” – 1/16” (.050”) away from the bow when the bow is at home position.  IE: The bow hair is “just off” the rosin when at home position.

 

The easiest way to adjust this is to first slacken the Rosin Holder screws and drop the holder to its lowest position, then power up the violin and let it find home.  Once the bow has stopped in the home position, raise the rosin holder bracket until the rosin is just below the bow hair, but not touching it.  Tighten the rosin holder bracket screws and check to make sure the rosin is not touching the bow hair.  If it is not, the violin is ready to play.  If it is, drop the holder down a bit until it is not touching and try again.

 

[Note: The first time you make this adjustment you may have to bend the rosin bracket slightly to line the rosin up parallel to the bow hair.]

 

[Note: A properly operating rosin holder lightly engages the bow several times during a typical performance.  It is normal for rosin dust to build up on the violin.  However, if the rosin is adjusted too close to the bow, excess rosin will be removed from the rosin tray which will needlessly create excess rosin dust on the violin and wear down the rosin.]

 

[Note: The rosin holder should be adjusted (ie: raised) after every few hundred pieces or so for optimal performance.  If it is not, no damage will result, but over time the tone may degrade somewhat.]