Low Humidity Problems & Related Repairs for String Instruments
Violin, Viola, and Cello Pegs are held in with compression and shrink when humidity levels drop and cause the following problems:
Broken strings are a direct result of students attempting to tune strings which have loosened as a result of the pegs slipping
Fallen or Broken Bridge
The bridge is held in place by the tension of the strings. When pegs slip and strings loosen, the bridge falls over.
Often when the bridge falls, the force of the bridge falling causes the bridge to crack and also causes damage to the top of the instrument.
The soundpost is also held in place by tension. If the pegs slip and the pegs loosen, the soundpost falls down.
Bridges Become too Low A second/replacement bridge will be necessary.
The body of string instruments is affected by changes in humidity. When there is a drop in humidity, the top of the instrument will sink down and the bridge will lower as a result.
Soundpost Cracks are BIG problem. A soundpost crack will reduce the value of the instrument by 50%.
When the top and back of the instrument shrink in times of extremely low humidity, the inward compression of the body presses against the soundpost which can cause a crack to develop (usually in the top, but sometimes in the back, as well).
Patching a soundpost crack is an intensive repair and often expensive.
Open Seams, Body Cracks, Detached Fingerboards, and Splitting Plys
Different types of wood are used in different places on string instruments and each wood may swell and contract at a different rate.
The glue used in violin-making is a water based glue. It essentially is designed to "pop" apart under pressure. When drops in humidity cause the body to shrink in different places, the body may separate or the glue may simply dry out.
Open seams which are left unglued will expand and cause further opening, warping, and cracking of structural parts which may result in devaluation of the instrument.
Cracks on the Body
When a seam doesn't "pop" open under the stress of a drop in humidity, the stress of woods shrinking at different rates will causes cracks to appear.
The fingerboard is glued on with--you guessed it-- the same water-based glue which holds the body of the instrument together. When that glued surface becomes too dry, part or all of the fingerboard may separate from the neck. In addition to it being pretty alarming when the fingerboard just falls off the instrument, a falling fingerboard can cause collateral damage to other portions of the instrument.
Separation of Plys
A lot of student-quality cellos and basses found in schools are partially or fully made with plywood. Plywood is a great choice for classrooms because it is better at taking an accidental bump than spruce or maple.
The humidity-related problem with plywood instruments is that you have added even more pieces of wood to the construction of an instrument. A traditionally-carved cello can be made with upwards of 80 difference pieces of wood. A plywood cello has even more wood than that because each ply top or back is at least 3-6 individually glued piece(s) of wood.
The edges of plywood instrument bodies may begin to separate at the plys when the instrument becomes too dry. We have even seen plys in the center of the tops of cellos separate in extremely low humidity. It's a mess!
Even small separated plys are susceptible to further separation and are vulnerable to getting caught, ripped off, or cracked.
Most violin, viola, cello, and bass bows contain horsehair as the primary playing surface.
Broken Bow Heads
When the horsehair is subjected to a drop in humidity, the hair on the bow will actually shrink. A dramatic enough change in humidity can cause enough tension to develop in the bow and can cause the head of the bow to simply snap off.
Once the head of a bow breaks off, the value of the standard student bow is typically a complete loss.
Broken Bow Sticks
A dry, wood bow stick is susceptible to cracks. If low humidity has dried the bow stick enough, simply tightening the bow for regular playing using the bow screw can cause the button of the screw to split the end of the bow apart.
Necks Coming out of Instruments
There are no screws or nails or bolts holding the neck in place in bowed, string instruments. There are simply 4 glue joints which hold the neck of a violin, viola, cello or string bass into its body.
Low humidity may cause the glue to dry out in 1 or all of these joints and the simple tension of the strings may cause the neck to simply come out of the instrument.
A neck which comes out abruptly can cause the fingerboard to slam into and crack the top of the instrument. The bridge also will most likely fall and may crack.
Stronger Wolf Tones
The drier an instrument is, the faster sound travels. This can cause the instrument to sound brittle and the increased "travel speed" highlights any and all wolf tones on instruments. To learn more about Wolf Tones, Click Here.