Monday, March 4, 2024
One topic that comes up in many of my conversations on general instrument maintenance is the importance of valve alignment. This simple adjustment to an instrument can have a major affect the way it responds, feels, and, most importantly, how well in-tune it plays.
Some quick math will explain the matter in relation to bore size and the obvious airflow disruption in the form of a "choke point" in the bore. We will start with a pristine example, the Jupiter JTU700.
When a piston is out of alignment, the port becomes ovular. Let's say the felt is old and worn-out, causing it to be half as thick as it once was. What was once .130" thick is now .065" thick.
From there, we divide .309 by .343, subtract the result from 1, and multiply times 100 to get a percentage.
This is a nearly 10% reduction in airflow potential, at either six or eight points (depending on the number of valves) through the instrument. The ledges that these misaligned valves create also introduce turbulence in the airflow, creating further restrictions in the playability of the instrument.
This affects intonation due to the way the sound waves travel through the instrument. Sound isn't simply a wavy line on a page, but rather a radiating series of compressions and decompressions. These compressions are contained within the tubing of the instrument and move most efficiently when a tube is perfectly round and they can equally radiate in all directions in unison. Once tubing is ovular, the sound wave may impact and vibrate off the narrowest point first, then, milliseconds later, the remainder of the wave makes contact with the widest point in the tubing. As this happens, the sound wave becomes jumbled and distorted compromising sound. The harmonic series becomes distorted as well, with non-uniformity in the resonating chamber.
Now that we know that worn-out felts can compromise sound and intonation, what options are there to fix the issue? Step one is a regular maintenance program, where instruments are sent to the shop every year or every other year. During these shop visits where a maintenance cleaning is performed, felts are typically replaced with standard felts, which are sized to closely fit the instrument's factory specifications. This material has worked well for over a hundred years and will continue to be mainstay material in the instrument repair world.
Now to get into real opinion: felt is old-fashioned. It wears out quickly, sometimes compressing after just a few months, which is an unrealistic regular service timeframe. It is also inaccurate. Modern synthetic materials like we use in our Springdale shop are durable, with known examples on instruments we service being five years old and still meeting the same specification as new. It is also highly accurate. We order all popular sizes from trumpet to tuba in .010" increments, with critical alignment shims coming in thicknesses thinner than a human hair!
If you think your valves may be misaligned, feel free to reach out to your local Palen Music Center and schedule a service for your instrument.
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