Tuesday, September 29, 2015

It's not the heat ... it's the humidity!

looking through condensation & rain

Well, sometimes it is the heat. But when a hammered dulcimer goes significantly out of tune, chances are, a change in humidity is the reason.

Anybody else on the east coast feeling a bit damp? and decidedly out of tune?

It has been raining here for a week, with no sign of letting up in the next few days. Don't get me wrong. It has been a lovely soaking rain ... just what my garden and the local water table need. It feels sort of like a rain forest ... hot and humid.

Actually, temperatures have not been that extreme, but the air conditioning has been running hard to keep the 100% humidity under control. Using my hammered dulcimer as an indicator, I would say the AC is falling behind.

You might have guessed. The dulcimer is uncomfortably out of tune, i.e. I must tune before I play. Don't you hate when that happens!

So what IS happening?

As you know, we have a lot of strings. Those strings stretched across the sound board create a lot of tension. Changes in humidity and temperature effect the tension, and in turn, effect tuning. A good dulcimer will hold its pitch fairly reliably ... until something causes it to go sharp or flat. Extreme temperatures (hot or cold) or sudden changes in temperature (more than 10 degrees) will certainly cause expansion and contraction of the wood with expected results, but temperature is typically less bothersome to our instruments than humidity.

How does humidity effect tuning? As Rouse the Spouse would say, "It's all physics."

Many dulcimers are built from solid wood. Real wood naturally absorbs and expels moisture:

  • swelling as it becomes more wet. The strings tighten. The pitch goes sharp.
  • contracting as it dries out. The strings become more slack. The pitch goes flat.

I am careful to keep my dulcimer safe from temperature extremes. I never leave it in the car for extended periods of time. I don't set it up it in direct sunlight. The temperature inside our house is maintained within a predictable range. Yet, twice a year I witness big seasonal adjustments in my dulcimer:

  • in the spring, the relative humidity goes up, the instrument goes SHARP!
  • in the fall, the relative humidity goes down, the instrument goes FLAT!
While it is true that we have officially entered the autumn season -- in central North Carolina we have not dried out yet. Once the cool, dry air of the late fall / winter season settles in and our heating systems are up and running (drying the air even more) we will be cranking those tuning pegs again!

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