Ask Dave: When is a Small Dent Considered Serious?

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Mark K. asks:

When is a dent in the tubing considered serious enough to affect the playing qualities of a horn? Does the location of the damage have any effect as well?

Dave replies:
Like most things in life the answer is, “well, it all depends.” As a rule of thumb (and I have seen different percentages here), a dent is beginning to be of concern when it reduces the diameter by 15% or more, and should absolutely be taken out when it collapses the tube over 25% of the diameter of the tube.

Why have I seen different percentages in this rule of thumb? Because, it depends! The second question is the key because, yes, the location of the indentation plays a big part in just how much effect even a small dent might have on the horn.

The creation of a standing sound wave in the horn results in changes in pressures. Some points in the tubing are critical to maintaining the pressure, and therefore the sound wave. If the dent is at that critical point then notes can waiver, can play flat, or just chip on attack. The tricky part is that as you change the harmonic series, those critical points in the horn are in different locations! So, a dent might be at one of those critical points for one series of overtones, but not others.

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Those minor dingers on your bell flare are probably of little or no concern.

But that tiny dent in your leadpipe may really mess up your horn. If your horn is not playing correctly after a dent, then get the dent removed.

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