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Do some mouthpieces have more friction than others? Yes.
Does it matter? Probably not.
The “mouthpiece” is everything leading to the melodica’s case. So, for example, a melodica tube constitutes a mouthpiece. The question of friction most often arises in the context of a smooth tube vs. a ribbed one, but there are other cases: short vs. long, straight vs. bent, wide vs narrow. etc.
“Does it matter?” in this case, refers to whether it affects the performance of the melodica in terms of power, responsiveness or anything else.
Let’s refer to the background post on Mass Flow, Speed, and Pressure, where we learned that the mass flow rate throughout a system is constant. The air that you put in is the same exact same amount as the air that flows out.
Friction doesn’t change this. More friction just means that you have a greater pressure drop across the length of the mouthpiece (Bernoulli’s equation assumes a system with no significant friction). The mass flow remains the same. When the air reaches the reed, the same amount of air crosses through the reed opening and it does so at the same velocity (because the velocity is only dependent on are of the cross-section through which the air flows). But it will have slightly less pressure, which will probably make the reed have a little less volume.
How much less? I don’t know—I suspect that the difference between a 57cm ribbed hose and a smooth one is tiny, but I don’t know. I also suspect that a musician would automatically adapt for any small drop in volume by blowing slightly harder.
To answer the question with complete certainty, one would need to have an air supply with a constant flow of air at a given pressure. Then one would need to measure the pressure of the air coming out the other end. One would also have to do some experiments on how different speeds and pressures affect the volume of a reed. As I said, the velocity at the reed should be the same, but with more friction in the mouthpiece, the pressure should be less.
A partly objective test could be done by performing a piece that demands a lot of air with two different mouthpieces (with a rest break in between). If the performer couldn’t notice any difference in either the sound or the amount of air required, then we might be able to conclude that the frictional difference is insignificant.
It seems that friction would make a difference in how the mouth, the lips in particular, engage the mouthpiece. So one player might prefer a smoother, another a rougher mouthpiece.
It seems that friction would make a difference in how the mouth, the lips in particular, engage the mouthpiece. So one player might prefer a smoother, another a rougher mouthpiece.
Alan, I’ve updated my post to define “mouthpiece” (it’s everything leading to the case, not just the part that touches the mouth) The question of friction, as I’ve heard it, usually concerns whether there is a loss of power due to differences in friction, so I’ve clarified that as well. Thanks for revealing that my post had some hidden assumptions
The issue you bring up is different, but I’m not sure exactly what how to frame it as a physics question. “Preference” is not a physics terms—it’s subjective and not relevant for this site. You are welcome to ask a question (as a new topic) if you can think of one for which an objective answer is possible
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