In the melodica community, some people believe that shorter mouthpieces are more “responsive”. A melodica, then, is most “responsive” when no mouthpiece is used—one blows directly into the instrument.
I’ve placed the word in quotes because it’s meaning is imprecise. On a physics site, we cannot answer a question phrased using words without clear definitions. In this post, I will go through some measurable quantities that might correspond to what someone might mean by the term “responsive”. My list may not be complete and it might be that even the people who use the term may not agree on its meaning.
I am not going to research anything here—I will just suggest things that can be measured and leave any investigation to other posts. If you have any other measurable quantities that you feel are associated with the term “responsive”, please add a response.
A “mouthpiece”, for our purposes, is everything between the mouth and the melodica’s air chamber entrance. Most mouthpieces are interchangeable; some are fixed.
The first item we can investigate is latency: how long does it take for air blown into the mouthpiece to flow out?
I will call the second item “power”. How much power (volume) is lost as a mouthpiece gets longer? Stated in terms of just the mouthpiece: how much slower does air flow out as the length increases?
Finally, we can test for accuracy. How does mouthpiece length affect the accuracy of the signal? In other words, how well does the airflow into the mouthpiece correspond to the airflow coming out?
There are other things besides length that may affect latency, power and accuracy. For example, the shape of the mouthpiece and materials used in its construction could also have an effect.