[Sincerely seeking] The reasons for the sound change of Shanghai Guoguang 24-hole echo harmonica

There is a certain frequency difference between the upper and lower reeds of polyphonic harmonica, which is used to realize the beat and form the feeling of "floating", which is also the reason why the timbre of polyphonic harmonica is different from other harmonicas. So if you play one format, there will be no vibrato, just play two. If the vibrato becomes too loud and affects the effect, it may be that the condensed water vapor on the reed changes the frequency, resulting in too big a beat. In addition, the structure of the 24-hole piano is similar. Please check if there are any screws near+1. If the screw falls off, it will vibrate with the sound, which will make the sound of the hole very noisy (I have encountered it before).