[Binyomin]

Neil, this is perfectly normal behavior for a melodica. When you press a key, you are releasing air through that reed opening. When you play two or three notes at the same time, the amount of air released goes up proportionately.

Similarly, unless you add more air, if you add another note while playing one, the available air pressure to the first note will drop, because that air is now escaping via two different reed openings.

I do think that the Hammond performs ok with regard to all of the notes speaking well at low and high volumes, but you should keep in mind that different sized reeds need more/less air to ‘speak’, and on a larger instrument (44 notes),the range between low and high makes this perhaps a tad more noticeable.

I’d be interested to hear what others here have to say on tis, as I have not spent as much time as some trying to comp and play melody at the same time.