But some differences are noticeable, especially when we take a closer look
The vent holes of the E are approximately 1″ long, while those of the D are close to 3/4″. Possibly this is to offset some of the muting effect created by other changes in the E.
The walls of the E’s enclosure are thicker than those of the D, making the enclosure of the E slightly heavier and, it would seem, more durable. This may have some dampening affect on the sound quality and/or volume of the P-37E.
The inside of the E’s enclosure is stamped “ABS+PLA”, which must refer to its “biomass-derived resin ‘Ecodia'” composition touted in Yamaha’s advertising, which is also being used in some of its recorders. As far as I can determine, this is a form of PVC for which Japanese inventors submitted a copyright application in 2009. The rationale for the invention is suggested by the “biomass derived” descriptor: it is better for the environment, it helps with global warming. Whether it actually has any acoustic advantages, we can only guess. It’s possible, but my guess is that the thickness of of the application is more likely to matter acoustically in a melodica.
The most conspicuous likely acoustic difference-maker in the P-37E is the approx. 17″ X 1 and 1/4″ strip of dense foam rubber that runs the length of the backside of the bottom of its enclosure. It is about 1/8″ thick. Insertion of some such strip is something about which we have speculated in past conversations. I experimented with lighter, thicker, more porous foam a few years ago, though only briefly and with uncertain results. There has also been experimentation with strips of wood, I guess on the theory that the presence of wood in a melodica can be counted on to produce a “more acoustic” sound. The concept is simple; Yamaha’s application looks good and seems to be one likely factor in (what I hear as) subtle improvements in the sound of the new P-37E.
The beauty of this improvement is that it is something we can easily try on other melodicas.
Another acoustic difference maker, according to Yamaha, is the thin strip on which the key pads rest. You can (short of more risky disassembly) barely see the air holes in this strip with a flashlight. The decreasing (or increasing) sizes of the holes determine the volume of air passing through when the key is depressed and the pad is lifted. Daren posted an image earlier.
Notice that the size of the openings does not gradually change from one end to the other. This surely cannot be the most effective application of the concept. There are just three sizes. I feel some unexpected resistance in blowing into the P-37D as I move up the keyboard. Acoustic implications seem likely. The quality of the sound may be improved. A slight difference in the playing experience may be felt. There may be a difference in bending notes or producing other effects.
Finally, it is often said that it is a disadvantage of the P-37D that moisture is vented inside its enclosure rather than out an escape hole. As a practical matter, that may be. The clearly visible escape hole below the moisture release button of the P-37E may look like an improvement. But has been there all along on the P-37D.