This is a very interesting question. We need the physicists here to answer!
I've never actually measured the decibels on my piano. However, my understand is that there is a dynamic interaction between pitch and loudness, or should I say, "perceived loudness". Apparently, it works both ways - changing pitch affects perceived loudness and vice versa. At least to my ears, higher pitch gives a perceived louder sound than lower pitch.
Yes, you're right that higher pitch gives a perceived louder sound. Check this out (though this article talks abt guitar, i believe the physics of human hearing still apply): http://www.phys.unsw.edu.au/music/guitar/guitarintro.htmlThere is this statement: Human ears are most sensitive to sounds...about two to four octaves above middle C.
But the problem is that I'm experiencing the opposite phenomenon on my keyboard - which is both intriguing and perplexing!
According to another article (http://nicholaspianos.com/press_release.htm), "Because low (bass) notes require more energy to sound as loud as higher notes, a larger and larger percentage of the piano structure must be created to create low notes. Similarly in an electronic sound system, a sub-woofer may need 100 watts to sound as loud as a tweeter consuming 1 watt."
So i have been wondering: do my lower keys sound louder, which shouldn't be the case, because of the poorer quality of my keyboard's electronic system? So like what kongwee says, price makes the difference here?
Do note than an electronic keyboard is vastly different to an acoustic piano. The reason is that an electronic keyboard (depending on the patch) has the sound programmed. Depending on the programming, the sound may be quite different across the keyboard. What is the model of your keyboard and the patch in question?
If it sounds that way on the earphones, I supposed that's the way the it is. It's not a high end keyboard, but the loudness should be the same across the keys. The patch name (sound) should be displayed on the LCD screen. Does your problem occur in every single patch or just a few of them?