By Rosanne Chong
Research have shown that perceived loudness by humans varies to a large extent with frequency and sound-pressure level. A low frequency sound would require a much higher sound pressure level to sound as loud as a high frequency sound. In other words, for the same sound-pressure level, a higher frequency sound would be perceived as much louder than a lower frequency sound.
The level of sound also affects human perception of pitch. For high frequencies, the pitch goes up as the level of sound is increased and for low frequencies, the reverse occurs. By understanding the complex relationship between quantitative measures of sound like frequency and sound-pressures with the human perception of sound, one can apply such knowledge to increase the quality of sound of the invisible speakers to be designed.
The space occupied also plays a part in affecting human auditory perception. In large enclosed spaces, such as auditoriums and music halls, surfaces might produce reflections of a high enough sound level to be perceived as audible echoes. This would affect the user’s perception of sound as compared to when they hear the same sound in an open space or a small narrow space. One interesting thing to note would be that, large enclosed spaces might not necessarily lower the quality of sound perceived due to the numerous unwanted echoes produced. If well designed to give lateral reflections of appropriate levels and delays, such spaces can add a sense of spaciousness to the music for the audience, thus improving the experience of the users through careful manipulation of their perception of sound through altering the space.
Moving on to the specifics of how the ears work to perceive sound, sound waves entering the ear canal would cause the ear drum to vibrate, which will in turn move the tiny chain of bones in the middle ear. The final bone in this chain of bones would then knock on the membrane window of the cochleas, making the fluid inside move. This fluid movement then triggers a response in the hearing nerve. One fascinating fact is that the outer hair cells of the mammalian cochlea seems to contribute greatly to the amplification of sound. Perhaps more in depth understanding of this could lead to further explorations in our speaker design.