Acoustics and Human Physiology: Part I

Dr. Paul "Doc" Tenney was instrumental in guiding us towards being as direct as humanly possible when it comes to communicating about saxophone equipment. When Doc first captioned these concepts to us, we had little idea what he was talking about, but our explorations have yielded that many saxophone makers, mouthpiece makers/refacers, and accessory makers often have a differential approach to saxophone marketing and acoustical understanding than what Doc taught us. NOTE: Our approach is not better, more ethical, and/or more substantive than any other approach; it is simply different. Different approaches can enrich conversations and further the pursuit of our musical journey.

Being direct starts with offering objective measures and terminology that the saxophone community can use to discuss saxophone acoustics and measurements. Over the course of several weeks, we reviewed emails from Doc on saxophone acoustics and human physiology from which we began drafting this post. We are offering no original thoughts here; we are simply reciting from Doc Tenney and our few undergraduate courses on physics and acoustics. If in reviewing the information you find something that should be cited or corrected or augmented, we eagerly invite your communication. Thank you very much.

The acoustical properties of saxophones are grounded in physics, and for those playing the saxophone in our universe, there is really no escaping this. When you place the saxophone mouthpiece setup in your mouth and provide adequate air support, the reed can begin oscillating. When the reed oscillates, it generates a pressure wave (greater than atmospheric pressure) in the saxophone’s conical bore. This wave of energy, a longitudinal wave in this instance, moves through the bore and radiates out open tone holes and the saxophone’s bell, from which the wave(s) will propagate through the air to our ears.

Propagation: Propagation refers to how sound, a mechanical pressure wave of alternating high pressure (compression) and low pressure (rarefactions) travels through elastic mediums, whether it be air, wood, metal, water, hard rubber, bone, etc. Sound travels at different speeds through different mediums, and temperature, humidity, and elevation can alter the speed in which sound travels through a given medium. The physical environment in which we live and play our instruments also impacts sound propagation as sound reflections, refractions, and attenuations can impact the manner in which we hear distinct sounds.

When sound travels through the air and the direction of propagation is parallel to the direction of vibration/oscillation, the wave is called a longitudinal wave. Waves that occur perpendicular to the direction of propagation are called transverse waves. While transverse waves are present on vibrating strings and quite visible on water, they can also propagate through solids. Please note that all sounds traveling through air are longitudinal waves.

Sound Perception: We hear sound in two distinct manners, which impacts our perception of sound. The first of these is air-conducted sound, which is propagated through air into the boney, spiral-shaped and fluid-filled conical cochleae of our ears, onto the basilar membranes thousands (16,000 to 20,000) of little hairs (yes, the wave is converted from a longitudinal wave into a transvese wave). The organ of corti, the human body’s microphone, sits on the basilar membrane and oscillates in conjunction with it.  These oscillations activate/trigger a chemical action that creates small electrical pulses, an action potential into an axon, which we perceive as sound. The second manner in which sound waves are propagated to our ears is via bone conduction. In bone conduction, sounds are propagated through the saxophone mouthpiece’s beak, into the maxillary central incisors, into the maxilla, into the cochleae of our ears, onto the basilar membrane . . .

Hearing via bone conduction is typically quite distinct from hearing via air conduction as human physiology tends to enhance lower partials and attenuate higher partials (We will discuss timbre, frequencies/partials/harmonics in a subsequent section). An excellent example of these two distinct manners of perceiving sound readily apparent when comparing one’s perception of his/her voice v. a playback of one’s recorded voice.

Please stay tuned for Part II. Thank you, and have a great day.

Allen Mouthpieces

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