Arduino Theremin Activity #2: Human Hearing
An Arduino theremin is used to illustrate the upper and lower boundaries of human hearing.
- 1 completed Arduino Theremin (Make Magazine or Open.Theremin)
- Powerful, inexpensive amplifier and speakers
- One computer with Frequency Analyzer (such as FreqAnalyst hosted in Audacity)
- Visual aids, handouts
SFU Acoustic Ecology Handbook – Threshold of Hearing:
- Loudness curve
Because this demonstration relies primarily on the extremes of the theremin’s range, the pitch control need not be calibrated for fine adjustments. It is important however, that you use the largest and most powerful speakers available to you in order to be sure they can reproduce the required frequencies. It is also not advisable to use expensive speakers due to the wear that extremely low frequencies can inflict on a system.
Having established the concept of frequency itself, and the general idea of “low” and “high”, it is time to describe the audio frequency range. The following visual aids may help:
[Image: Hearing ranges of different animals]
20Hz is usually given as the lowest frequency that the human ear can hear as a continuous tone. If your setup allows it, play a tone slightly below 20Hz and gradually raise it. It should sound like a rapid series of clicks which blend into a single tone. This is because of the physical limitations of the cochlea.
20kHz is typically cited as the highest frequency audible to human ears, although in practice it varies. Younger people are generally more sensitive in the upper range. Try playing a tone slightly above 20kHz and have students raise their hands if they can hear it. Gradually lower the pitch until everyone can hear it.
One important aspect of hearing is that our sensitivity varies over the audible frequency spectrum. Sounds with the same amplitude will differ in “loudness” (our subjective experience) depending on their frequency. The famous Fletcher Munson curve illustrates this clearly.
[Image: Fletcher Munson curve]
You can test sensitivity differences by fixing the volume of the theremin in one position and slowly sweeping the pitch upward while students draw curves on paper illustrating any changes in loudness that they perceive. You will likely see a general resemblance to the diagram above, although the speakers you use to produce your sound will also influence your results, as will other factors.
Listening exercises and evaluations can be conducted on an ongoing basis to build aural awareness and provide a reference point for the theoretical knowledge. Because identifying individual frequencies is extremely difficult, for evaluation purposes it is probably best to focus on relationships between pitches.
Conversion between Hz and kHz, limits of audibility, differences in sensitivity, and basic terminology are all obvious choices for evaluation.
The ear training component of the exercise can be used to help students establish a sense of high, mid, and low frequencies. More adept students may be able to make more precise numerical estimates. Especially keen listeners may be able to use the theremin to produce pitches within a specified range, or to make close estimates of pitches produced by someone else.
Hearing ranges of other animals:
We encourage teachers to use and alter these lesson plans. But, don’t be shy! Please let us know what you do and send us photos, videos, or notes. We’d love to hear from you. email@example.com