The Study of Sound Waves & Concert Time w/ David Wirth

During the school year a student will invariably ask me what topic I enjoy teaching the most to
which I will respond emphatically “ALL OF IT!" But in all honesty the topic of sound waves is
nearest and dearest to my heart and will cause the release of a little dopamine just thinking
about it.

So you can imagine the choice I made when I was selected to become an Arizona STEM
Acceleration Project Fellow (ASAP) a few years ago and Mike Vargas, one of its directors,
challenged its 500 fellows to write up and share some of their most successful and favorite
STEM lesson plans. And this challenge was backed up with support from the fellowship in the
form of STEM professional development and funds to support the lessons we created. My
favorite lesson plan on sound waves is called “Concert Time” and is included with close to 4000
other favorite lesson plans from the ASAP Fellows in a website which is easily accessible and
searchable. The majority of the turnkey and detailed STEM lesson plans are designed for
elementary and middle school students.

I enjoy the lesson dubbed “Concert Time” for many reasons. First, it's inexpensive and doesn’t
require a lot of resources. The only requirements are a set of six common soft drink bottles, a
cell phone downloaded with a free app and a little water. And finding a few cell phones in a
class full of middle school students is usually not an issue. If cell phones are banned in your
district then direct-connect sensors can also be used. Secondly, this lesson is highly
motivating and often generates lots of smiles, giggles and an unforeseen and unadulterated
applause at the end when students accomplish the given task.

The lesson begins with the instructor promoting an upcoming concert to be held in the
classroom. But the concert lacks musicians. The students are then informed that they will be
the musicians for this concert which will start in about 45 minutes. This gets the students
attention and helps them to focus on the instructions to follow. The information for this lesson
and instructions is given on powerpoint slides that can be used in class and are available on the
aforementioned website. Students should have the prerequisites of basic math skills and a
simple understanding of frequency before beginning this lesson. If not, I’ve also created a
hands-on lesson frequency on the same site which can again be implemented with just a few resources. To have the most success I would suggest giving both lessons.

The concert song to be played requires six different notes. Each lab group is given a common
12 ounce soft drink bottle and assigned a note to play. One group, for example, may be
assigned the note “A” with its associated frequency of 220 Hz. The students will adjust the level
of the water in their bottle and blow over the top creating a desired resonant frequency. A free
cell phone app called PhyPhox is used to measure the frequency of the generated sound wave.
The biggest challenge is usually finding a student who can successfully and regularly cause a
bottle to resonate. But the students enjoy discovering which student in their group possesses
that talent.

Precautions should be taken to prevent the spread of bacteria during this process. I make a box of antiseptic wipes available. The student selected to be the musician will usually
maintain that role throughout the activity.

Fig 1. Two students measuring the frequency of the resonant sound wave.

A cell phone with the app is then held near the top of the vibrating bottle capturing the frequency
of the sound waves. (Fig. 1) Students can use the app to determine how to adjust the water
level in order to get their assigned frequency. Several trials may be necessary as students
work towards calibrating their water bottle instrument. Once finished, the groups will wait for
the concert to begin. Every once in a while, a group thinking they are finished will prematurely
dump the water proving that they missed the whole point of the activity.
The following graph (Fig. 2) was created with the PhyPhox App. Data was pulled from this
graph to calculate the frequency. This group was assigned a frequency of 220 Hz (note A) and
they calculated a frequency of 200 Hz in this trial. The students will then add a little water to the
bottle and measure again. This process will continue until they get as close to 220 Hz as
possible.

Fig 2. Sound Wave data from the Phyphox App.

An announcement is then made and the students are instructed to gather for the concert. Each
group sends their musician to the front where they line up in the ascending order of their
assigned notes. The first test is for the students to play their notes in order, almost a full scale.
The instructor grabs a meter stick and uses it as a baton in order to direct the concert. And the
musicians play their notes as they are directed by the conductor. The conductor (this is you)
really needs to ham it up to get the full effect. The success of the concert will depend on how
smoothly the scale is played. And it's usually pretty obvious if any note is off. Some quick last
second adjustments can be made if necessary in order to produce a better product for the
audience.

It’s now time for the concert! The notes for the song are projected on the front screen and the
musicians gather around in a semicircle facing the screen. The conductor (you) stands in the
middle and points to each note in turn with their “baton” which instructs the given musician to
play their note. The success of the concert will be determined largely by whether the audience
recognizes the song or not. This is easy to quantify as one only needs to watch the audience

and observe their smiles and grins as they start to recognize the song being played.
Sometimes they will even start to sing along which is a good sign. The concert usually ends
with a triumphal applause from the audience and a sigh of relief from the performers. The
students enjoy this activity and develop a better understanding of sound waves, their various
components and one of their applications. They also develop a better appreciation as to why
this could be their teachers favorite lesson. Additional information about this lesson can be
found on the Arizona STEM Acceleration Project website.

1: https://stemteachers.asu.edu/
2: https://stemteachers.asu.edu/stem-lesson-plans
3: https://stemteachers.asu.edu/stem-lesson-plans/concert-time
4: https://www.vernier.com/product/go-direct-sound-sensor/
5: https://stemteachers.asu.edu/stem-lesson-plans/whats-your-frequency
6: https://phyphox.org/