To test the sonic feasibility of my Coleman cooler, I carried out basic measurements using two Samsung Galaxy S26 Ultras. This post details those efforts and results.
Initial experiments
Since half the initial experiment design hinges on the impact of sound and music, I wanted to test the feasibility of the cooler as a sonic isolation chamber. To get a rough idea of the Coleman’s performance, I used two smartphones, both Samsung Galaxy S25 ultras; one phone (A) acted as the emitter and the other phone (Phone B) acted as the receiver.
In Experiment 1, On Phone A, the Sound Spectrum Analyzer app (v11.2) was used to produce sine wave signals with frequencies of 250, 300, 350, 400, 450, 500, 550, 600, 650, and 700 Hz. The spectra of each tone were captured on Phone B using the Spectroid app (v1.1.2) to demonstrate the tone’s spectral purity. In this scenario, Phone A and Phone B are both outside the cooler.
In Experiment 2a, Phone A was tasked with emitting a 500 Hz tone from the Sound Spectrum Analyzer app, and Phone B was tasked with measuring the tone’s loudness outside the cooler as shown above. Experiment 2b was similar, except Phone B was placed inside the cooler and the lid to the cooler was tightly shut. In Experiment 2c, both phones were placed inside the cooler, and the lid was tightly shut. In this experiment, the loudness of Phone A was measured using the Sound Meter app (v1.0.4).
Results
Experiment 1
Spectra for each frequency are illustrated below; the table beneath the image summarizes the peak signal’s power level and frequency.
While the text in the images of Experiment 1 Results are small, the blue text in each image depicts the peak frequency. If you were to zoom in on one of those peaks, it would look like this enlarged plot:
and the blue text would detail the power level (-37 dB) and peak frequency (349 Hz). For all 11 frequencies, those values are listed in the table below. Here, the rows represent the emitted frequency, detected frequency, and detected power.
Based on the results of Experiment 1, the emitted frequencies and detected frequencies match very well; in each case, the main signal is prominent, while other harmonic signals also occasionally appear (ex. 350 Hz, 400 Hz, etc.). The largest variation is seen in the power levels, and this is due to the Sound Spectrum Analyzer app. During the experiment, it was found that playing a tone the first time was markedly louder than any subsequent time the same frequency is played. The only want to combat this was to shut off the phone’s screen, log back in, and immediately play the next tone. Nonetheless, the point of the experiment was to demonstrate the purity of each tone and validate its frequency.
Experiment 2
The shopping list for my first experiment rig consists of the following ite
In the above figure, plot (a) shows the background noise level without speakers. Other than the two peaks at the beginning of the time series, the average noise level sits at ~40 dB.
Plot (b) illustrates two cases. The first case, region I, represents the case where Phone A is outside the cooler playing a 500 Hz signal, and Phone B is inside the cooler, recording the signal (experiment 2b); the average signal here is ~30 dB. Region II indicates the cooler lid being opened. Phone B is extracted during this time, and region III represents both phones sitting outside the cooler (experiment 2a); the average signal power here is ~61 dB.
Plot (c) illustrates the final experiment, experiment 2c, in which both phones are placed inside the cooler. The signal recorded during this time is denoted in region IV, demonstrating an average signal of ~76 dB.
Conclusion
Although these are not the speakers we will be using during the experiment, it’s good to see that the cooler is providing ~30 dB of noise suppression at 500 Hz, because it bolsters my confidence that the cooler will work as both a thermal insulator and an acoustic isolator, especially when the signal inside will be boosted another 15 dB in strength when the speakers are placed inside the cooler during experiments.
Next, I’ll need to pick out lighting, a CO2 measurement sensor, and design the tray to hold the unit cells in place.