In spring 2021, I visited Echo Amphitheater, a naturally formed amphitheater near Abuiquiu, New Mexico. Despite being central to wild west folklore, the site has never (to my knowledge) been studied for its acoustical properties. To gain a better sense of the exotic acoustics of the amphitheater, I recorded myself clapping my hands four times with a TASCAM DR-05 field recorder. Below is the original data, as well as (limited) analysis of the echo times, decay, and bandpass of the canyon. As I learn more about acoustics, I hope to more carefully analyze the data, and maybe visit the canyon again.
Table of Contents
Below are the four handclaps. Feel free to download, share, analyze, etc.
The annotated waveforms below identify the first four echoes and indicate their order.
In the table below, the time between each echo from the previous echo is recorded. The initial clap is set at t = 0.
|Clap #||1st order echo time (s)||2nd order echo time (s)||3rd order echo time (s)||4th order echo time (s)|
We can find the decay factor (measured in dB per echo order) of the canyon by analyzing the intensity of the initial claps and the first-third-order echoes (the fourth order echo was too faint to accurately measure the intensity). The decay factor is average of the slope of the graphs below.
The decay factor was calculated to be -12.225 dB/echo order.
In addition to modulating the delay and amplitude of the input signal, and the amphitheater modulates the spectrum, acting as a low-pass filter. This can be seen below:
Since the peak of the initial clap was around 1000 Hz, the bandwidth (BW) is about three octaves:
We see a similar ~three octave bandwidth (BW) for claps 2-4: