  Sound reconstruction via arbitrary objects has been a popular method in
recent years, based on the recording of scattered light from the target object
with a high-speed detector. In this work, we demonstrate the use of multi-mode
fiber as a medium that enables reconstruction at a much further distance. By
placing a speaker near the fiber and using a high-speed camera with a maximum
region of interest, we show that it is possible to reconstruct the sound
without relying on specific grain information in the speckle. Basic filtration
techniques and spectral subtraction methods are employed to improve the signal
quality. After applying band-stop and high-pass filters, the magnitude-squared
coherence between the original sound and captured data is 0.8 at fundamental
frequencies. The proof-of-concept method that we introduce here can be extended
to monitor the vibrations of earth's crust and civilian buildings for
structural safety.
