# Inverse Doppler Effects in Pipe Instruments

## TL;DR

This paper reports the experimental discovery of inverse Doppler effects in recorder and clarinet, revealing their broadband negative refractive indices and suggesting they are early acoustic metamaterials with implications for future metamaterial design.

## Contribution

It demonstrates inverse Doppler effects in common pipe instruments, showing they function as broadband acoustic metamaterials with negative refractive indices.

## Key findings

- Inverse Doppler effects detected at all pitches
- Calculated effective refractive indices are negative and pitch-dependent
- Recorder and clarinet may be the earliest man-made acoustic metamaterials

## Abstract

Music is older than language, and for most of human history music holds our culture together. The pipe instrument is one of the most popular musical instruments of all time. Built on the foundation of previous flute and flute-like acoustic metamaterial models, we herein report the experimental results of the inverse Doppler effects discovered in two common pipe instruments - recorder and clarinet. Our study shows that the inverse Doppler effects can be detected at all seven pitches of an ascending musical scale when there is a relative motion between a microphone (observer) and abovementioned two pipe instruments (source). The calculated effective refractive indices of these two pipe instruments are negative and varying across a set of pitches, exhibiting a desired characteristic of broadband acoustic metamaterials. This study suggests that recorder and clarinet may be the earliest man-made acoustic metamaterials known so far, offering a new explanation why pipe instruments have enjoyed wide popularity in Europe and Asia over the past hundreds and thousands years. This newly discovered phenomenon would also offer a clue into designing next-generation smart broadband double-negative acoustic metamaterials with varying refractive index.

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Source: https://tomesphere.com/paper/1802.08382