Rotary woofer

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A TRW-17 Rotary Woofer

The Rotary Woofer, invented by Bruce Thigpen of Eminent Technology, is designed to reproduce audio frequencies from near zero Hz to 20 Hz. It is aimed at the home theater and professional audio markets.

1 Introduction
2 How it works
- 2.1 Abstract from Yeowarts and Evan's paper
3 Citations
4 External links

[edit] Introduction

As early as 1974, researchers were aware that the human could hear below 20Hz, but that the ear was much less sensitive to these frequencies. Increased sound pressure levels are required to perceive sounds below 20 Hz.

Typical subwoofers using moving cones don't couple well with air below 20 Hz, and thus their sound pressure level (SPL) falls off significantly below this frequency. A new method was needed to produce the required SPL, if people were to perceive the very low frequency content available in recorded material. The rotary woofer was developed as a way to displace far more air than is possible using moving cones, therefore making very-low frequency reproduction possible.

[edit] How it works

[edit] Abstract from Yeowarts and Evan's paper

This paper presents new binaural hearing threshold data obtained (a) by an earphone method over the frequency range 5–100 Hz and (b) by a whole body chamber method over the range 2–20 Hz. The results obtained are in excellent agreement with recent reported data. The binaural to monaural listening advantage appears to remain at 3 dB throughout the frequency range. A good approximation to the binaural threshold of hearing may be formed by lines from the point 92.0 dB SPL at 15.5 Hz with slopes of 12.3 dB/octave for frequencies below 15.5 Hz and 22.2 dB/octave above. ©1974 Acoustical Society of America

This suggests that for sound to be perceived at 7-8Hz, that the 7-8Hz SPL would have to be 12.3dB higher than the 92.0dB SPL required at 15.5Hz. This means that 7-8Hz SPL would require at least 104dB of SPL to be perceived. For 3Hz to be perceived, the SPL would need to add another 12.3dB, or reach 116dB of SPL to be perceived.