Sweeping Echo

"Reflected sounds whose tone goes up with time"

We discovered a phenomenon that the tone of reflected sounds rises with time when a single handclap is produced in a hallway with a square section, or a rectangular room having rigid walls, ceiling and floor (called a reverberation room).

You can download the sound as a wav file by selecting the word "sound" and choosing "Save Target As ..." from the File menu.

When you play the file, you will hear a strange sound at the instant of the handclap together with its reverberation.

3-dinensional

2-dinensional

[ sound (156KB)]

Rectangular reverberation room.

[ sound (32KB)]

Hallway with square section.

The figure below shows a frequency analysis of the sound recorded in the reverberation room.

It shows that the frequency increased linearly to about 1.5 kHz during about 0.5 seconds. Also in the figure are multiple components whose frequencies rose linearly at relatively slow speeds. These components sound strange.

NTT Cyber Space Labs. explains the phenomenon by using a mathematical model. For details, see the following references.

Kenji Kiyohara, Ken’ichi Furuya and Yutaka Kaneda,
"Mechanism of the low-speed sweep sound perceived in a regular-shaped reverberation room.”　J. Acoust. Soc. Jpn. (E) 21, 4 (2000) pp. 233-235.

Kenji Kiyohara, Ken'ichi Furuya, and Yutaka Kaneda:
"Sweeping echoes perceived in a regularly shaped reverberation room ," 　J. Acoust. Soc. Am. Vol.111, No.2, 925-930 (2002).

Kenji Kiyohara, Ken'ichi Furuya, Yoichi Haneda and Yutaka Kaneda:
"Measuring sweeping echoes in rectangular cross-section reverberant fields,"
ACTA Acustica Vol. 97, 278-283 (2011).

[ Detail Explanation of Sweeping Echoes ]