Sound Absorption Performance of Wood in a High Frequency Range I. Composing a measurement method in a high frequency range

It is assumed that owing to its porous nature wood has sound absorption capability, but it is not clear that the structure of wood is reflected enough in the sound absorption characteristics in the measurable spectrum range up to 6400 Hz with a normal measuring device. Therefore the authors constructed new equipment for measuring in a higher range spectrum and attemped an actual survey. Usually the sound absorption coefficient is given at the 1/3 octave band center frequency. However, with our new machine it was necessary to devise a measuring method that gives reasonable sound absorption coefficients. We suggested a method to extract the local minimum of raw sound absorption coefficients. By this method, it was confirmed that a characteristic spectrum was seen in a high range of more than 7700 Hz of the sound absorption coefficient of wood, showing delicate differences between species of wood or wood sections.