Qualifying freefield and reverberation rooms for frequencies below 100 Hz

Variability of low frequency sound transmission measurements

“…Numerical simulations were presented using the mean pressure over the whole volume in the source room and the average intensity in a cross section in the receiving room, indicating an improvement in the dispersion of the results. A similar solution has been also proposed by Fuch et al 26 using special broadband resonator absorbers, and by Pedersen et al 12 placing absorbing material in the receiving room only. The intensity method has also been used for low frequency sound transmission measurements, and its results compared with the traditional method by several authors.…”

Modeling of influencing parameters in active noise control on an enclosure wall

“…The possibility of using an active barrier to reduce the acoustic transparency of a partition wall is investigated by simulating sound field in a noisy rectangular room with and without the ANC. The noise source is simulated as a point monopole placed in different positions of the room; the acoustic field that it generates is modeled with the virtual image sources technique, that identifies the images of the ''real'' source by a mirror effect on each enclosure boundary [15,16]. The image source technique has been chosen for the following reasons: the validity of the image source model for the determination of the point-to-point transfer function of the room across a wide frequency range has already been demonstrated [15]; due to the important number of calculation to do, the model had to be relatively simple.…”

“…Since the first natural frequency of the room is 34 or 50 Hz (depending on the adopted configuration), the maximum investigated frequency (300 Hz) is almost six times larger than the first room natural frequency. Conversely, the lowest investigated frequency (25 Hz) has been included to investigate the efficiency of the method at very low frequencies, where there is a growing interest in the acoustic behavior of enclosures [16]. In the practical problem for which simulations have been carried out, the largest part of noise is between 80 and 150 Hz, thus parameters of the ANC system has been optimized for these frequencies.…”

Requirement for low-frequency reverberation in spaces for music: Part 1: Smaller rooms for different uses.

“…In the course of the present research into the relevance of the bass domain for noise control and acoustic quality and comfort in rooms, Fuchs, Zha, and Drotleff (2005) had to develop a special technique for measuring an effective absorption coefficient, α e , frequency dependent below 125 Hz (Zha, Fuchs, Nocke, & Han, 1999). Meanwhile, a lot of experience could be gathered from hundreds of projects qualifying free-field and reverberation rooms for the lf end of the spectrum (see Fuchs, Zha, & Pommerer, 2000). The detrimental effects of room modes on speech intelligibility in communication rooms was first discussed, and possible improvements were documented, for example, by Fuchs, Zha, Zhou, and Drotleff (2001).…”