Noise control of a vacuum-assisted toilet: structural vibration damping

Vacuum-assisted toilet noise can be unsettling and even uncomfortable. One common way to reduce noise levels is to damp structural vibrations that radiate sound. Constrained layer damping (CLD) treatments were investigated for their effectiveness to reduce the radiated noise level on a vacuum-assisted toilet. To find the modal response of the toilet bowl, a commercial vacuum-assisted toilet was excited with a shaker and measured the velocity response of the inside of the bowl with a 3-dimensional scanning laser Doppler. The bowl was also scanned with an accelerometer during a repeated flush cycle. A microphone placed one meter above the bowl measured the radiated sound level. 3M 4014, Pyrotek Decidamp CLD, and Velcro were each applied to the bowl to determine the reduction in structural vibrations and sound radiation. The front-half of the bowl’s rim had the largest velocity amplitude. Structural vibrational energy concentrated around 100-500 Hz while radiated sound concentrated around 300 Hz–2 kHz. Applying damping materials reduced structural vibrations, sometimes by 20 dB. Lightweight treatments certainly can reduce structural vibrations.