Permacon is a manufacturer of paver stone products. Their Bolton plant is located about 200 metres from a residential subdivision. Some residents complained of hearing Permacon’s block making machine in their basements.
Aercoustics was retained by Permacon to investigate, recommend and design the noise reduction measures and verify the results.
Permacon’s block machine produces paver blocks by pressing and cementateous powder into a mold and vibrating it. The machine was anchored to a concrete foundation. There was a characteristic hum, at frequencies of 100 Hz and 120 Hz, at double its operating speeds, which could be heard near the machine and in the basements of some houses more than 200m away. The noise could only be heard occasionally outside of the houses.
We determined that the dominant path of the noise intrusion was ground-borne -vibration generated by the machine was traveling through the ground and exciting the basement walls of the houses, which the walls then re-radiated as noise. The maximum noise intrusion in the basements was measured at 30 dBA. The floor and wall vibration levels were imperceptible. After baseline measurements at a reference location, we defined the noise reduction goal at 20 dB.
Isolation of the block machine was the only practical noise control method and we provided the design. The challenge was specifying a system soft enough to meet the noise reduction goal, but stiff enough to limit the vibration of the machine itself. (The softer the vibration isolators, the more the machine’s frame would vibrate.) The block machine’s manufacturer opposed any vibration isolation.
As a result, the block machine noise was inaudible and the vibration levels imperceptible. We confirmed that the ground vibration reduction at the reference location and conducted measurements in the basements of the affected houses.
Permacon also noted that the effect of the vibration isolation was that the paver product was more consistent, but the machine required more frequent maintenance.