Northern Devon Healthcare NHS Trust planned to build a medical school within a gymnasium area. A plant room directly above the solid concrete ceiling slab was producing a strong tonal sound within the gym below. Acoustics design had to meet both Building Bulletin 93 for the teaching areas and Health Technical Memorandum (acoustics) for hospitals.
Soundguard Acoustics Ltd was contracted to identify the noise source and provide a solution to the problem. Octave Band testing determined that a tonal element to the noise was occurring at 25 - 31Hz, given the solid construction of the building and the heavy concrete ceiling slab the sound transmission was identified as structural vibration. In addition, the room volume and dimensions was enhancing this particular tone and forcing the whole room into reverberation.
Assessment in the plant room identified a centrifugal pump used to supply forced air to the main Surgical Theatre as being the problem. The weight and rotation speed of the pump correlated exactly with the noise breakout below and predicted a dominant frequency of 24Hz. Although the pump was mounted on an isolated frame, the isolators had collapsed and bridging of the frame with later installations had occurred. Suitable isolators were specified, couplings were replaced, bridging paths were removed and the fan was balanced and serviced.
The result was an effective solution that eliminated all transmitted noise and enabled the gymnasium area to be free of any tonal or reverberation noise.
