The driver noise level of this Manitou forklift truck was 93dB(A) at full engine speed and load. The detailed diagnostic measurements showed the dominant source to be the engine cooling fan.
The somewhat agricultural cooling fan was changed for a more efficient and quieter unit and tuned acoustic absorbent was fitted in the cab roof to reduce the standing waves. These measures reduced the hearing damage risk by 75% (6dB) at virtually no cost. When evaluated over the typical worst-case working day, these noise reduction measures ensured that the operator noise dose was well below 85dB(A).
The remaining noise was dominated by tones from the hydraulic pump as shown here. Interestingly, whilst the hearing damage risk was substantially reduced, at full engine speed you can hear from the recording that the noise actually sounds louder as the characterless broadband noise from the fan that had masked the tonal noise from the hydraulic pump had been reduced.
Whilst it would have been relatively easy to reduce the now dominant hydraulic noise by 5dB - 10dB, the client considered that further retrofit measures were unnecessary.
