# Noise Source Identification in Training Facilities and Gyms
## 4 Acoustic Measurements  
Acoustic measurements were carried out with a class 1 sound level meter. The analyzer microphone was placed at a distance of 2 m from the noise source and a height of 1.5 m, which represents the average spacing between trainees during exercise. Equivalent continuous A-weighted sound level LAeq and peak sound level LApeak measurements were carried out over 4 s. Vibration measurements were carried out with a 4 channel 24-bit data analysis system. Acceleration measurements in the vertical direction (perpendicular to the floor surface) were taken simultaneously to the acoustic measurements, with the use of two piezoelectric accelerometers placed in front of the plate impact points directly on the floor, at a distance of 2 m from each side of the barbell. The registered background LAeq was equal to 48.5. The first measurements were carried out while a weight lifter performed the jerk part of the clean and jerk lift. The loaded barbell weighting 60 kg was picked by the lifter from the jerk boxes, racked into the clean position, and jerked to the top overhead lockout. From the top position, the barbell was released to freely drop onto the jerk boxes. In the second measurement, it dropped onto jerk boxes with high-density acrylonitrile butadiene rubber padding on the plate landing surface and in the last case, onto the hard rubber-covered floor. Acceleration data acquisition was started by an 0.2 s pre-trigger on one of the accelerometers. Figure 6 presents the sound pressure level decay acquired during each measurement. It can be seen that the highest sound pressure level was registered during the barbell drop onto bare jerk boxes. The acoustic signal decay is lower than in the other measured cases. Due to the hard surface of the plywood and the lack of energy dissipation phenomena, a bar rebound can be observed at around 0.6 s of the measurement, causing a second significant impact excitation on the jerk boxes and an increase in the sound pressure level and the LApeak was equal to 126.4 dB(A). The application of rubber pads on the top of the boxes resulted in a stronger overall decay of the acoustic signal. The rebounding of the barbell was strongly reduced, which limited additional impacts onto the jerk boxes. The LApeak was equal to 112.9 dB(A). In the last investigated case, where the barbell was dropped from the overhead locked position directly onto the hard rubber floor, this resulted in the lowest sound pressure levels and slightly better signal decay than in the case of jerk boxes with rubber padding, and visibly better than in the case of bare jerk boxes. Additional impacts caused by rebounds, visible around 0.4 s and 0.6 s, did introduce  
Figure 5: Weightlifting barbell loaded with bumper plates placed on plywood jerk boxes. Reprinted with the permission of Reference [28]. Copyright 2008 Fringe Sport. an increase of the acoustic pressure level; however, the overall levels were still lower than in other cases, with an LApeak value of 99.0 dB(A). The LAeq value during the drop onto the jerk boxes was equal to 90.5 dB(A). The application of additional rubber padding did reduce the LAeq to 84.7 dB(A), allowing a 5.8 dB(A) reduction. The direct overhead barbell drop onto the rubber flooring of the room generated an LAeq value of 76.6 dB(A). The acceleration signals acquired simultaneously to the sound pressure are presented in Figure 7. The highest acceleration values are visible in the case of the barbell drop onto the jerk boxes. The application of rubber padding decreased the peak acceleration and reduced the rebounding of the barbell. Counterintuitively, the barbell's impact from the overhead locked position onto the ground corresponded with the lowest acceleration peak values, with visible rebounding of the barbell. The second set of measurements were carried during a 90 kg barbell deadlift. The acoustic pressure was recorded simultaneously to the acceleration data, as described in the previously discussed measurements. The LApeak and LAeq values were defined for both landing surfaces.