# Noise Source Identification in Training Facilities and Gyms
## 2 Research Object Description  
The acoustic measurements were conducted in a CrossFit box created in an adapted industrial site. The fitness club is part of a terraced warehouse-like building. The main part of the CrossFit box is a 1000 m\({}^{2}\) open space physical exercise area. The 42 m long, 24 m wide, and 5 m high space is equipped with standard CrossFit box equipment, such as pull-up stations, bikes and rowers, weightlifting platforms, plyo boxes, as well as smaller equipment, such as barbells, kettlebells, dumbbells, medicine balls, etc., placed in racks and custom stands. The open space area is divided into subareas by the group of equipment and the physical activity type to be performed rather than physical barriers, such as walls or enclosures. The only additional construction elements except for the walls, roof, and floor are four pillars supporting the roof structure (Figure 2). The main part of the floor is tailed with 0.02 m thick NBR shore A 75 rubber panels (Figure 3) while other building surfaces are covered with conventional paint. The presented setup is a good representation of an average trending training facility, which can be found all-around the globe.  
Figure 1: Destroyed fitness center floor.  
Figure 2: Industrial site adapted to a CrossFit box.  
Reverberation time measurements were conducted with use of an approximated impulse excitation in the form of a large balloon blast [20] at an unoccupied state. Due to the unusual case/type of enclosure and the preliminary nature of the investigations, a balloon blast was chosen instead of a Dodecahedron speaker due to the ease of use and successful application by other researchers [21; 22; 23; 24]. Measurements at six points at the area of physical exercise led to a value of the average reverberation time t_60 [8; 22; 23] of 2.95 s. Measurements were conducted in six points, evenly distributed across the training venue. The distance between neighboring points was 10 m, two columns with three rows of points, and the average distance to the nearest wall was equal to 5 m. The averaged sound pressure level decay is presented in Figure 4.  
A simple reverberation time calculation was conducted using the Norris-Eyring expression and Fitzroy relationship in order to compare the measured values. Surface acoustic absorption values (Table 1) for the walls, ceiling, flooring, doors, and windows were chosen based on values presented in the literature [25; 26]. Noise reduction coefficients NRC were calculated based on the acoustic absorption coefficients at four middle octave band frequencies (250, 500,1000, and 2000 Hz) for the room's surfaces, doors, and windows.  
Figure 4: Averaged sound pressure level decay.  
Figure 3: Industrial site adapted to a CrossFit box: weightlifting platforms and glyometric boxes.  
Using the Norris-Eyring expression [26], the estimated reverberation time was equal to 33.020 s. The reverberation time calculated with Fitzroy relationship [26] was equal to 33.104 s. The difference between the measured and calculated reverberation time can be caused by differences in sound absorption parameters, geometrical differences of the room, modifications applied to some sections of the roof where additional insulation was introduced, and lastly by the numerous exercise equipment and weightlifting platforms, which introduce additional absorbing surfaces. The reverberation time calculation did not include additional equipment, such as sand bags, medicine balls, rubber and foam components of other fitness devices, bumper plates, and weightlifting platform rubber panels, which can often add some sound absorption to the analyzed room.