When a 60kg barbell and bumper plates are dropped from overhead (about 2 meters), they first gain kinetic energy due to the force of gravity.
In this case, the velocity of the object when it hits the ground (ignoring air resistance) is approximately 6.3 m/s. The kinetic energy of the barbell and plates, when they hit the ground, is approximately 1190.7 Joules.
When the barbell and plates hit the ground, this kinetic energy is rapidly converted into other forms of energy, including sound energy. The loud noise you hear is the result of this energy conversion. The kinetic energy causes the barbell and plates to vibrate, and these vibrations travel through the air as sound waves. The larger the kinetic energy (which depends on the mass and velocity of the falling object), the louder the sound will be.
The only one of these that is not really addressable, unless you want to compromise your programming, is point 3, the weight of the bar being dropped. Everything else can me mitigated to some degree.
The biggest contributor to noise in my opinion is the construction of the bar. Bearing bars are better than bushing bars, needle bearings are better than ball bearings, and the more needle bearings the better.
Barbells with bushings can make more noise than barbells with bearings due to the differences in how these two types of mechanisms handle rotational motion.
Bushings: Bushings are simple cylindrical sleeves that fit between the bar and the sleeve (the part of the barbell that holds the weights). When you lift the barbell, the sleeves rotate around the bushings. Bushings are typically made of brass or bronze, and they provide a smooth, but not frictionless, rotation. This means that when a barbell with bushings is dropped, the impact can cause the bushings to rattle or vibrate, creating noise.
Bearings: Bearings, on the other hand, are complex mechanisms that allow for a smoother and more efficient rotation. They consist of small balls or rollers that reduce friction between the bar and the sleeve. Because of this reduced friction, barbells with bearings are less likely to rattle or vibrate when dropped, resulting in less noise.
Needle Bearings: Needle bearings, work in the same way only they spead the energy of a drop over a larger surface area. More needle bearings creates a larger surface area again. All of this results in less wear and less wear means less movement and rattle when a bar is dropped hundreds of times.
SOLUTION: Regularly maintain and tighten any loose parts on your barbells. If noise is a real problem for you, consider upgrading to needle bearing bars.
When dropping bumper plates, wider plates are often quieter because of how they distribute the force of the impact.
Here's a simple explanation:
Surface Area: Wider plates have a larger surface area that comes into contact with the floor. This means the force of the impact is spread out over a larger area, reducing the pressure on any one point. This can result in a quieter sound because less force is being transferred directly into the floor at a single point.
Material Compression: The wider plates are also less dense in construction. They have more material that can compress and absorb the shock of the impact. When the plates hit the ground, the material of the plate compresses, absorbing some of the energy and reducing the amount that gets converted into sound.
Stability: Wider plates are generally more stable when dropped, meaning they're less likely to bounce or roll, which can create additional noise.
Solution: Consider using wider, less dense bumper plates made from materials that can absorb shock effectively. This will reduce the amount of energy converted into sound.
The height from which the barbell is dropped also affects the noise level. The higher the drop, the greater the velocity and force of impact, resulting in a louder sound.
Solution: Teach members to lower the barbell closer to the ground before releasing it. This reduces the height of the drop and, consequently, the noise.
The type of surface the barbell is dropped on significantly affects the noise produced. Hard surfaces like thin, hard rubber on concrete tend to amplify the noise, while softer surfaces like thicker, less dense rubber mats can absorb some of the impact.
Solution: Invest in high-quality, thick rubber flooring designed for weightlifting. Also, if practical, consider lifting on platforms or using drop pads for your problematic class times.
The acoustics of the room can amplify or absorb the noise from dropping barbells. Larger rooms with hard surfaces (like mirrors, windows, or concrete walls) will have more echo, increasing the perceived noise.
Solution: Install sound-absorbing materials, such as foam panels, on the walls and ceiling. This can significantly reduce echo and overall noise levels.
Understanding these factors and implementing the suggested solutions can help reduce the noise produced by dropping barbells. This will not only make your gym a more pleasant environment for your members, but also help maintain good relations with your neighbours.