In this article, we will use our knowledge of Pickleball Noise Fundamentals and Pickleball Noise Propagation to evaluate the effectiveness of sound barriers that are commonly installed around pickleball courts.
The Problem
Assume that a residence is located 60m (about 200 ft) from a pickleball court, and the background (ambient) noise level measured at the residence is 50 dB. Will the resident hear the pinging and popping of the paddles from the court? If so, how much louder will the resident perceive the noise over background levels? How much would this noise be attenuated if a sound barrier was installed around the court?
Sound Level Calculation
We will first need to know the peak sound pressure level (SPL) at the instant when a paddle strikes a ball. Unfortunately, this information does not appear to be available on the internet, and because of the extremely short duration of this event, it is difficult to capture the peak SPL with a standard sound level meter. In our discussion of Pickleball Noise Fundamentals, we assumed that the impact noise would be about equal to that of a framing nailer hammer striking a plywood sheet. This yielded a sound level of 120 dB at a distance of 1 meter from the paddle when measured with the “impulse” sampling rate.
Using the spreading loss equation that we discussed in our previous article (Acoustic Fundamentals), we can determine the change in sound pressure level (ΔSPL) from the source to the receiver, that is,
With R2 = 60m and R1 = 1m, ΔSPL = 36 dB. Therefore, at the residence the 120 dB sound of striking a pickleball is reduced to 84 dB. This sound will be noticeable because it is 34 dB, or a factor of ten times louder than the ambient noise levels (50 dB). Since we know that the SPL of normal conversation is about 60 dB, the sound is 24 dB or a factor of five times louder than normal conversation!
From this analysis we conclude that the sound of the pickleball striking the paddle is more than just a nuisance, because the perceived loudness level is ten times louder than ambient noise and five times louder than normal conversation! What can be done about this?
Sound Barriers
The construction of sound barriers is usually the “go to” strategy for community planners. Sound barriers are typically installed on the fences of pickleball courts to prevent sound from the court from propagating outside of the court. The term “sound barrier” is often used interchangeably with the term “sound absorber”, however, there is a scientific distinction between the two.
Barrier materials are not capable of absorbing sound per se, and must rely on the so-called “mass law”. Essentially, acoustical energy is dissipated through the acceleration of the mass (called inertial damping) and hysteretic damping within the barrier material. In most structural barrier materials, the hysteretic damping is small. Therefore, the majority of the energy that is dissipated by an acoustic barrier is through inertia or mass effects. The greater the mass, the more acoustic energy is dissipated.
Sound barriers consist of sheets of mass loaded vinyl (MLV) that are hung onto the surrounding fences. MLV was invented in the 1960s as an alternative to using lead sheets for the soundproofing of walls inside houses. MLV is comprised of polyvinylchloride (PVC or just plain “vinyl”), that is loaded or impregnated with a heavy inert material, such calcium carbonate or barium sulfate.
There are only a handful of manufacturers that produce MLV, although there are literally hundreds of vendors that sell the same MLV on the internet, branded under their own company name. Many of these vendors claim that their MLV has almost “magical” properties of being capable of converting acoustical energy into thermal energy (acoustic absorption). However, this effect, which comes about from viscous damping in the vinyl material, is small. For the most part, all MLV’s sold by the different companies are the same and are differentiated only by their areal density (mass per square foot). A typical outdoor MLV will have an areal density of two pounds per square foot (2 psf).
Sound barriers work by reflecting the incident acoustical waves, thereby preventing acoustical energy from being transmitted to the other side of the barrier (Figure 1). In real life, some portion of the incident acoustical energy is reflected, some of it passes through the barrier, and some of it diffracts over the top of the barrier and through gaps (often called “flanking paths”).
MLV’s are rated according to their sound transmission class (STC), which is measured in an acoustic laboratory where flanking paths are eliminated. The STC rating loosely indicates the transmission loss through the barrier, which is the amount of acoustic energy that can be attenuated by the barrier (in the absence of flanking paths). Therefore, a sound barrier with an STC rating of 25 will reduce the incident acoustic noise by about 25 dB.
The major limitation of sound barriers is that sound will diffract over the top of the barrier and through holes and openings. The amount of sound that is diffracted over the top of a noise barrier is dependent on the path length difference between the direct path between the source and receiver and the path in which the sound would need to take to reach the receiver by going over the barrier (Figure 2).
Using the path length difference, it is possible to calculate the amount of sound attenuation that an acoustic barrier will provide by use of the Fresnel equation:
Where N is the Fresnel number and λ is the acoustical wavelength. In our example, let’s assume the following:
- The ball is struck at a height of 1m
- The height of the fence is 3m
- The distance from the paddle to the fence is 3m
- The distance from the fence to the house is 57m
- The frequency of the sound from the pickleball paddle is 500 Hz (corresponding to an acoustical wavelength of 0.7m)
From this, we calculate that A=3.6m, B=57m, which corresponds to a Fresnel number of 1.0. At a Fresnel number of 1.0, we see from Figure 3 that for a stationary sound source, the barrier attenuation is about 15 dB.
If the noise from the pickleball paddle is 120 dB, the amount of noise going over the barrier will be (120-15) = 105 dB. If the STC of the sound barrier is 25, the amount of noise going through the barrier will be (120-25) = 95 dB. Sound levels are logarithmic quantities that do not add arithmetically, so we must use the following logarithmic equation to combine them:
Therefore, the total amount of sound transmitted through the barrier, considering the transmission loss of the barrier and diffraction over the top of the barrier, will be about 105 dB. Subtracting the 36 dB we calculated above for spreading loss, we find that the sound level at the residence will be about 69 dB, which is 19 dB greater than the ambient acoustic levels (50 dB). This will be perceived by the residents to be almost four times greater in loudness than ambient levels! The problem is exacerbated when multiple pickleball hits happen simultaneously.
How Effective are Sound Barriers?
Comparing the sound levels at the residence before (84 dB) and after the installation of the barrier (69 dB), we see that the barrier is capable of attenuating 15 dB of the impact sound. In practice, we would expect that the barrier will be less effective due to several factors:
- Flanking paths and holes will enable unattenuated sound to pass directly through the barrier.
- Acoustic reflections off of adjacent barriers, nearby structures, and trees will provide a direct sound transmission path to the residence.
- Reverberations within the enclosed court will prolong the sound duration, cause echos, and amplify the impact noise like the soundbox of an acoustic guitar.
- Refraction by the atmosphere (i.e., inversion layers) can direct the sound downward towards the residence at certain times of the day.
Acoustical engineers will therefore conservatively estimate that sound barriers such as those used on pickleball courts will provide only 10 dB of sound attenuation. Although a 10 dB reduction of sound level equates to a halving of the perceived loudness level, it is often not adequate to satisfy homeowners and communities. Furthermore, vinyl barriers that are hung on fences are prone to weathering and tearing and may not otherwise be suitable for use in high wind areas.
What are the Alternatives?
Since sound barriers do not appear to be effective, it is not surprising that residents who live near pickleball courts have resorted to the draconian measures of stopping pickleball court construction, removing or relocating pickleball courts, limiting playing hours, or requiring the use of special low-noise balls or paddles. It is incumbent upon pickleball equipment manufacturers to develop solutions for the noise problem and for the US Pickleball Association (USAPA) and other industry and governing organizations to approve them for use.
In future articles we will evaluate so-called low-noise paddles and balls to determine how effective they are in reducing pickleball noise. We will also analyze standard pickleball paddles and pickleballs to determine why they are loud, and how they can be modified to reduce the amplitude of the impact sound while preserving their playing characteristics.
