January 2020 Newsletter: The Big Bang Theory

Please stop jumping… I can’t sleep! Almost everyone has experienced this problem, whether you live in a multi-family building or single family home. The world of acoustics has several testing standards to represent the impact isolation of floor/ceiling assemblies through objective ratings; standards developed by American Society for Testing and Materials (ASTM), International Organization for Standardization (ISO), and Japanese Industrial Standards (JIS) guide consultants to make sure tests conducted by one firm can be compared to those conducted by any other. Some testing methods, like those used in Korea and Japan, can be more realistic than those used in the U.S. Read on to learn more about testing methods in the United States and Asia.

Ideally, the most accurate and realistic test method would be to use impact sources such as walking adults or jumping and running children. Unfortunately, these sources are hard to reproduce and repeat. The next best method is to use an impact source that accurately simulates these real world sounds.

In the U.S., the standard we generally follow for field tests is ASTM E1007, which uses a tapping machine: a purpose-built device that generates impact sounds imitating someone walking with hard-sole shoes. Five steel hammers are dropped 10 times per second, and the sound level generated in the space below is measured. This tapping machine was developed in 1947 when more people wore hard-sole shoes, which is becoming much less common.  Click this link for a Tapping Machine Video Clip.

In Korea and Japan, heavyweight impact sources that produce more low-frequency sound and less mid- and high-frequency sound are common and include the Bang Machine and Impact Ball. Both of these sources used in test procedures in JIS A 1418-2.

The Bang Machine consists of a tire on a long arm and simulates events such as children jumping or running. The tire of a Bang Machine is dropped from 85 cm above the floor; with its heavier weight, it can generate more low-frequency impact sound. A drawback is that the impact force of the Bang Machine is 4200 Newtons (N) and is above the range of actual impact forces – children running and jumping is between 600-1000 N and 2000-3000 N, respectively. Additionally, the force is so great that it may damage wood-frame structures. Click this link for a Bang Machine Video Link.

The Impact Ball was specifically developed to reduce the potential damage to structural components and is made of SBR (Styrene Butadiene Rubber) or silicone rubber. It is simply dropped from 1 meter above the floor and generates an impact force of about 1500 N.

When comparing the three sources, the Impact Ball (orange dotted line) generates the most similar frequency characteristics to that of children running and jumping (solid pink and blue lines) in a residential building as compared to the other impact sources.

The Bang Machine and Impact Ball test methods are not adopted in the U.S. yet, but we hope they come to this side of the globe soon. According to the studies, the characteristics of these test methods are closer to what people experience in a multi-family building. In the meantime, we will continue to hammer away with our Tapping Machine while taking some testing cues from Korea and Japan. Just give us a knock.
December 2019 Newsletter: Why You Feel What You Hear