Acoustic Consultants are often tasked with analyzing the noise absorption in rooms, studio garages, and storage spaces. The primary challenge in this type of analysis is to find a dynamic signal analyzer with portability, high sampling rate functionality, and complex analysis. The rugged CoCo-80X with a sampling rate of up to 102.4 kHz paired with EDM Post Analyzer software featuring Acoustic Analysis and Sound Power is the optimal solution to meet these needs.
MD Acoustics, LLC recently demonstrated the capabilities of Crystal Instrument’s CoCo-80X and EDM Post Analyzer through a case study comparison on the absorption properties of an egg carton versus acoustical foam, an exciting and recurring question in the acoustics community.
An array of 4 microphones, a speaker, and two specimens (egg carton and 1.5” acoustical foam) were arranged in an anechoic chamber at an MD Acoustics facility in Gilber, AZ as shown below.
Acoustic foam (1.5”) and egg carton setup in anaechoic chamber
In each recording, the speaker was placed at the same distance from the specimen. A linear array of two-microphone probes was placed at each upstream and downstream locations, with the specimen in the midpoint between the upstream and downstream probe locations. The recordings were made over a 10-second period and were post-processed using EDM Post Analyzer, as shown in the figure below.
Data displayed in EDM Post Analyzer software
Three situations were analyzed for comparison purposes. The first situation was the measurement of the air since no specimen was placed. The second corresponded to the egg carton, and the third corresponded to the 1.5” acoustical foam. The absorption coefficient was calculated using a method like the transfer function method. The frequency range targeted was 63 Hz to 4 kHz. The absorption coefficient measure for each condition is shown in the table below.
| Material | Absorption coefficient | TL [dB] |
|---|---|---|
| Air | 0.98 | 2.2 |
| Egg carton | 0.63 | 5.1 |
| 1.5” Acoustical foam | 0.91 | 5.2 |
Absorption coefficient values follow the assumption that the acoustical foam would perform better than the egg carton. Also, the transmission loss (taken as the level difference between upstream and downstream positions) is similar for both materials, and both TL values are higher than the TL value when nothing was installed.
The figure below shows the one-third octave band analysis. The egg carton has high absorption coefficient values for frequencies below 630 Hz and a massive dip at 1.6 kHz. Additionally, the spectrum obtained for the foam is regular over the complete frequency range analyzed, providing a superior sound absorption solution over the egg carton option. The absorption coefficient measured for the sample of egg carton is weak between 630 to 3150 Hz.
In conclusion, using egg cartons for sound absorption wall treatment will not work for all the frequencies. Depending on the sound environment where the application is meant to be, the egg carton solution will not be as effective as the acoustical foam. Keep in mind that the samples measured at this time were regular egg cartons found at grocery stores with some humidity content. The acoustical foam is 1.5” thick and is engineered for sound absorption. With that being said, it is possible to find some different values in other experiment results.
At MD Acoustics the use of the CoCo-80X has been essential for projects involving flexible measurement methods with complex variables to acquire. On this occasion, we acquired data using 4 channels.
For more information on how the CoCo-80X can help with your acoustics measurement and analysis, please contact sales@go-ci.com.