Acoustic Testing in the development and verification of Acoustic Products
Acoustic testing of an acoustic product to determine the acoustic performance is important for several reasons.
By knowing the acoustic performance metrics, such as sound absorption coefficients, transmission loss, or sound isolation ratings, one can assess how well the product can reduce noise or enhance sound quality in a specific environment.
Different spaces and applications require specific acoustic properties, and by evaluating and understanding the performance characteristics an informed decision can assist in choosing the right product for the given purpose.
Architects, and acoustic engineers rely on accurate data to model and predict the behaviour of sound in a given space. This information helps in optimizing the layout, materials, and treatments to achieve desired acoustic goals. Informed decisions can then be made when selecting acoustic products.
An example would be an open plan office would need an acoustic product with sound-absorbing properties to reduce reduce reverberation to control noise and improve speech intelligibly, whilst a theatre might require more diffusion and a product which will assist with longer reverberation times to achieve a desired reverberation effect.
Overall, understanding the acoustic performance of a product provides valuable insights into its functionality, aids in product selection, and enables the creation of optimal acoustic environments.
The years of testing by Acoustic Worx has culminated in the development of a Range of Acoustic Products, precision engineered for the built environment. The products have been designed to maximise acoustic absorption and absorption bandwidth, whilst reducing costs associated with high end designs. Real value forms the core of our functionally developed range of world class acoustic solutions.
Development & Verification of Acoustic performance for the motor vehicle industry.
Acoustic Testing is important in the Automotive Industry who are continually striving for low NVH (Noise, Vibration and Harshness) for all parts fitted into motor vehicles. Ultimately it is about the quality of the driving experience, which sells cars….. and noise plays a big part in this. Low noise equates to a more relaxed and pleasant drive. Parts developed and produced locally in South Africa, must be performance driven, not only for our local market but to compete for international business.
The development of the electric car, reduces combustion noise but other noise sources are still present like wind noise, tyre noise, drive train noise etc. This highlights a shift in focus of noise control materials, areas previously masked by combustion effects. There are many factors that affect the acoustic performance of a material such as porosity, tortuosity, characteristic viscus and thermal lengths, air flow resistivity, weight, thickness, density and many more.
Acoustic Testing – Impedance Tube Testing
Absorption Testing in accordance with ISO 10534-2
Transmission and Insertion Loss Testing in accordance with ASTM E2611-17
Impedance Tube Testing is widely used for measuring acoustic performance as a function of frequency in the development stage of product design. The results show normal incidence (sound incident on a surface at 90 degrees). The frequency range of testing is a function of the tube length, tube inner diameter and microphone diaphragm diameter. Tests are performed at predetermined locations with very accurate distances between microphones and distance to the sample face. A discrete Fourier transform derives the transfer function, the reflection coefficient and the absorption coefficient. In the case of insertion or transmission losses, the number of microphone measurement locations increase and measurements are performed with two different terminations.
Acoustic Worx developed tube sets are precision engineered for accuracy and includes in house software to measure and process the results.
Acoustic Testing – SILT Cabin
Sound Insertion Loss Testing (SILT) is measured based on SAE J1400 (Society of Automotive Engineers).
Acoustic Worx Silt test station is made up of two chambers, one of which is an excitation chamber and the other a receiver chamber. The SILT Cabin determines the accumulated decrease in sound pressure of waveform energy as it passes thru a barrier. Transmission Loss and Insertion loss measurements are used extensively in the motor industry for product developed / design to control noise. This test process can also measure acoustic performance of materials used in buildings such as doors, glazing, window seals, drywalling, ceiling tiles etc.
Acoustic Testing – Alpha Cabin
Random Incidence (all angles) absorption testing is defined in ISO 354 and ASTM C423
An Alpha cabin is a 1:3 scaled version of a full Reverberant Chamber. All walls are angled and additional internal diffusion creates a dense sound field. Parts are measured on the chamber floor in regular “A” mounting or on standoffs for “E” mounting.
Alpha Cabin testing is used extensively by material manufacturers and automotive manufacturers to determine the acoustic absorption performance of materials and moulded parts. Materials often comprise of a number of different layers, solid, elastic, porous, impervious and resistive thin layers with most of the elements varying in thickness. Parts are shaped and have various mechanical and mounting constraints.
Acoustic Worx Alpha Cabin is used extensively for acoustic performance testing and product development.
Acoustic Testing – Air Flow Resistivity Meter
Air Flow Resistance shows, in an indirect way, the structural properties of a material and its ability to perform as an adiabatic absorber. This is useful for 2 purposes:
- In relating the acoustic properties of a material to its structure and method of manufacture
- Quality control to ensure uniform acoustic performance in production.
AFR is a function of air flow pressure differential, sample size and sample thickness.
This type of test apparatus can measure
- Air Flow Resistance in Pa.s/m3
- Specific AirFlow Resistance in Pa.s/m
- Air Flow Resistivity in Pa.s/m2
- Linear Air Flow Velocity in m/s
Understanding these parameters of open-cell porous materials is vital in developing an effective acoustic product for noise, reflection and reverberation control. Acoustic Worx has developed a highly accurate Air Flow Resistivity Meter for product development but also to ensure we maintain the best possible acoustic results for our clients.
