Design Considerations for Acoustics Solutions

Following on from our high-level training programme to 15 engineers, on design considerations for acoustic solutions, we would like to share some of the content, to help you understand acoustics, and some of the misperceptions.

The topics we will cover are as follows:

• The Properties of Sound
• Acoustic Measurement Options
• Acoustic Materials and Performance
• Airborne Noise and Structure Borne Noise      

The Properties of Sound

Sound is an audio sensation caused by pressure variation which are produced by vibration.  The unit of measure is decibels (dB), and is used because the audible human range is vast. The most important property of sound is the frequency which is the number of vibrations or pressure fluctuations per second. The frequency gives the wavelength which has a huge effect on acoustic material selection.

The Decibel Scale

In layman’s terms, is where the human ear can hear the difference between a pin dropping and a jet engine.  The difference being 120dB or 1000000000000 times higher!  At the lowest end of the audible scale OdB, a sound 10 times more powerful is 10dB, a hundred times more powerful is 20dB, and a sound a thousand times more powerful than near silence is 30dB. The decibel scale is not strictly a unit of measure it is a ratio from the threshold of human hearing.

Sound Pressure & dB

A 3dB change in the noise level is generally only just noticeable to the human ear, even though it is a doubling/halving of sound energy.  A 10dB change in level is perceived as a doubling/halving of the loudness but in fact represents a 10 fold increase/decrease in sound energy.   

Acoustic Measurement Options

Sound Pressure is measured at a distance from the noise source.  Sound Power values are calculated based on sound pressures and surroundings.  Sound Intensity is the amount of energy flowing per unit time through a unit area that is perpendicular to the direction in which the sound waves are travelling. The analogy is that if the sound power is like the wattage of a heater, then the sound pressure is the room temperature. Sound Meters gives good overall values and can offer frequency data as well as average sound pressure over time Leq. Acoustic Camera Beam Forming can measure Sound Pressure and Sound Intensity.  The most accurate and detailed measurement because of the nature, and number of microphones capturing sound waves crossing the microphone array.  Acoustic Camera Beam Forming is a very efficient technique for identifying important noise contributors.  The software gives camera images to compare levels radiating from different locations.

Acoustic Materials and Performance  

Virtually all noise control problems can be represented by a simple energy flow diagram, as this generally gives rise to two main options of control 1. To reduce the noise at source or 2. To impede the acoustic energy along its transmission path.  In almost every situation the mechanisms by which a sound is generated, and the location of the machinery/equipment responsible will largely dictate the most efficient treatment options. Sound Absorption materials reduce the sound pressure levels by absorbing the energy.  Absorption coefficient is defined as “the ratio of energy absorbed by a material to the energy incident upon its surface”.  Building materials are rated by their coefficient (NRC).

Airborne Noise and Structure Bone Noise

Airborne Noise measures vibrations through the air, whereas Structure Bone Noise is the vibrations through a solid structure and can be much more difficult to  treat.

Ventac’s Acoustics Laboratory 

Our Acoustics Laboratory located in our HQ in Blessington, Co Wicklow, Ireland, is the state-of-the-art Acoustics Laboratory, and Ireland’s largest and only commercial Acoustic Laboratories.   Ventac’s acoustic laboratories are used for acoustic materials development, vehicle noise testing and building materials acoustic analysis. Ventac can perform the testing required to bring new products and systems to market or can help in designing and specifying acoustic research and development within our test facilities for the Vehicles and Industrial Industries. Contact our Acoustics Team to discuss your Acoustic Testing and Development Requirements.  T: +353 (0)45 851500 or  info@ventac.com.