Understanding acoustics,
Sound absorption & sound transmission
Explanation of ratings and terminology
To understand the results of acoustic or sound absorbing foam a few technical terms are explained.
Sound Absorption (Acoustic Foam)
Sound absorption is often needed when source and receiver are in the same room, commonly referred to as acoustic foam. Used for purity of sound and reducing reverberation, for high quality recording studios and comfortable public spaces, such as: restaurants, sporting facilities and theatres.
Transmission Loss (Sound Proofing)
Transmission loss is reduction of sound when the receiver of the noise is outside of the room in which the noise is coming from.
Used in many projects for safety or noise complaints. Some application include: construction, transport, manufacturing, industrial and body corporate.
Decibels (dB)
Put simply, the loudness or volume of something in a space. The decibel scale is logarithmic, which means that the difference between two decibel values increases the higher the value. For example, 100dB may be very loud, whereas 110db is unbearably loud. But another example, also increasing the dB reading by 10 would make a seemingly quiet room at 40dB increase to 50dB with the slightest sound.
Audio Frequency (Hz)
Often referred to as pitch. For example, a low frequency sound being a bass drum and a high frequency being a whistle.
Noise Reduction Coefficient (NRC)
Acoustic foams and noise reducing solutions often use Noise Reduction Coefficient (NRC). This is an average rating across a wide range of frequencies, 250, 500, 1000 and 2000 Hz. How much sound a material can absorb is given as a number between 0 and 1, 0 being 0% and 1 being 100% absorption in a specific testing environment.
However NRC fails to show results for frequencies lower than 250 Hz, or 250 Hz itself - it’s these lower frequencies where true noise reducing solutions get results.
Sound Absorption Coefficients
This measures how much sound is absorbed by a material compared to how much sound hits it at various frequencies usually displayed in a table or graph. It ranges from 0 (no absorption) to 1 (total absorption) in its specific EN ISO 11654 – Class A testing environment.
Transmission Loss
Reduction of Decibels (dB) at specific frequencies, the difference in decibels is measured by mounting a sample of a material in an opening between two standardised reverberation rooms.
What is Electrolysis and galvanic corrosion?
Galvanic Corrosion is the corrosion that occurs when two dissimilar metals are used together in a structure and exposed to an electrolyte (salt water, chemical, petrol) and the less noble of the 2 metals will corrode. For example; aluminum sheet with steel fasteners on a boat. Some pairings of metals are more at risk of galvanic corrosion. Check a galvanic series or chart.
Electrolysis is the acceleration of the galvanic corrosion when electricity is introduced to the metals in question. Connected by an external electrical source, the less noble metal experiences accelerated galvanic corrosion.
while both processes involve metals and electrolytes, their dependence on an external voltage source distinguishes them.
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