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Acoustic Transfer Functions
Acoustic Transfer Functions
What are ATFs?
- An acoustic transfer function (ATF) is defined as the relationship between a sound level of a source, and the sound level at some remote point known as the receiver.
- For example, the ATF of a vehicle's bulkhead / firewall expresses how much lower the noise of the vehicles engine is inside the passenger cabin, than inside the engine bay.
How important are ATFs?
- Along with the sound level a given sound source might have, the ATF plays an important role in how much sound is observed by the receiver, or in practical terms how isolated the driver or passenger feels from the vehicles noise sources such as the engine, electric motor, or tyres.
- Optimisation of the vehicles ATF’s plays a crucial role in the overall refinement of a passenger vehicle.
How are they measured?
ATF's are normally measured in one of two ways:- - Directly - A small loud speaker or sound source is placed at the sound source, and a microphone placed at the receiver
- Reciprocally - A sound source is placed at the receiver location, and a microphone placed at the sound source location
- Directly - A small loud speaker or sound source is placed at the sound source, and a microphone placed at the receiver
- Reciprocally - A sound source is placed at the receiver location, and a microphone placed at the sound source location
The ratio of the level between source and receiver levels is normally expressed in terms of either:-
- Pressure to Pressure (/)
- Volume Velocity to Pressure (Pa/m3/s)
Other types of transfer functions deal with the relationships between a vibrating source and an acoustic receiver (NTF), and where both the source and receiver are vibrating (VTF).