A Comprehensive Approach to the Science of Sound
Gone are the days of relying on the very small world of master acousticians with a background in aviation to handhold our VIP thermal and acoustic efforts from infancy to post flight analysis. While our industry does still depend on the oversight of credentialed acousticians, today Luminary is driven to design less by old wisdom and more by the advanced technology employed at cruising altitude.
Standard ISO 5129:2001 testing at each seat position with a hand held microphone has been supplemented with a circular carbon fiber disc housing an array of up to 384 microphones. In addition to our exhaustive ground testing, ISO, FFT, Cabin Absorption and Vibration analysis, we can now see the sounds and sources of noise!
Welcome to the world of acoustical imaging, a relatively new technology allowing a full 360-degree overview sound field map in the aircraft cabin without making any assumptions about the sound field. The technology has just recently become small enough to be able to implement in an aircraft cabin and its benefits are changing the way we design our performance cabin comfort systems.
There is no more relative guesswork in isolating individual noise sources, installation problems with over-frame blankets, gaps in interior panels, noisy windows, emergency exits, and parasitic noise such as hydraulic pumps, ECS systems, etc. We can now pinpoint problem areas down to the millimeter.
Along with sweeping material bench testing bringing in the best performing materials in each category (damping, insulation, isolation etc.) with NO ties, allegiances or bias to suppliers, we are dramatically increasing our in-house R&D resources. Suffice it to say that we will be aggressively targeting the noise level records we previously set on VIP aircraft.
As always, independent acoustic analysis is used to verify ALL Flight Environments Cabin Comfort System noise level results.
Descriptions of Testing and Analyses
In addition to acoustical imaging, we use the following testing methods:
Standard ISO In-Flight Testing: Testing and reporting is conducted in compliance with ISO 5129:2001 Acoustics – Measurement of sound pressure levels in the interior of an aircraft during flight. This testing provides an overall snapshot of noise levels at each seated position. The results are the third octave band sound pressure levels, overall sound pressure levels A-weighted and Linear, and Speech Interference Levels (SIL3 and/or SIL4).
Fast Fourier Transform (FFT) Measurements: FFT measurements provide a very narrow frequency band and can help identify tonal noises from pumps and engines. The exact frequency and contribution of the blade passage frequencies of the propeller can also be analyzed.
Vibration: Vibration measurements can quantify the feelable vibration (frequencies below the audible range for humans not detected in the SPL measurements) in the aircraft floor and determine the contributions of structure borne noise vs. airborne noise. This testing can also be used to determine the effectiveness of isolation mounts for monuments. Broadband, one-third octave and narrow band (FFT) analyses can be completed on the vibration data.
Ground Testing Sound Pressure Levels (SPL): Through ground sound pressure level testing, we will attempt to isolate the individual contributions of such components as the ECS system, engine, hydraulic pumps, APU, fuel pumps, etc. We will measure the air velocity of the ECS systems. Acoustical imaging can also be completed on the ground for further study of parasitic noise.
Sound Absorption in Cabin: Through one-third-octave band reverberation testing the overall sound absorption present for each one-third-octave band in each cabin configuration can be determined and compared.
Bench Testing of Sound Transmission and Absorption: Testing and reporting in accordance with ASTM 2611-09: Standard Test Method for Measurement of Normal Incidence Sound Transmission of Acoustical Materials Based on the Transfer Matrix Method provides a method to study the transmission loss and absorption characteristics of the fabrics, foams, barriers, underlayments, carpets, and composites proposed for the aircraft cabin. The results of the testing include the transmission loss and absorption coefficients for each one-third-octave band.