Elliott Aviation’s Sound Management System

A corporate aircraft cabin should provide you with a quiet, in-flight business office, a relaxing environment where you can enjoy normal conversations, a place to have meetings or catch a few winks before your next business destination.

And now your King Air interior can give you all those benefits, thanks to the Elliott Aviation Sound Management System, incorporating UltraQuiet Active Noise Control (ANC).

The UltraQuiet system continually samples interior sound with microphones, sending information to a digital processor. The processor generates mirror image sound waves which are broadcast through strategically placed loudspeakers, countering the unwanted noise. Our proprietary engineering for passive noise reduction compliments the UltraQuiet system, further reducing interior sound levels. The total result is a cabin and cockpit you must experience to fully appreciate.

Simply put, your King Air cabin can be as quiet as some business jets with our Sound Management System. Fully proven in commuter airlines, it increases productivity and significantly reduces fatigue for passengers and crew. The System is surprisingly affordable and is available for aftermarket installation in the King Air 200, 300, and 350, the Beechcraft 1900D airliner and the Twin Commander.

More On Active Noise Control (ANC)

The Principle

Active Noise Control technology was discovered in the 1930's, and for many years scientists attempted to implement the physical theory. However, it was not until the advent of microprocessors and faster computing capacity that commercial applications for a wide variety of industries and products became viable. For example, in the automotive arena, electronic mufflers, engine mounts and cabin quieting systems are being developed to quiet motor vehicles.

The basic principle of Active Noise Control (ANC) is that an additional source of sound or vibration is introduced to provide an anti-phase image of the unwanted disturbance. If one sound wave is the negative of the other (that is, the high pressure region of one matches the low pressure region of the other, and vice versa), then the result will be constant pressure, or silence.

In the case of ANC, the level of unwanted noise is reduced or canceled by using loudspeakers to generate anti-noise, or the mirror image of the unwanted noise, in the area where noise reduction is required. The canceling sound signal has to equal in frequency and amplitude, but exactly opposite in phase.

Current ANC systems rely on having the ability to anticipate or predict the characteristics of the noise; in other words, the noise has to be periodic or tonal in nature, such as that generated by turbine blades. At the current level of technology, it is not possible to cancel random or broadband noise caused by airflow outside the aircraft. In any event, as far as passenger aircraft are concerned, it is probably not desirable to create an unduly quiet environment, in which conversations can be overheard. Nor is it desirable that the cancellation signal should interfere with or suppress human speech.

The wavelength of unwanted noise is a key factor in terms of achieving active noise cancellation over a wide area: long wavelengths (low frequencies) provide the opportunity for noise control throughout an aircraft cabin. However, only localized cancellation is achievable at short wavelengths (high frequencies). Thus, ANC is particularly appropriate and effective for controlling unwanted noise at frequencies below 500 Hz, such as the tonals generated at turboprop Blade Passing Frequencies (BPF).

Active Noise Control Implementation

This photograph shows the basic system components: a high-speed Digital Signal Processor (DSP), a microphone and a loudspeaker.

Each loudspeaker makes its own unique sound, tailored by the control system, to ensure that the sound field matches the propeller noise. The DSP operation is based on the sound during one blade passage being very similar to the sound in the following blade passage. A King Air 200 requires 12 loudspeakers to reduce the average sound level by 6-9 dBA; fewer loudspeakers give lower attenuation. The microphones, strategically positioned in the interior trim, provide the DSP with information about the residual noise in the cabin. This information is used to maintain the System's performance as the propeller speed changes and the sound level varies.

Propeller tachometers (synchrophasers) are used to monitor the synchronization of the canceling sound with propeller RPM, and thus allow the System to be selective in attenuating only the propeller noise. This ensures that speech and all other communication in the cabin can be heard, uninterrupted. The system can reduce noise occurring throughout the entire flight envelope, from takeoff to touchdown.

System Maintenance

The UltraQuiet system is designed to require no scheduled maintenance. The DSP has extensive, built-in test capabilities which can identify and localize a System fault to a single area. A single indicator is used to signal a fault condition. Detailed diagnostic data can then be obtained through the use of a carry-on maintenance terminal (laptop computer).