Direct-field acoustic testing

The system employs high capability acoustic drivers, powerful audio amplifiers, a narrow-band multiple-input-multiple-output (MIMO) controller and precision laboratory microphones to produce an acoustic environment that can simulate a helicopter, aircraft, jet engine or launch vehicle sound pressure field.

The technique uses normal incident plane waves in a shaped spectrum of acoustic noise to impact directly on all exposed test article surfaces without external boundary reflections.

Depending on the geometry of the test article this could produce magnitude variations on surfaces due to phasing differences between the plane waves.

The entire process from load-in to load-out can be accomplished in no more than 4 days for a large satellite or similar aerospace structure.

The test system uses a “building block” approach to form combinations of equipment to satisfy the environmental requirements.

The mobility and “building block” approach allows this method to be tailored for each application and to provide a more timely and cost effective test solution.

However, reflections from the test article can be minimized with the microphone oriented toward the sound source with a 0 degree incidence.

[3] Most modern day, quality measurement, free-field microphones are factory adjusted to compensate for incident angle.

The pre-test is also used to verify any special control features such as; abort tolerances, response limits, field shaping and emergency shut-down procedures.

The convenience, low cost, and mobility of this method distinguish it from conventional testing and are the primary reasons for its growing popularity.

The method is convenient because all required sound system, power generation and distribution and data acquisition and control equipment is brought to the test site.