A new techrique known as beamforming has been used for determining noise location of
passing vehicles. Traditional pass-by noise tests are useful for detecting the sound level of
noise sources on a vehicle during operation.    35    Pass-by noise source identification takes
this one step further by identifying the source of the noise as well, so engineers can fine-tune
vehicle design to ninimize noise.
         36    NAH operates in a sound's so-called "near field," within one or two wavelengths
of the source, where sound waves act as circular waves emanating from the source.
Beamforming, on the other hand, is more suited to the far field, located at roughly seven
wavelengths from the noise source, where sound waves act as planar waves. If you can think
of a sound source like a pebble falling in water, then sound cmanating from the source is likc
the waves that come from where the pebble hit.    37     If you are standing far away on tho
shore, however, the waves no longer look like circles but just a straight line coming toward
you. Sound waves behave in the same way. Because measurement sensors can often not be
closc enough to passing vehicles to be in the near field and perform NAH, beamforming is the
preferred technique for noise location in such applications.
         38    This application note strives to offer best techniques for performing beamforming
on passing objects so that the end result is an accurate analysis of noise on vehicles.

【題組】35.
(A) When you are close to where the pebble fell, the waves are clearly in a circle, centeredon where the pebble fell.
(B) These arc measured to ensure compliance with laws that govemn acceprable soundemitted from a vehicle.
(C) Engineers can use several analysis techniques to identify aoise sources includingnear-field acoustic holography (NAH) and beamforming.
(D) Beanforming presents several challenges including simultaneously measuring a largenumber of microphone sensors, transmitling and saving this large amount of acquiredwavcform data, and being able to quickly process large data sets.