A new technique known as beamforming has been used for determining noise location of
passing vehicles. Traditional pass-by noise tests are uscful for detecting the sound level of
noise seurces on a vehicle duzing operation.    35    Pass-by noise source identiication takcs
this onc step further by identifying the source of the noise as well, so engineers can fine-tune
vehicle design to mimimize noisc.
         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 cmanating from the source.
Beamforming, on the other hand, is more suited to the far field, located at roughly seven
wavclengths from the noisc source, where sound waves act as planar waves. If you can think
of a sound source like a pebble falling in water, then sound emanating from the source is like
the waves that come from where the pebble hil.    37     If you are standing far away on the
shore, however, the waves no longer look like circles but just a straight line coming toward
you. Sound waves behave in the same way. Bccausc measuremnent sensors can often not be
close enough to passing vehicles to be in the ncar 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 arc closc to where the pebble fell, the waves ans clcarly in a circle, centeredon where the pebble fell.
(B) These are measured to ensure compliance with laws that govern acceptable soundemitted from a vehicle.
(C) Engineers can use scveral analysis tochniques to identify noise sources includingnear-field acoustic holography (NAH) and beamforming.
(D) Beamforming presents several challenges including simultaneously measuring a largenumber of microphone sensors: transmitting and saving this large amount of acquiredwaveform data, and being able to quickly process large data sets.