Brüel Acoustics
Large Standing Wave Tube
40BB
In order to construct the most effective Anecho test rooms Brüel
Acoustics has developed, constructed, and use a large SWT 40BB.
The tube is a
new construction as it is built up of sand filled plywood sheet.
With this
technic the walls in the tube are very "dead" and have no resonance.
The
frequency range extent down to a wavelenght of 8 m, (40 Hz) and with one
microphone up to 380 Hz.
By using an intensity probe the performance of the
SWT can be used up to 6 kHz, which is unique for a large SWT.
It cannot be
avoided that these very low frequencies are filling the whole room with a high
sound pressure.
It is therefore advisable that the microphone and its
trolley are in another room, see fig.
By using a small intensity probe and
scan a cross section of the tube, reflection for very high frquencies can also
be determined.
This is more simple than using the inverse square law, which
is normally done to measure the performance in the finished test room.
The
tube is designed to handle a 40 x 40 cm2 sample. But can also handle a complete
module element 40 x 40 x 40 cm3 from Anecho chamber 62BA.
In the lid is a
large glass window so both the sample under test and the moving microphone and
intensity probe can be supervised.