Sound standing wave

Impedance Tube Test Methods. There are two impedance tube test methods ASTM C384-90a (3) and ASTM E1050-90 (4). Test method C384-90a makes use of a tube with a test specimen at one end, a loudspeaker at the other, and a probe microphone that can be moved inside the tube. Sound emitted from the loudspeaker propagates down the tube and is reflected back by the specimen. A standing wave pattern develops inside the tube. 

ASTM E1050-90 also makes use of a tube with a test specimen at one end and a loudspeaker at the other end, but iastead of a single movable microphone there are two microphones at fixed locations ia the tube. The signals from these microphones are processed by a digital frequency analysis system which calculates the standing wave pattern and the normal iacidence sound-absorption coefficients. 

An alternative approach to dust and mist suppression is the use of acoustic standing waves. When a sonic standing wave is set up in air the particles suspended in the air will migrate to the nodes of the sound wave and this phenomenon has been used in a variety of applications. Smoke particles normally remain suspended in air for a considerable period because of they are extremely light. In an acoustic field they will become concen-... 

Vs is the average speed of sound waves in the solid v is the frequency of the standing wave V is the volume of the solid... 

Briefly the action taking place is as follows When the column is made to resonate by adjustment of the reflector on the end opposite to the sound-producing mechanism, the radiated and reflecting waves interfere in such a manner as to produce a standing wave. The nodes and antinodes correspond to minimum and maximum intensities of sound. 

The quartz-crystal interferometer has been used mainly for obtaining sound velocities with high accuracy (0.1 % or better) over the range of frequency-to-pressure ratios from about 50 kHz/atm to 100 MHz/atm. The phase velocity V =fk is obtained through measurements of the wavelength X at accurately known frequencies. The common design employs a precision-cut quartz crystal opposed by a movable reflector, between which standing waves... 

The absorption technique employed by Parker [122] is a modified version of the resonance tube described by Knotzel and Knotzel [123], It consists of a Pyrex glass cylinder, 5 cm in diameter and about 75 cm in length. A cylindrical brass piston is used to generate standing waves in the tube. The sound pressure Pn is observed for frequencies near any of the n resonant frequencies / for the tube, and the resonance half-width <5, in Hz, is de-... 

We examine the effect of the standing waves across the plate on "the three dimensional stress fields at the crack-tip. We consider those sound waves which propagate with the crack, i.e., o> = /5 v. In this case the quantity, given by Eq. (25b), for example, can be written as. 

Yasuda and Kamakura [3] and Mandralis and coworkers [4] have demonstrated that it is possible to generate standing-wave fields between a transducer and a reflecting wall, although of much larger dimensions (1-20 cm) than across a FFF channel. Sound travels at a velocity of 1500 m/s through water, which translates to a wave of frequency of approximately 6 MHz for a 120-pm thick FFF channel. 

It is most important that the shape of the target allows it to act as a perfect absorber. Almost always some additional systems are required in the chamber to absorb the sound wave and thereby avoid side influences from reflected or standing waves on the target. Typically paraffin wax or linen are used for this purpose. 

---