An asymmetric port is one in which the port extends outwards from the resonator selleck cavity. All parts except the port were made of clear Perspex? (150 mm diameter, 5 mm thick walled tube and Inhibitors,Modulators,Libraries 12.5 mm thick flats for end plates) to allow easy machining and visibility of samples within the chamber. The port was made of extruded 50 mm aluminium tube with a 3 mm wall thickness giving an internal port diameter of 44 mm. The chamber lengths were 63 mm, 127 mm and 190 mm. Chamber end plates were O-ringed to seal against the chamber tube as well as the port plates. Port plates and chamber end plates were fastened using a combination of threaded rod and threaded studs secured with wing nuts. The advantage of this system was rapid and easy switching of chamber sizes and port configurations.
Two PCB103A sound pressure microphones Inhibitors,Modulators,Libraries (PCB Piezotronics Inc. New York, NY, USA) were used to measure resonant frequency and amplitude. The first was spaced 20 mm from the port opening, and the second was centre-mounted in the chamber base (Figure 1(b)). The chamber microphone plate was removed for liquid volume measurements and a replaced with a blank. The PCB microphone amplitude was calculated using the measured voltage signals referenced to a 1 V source to give outputs in decibels (dB). The primary sound source for this investigation was a full range, eight-inch, polycarbonate cone driver in an infinite baffle enclosure. The enclosure was optimally designed using Thiele and Small [11�C13] design parameters.
A National Instruments PCI 6221 M series Data acquisition card was used for the signal generation for the acoustic inputs and analysis of the signals from the microphones and temperature sensor. Both generation and acquisition Inhibitors,Modulators,Libraries were implemented at 40,000 samples Inhibitors,Modulators,Libraries per second, i.e., 40 kHz. Using a high sample rate facilitated smoothly generated fractional sine waves. A 100 W Digitech AA-0470 audio amplifier was used to drive the loudspeaker at a nominal 80 to 90 dB. A resistive Batimastat temperature device (RTD) was used to provide speed-of-sound temperature compensation. Software was designed using National Instruments LabVIEW? and used to generate and acquire frequency data.A three-stage hunting algorithm was developed to find and reduce the time required to identify the resonant frequency. First, pink noise was applied to the resonator to establish an approximate resonant frequency, Chanaud .
Once determined, a 2 Hz frequency sweep was used to further isolate the resonant peak. Lastly, a very narrow 0.1 Hz sweep was applied to detect the resonant frequency to a precision SAHA HDAC of 0.005 Hz. The hunting technique reduced the resonant frequency identification time from many minutes, for traditional frequency scanning, to approximately 40 seconds. Quicker times were possible at the expense of accuracy, for example a 20 second hunting time quartered the maximum achievable accuracy.