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Synchronous time averaging technique is the most powerful method of measuring performance parameters related to high performance ducts, silencers and enclosures. For high performance silencing equipment, the silenced levels are usually below the ambient noise levels and can not be measured with conventional instrumentation. Using the synchronous averaging method, acoustic and vibration signals buried by as much as 30 dB below the ambient noise levels can be accurately measured. Sophisticated hardware and software that make up the measurement system are one of a kind in North America and include a sound production system (see below) capable of producing close to 130 dB of sound power. The system has been successfully tested and used in many projects to accurately determine the noise reduction of enclosures and ducts as well as insertion loss of powerful silencers.
Accurately estimating induct sound power is vital in assessing the performance of silencing equipment and resolving contractual disputes related to such performance guarantees. While there are off-the-shelf products available for measuring induct sound pressure levels, they are not suitable for gas turbine induct exhaust measurements where duct wall thickness could be as much as 7 inches and exhaust gas temperature could reach 1200 Fahrenheit. Tacet induct microphone probes are designed specifically for the purpose of measuring induct sound pressure levels in gas turbine exhaust systems. These probes have been carefully designed and calibrated and have been used in numerous projects with great success. Tacet is currently involved in drafting a new ASTM standard for induct sound pressure measurements.
This technique is used to extract noise signals from turbulent flow fields such as ducts and exhaust stack outlets. This simultaneous two-channel measurement technique along its proprietary in-house developed software yield the average correlated noise for the two microphones by filtering out over 15 dB of uncorrelated turbulence or "flow noise" caused by flow over the microphone. This technique is particularly useful for estimating the actual sound power level in ducts.
Our state-of-the-art sound & vibration measurement system combines a simultaneous 12-channel data acquisition system with proprietary signal processing techniques and software to accurately define the noise source by identifying relative contributions of gas path and breakout levels to the overall noise emitted by the unit. This is necessary to determine how the individual sources should be treated and what level of reduction one would expect as a result. Moreover, depending on the nature of the problem data collection may take place over an extended period of time such as a recent project where the 12-channel simultaneous data collection (at a rate of 10 kilo-samples per second per channel) lasted for 1.5 hours to identify transient noise problems associated with the start up cycle of the engine. Typically, these measurements include multiple induct, stack outlet, casing vibration and far field transducers.
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Last modified: 04/11/06 |
