Acoustic Associates, Ltd.

I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I

Specialists in Hearing and Acoustics

 

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Engineering Noise Surveys

 

The purpose of an engineering survey is to investigate what methods can be implemented to reduce equipment noise emissions. First we examine equipment operation to familiarize us with the problem and to assess the location of employees relative to the equipment noise sources.

 

In addressing equipment noise reduction, a reasonable noise level criterion should be established. A criterion which is too stringent can mean high costs - such costs often increase exponentially with each decibel reduction. The criterion should be established by reviewing applicable regulations or industry standards.

 

Once a goal is established, equipment noise emissions are sampled using ANSI type I precision rated instruments. In most cases, we use a digital hard disk drive recorder to have complete flexibility in analyzing the noise in our laboratory. In other cases, we use a portable Hewlett-Packard Real-Time Frequency Analyzer. In either case, our aim is to obtain 1/3-octave band spectra to identify the frequency content of the noise. This information is important to specify the proper control methods and materials.

 

COHERENT output analysis - In assessing the noise of equipment, several methods are available to identify and rank order the importance of equipment components and transmission paths. For example, coherent output analysis is a two microphone method to determine what portion of the overall noise level is related to a suspected component source. This technique is best suited to smaller equipment items.

FFT ANALYSIS - A very common diagnostic technique is FFT analysis. This is a high speed mathematical process used to identify the frequencies of prominent tones. Dominant sources are identified when these tones are matched to the rotational frequencies and harmonics of a suspected component source.

NEAR-FIELD MEASUREMENTS – When sound pressure measurements are made, the data must be carefully interpreted. This is because adjacent sources, reflective surfaces, and room reverberation can contaminate the readings. Near-field measurements are sound pressure measurements made very close to component sources – such as motor drives, gear units, equipment housings, ductwork, and piping – to help rank order the contribution of these individual sources to the overall noise problem. When used by a professional with experience, this method is quick and efficient.

SOUND INTENSITY MEASUREMENTS - The most definitive diagnostic approach is to use sound intensity measurements to determine the sound power of equipment components. While sound power is commonly determined in the lab, it requires that the source be isolated and placed in a special room. Sound intensity, on the other hand, has the unique ability to measure sound power in common industrial environments. Such an analysis allows us to rank order the importance of difference equipment components based on hard quantitative data.

 
 
 

1278 West Northwest Highway, Palatine, IL  60067

phone: 847-359-1068     fax: 847-359-1207

email: info@AcousticAssociates.com