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Navcon Engineering Network |
701 W. Las Palmas Dr. Fullerton, CA 92835 U.S.A Phone 714.441.3488 E-mail: webinfo@navcon.com |
| Noise & Vibration Consultants | ||
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Navcon Hardware Products: Acoustic Screening Chamber
The Acoustic Screening Chamber (US and International Patents) is a test system used for the acoustical testing of small products [i.e. hard disk drives, optical drives, spindle motors, electronic transformers, switches, etc.] The ASC is constructed of an inner "diffuse" sound field chamber housed within an exterior barrier chamber/housing. Its small footprint (L-5' x W-5' x H-6') and large sound transmission loss design allow it to be used in offices (for example, an office cubicle) and/or in areas with high ambient noise levels such as in an assembly shop or manufacturing warehouse.
The ASC can be constructed with either welded seams or a portal frame. The portal frame construction is recommended when the test chamber is to be installed in small offices or transported between facilities. The ASC comes with four precision (Type I) microphones, power supplies and signal conditioning. As an option, Navcon will supply a four channel narrowband/octave band data acquisition system.
The basic principal of operation is as follows: 1) the sound field within the inner chamber is diffuse (i.e., the sound field is constant throughout the chamber with minimal standing wave effects), 2) the item under test is placed within the inner chamber and energized, 3) the sound field builds up within the inner chamber, 4) a set of microphones are rotated within the chamber and a spatial/temporal average of the sound pressure level is recorded (narrow band and/or octave band), 5) the noise emission characteristics of the item under test are documented within approximately 30 seconds. The recorded sound pressure spectra can be correlated back to sound power through a chamber calibration function.
The measurement speed, repeatability, footprint and exceptional sound transmission loss make the ASC an incredibly powerful tool for design engineering and quality departments. It can be used to: quickly assess design changes, trend noise emissions over time, conduct lot testing, document the acoustic signature of individual products and screen subcomponent noise emission (for example spindle motors).
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Acoustic Screening Chamber: The chamber shown in the photo is installed in the Research & Development Department of a hard disk drive manufacturer. The noise data is recorded using a 4 channel Hewlett Packard 35670A analyzer. The data collected by the HP analyzer can be opened in a spread sheet program (such as Excel or Lotus), MATLAB or other data base program. |
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Looking into the inner chamber, a hard disk drive is mounted on a vibration isolation test fixture. Four microphones are installed on the rotating boom assembly. The microphone signals pass through a slip ring to connectors on the outer housing. The front panel control allows the operator to set the rotational speed of the boom. |
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Typical narrow band sound pressure spectra recorded for a hard disk drive running at 5400 RPM and 7200 RPM. The recorded levels are amplified due to the ASC reverberant sound field characteristics. The basic method assures the measurement of all discrete tones. |
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Typical one third (1/3) octave band sound pressure spectra recorded for a hard disk drive running at 5400 RPM and 7200 RPM. The recorded levels are amplified due to the ASC diffuse sound field characteristics. The chamber calibration curve can be applied and the sound pressure spectra related back sound power. |
