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ACO Pacific - Model 511E -Sound Level Calibrator
1000 Hz. 0 dB Reference Point for: A, B, C, D Weighting. 2 Output Levels - Permits Range testing. 94 dBSPL = 1 Pa. 104 dBSPL. Accuracy - Meets IEC942. +/-0.3 dB @ 23 C° Type 1L. +/-0.5 dB 0 to 50 C°. Power 9Vdc Alkaline Battery (NEDA 1604A). Diameter 1 1/8 inches. 1/2 inch adaptor Q3 (Included with 511E ). Adaptors - Optional. Q1 - 1 inch. Q2 - 20 mm. Q3 ( Supplied with 511E) - 1/2 inch. Q4 - 10mm. Q7 - 1/4 inch.
Why 1 kHz as a test frequency?
Accepted internationally 1 kHz represents the "0 dB" reference point of A, B, C Weighting and other filters utilized in acoustic measurement. The Pistonphone - a mechanical sound source - offers a slightly higher degree of accuracy at a substantial increase in cost. In addition, the 200 or 250 Hz operating frequency is mechanically limited and not suited for measurements of filtered inputs. The 0.2 dB accuracy is quickly lost in the 0.7 to 1.5 dB tolerances acceptable for weighting filters at frequencies around 250 Hz.
Why 94 dBSPL?
International standards have established 1 Pascal (Pa) as 94 dBSPL. This reference point is now accepted for specifying the sensitivity of microphones. The uBar found in some specifications refers to 74 dBSPL (20 dB less than 1 Pa).