Tham khảo tài liệu 'noise and vibration control episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | TM 5-805-4 AFJMAN 32-1090 Table C-11. Overall and A-Weighted Sound Pressure Levels in dB and dB A at 3-ft. Distance for Pumps. o_ n__ Drive Motor Nameplate Power Speed Range r rpm Under 100 hp Above 100 hp Overall sound messure level dB 3000-3600 71 10 log hp 85 3 log hp 1600-1800 74 10 log hp 88 3 log hp 1000-1500 69 10 log hp 83 3 log hp 450- 900 67 10 log hp 81 3 log hp A-weighted sound level dB A 3000-3600 69 10 log hp 82 3 log hp 1600-1800 72 10 log hp 86 3 log hp 1000-1500 67 10 log hp 81 3 log hp 450- 900 65 10 log hp 79 3 log hp dB in the octave bands containing the impeller blade passage frequency and its first harmonic. These Would usually fall in the 1 000 and 2 000 Hz octave bands. The data of tables C-11 and C-12 are summarized in figure C-4. Table C-12. Frequency Adjustments fin dB for Pumps. Octave Frequency Band Hz Value to be Subtracted From Overall SPL dB 31 13 63 12 125 11 250 9 500 9 1000 6 2000 9 Uooo 13 8000 19 A-weighted dB A 2 C-12. Fans. a. In duct noise. Recent issues of ASHRAE publications provide updated methods for estimating the in-duct noise of ventilating fans. Manufacturers also furnish in-duct PWL data of their fans on request. A current ASHRAE estimation is given by equation C-5 LW Kw 10 log Q 20 log P BFI C eq C-5 Where LW the in-duct sound poWer level of the fan at either the inlet or discharge end of the fan KW the specific sound poWer level for the particular fan design Q is the volume floW rate in cfm min. and P is the static pressure produced by the fan inches of Water gage . Values of KW for the octave bands and for various basic fan blade designs are given in part A of table C-13. The blade passage frequency of the fan is obtained from fan RPM x no. of blades 60 and the blade frequency increment BFI in dB is added to the octave band sound poWer level in the octave in Which the blade passage frequency occurs. It is best to obtain the number of blades and the fan rotational speed from the manufacturer to calculate
