Trane TRG-TRC007-EN Equipment Sound Rating, period four, Distance Correction in a Free Field

period four

Equipment Sound Rating

notes

Distance Correction in a Free Field

air-cooled chiller Lp1 = 95 dB Lp2 = 83 dB

r1	= 30 ft			lot
	(9.1 m)			line
		r2	= 120 ft
			(36.6 m)	Figure 55

In practice, this equation is commonly used to determine how loud a piece of equipment will be at a given distance. For example, the manufacturer of an air- cooled chiller lists the sound-pressure level of the chiller as 95 dB at a distance of 30 ft (9.1 m) from the chiller. This equation can be used to estimate the sound-pressure level at a lot line, which is 120 ft (36.6 m) from the chiller. In this example, the sound-pressure level at the lot line is 83 dB.

Lp2 = 95 dB – 20 log10 [120 ft / 30 ft] = 83 dB

(Lp2 = 95 dB – 20 log10 [36.6 m / 9.1 m] = 83 dB)

This equation is only valid for sound pressure. It cannot be used to convert sound power (Lw) to sound pressure (Lp). Also, it is only valid in a free-field environment.

50 TRG-TRC007-EN