Product Manual

Large diameter pipes, whether they are PVC, concrete, steel, or iron, transmit

much less sound from water leaks and produce lower frequency sounds than

small diameter pipes. Because of their mechanical properties, large diameter iron

and steel pipes, such as 24 inches diameter and greater, resonate with much lower

frequency leak sounds than the smaller diameter iron and steel pipes, such as 6

inches and 8 inches. Extremely large concrete and steel pipes, such as 96 inches

or more, make very little "orifice pressure reduction" sound at their water leaks.

Figure 4-3 Absorption of Sound Frequencies by Soil

Sandy soil and very loose soils, particularly over a freshly buried pipe line, do not

transmit the sounds of water leaks very well, nor do water saturated soils such

as bogs and swamps. Hard, compacted soil transmits the sounds of water leaks

best. Soil absorbs the sounds of water leaks very quickly, and it is very difficult to

hear the sounds of water leaks from lines deeper than 7 or 8 feet. Leaks in water

lines that are only 3 or 4 feet deep are much easier to hear at the ground's surface

than leaks in deeper lines. The attenuation of sound in low frequencies in soil is

approximately 40 dB for every 3 feet of depth. Also, the higher frequencies of

sound are absorbed more quickly in soil than the low frequencies, as shown in

Figure 4-3 and Figure 4-4.

4-3

100 - 20,000 Hz

100 - 10,000 Hz

100 - 1,000 Hz

Water Leak Detector

Water Leak