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People who live in multi-unit apartment buildings often need to be careful not to bathe late at night, because their neighbors will be able to hear the sound of the water going through the pipes.

As I understand it, this sound is made by turbulence which occurs when the water moves through a small orifice such as the valve of a faucet or shower. The vibrations caused by the turbulence travel through the pipes and this is why they can be heard in a neighboring unit.

I have long wondered why we don't prevent this sound transmission by installing mufflers in water plumbing. They would be installed upstream of the constriction point and could consist of any number of shapes encouraging sound to reflect back toward the source. For example, replacing a section of pipe with a pipe of a larger diameter should create two points where sound can reflect, diminishing transmission. Inserting an "S"-shaped segment should have a similar effect. These principles are also used in designing air ventilation ductwork which blocks sound transmission.

Automobile exhaust mufflers come in a variety of shapes and sizes, such as in this 2007 patent or this 2012 patent:

old muffler example new muffler example

Can anyone explain why the principles that we use to block transmission of sound through tubes of gas, such as the exhaust system of an internal combustion vehicle, or ductwork for a home theater system, aren't useful to create silent plumbing?

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    $\begingroup$ And fit loads of mufflers to then have users complain of low flow and poor pressure... $\endgroup$ – Solar Mike Jan 28 at 9:36
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    $\begingroup$ The sound is not transmitted through the water in the pipe, but along the pipe itself, and through the walls of the building where the pipe is fixed to the walls. $\endgroup$ – alephzero Jan 28 at 12:55
  • $\begingroup$ Reasonable speculation @SolarMike, but as you can see in the second muffler diagram, it's not necessary for a muffler to significantly obstruct the flow $\endgroup$ – Metamorphic Jan 29 at 15:57
  • $\begingroup$ @alephzero, if the sound is transmitted along the pipe itself, even easier - just replace a section of pipe with plastic or rubber. $\endgroup$ – Metamorphic Jan 29 at 15:57
  • $\begingroup$ @Metamorphic so have you calculated the expansion and cobtraction losses? $\endgroup$ – Solar Mike Jan 29 at 16:00

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