Noise energy

High speed moving parts in air cause pressure waves (sound) because they excite the gas mollecules. If you could operate these machines in a vacuum they would be silent save for any conducted vibration. If you take the time to sit and think it through the answer will come to you. Lots of high speed moving parts transfere lots of energy. The answer to your design thoughts is simply NO.

A compound double-expansion marine steam engine, as recently inspected underway aboard the pleasure boat 'Olive' based 5km from these coordinates, is virtually silent in operation apart from the sizzle from the boiler and the ordinary clanking from the reciprocating parts. Being fitted with an exhaust steam condenser in the bilges, the thermodynamic efficiency of this machine is higher than for a machine with an exhaust to atmosphere. 'Vorsprung durch Technik', as they say in Germany.

You are correct in that the majority of the noise is a result of inefficiency.

You are correct that better engineering would eliminate most of the noise.

Here is an example where better engineering produces better efficiency and a quieter engine:

https://silentaircraft.org/object/download/1929/doc/AIAA-2006-1323-758.pdf

and.....the electric motor

"when thet are trying to achieve maximum efficiency/power output "

Your assumption is false. There has been no desire to reach this goal. The first Model T Ford acheived 25 miles per gallon. The average consumption today of North American vehicles is...wait for it ...25 miles per gallons

Inefficiency causes...continuous and guaranteed: wear and tear, breakdowns, repairs, sales of more inefficient parts. sales of more vehicles, sales of oil and gas, and plenty of jobs.

Efficiency causes... one time buys, -- no more sales, bankruptcy

Apparently, according to the blogset "Why is North UP?", noise can be a useful device for relieving a continuous diet of serious discussion.

Only in sound production, which ironically is the initial setting for the term 'noise' is it considered a completely negative aspect, the opposite of coherent 'sound'.

I suspect in operating machinery then, that noise is not only a necessary component for relieving serious work (dissipation of excess energy), but an indicator of how well the machine is operating (Uh-oh! What's that noise?).

It has just become aparent to me that there is a third use for noise. This response, being itself noise, is an example of its definition as the ability to put (wasted) time into a discussion without getting useful results, kind of like an April fool's joke played near May.

Mark

...initial setting for the term 'noise'...

Interestingly enough, with sound defined as root-tonal sound, having a root, fundamental, dominant, coherent, frequency, is more likely to bare some viable energy, to be extracted or converted from.

The higher the harmonic contents, i.e, the more different frequencies weaved into the sound, the more energy you invest in it, and the less you can extract from.

Just a humble note.

A fascinating subject to explore and research, not of very high expectation though.

US automotive car mfg's have engineers working in the "NVH" (Noise, Vibration, and Harshness) group and that is their goal; to reduce or eliminate NVH. I'm sure auto mfg's outside of the US have the same.

I remember one vehicle that they developed (i'm guessing about 10 years ago) that was so silent you could not hear the engine. The next year they increased the noise because the owners complained. Apparently thay liked the noise. the gutteral sound of power. They wanted to sound like a race car.

Sorry, I cannot remember the brand or find a reference to it on the web.

The Suzuki Swift ZXi ?

It would make sense, that folks feel out-of-control with a quiet car. Not I though. That's why I'm sold on electric

I believe it. You would not believe the amount of time, evergy, and money that goes into tuning the exhaust system (muffler primarily) so that it has an appealing sound that suits the car. Its actually a major milestone in a new car project and has to be signed off by upper management.