What is the relationship between harmonics and NVH in automobiles?

[k.udhay]

I had a chance to go through a lecture on general NVH issues in Automobile engineering. The faculty used to say "first harmonic", "second harmonic" etc. during the course. I found in wikipedia to know that harmonics are multiples of frequency of vibration.

What has harmonics got to do in NVH subject? Thanks.

 

[slashragnarok]

NVH Wikipedia page. It says there "In some cases the NVH engineer is asked to change the sound quality, by adding or subtracting particular harmonics, rather than making the vehicle quieter."

Thanks

 

[k.udhay]

But what happens by reducing or increasing the harmonics? And how to reduce or increase that in a car design?

 

[slashragnarok]

Okay being a musician I can tell you that altering the harmonics change the quality or timbre of the sound. You know when you hear the sound of an engine, if you like it or not. We say we like the sound of a Lamborghini Gallardo etc. That's what a NVH engineer's job is. To make the sound of the car pleasant. Try reading this NVH

 

[Baluncore]

It gets confusing when the fundamental frequency f, is described as having a first harmonic at 2*f.
The fundamental is really the first or “fundamental” harmonic of the harmonic series.
The fundamental at frequency f, has a second harmonic is at 2*f, the third at 3*f, etc.
There is no energy present in the spectrum between the integer harmonics of a vibration.
Broadband energy between the harmonics is called noise.
http://en.wikipedia.org/wiki/Harmonic

Any repetitive vibration can be analysed as a fundamental frequency with integer multiple harmonics.
The higher harmonics are usually generated by non-linear characteristics of the oscillator.
Different generation mechanisms often effect the odd and the even numbered harmonics differently.
Modification of the amplitude of harmonics will change the perception of the sound.

Some vibrations are tuned, while some are determined by engine RPM.
Subsonic beats can occur between the harmonics of different frequency vibrations at different RPM.