What is the relationship between harmonics and NVH in automobiles?

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Discussion Overview

The discussion revolves around the relationship between harmonics and Noise, Vibration, and Harshness (NVH) in automobiles. Participants explore how harmonics influence sound quality in vehicle design, particularly in the context of engineering practices and musical analogies.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant notes that harmonics are multiples of the frequency of vibration and questions their relevance to NVH.
  • Another participant references the NVH Wikipedia page, indicating that NVH engineers may alter sound quality by modifying specific harmonics rather than solely focusing on reducing noise.
  • A participant inquires about the effects of increasing or decreasing harmonics and how this can be achieved in car design.
  • A musician contributes that altering harmonics can change the quality or timbre of sound, suggesting that NVH engineers aim to create pleasant engine sounds.
  • One participant expresses confusion regarding the definition of harmonics, clarifying that the fundamental frequency is the first harmonic, with subsequent harmonics occurring at integer multiples of this frequency.
  • It is mentioned that different generation mechanisms can affect odd and even numbered harmonics differently, and that modifying harmonic amplitudes can influence sound perception.
  • Some vibrations are described as being tuned, while others are linked to engine RPM, with subsonic beats potentially occurring between harmonics at varying RPMs.

Areas of Agreement / Disagreement

Participants express various viewpoints on the role of harmonics in NVH, with no consensus reached on the specific methods of altering harmonics in automobile design or the implications of such changes.

Contextual Notes

There are unresolved questions regarding the practical application of harmonic modification in vehicle design and the specific effects of such changes on sound quality.

k.udhay
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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.
 
Engineering news on Phys.org
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
 
But what happens by reducing or increasing the harmonics? And how to reduce or increase that in a car design?
 
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
 
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.
 

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