# Doubt in Noise Vibration and Harshness (NVH)

• k.udhay
In summary: Thanks for your reply. But can you kind of explain me in detail pl.? You can assume me as a person completely new to NVH.In summary, a first order frequency is 1 vibration per cycle, a second order frequency is 2 vibrations per cycle, and a third order frequency is 3 vibrations per cycle.
k.udhay
What does a first / second / nth order frequency mean physically?

first order would be 1 vibration per cycle, 2nd would be 2 per cycle. a v8 combustion engine will have a normal 4th order frequency. think of a tire with a lump on it for first order then think of a tire with 2 lumps on it for second order.

1 person
Hi 462chevelle. Thanks for your reply. But can you kind of explain me in detail pl.? You can assume me as a person completely new to NVH.

There really isn't anything more to it than that.

An order is a frequency that changes proportional to the reference speed. The number of the order is how many events occur per cycle.

For example:

A vibration that occurs once per rev would follow this frequency. It is said to be first order. 1st order vibration is typically an out of balance.

A shaft rotating:
600rpm would have a frequency of 10Hz
1200rpm would be 20Hz
2400rpm would be 40Hz

Because 600 revs per minue / 60 seconds = cycles per second

A vibration that occurs two times per rev is 2nd order and would have
600rpm = 600*(2/60) = 20Hz
1200rpm = 1200*(2/60) = 40Hz
2400rpm = 2400*(2/60) = 80Hz

Lets suppose that the shaft we are referencing against is an input chast of a gearbox, with input teeth:

1st gear: 13 teeth
2nd gear: 21 teeth
3rd gear: 33 teeth

And we are detecting a whine of
1000rpm = 216.66Hz
2000rpm = 433.33Hz
4000rpm = 866.66Hz

We can do the same calculation in reverse, to work out the order of the whine, and thus what gear is causing the whine.

216.666/1000*60 = 12.9999 = 13th order

The whine is occurring 13 times per rotation of the shaft, which corresponds to the 1st gear driving teeth.

1 person
Thanks a lot, Chris. I am clear about order of frequency.
I am just extending this question to a different topic. What is Gear whine by the way? Does it have a definition? What are the conditions for whine to occur? Thanks.

If you have an improper set up rear differential in a vehicle, whenever you are accelerating on the drive side if it can whine. When you let off of the throttle it will quit whining, because it is on the coast side. You can also refer to manual or automatic transmissions. Manuals are usually the worst when it comes to whining. Whenever you set up a differential. The pinion depth must be precise, so that when you install the carrier the teeth mesh correctly. You also have to consider the backlash(distance between the gears.)

1 person
Thanks, 462chevelle.

## What is NVH?

NVH stands for Noise, Vibration, and Harshness. It refers to the unwanted sound, vibration, and harshness that can occur in a vehicle or other mechanical system.

## What causes NVH?

NVH can be caused by a variety of factors, including engine and transmission design, exhaust system design, road conditions, and vehicle age. It can also be influenced by the materials used in the construction of the vehicle.

## Why is NVH important?

NVH can affect the overall comfort and performance of a vehicle, as well as the safety and durability of its components. It is important for manufacturers to minimize NVH in order to improve the overall driving experience and meet customer expectations.

## How is NVH measured?

NVH is typically measured using specialized equipment such as microphones, accelerometers, and sound level meters. These tools can capture and analyze sound and vibration data, which can then be used to identify and address NVH issues.

## What are some methods for reducing NVH?

There are a variety of techniques used to reduce NVH, including sound insulation and absorption, vibration isolation, and tuning of engine and exhaust systems. Careful design and selection of materials can also play a role in minimizing NVH. Additionally, regular maintenance and upkeep of a vehicle can help prevent the development of NVH issues.

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