Dav, another suggestion is to develop a noise map contour by using an array of microphones and testing the engine at different rpm have developed and used this technique to support many OEMS during engine development.
It really all depends on how accurate a picture you want to get of the noise sources and their contributions.
Do you have a specific problem at a particular speed? Is the noise low or high frequency? Where are you measuring the noise. Is the truck fitted with a cab, steel frame and glazed? Does it occur during a particular operation, e.g. under load from the steering or hydraulics. I recently had a vibration problem on a GM V6 when under steering load and it was the torsion damper on the d/shaft but under normal load it was OK. The noise could be caused by a worn or out of balance part. Have you had this problem on other machines of the same model. These are just some of the things to consider. Does it happen when the engine warms up, I had a problem once where a noise occurred when the engine was warm and discovered it as due to a modal shift in the exhaust system when the exhaust rose above a certain temp.

i agree edward
way more complicated than it should be definatly ;o)

The other contributors to this discussion have a point but noise source contribution cannot be accurately quantified by simply placing a microphone close to the noise source. For one the closer you measure to the source you are measuring in the near field and secondly you cannot eliminate the contribution from other sources. Decibels (dB) is a non linear scale, i.e. 60dB plus 63dB does not equal 123dB. As a general rule any measurement made that is more than 10db less than the max measurement will have little or no effect to the overall noise level recorded, i.e. 50dB plus 60dB equals approximately 60dB. Also two measurements made with the same overall level of say 60dB can sound completely different depending on the spectral content. There are many excellent and reliable test and simulation software packages but regardless of what equipment you use unless you take good accurate repeatable measurements to obtain good raw data the software you use won't make any difference. The rule of gold in, gold out applies. You also have to consider the noise path, is it structure or airborne or both. Once the noise paths and sources are quantified then you can examine the spectral content to identify problem frequencies. Engine noise in a 4 cylinder engine will typically exhibit booming noise generated by the out of balance forces and is dominated by the second order. However there can be numerous other sources such as intake resonances, exhaust noise, shell noise, heterodyning noise caused by crankshaft bending or as in earlier times by unequal manifold ducts. Then there are ancillary noises such as pumps, alternator etc. In general changing the noise source can be difficult and expensive, palliative treatments to reduce the noise path maybe more practical, e.g. if the problem is low to mid frequency then applying heavy layer insulation to the cabin and damping to lightly damped less stiff panels will help. If on the other hand the problem is high frequency, typically above 1KHz then applying absorption materials will be the route to go. Car engines are much more refined than forklift engines in general, employing active mounts and advanced algorithms however some manufactures are better than others also some engines are direct transplants from the automotive sector. Ancillary noises can be tested by removing components and testing to see the effect on the noise level. Where parts cannot be removed it may be possible to apply noise treatment to them, measure the noise and quantify their contribution. It may be possible to make some prototype parts e.g. intake branch or helmholtz resonator to quantify intake noise. If you have access to CAD data and the financial resources then with the help of a consultancy such as Ricardo, AVL, Pelzer, Ove Arup, Rieter or some other group a model could be developed to simulate noise levels and carry out what-if scenarios. Although this is expensive, time consuming and only applicable if you were the manufacture and wanted to refine existing and future models.

we may be making this way more complicated than it is.
perhaps defining the requirements a bit closer is in order
are you trying to pinpoint where some some noise is coming from?
have you considered a funnel, rolled up tube, long screwdriver with the handle to the ear? or stethoscope?
there are lots of directional microphones and computer programs that would allow you to run a virtual oscilloscope and select only certain wavelength/frequency.

well Dav, there are all sorts of sound meter's out that can measure ambient noise levels in a broad area but as for measuring a noise level on a component on a lift or any other type of equipment i cannot find any electronic device that will do this. There are tool trucks like MAC and SnapOn that sell stethoscopes that can allow you to put the probe on a component and hear the noise it makes but as for measuring its sound level? It does not have an electrical interface, its just like a doctors stethoscope you wear on your head.
I'll keep searching but i doubt you will find anything like what you are describing.
The only way you might get even close to measuring the sound level a component puts out is to put the sound measuring device next to it and see what it measures, it should measure higher near the component and give you a rough estimate of the sound it is emitting.

just a thought

Hi Davcom,

A noise level meter will measure the overall noise level, you can apply different weightings such A, B C or lin which is no weighting. You can get meters with built in frequcency analysers such as 1/3 octave analysis, which will give you an insight into the frequency spectra although narrow band analysis is better. I guess you are looking at interior cabin noise. To identify noise sources there are several techniques such as windowing and TPA (Transfer Path analysis). This requires more advance instrumentation and experience. Suppliers such as Bruel & Kjaer, LMS, Nosrsonic, etc sell this equipment. To get accruate, repeatable results a semi anechoic chamber is best to test the machine in. If it is engine noise that you are concerned with then some simple order tracking measurements will help identify any particular engine speeds where the noise is a problem. If you would like to discuss in more detail email me austinruby at msn dot com. I'm based in Ireland and worked as an NVH engineer before moving into the forklift business.

Hi Swoop223,

I appreciate your help.

yes unforunatly most of these db meters are designed to pick up a broad range of mainly ambient noise in a large area. I can look around and see if i can find something that might be more specific.

Hi Swoop223,

I have a Roline Sound decibel meter, but this will only measure the total noise level. Even if you place the device close to the component, there will always be background noise of the engine and the other components. The problem been is that if there is two components with db reading of 60db the device will measure 63db, so you wont know the split from this device reading. Maybe if there was a device to pick up the frequencies of the noise?

Have ever try to single out noise levels of a truck before?

a simple db level measurement device could achieve this goal if you are looking for specific sound levels that each component of the truck makes during operation.