Hello Mark thank you for the feedback and sorry, I should look more closely at “Attachments” before asking for files that are already included.
I have downloaded the pddata file and listened very closely to the audio. I have noticed an intermittent squeak type noise similar to drive belt (as you have mentioned).
I can also hear a tapping noises that’s comes into the audio but not sure it’s relevant?
From the data I have, the engine speed appears static fixed at 750 rpm and the engine speed signal also appears lost part way through the capture.
Would it be possible to retake the capture with the rpm captured from either the OBD or the crankshaft position sensor into channel A?
Here the rpm would be accurate for analysis throughout the capture.
Can I ask if the position of the microphone was altered during the capture?
The signal history displays a higher amplitude at the beginning of the capture. (The squeak noise appears later on through the signal highlighter captured in the image below.)
If we are to focus on the squeak noise (which sounds intermittent) the area of interest you have highlighted (600 Hz) is present throughout the capture. (I would expect that peak to rise and fall)
Looking and listening to the data very closely, when the squeak develops, a peak is present around 113.16 Hz. Multiply this value by 6 and were in the range you have highlighted 678.96 Hz.
Could this be due to the fact that the microphone can detect something in this frequency range not audible by ear due to back ground noise?
Could the peak at 113.16 Hz be our fundamental frequency and the peak at 678.96 Hz be 6th harmonic frequency of the fundamental frequency. To be totally honest, I do not know!
What I do know is 113.16 Hz is too low an audible frequency to generate a squeak noise (Squeaks are a higher frequency)
They do however coincide very nicely and display some of the highest amplitudes (60-70 dB) with 6 cylinders being the connection to our 6th Harmonic.
I don’t believe these peaks can be ignored but I would recapture the data with a fixed microphone and true engine speed input throughout the capture.
A good tip hear would be to down load “audio frequency generator” software as it can often help you to home in on noises in order to locate the frequency of interest.
This will help you to identify the frequencies of noise as you become more experienced.
You can play the audio captured in your NVH software through headphones whilst introducing matching frequencies from the audio generator software.
Here you can be sure the peak you see in the frequency chart of the NVH software during playback matches the frequency generated by the audio frequency generator.
I know exactly where you are Mark and what you are trying to get at with regards to any potential warranty on this engine.
Moving onto your “Publication 1” attachment.
The area you have highlighted around 699 Hz in the frequency chart may well be the sound we hear, but this could be inaudible to the ear as a result of background noise.
The frequency chart indicates the level of sound (dB) in direct relation to the frequency of rotating parts within the engine bay (If they are linked) and the frequencies that are applied to the microphone (if external and unrelated)
The frequency spectrum of 0-1000 Hz (our frequency chart in your capture) will display all audio frequencies present at the microphone.
Noise levels (dB) generated as a result of engine speed alone will appear at a frequency of 12.5 Hz at 750 rpm (E1) at the relevant sound level (dB)
Noise levels (dB) generated as a result of an electric cooling fan will appear at a frequency somewhere within the 0-1000 Hz spectrum at the relevant sound level (dB)
Both are visible in the frequency chart (0-1000 HZ spectrum) but neither are directly related.
The scales you have mentioned in the signal history and the frequency chart are not the same and this will be rectified as what you have identified is a bug.
The signal history graph is best utilised as a visual indictor of activity detected by the microphone.
The dB value however in the frequency chart is correct and is an absolute measurement of the signals captured by the microphone
The NVH software requires vibrations and noise to be present for a minimum of 2-4 seconds before it can process and display the frequencies of interest associated with the signals measured by the accelerometer or microphone.
Unfortunately the spikes you have highlighted are not audible for long enough.
With that said, the spikes will still be incorporated into the calculations and all frequencies will be displayed in the frequency chart.
This would be an average of all signals contained inside the signal highlighter, including the spike in the calculation but not displaying a frequency value specific to the spike alone.
I hope this helps, take care……..Steve