I can remember a forum post some time ago about a request for a “real-time” feature within the NVH software with regards to measuring harshness such as knocks, creaks and squeaks.
Such noises/harshness (whilst annoying) are present for a very short period of time with insufficient energy to be transferred and displayed in the Frequency Display (FFT) of the NVH user interface.
Well, the great news from Pico (thanks to the software team) is that we can now introduce the “Time Domain” feature of NVH in the latest Automotive Beta release 188.8.131.521
So why the “Time Domain” feature?
Well, how often are we presented with squeaks, creaks, rattles and knocks etc.?
For those who have used the NVH software, you may have noticed the effect on the signal history chart when monitoring vibration/noise when the vehicle hits a pot-hole?
The event (pot-hole strike) is captured in the signal history as this displays the input of the attached mic or accelerometer live (relative to time).
Such events are not transferred for view in the Frequency display as we require a minimum of 2.5 seconds of continual disturbance in order to process the event.
Until now, symptoms such of these would be reserved for “listening devices”, enabling the technician to listen to the intensity of noises delivered to a headset from microphones placed about the offending area of the vehicle. The results however are subjective and open to misinterpretation
Example of Time Domain in action:
Using contact microphones whilst looking for a suspension knock over uneven road surfaces at low speed, 4 x contact mics were attached to 4 possible offending suspension components in order to locate the source of the knocking sound.
The image below demonstrates a typical set-up using Multiple Sensor Mode where our contact mics have been selected, connected to the TA149 interface units and located at point about the suspension recorded in the notes section.
I cannot stress at this point how important it is to get the set-up correct and indicate how and where you have placed your mic’s. If this information is not correct your diagnosis will be off course. (Notice my mistake for channel D as I have not selected “microphone”)
The vehicle was then driven at low speed over uneven ground to produce the knock whilst the “Time Domain” display is selected. The green markers in the signal history denote when the knock occurred and you can listen to the knock via headphones connected to your PC.
To listen to each knock individually (each mic in turn) right click on the Time Domain display and select “channel in view” Here you can select the channels you wish to view, measure and listen to via headphones.
Removing “channels from view” allows the technician to analyse the input from each mic individually. Based upon the peak amplitudes captured, we can locate the source of the knocking noise and replace the relevant component. In the case below the NSF lower suspension arm produced the highest amplitude (during the knock) which was later confirmed as lower wishbone ball joint.
Over and above the Time Domain feature we have additional features available under the “Options” tab of the NVH software.
1. Load Audi Files will allow for .wav files to be loaded into the NVH software for analysis. Typical scenarios would be sounds/video recorded by customers via Smart phones. Here we obtain the customers recording, extract and convert the audio file to a .wav audio file (using third party software) and then import into the NVH software for analysis
2. Function Generator will allow for the playback of audio at specific frequencies. This feature will allow technicians to listen to audio played back at specific frequencies and match the audio to sounds present on a vehicle. This could be a transmission whine measured using the NVH mic at 1200 Hz. How do we know what 1200 Hz sounds like? Using the function generator we can playback audio at 1200 Hz and confirm the playback matches the pitch of the transmission whine. Our peak amplitude measured using with the mic at 1200 Hz is therefore relevant to the whining transmission as the measured frequency pitch matches the audio playback
We can manipulate this feature to playback audio into the vehicle In Car Entertainment system (ICE) via the PC headphone socket, streamed from the PC via Bluetooth or FM Modulator if the vehicle is without Aux and Bluetooth. So why would this be useful?
Customers who complain of interior rattles will often have difficulty in describing the sound or pin pointing the location. If we playback variable low frequencies into the ICE using the Function Generator and increase the volume we can generate rattles inside the cabin that can be confirmed by the customer and assist the technician with location. In this scenario the technician identifies the rattle with the customer present and area of the cabin at fault.
Onward and upward with NVH and there is so much more to come.