Peizo electric microphones and a lab scope to locate the source of noises

Diagnosing noises can be tricky sometimes. Well, maybe more than sometimes. We've got a lot of tools we can use; Our ears obviously, screw drivers, stethoscopes, even a steelman chassis ear. But how do you analyze that information? You hear it and it's gone. Wouldn't it be great if you could get the noise into a lab scope so it can be analyzed, saved, studied and shared? I've seen the NVH kit from Pico but I haven't actually used it. I do have some peizo electric microphones I bought on Amazon, though. So, I wondered if I could use them to analyze and locate the source of noises.

I glued small neodymium magnets to the microphones so they'd stick to metal. I did some experiments testing their ability to pick up various sounds in different materials. What's great about a fast lab scope like a Picoscope is that I was able to measure the speed of sound in steel with the microphones as close as a couple inches from one another. Basically the waveform would show which of two mics picked up a noise first. With this and also using the amplitude of the waveform I predicted I could locate the source of noises fairly quickly and accurately.

I'll attach some pictures to show a real world test of this to locate the source of an upper end ticking noise in a Chrysler. I moved the mics around until I had the greatest amplitude and determined that the source of the noise was a loud rocker/cam in cylinder #5. After removing the valve cover I found cylinder #5 intake cam lobe worn.

I'll also post a YouTube link showing a couple videos I made experimenting with this before actually using them to diagnose anything.

I just wanted to share because this is proving to be very helpful when diagnosing noises. I hope it helps someone. Thanks!

First video: Simple test showing the ability of the mics and lab scope to pick up noises.

Second video shows examples on a vehicle. Same concept, no vehicle defects. Just a demonstration.

I've been wanting the NVH kit for a while, now. (Gotta get Pico, first).

I, really, like what your doing, here. I see a lot of potential.

Tried the Contact Piezo microphones that are ready mounted on a clip for use on acoustic guitars but didn't have much luck with them. , in the end I bought a cheap Chinese clone of the Chassis Ear and Sealey Electronic Stethoscope. Using a headphone splitter I listen to the output and feed it in to a scope or an Android device at the same time.

This thread started by Tyler in the early days of the site might interest you Link to thread

I also built a pressure pulse sensor with a piezo disc but it was a bit too fragile and I found a low cost source for a ready built pro one..

That's pretty slick. I'm finding that there's all kinds of cool uses for these type of sensors.

I also built a pressure pulse sensor with a piezo disc but it was a bit too fragile and I found a low cost source for a ready built pro one..

Interesting that you bring that up, 'cause I just ordered some parts to make another one. :lol: Was the sensor disc itself too fragile? Also, link to the pro one?

Thanks for the link, good read. I'm definitely having success with these peizo discs, for example the worn cam lobe. I came from the Honda dealer where i had more than my fair share of NVH work. Being able to read the time delay between microphones to pinpoint the source of noises really is a flat raters tool. Imagine having to locate a body creak from a bad spot weld without a tool like this. Using these mics on the body, homing in on the exact location would be fast. Again, the key in this example would be watching the time delay between a couple of mics.

I know there's more uses for this and I'll keep updating as I go.

Customer complained of a noisy wheel bearing. Yes, I could have used my stethoscope, and I did afterward just because. The top channel is the right front. The bottom channel is the left front. I did confirm a bad left front wheel bearing. Not only is this a good diagnostic tool but it's also a great way to give the customer something visual to show your diagnosis. Also, a great way to confirm a repair and show the customer the before and after.

Was this taken with the transmission in drive and the wheels spinning? It's a new test, but I'd guess that bearing is pretty darn rough. :lol:

Also, how'd you have the microphone attached to the suspension? On the knuckle, spring?

Tyler wrote: Was this taken with the transmission in drive and the wheels spinning? It's a new test, but I'd guess that bearing is pretty darn rough. :lol:

Also, how'd you have the microphone attached to the suspension? On the knuckle, spring?

The transmission is in drive, on a lift, 30mph+-

The microphones have neodymium magnets glued to them. The mics are placed on the hub/bearing bolt on the back of the knuckle.

Here a before and after of a waveform I posted earlier showing a peizo electric microphone picking up a noisy worn camshaft.

In the before picture you can clearly see the spikes everytime the can makes noise. In the after picture all the noise is gone. All that remains is the normal engine oscillations. There are some random spikes which is most likely just electrical noise.

The only difference between the two waveforms is that the time scale on the before and after are different. My mistake there. But the results clearly show the viability of these mics as a diagnostic tool.

Nice

Very cool, I suck at finding suspension noises!

Hello!


Could you please give a link to the microphones that you bought?

ivoalaska wrote: Hello!


Could you please give a link to the microphones that you bought?

Vktech® 12Pcs 27mm Piezo Discs with Leads Mic Drum Trigger Acoustic Pickup CBG Guitar www.amazon.com/dp/B016CW1WK6/ref=cm_sw_r_cp_apa_UcFeAbJC638GA

I glued small neodymium magnets to them so they'd stick to metal objects with a constant pressure.

Following this thread with interest I really want to give it a try but I have been a bit busy.