Ping Jim Wilkins: Audio filter

Yo Jim -- and anyone else who may be interested.

I spend an hour last night tracking down some noises in my furnace blower, using my usual piece of aquarium hose stuck in my ear , and I wondered i f there might be a market for an advanced kind of mechanic's stethoscope -- something that ought to be a piece of cake for someone like you.

Maybe something like this is on the market. If so, forget it. If not, consi der this:

I had two noises, from different sources, and the interference between them made it all but impossible to find the origins of the noises. One was some mechanical interference between the centrifugal fan and its housing, at on e end of the armature shaft; the other was vibration resulting from stickin ess in the centrifugal throw-out switch (a fail-safe switch that prevents t he gas valve from opening), at the other end of the shaft. I finally took t he whole thing apart and found both problems, but it wasn't easy to find th em when the motor wasn't running.

So, I wondered about the idea of making a small, cheap, battery-powered amp lifier, with a mike and a headphone jack, that contained a couple of active , adjustable audio filters, one high-pass and another low-pass. Made a notc hing filter or bandpass filter to make it slick.

I don't play with engines much these days, but I can recall times when such a device would have made quick work of tracking down engine noises.

There it is. If you make it and sell it, the idea is yours. Watch out for p atents.

Reply to
edhuntress2
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I spend an hour last night tracking down some noises in my furnace blower, using my usual piece of aquarium hose stuck in my ear , and I wondered if there might be a market for an advanced kind of mechanic's stethoscope -- something that ought to be a piece of cake for someone like you.

Maybe something like this is on the market. If so, forget it. If not, consider this:

I had two noises, from different sources, and the interference between them made it all but impossible to find the origins of the noises. One was some mechanical interference between the centrifugal fan and its housing, at one end of the armature shaft; the other was vibration resulting from stickiness in the centrifugal throw-out switch (a fail-safe switch that prevents the gas valve from opening), at the other end of the shaft. I finally took the whole thing apart and found both problems, but it wasn't easy to find them when the motor wasn't running.

So, I wondered about the idea of making a small, cheap, battery-powered amplifier, with a mike and a headphone jack, that contained a couple of active, adjustable audio filters, one high-pass and another low-pass. Made a notching filter or bandpass filter to make it slick.

I don't play with engines much these days, but I can recall times when such a device would have made quick work of tracking down engine noises.

There it is. If you make it and sell it, the idea is yours. Watch out for patents.

Reply to
Jim Wilkins

There definitely are electronic stethoscopes on the market. You can buy them at auto parts stores. They have some sort of vibration mike on the end of a long rod, so you can poke the rod down into the works where engine accessory bearings are.

Jon

Reply to
Jon Elson

Yeah, I've seen those, but I thought the active filters would make them a l ot more useful in something noisy, like an IC engine. I made some audio fil ters for use in ham radio a couple of decades ago, and they were great when I was playing with direct-conversion receivers, which let a lot of noise t hrough.

Reply to
edhuntress2

Yeah, I've seen those, but I thought the active filters would make them a lot more useful in something noisy, like an IC engine. I made some audio filters for use in ham radio a couple of decades ago, and they were great when I was playing with direct-conversion receivers, which let a lot of noise through.

Reply to
Jim Wilkins

Er...ah...well, yeah, I guess. Then you have to teach users how to read the displays.

Reply to
edhuntress2

They have been on the market for decades.. Steelman Engine-ear and Chassis-Ear, along with 8-Mile-Lake and SKF TMST3 are pretty common in the industry. The Chassis-Ear has several remote sensors you can install in multiple places and switch between them on the run.

Reply to
clare

Cardiologists stethophones have had ambient noise reduction for a few years already. It makes hearing heart noises a lot easier. They are digital devices with DSP circuitry.

Reply to
clare

Look what $150 can buy - for the medical field --

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Reply to
clare

and what is availble for "medical" use for under $100

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Reply to
clare

Users already have to learn how to interpret the sounds. This could show if the sound is related to the speed of the crankshaft, or of the camshaft, alternator, etc.

The upper and lower filters could isolate individual sounds which they both see and hear. Without the display they don't know what the filters are doing.

-jsw

Reply to
Jim Wilkins

r, using my usual piece of aquarium hose stuck in my ear , and I wondere d if there might be a market for an advanced kind of mechanic's stethoscope -- something that ought to be a piece of cake for someone like you.

hem made it all but impossible to find the origins of the noises. One was s ome mechanical interference between the centrifugal fan and its housing, at one end of the armature shaft; the other was vibration resulting from stic kiness in the centrifugal throw-out switch (a fail-safe switch that prevent s the gas valve from opening), at the other end of the shaft. I finally too k the whole thing apart and found both problems, but it wasn't easy to find them when the motor wasn't running.

amplifier, with a mike and a headphone jack, that contained a couple of act ive, adjustable audio filters, one high-pass and another low-pass. Made a n otching filter or bandpass filter to make it slick.

uch a device would have made quick work of tracking down engine noises.

Too little, too late, once again.

Reply to
edhuntress2

Too little, too late, once again. Ed Huntress

===================== Don't feel bad, I was the assistant to brilliant engineers working at the leading edge yet I never invented anything commercially valuable. All my contributions were kick-yourself-for-missing-it simple.

-jsw

Reply to
Jim Wilkins

For my part, I always invent things that have been in use for 30 or more ye ars.

My uncle had the knack, but he never patented anything. He did get Ocean Ci ty Reels (now a part of Penn Reels) to pay him a bunch of money for his sta r-drag fishing reel, back in the 1920s. I still have the duplicate; he made two of them, all silver-brazed from Monel. I should upload a photo of it s ome time.

Reply to
edhuntress2

Hmm ... makes me think of a mechanic's stethoscope which I used to have which might have helped here. Instead of having the usual stethoscope "Y" to direct one sensor to two ears, it had a separate hose from each earpiece, which went to a round plastic pillbox with a hole and nipple in the center of one side, and a threaded nipple in the center of the other side into which a length of 1/8" brass rod screwed. At the end of the rods were corks for contact to the device.

This gave a stereo signal, so you could tell which sensor was louder and thus which was closer to the source of the noise.

Instead of a microphone, use an old phono cartridge with a brass whisker where the needle normally was held. (Ceramic or Crystal cartridge -- not the fancier stereo cartridges of higher quality and lower stylus force which came later.) Astatic was the brand of one of these types. I wonder if you can still find them on eBay?

Nope! Nothing old enough. What you need should be mono, with a single pair of terminals, and a thumbscrew in the front to lock the new stylus (or the brass rod) into.

It sounds interesting -- and more so if you can do stereo pickups with old phono cartridges. :-)

Enjoy, DoN.

Reply to
DoN. Nichols

That sounds nice and simple. I really like simple. d8-)

I think I have a couple of those old phono cartridges in the attic somewhere. With my pack-rat tendencies, I usually save the old one when I put a new thingy in.

What I *don't* have is much ambition to pursue things like that. If it isn't fishing. photography, or boat gear, I try to avoid it. Time is becoming precious.

But thanks for the thoughts. I really like the stereo stethoscope idea.

Reply to
edhuntress2

For my part, I always invent things that have been in use for 30 or more years.

Reply to
Jim Wilkins

Wow. Unless it was a life-saving antibiotic, at least the patent has run out.

Reply to
edhuntress2

Vaccination is that old, but fortunately we don't suffer the other medical procedures of that era.

Reply to
Jim Wilkins

True.

But we all still wish the doctors weren't so barbaric nowadays. I can't wait for the medical community to discover and conquer PAIN.

Reply to
Larry Jaques

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