DIY knock ears
12-19-11, 04:08 PM
#1
DIY knock ears
being that some engine management systems have no way of logging or sensing knock(cough*microtechPOS*cough) you will have to find alternative ways of measuring knock. there generally is 2 ways of doing this, one is with a piezoelectric sensor on the block with a box dampening the signal telling you when knock is occurring which sometimes does not give desired results as every engine generates rhythmic noises at certain times and the sensor has to be accurate and calibrated around your "normal" engine noises.
the second method is with a microphone attached to a hard surface on the block near the combustion chamber.
"knock ears" are by far cheaper than some of the knock boxes, microphoned ears generally start at $100 and go up from there, knock boxes at about $400 and up, some DIY kits are a little bit less.
anyways, being a DIYer i found this article on how to make your own ears and decided to try it out:
http://www.autospeed.com/cms/A_0348/article.html
http://www.autospeed.com/cms/article.html?&A=0353
there are many different types of amplifiers you can use to make the ears with, i chose a basic design as to not waste a bunch of money if the results weren't to my liking.
i started out with a "listen up" pocket amplifier which is basically like a hearing aid that sits in your pocket with a headphone jack and built in microphone. you can find them pretty much dirt cheap but some others may give better results.
it is basic to disassemble popping each side cover off to reveal the 4 screws holding the case together it came apart in about 2 minutes showing the circuit board and microphone.
i marked the board and mic for polarity, doesn't really matter how you mark it as you will just be running new wires in the same polarity as you marked it and desoldered the mic from the board.
i just grabbed some CAT5 cable used for connecting computers to one another, got a 14' length and chopped the connectors off, chose the orange and brown wires(orange + and brown -) and cut the wires back about 1.5" and stripped the wires and hacked off the other 6 or so unused wires in the bundle.
now with the wire ready i trimmed it and inserted it through the holes in the board and soldered the connections for the mic wiring. trim a small slot in the case where the mic hole was for the cable to come through and reassemble the case/board using the case to hold the cable inside the housing.
now taking a battery clip, remove the boot and slide it over your wiring to reinstall later. run the wires through the crimp slot that will hold the cable to the clamp and solder the orange and brown wires to the correct polarity marked on the microphone, seal up the connections with liquid tape or some small shrink tubing. now you can tie or glue the mic to the clamp and pinch the holder to the cable on the clamp so that it won't slip loose if you tug on it accidentally. slide the boot over the assembled clamp.
now test the unit and see how it works.
i have not tested it thoroughly yet but so far it seems to do it's job. whether it will pick up light knock in a rotary engine i have yet to determine but on the diesel mercedes i could definitely hear plenty through the thick cast iron block as each "squish" of the detonation cycle occurred.
worst case you have a remote spying device for about $25 to listen to your siblings in the next room over. remote ears do work well for isolating noises while driving the car that you otherwise may never be able to diagnose to it is handy for other things as well.
it was a fun little project that took more time shopping than actually doing.
the second method is with a microphone attached to a hard surface on the block near the combustion chamber.
"knock ears" are by far cheaper than some of the knock boxes, microphoned ears generally start at $100 and go up from there, knock boxes at about $400 and up, some DIY kits are a little bit less.
anyways, being a DIYer i found this article on how to make your own ears and decided to try it out:
http://www.autospeed.com/cms/A_0348/article.html
http://www.autospeed.com/cms/article.html?&A=0353
there are many different types of amplifiers you can use to make the ears with, i chose a basic design as to not waste a bunch of money if the results weren't to my liking.
i started out with a "listen up" pocket amplifier which is basically like a hearing aid that sits in your pocket with a headphone jack and built in microphone. you can find them pretty much dirt cheap but some others may give better results.
it is basic to disassemble popping each side cover off to reveal the 4 screws holding the case together it came apart in about 2 minutes showing the circuit board and microphone.
i marked the board and mic for polarity, doesn't really matter how you mark it as you will just be running new wires in the same polarity as you marked it and desoldered the mic from the board.
i just grabbed some CAT5 cable used for connecting computers to one another, got a 14' length and chopped the connectors off, chose the orange and brown wires(orange + and brown -) and cut the wires back about 1.5" and stripped the wires and hacked off the other 6 or so unused wires in the bundle.
now with the wire ready i trimmed it and inserted it through the holes in the board and soldered the connections for the mic wiring. trim a small slot in the case where the mic hole was for the cable to come through and reassemble the case/board using the case to hold the cable inside the housing.
now taking a battery clip, remove the boot and slide it over your wiring to reinstall later. run the wires through the crimp slot that will hold the cable to the clamp and solder the orange and brown wires to the correct polarity marked on the microphone, seal up the connections with liquid tape or some small shrink tubing. now you can tie or glue the mic to the clamp and pinch the holder to the cable on the clamp so that it won't slip loose if you tug on it accidentally. slide the boot over the assembled clamp.
now test the unit and see how it works.
i have not tested it thoroughly yet but so far it seems to do it's job. whether it will pick up light knock in a rotary engine i have yet to determine but on the diesel mercedes i could definitely hear plenty through the thick cast iron block as each "squish" of the detonation cycle occurred.
worst case you have a remote spying device for about $25 to listen to your siblings in the next room over. remote ears do work well for isolating noises while driving the car that you otherwise may never be able to diagnose to it is handy for other things as well.
it was a fun little project that took more time shopping than actually doing.
Last edited by RotaryEvolution; 12-19-11 at 04:28 PM.
12-19-11, 05:10 PM
#4
plugs being a last resort area, a bad plug will likely kill the mic.
and your favorite .45 caliber Kimber earmuffs over the headphones will cancel out any ambient noise you may hear through the small earphones.
it also has a cool blue LED when it's on that is mad JDM tite!
and your favorite .45 caliber Kimber earmuffs over the headphones will cancel out any ambient noise you may hear through the small earphones.
it also has a cool blue LED when it's on that is mad JDM tite!
Last edited by RotaryEvolution; 12-19-11 at 05:15 PM.
12-19-11, 05:42 PM
#6
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All I have to say is thank god I am 4g63 guy, and thank god for DSMLink. This is really cool karack, but I am very thankful I will never have to deal with something like this lol.
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01-27-12, 03:47 PM
#8
time for some feedback on this as i have tuned 2 cars since with it.
the first FC i tuned at 494whp never had any sign of knock so i could never verify that the ears really were working.
the 2nd was an FD at 297whp that i was able to detect small hints of detonation before the knock sensor was even reading anything(anything above a 60 knock reading with the PFC, 90+ is usually where most people start to take it seriously). adjusting the timing tables to be more conservative eliminated the issue and you could tell the difference between the detonation pops and overly rich ignition fouling stutters(was pushing alcohol/water injection as well).
the CAT5 cable i used does pick up a bit of ignition noise so i will likely be trying to find some better shielded cable for the microphone pickup to eliminate some of the ambient electrical noise.
but so far for $25 it has served as a good rotary tuning aid and i'm sold on this over trusting any installed knock sensor. i already knew knock sensors usually are untrustworthy but not by this margin.
the first FC i tuned at 494whp never had any sign of knock so i could never verify that the ears really were working.
the 2nd was an FD at 297whp that i was able to detect small hints of detonation before the knock sensor was even reading anything(anything above a 60 knock reading with the PFC, 90+ is usually where most people start to take it seriously). adjusting the timing tables to be more conservative eliminated the issue and you could tell the difference between the detonation pops and overly rich ignition fouling stutters(was pushing alcohol/water injection as well).
the CAT5 cable i used does pick up a bit of ignition noise so i will likely be trying to find some better shielded cable for the microphone pickup to eliminate some of the ambient electrical noise.
but so far for $25 it has served as a good rotary tuning aid and i'm sold on this over trusting any installed knock sensor. i already knew knock sensors usually are untrustworthy but not by this margin.
Last edited by RotaryEvolution; 01-27-12 at 03:52 PM.
01-27-12, 05:00 PM
#10
knock sensors pick up certain amplitudes of knock(and also normal engine noise), for rotary applications the knock sensors seem to still be not sensitive enough to detect light knocks before real issues become apparent and generally that is too late. jokingly i said on the dyno last night when someone asked what it sounds like when these engines fail i said "silent but deadly". but that is actually about the truth of it.
most tuners won't even attempt to tune these engines for the reason that it is difficult to reliably tell when you are pushing things too far.
most tuners won't even attempt to tune these engines for the reason that it is difficult to reliably tell when you are pushing things too far.
Last edited by RotaryEvolution; 01-27-12 at 05:04 PM.
02-13-12, 03:18 PM
#14
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interesting. you're right too, i think even the factory ECU stops looking at the knock sensor over 5000rpm or so.
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