Hear for knock

billman · November 09, 2010, 08:06:05 AM

I was wondering how is everyone listening for knock?
I am currently using a harness made and listen directly to the knock sensor but i am a bit confused about the sound i must listen for.

some say knock is the sound found in this clip between 21-24 seconds a sound similar to the sound that you can get from flexing a piece of sheet metal.

http://www.efiexpress.com/downloads/knock.mp3

On the other hand, when I hear the knockbox reference files, you hear that at the regions where it should not have any knock there is a noise like engine harmonics that are not dangerous but sounds similar to the flexing metal sheet thing. The middle sections where they raise the ignition it is clear to hear knock just as rain falls on a metal sheet.

http://www.theknockbox.com.au/content/view/8/8/

The question is are both sounds dangerous?

Can please someone experienced describe it please?

GintsK · November 09, 2010, 11:15:35 AM

First track - it can be recorded without frequency filter. Usually when tuning there is no so massive knocking, because we start with retarded and slowly go to more and more advance until hearing knock.

Knock initially comes not as regularly sound, but randomly. Big rain drops on metal roof is good comparison.
KnockBox files are recorded using bandpass filter. And it allows to work more comfortable.

billman · November 09, 2010, 12:09:31 PM

Is the 21-24 seconds on the first clip knock or harmonics?

How can I implement. Band pass filter? Couple of condensers?

GintsK · November 09, 2010, 01:12:15 PM

Yes, around 22s.

No idea. I have solution consisting from separate filter and amplifier for headphones.

I think best in the market could be KnockBox.
another is Knock Block from Link. But I am not sure is sound filtered. Link dealer said yes, but manual lead to think oposite. It would be good if someone ascertain this detail. Kit includes headphones with active noise canceletion!
Phormula listener is total crap! I have it.
Gizzmo - do not knew. Not so good feedbacks regarding filtered sound to headphones.

Gints

billman · November 09, 2010, 01:54:31 PM

@Gints
You think second 22 is harmonic noise or knock? I cant tell from what you written.

I use a motorcycle intercom amplifier that connects to headphones. Maybe I can put between sensor and amp a simple bandpass filter used in audio systems and enhance the 7khz region I am interested about.

Can maybe the developer see the knock thing into this matter? Even if I or others are very carefully raise the timing and listen it would be always goo to have this feature working since we don't drive with earphones all the time.

[email protected] · November 09, 2010, 02:25:33 PM

Knock sensor -> Laptop running Audacity with the FFT filter set to band pass the knock frequency - go for the primary and secondary harmonics -> headphones

GintsK · November 09, 2010, 02:39:35 PM

Billman, it sounds like knock to me.

Rob, thanks for advice! I will try this out!

billman · November 09, 2010, 03:28:18 PM

I tried Audacity but i can't get it to work realtime. I must record and then set the bandpass filter.

Another programm is Spectrum Lab but there i can't set it as high as i need at 7000hz.

GintsK · November 10, 2010, 06:22:51 AM

Quote from: billman on November 09, 2010, 03:28:18 PM
I tried Audacity but i can't get it to work realtime. I must record and then set the bandpass filter.

Another programm is Spectrum Lab but there i can't set it as high as i need at 7000hz.

I got listen Audacity live sound but can't find possibility to do any processing. Rob?

Kenny Watson · November 10, 2010, 07:05:54 AM

The first clip is not great, the motor is noisy in general IMO. If that were my motor I'd be inclined to change the mounting locaiton of the transducer, or pull 5 degrees from the whole map and get what I know is a clean pull to compare it to.

Part of it is not just knowing what you motor sounds like when it is knocking/having irregular combustion events, it's knowing what a clean pull sounds like.

billman · November 10, 2010, 07:39:53 AM

first clip is not mine but i get what you mean.

i can hear a clean run when i rev the engine out in neutral or with low load. However even in the first clip you can listen to a sound differentiation from 21-24. then it goes back to quite.

I posted a question to DIYForum on how to make a simple passe bandpass filter from 6800-7200Hz for real time filtering.

[email protected] · November 10, 2010, 08:52:21 AM

Band pass filters are not EFI specific:
http://www.electronics-tutorials.ws/filter/filter_4.html

billman · November 10, 2010, 09:28:00 AM

I know sorry i didn't write it correct DIY Audio Forum!

http://www.diyaudio.com/forums/analog-line-level/177004-stereo-bandpass-filter.html

I just cant calculate the component values but i can try....

Pet · November 10, 2010, 01:06:17 PM

Try FilterLab free soft from Microchip - it's nice tool for designing active filters with MCPxxx OP amps from that company.

www.mervart.eu/knock/flab1.PNG
www.mervart.eu/knock/flab2.PNG

multiplex · November 10, 2010, 03:19:08 PM

some of you will probably find this a bit wacky, but here is what i've done.

bought a 'cheap' battery powered mixer that has a 3 band EQ. made a little wiring harness that splices into my knock sensors. and then use my DJ headphones for monitoring.

so i can filter out some of the engine noise, and even pan the two knock sensors i have to left and right channels.

other option would be to use this setup to record into a laptop at proper audio levels.

unfortunately i haven't had much time to play around with it or use it to 'tune' yet.

whole setup was around 100 dollars

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Hear for knock