I have read that quite a few car manufactors have changed their "normal" knock sensors to "2nd harmonic tuned" knock sensors lately. Those later type of knock sensors do need different settings. (double of the "normal" knock frequency) Does anyone know what Subaru is using on their engines during the years? Link is showing that from MY01 Subaru is using "2nd harmonic tuned" knock sensors. I assume it's wise to use double the "normal" knock frequency in the Syvecs Knock Control setup. Anyone who has measured the actual frequency of the knock signal on a MY01 or later Subaru?
Mark.
Knock Frequency
Re: Knock Frequency
Measure - take sample, for example with Windows audio recorder and analyze it using Audacity or with some other spectral application. If the resonant frequency is around 5.7-6 kHz then it's 'usual' type, if doubled then 2'nd harmonic tuned one.
From memory Subaru has first order sensor, but measure to make sure.
From memory Subaru has first order sensor, but measure to make sure.
Re: Knock Frequency
Mark,
From what I have read about the "2nd harmonic" approach is that it has nothing to do with the sensors since they are wideband sensors anyways. The METHOD of measurement is what is different. The reason some manufacturers went to listen to the 2nd harmonic to trace knock was due to the fact that other engine noises which are normally very close to the 1st order knock frequency makes it sometimes difficult to distinguish actual knock from engine noise.
This noise may be in the 5k-7kHz range. EG. The Subaru 2.5L has a specific knock frequency of 5.68kHz as a base frequency. The 2nd harmonic would put it at 11.36kHz. You should probably find that at this frequency IF there is activity it will be knock rather than other engine noises which won't have such a high frequency. However being the 2nd harmonic it is a lot lower in amplitude which makes it more difficult to properly pick up.
Hope this makes sense.
Cheers,
Jasper Kopinga
CS Racing
Taiwan.
From what I have read about the "2nd harmonic" approach is that it has nothing to do with the sensors since they are wideband sensors anyways. The METHOD of measurement is what is different. The reason some manufacturers went to listen to the 2nd harmonic to trace knock was due to the fact that other engine noises which are normally very close to the 1st order knock frequency makes it sometimes difficult to distinguish actual knock from engine noise.
This noise may be in the 5k-7kHz range. EG. The Subaru 2.5L has a specific knock frequency of 5.68kHz as a base frequency. The 2nd harmonic would put it at 11.36kHz. You should probably find that at this frequency IF there is activity it will be knock rather than other engine noises which won't have such a high frequency. However being the 2nd harmonic it is a lot lower in amplitude which makes it more difficult to properly pick up.
Hope this makes sense.
Cheers,
Jasper Kopinga
CS Racing
Taiwan.
Re: Knock Frequency
O.K. From what I've read on the Link website it appears to me that the sensors are "tuned" for the 2nd harmonic and that's what has the highest amplitude when knock occurs. I will record some knock and analyse when I find some time.
Mark.
Mark.
Re: Knock Frequency
No knock, but sensor resonant frequency, so called '2nd order sensors' are self resonating in nature, producing largest output voltage at resonant frequency.
Fex.
ERAS-KN - Non-Resonant Knock Sensor, ERAS-KR - Resonant Knock Sensor
http://www.ngkntk.co.jp/english/product ... as-kn.html
Fex.
ERAS-KN - Non-Resonant Knock Sensor, ERAS-KR - Resonant Knock Sensor
http://www.ngkntk.co.jp/english/product ... as-kn.html