Question Regarding "Phase Difference"

[AlexMk7]

I am currently in the process of reading Beyond the Apex, Polyphony's recently released app and introductory guide to automotive engineering/tuning. I was just reading part 1, where basic physics principles are discussed and as I was reading the section that talks about phase difference in vibration systems (page 30) I became confused. It is stated that phase difference is the "difference in the rhythm of the vibration [of two systems]". As an audio engineering student, I have a bit of background knowledge regarding phase. From what I have learned, phase difference could be described as the difference in angles between two periodic waves. That is, how offset the vibrations of 2 systems are, NOT the difference between their frequencies. The guide goes on "explaining" how increasing the frequency of one system would increase the phase angle to specific values which to me is completely wrong. Sure, a momentary increase in the frequency of one system would create an offset, but permanently increasing it would mean the 2 systems would vibrate at different frequencies and therefore their phase difference would be varying continuously. Am I missing something or is this disgustingly inaccurate?

 

[TurnLeft]

This seems very interesting but having not read this manual makes it hard to understand what is being said. I will try to see if I can find a charitable soul who can download it for me to read, I don’t have an Ipad or Iphone.

I’ve been working on trying to find the right wave between the front and rear spring rates, I don’t know if this is the subject that is discussed here.

 

[DolHaus]

Start at the beginning...

What do the phase differences relate to?
What are you trying to achieve?

 

[AlexMk7]

This seems very interesting but having not read this manual makes it hard to understand what is being said. I will try to see if I can find a charitable soul who can download it for me to read, I don’t have an Ipad or Iphone.

I’ve been working on trying to find the right wave between the front and rear spring rates, I don’t know if this is the subject that is discussed here.

Here is a dropbox link to a PDF version, the part i'm referring to begins on page 30: https://www.dropbox.com/s/y27pxwqvg7scnnt/GT6 Beyond The Apex.pdf?dl=0

Please let me know if what you are referring to relates to this.

Start at the beginning...

What do the phase differences relate to?
What are you trying to achieve?

I'm trying to figure out whether i'm not understanding something or whoever wrote the guide is themselves confused with the concept of phase difference. I noticed minor mistakes here and there so i'm allowing myself to doubt the validity of this information. What i'm thinking and what a quick search will confirm is that phase difference is the offset between the phase angles of two periodic cycles/motions/waves (whatever you want to call it). What the guide is claiming (at least that's my understanding of it) is that phase difference describes the difference in the frequencies (they use the term "rhythm") of the cycles/motions/waves AND that specific/constant phase differences (90° and 180° specifically) are introduced by having one system vibrate slower or faster than the other. That doesn't make sense because if the two systems are not vibrating at the exact same frequency, their phase difference would constantly be changing (and creating what is referred to as a "beat frequency", but that's another topic). I'm hoping someone who has a better understanding of physics than I do might point out a missing piece of information or something i'm misinterpreting that would make sense of what is being said in the guide. Please have a look at it for yourself, I should have posted that link in the OP to begin with. Apologies for the lack of supporting material...

 

[Litchi]

Here is a dropbox link to a PDF version, the part i'm referring to begins on page 30:

Is this version legal ?

 

[AlexMk7]

Is this version legal ?

No idea, but considering that the app is free I don't see why it wouldn't be.

 

[DolHaus]

Here is a dropbox link to a PDF version, the part i'm referring to begins on page 30: https://www.dropbox.com/s/y27pxwqvg7scnnt/GT6 Beyond The Apex.pdf?dl=0

Please let me know if what you are referring to relates to this.



I'm trying to figure out whether i'm not understanding something or whoever wrote the guide is themselves confused with the concept of phase difference. I noticed minor mistakes here and there so i'm allowing myself to doubt the validity of this information. What i'm thinking and what a quick search will confirm is that phase difference is the offset between the phase angles of two periodic cycles/motions/waves (whatever you want to call it). What the guide is claiming (at least that's my understanding of it) is that phase difference describes the difference in the frequencies (they use the term "rhythm") of the cycles/motions/waves AND that specific/constant phase differences (90° and 180° specifically) are introduced by having one system vibrate slower or faster than the other. That doesn't make sense because if the two systems are not vibrating at the exact same frequency, their phase difference would constantly be changing (and creating what is referred to as a "beat frequency", but that's another topic). I'm hoping someone who has a better understanding of physics than I do might point out a missing piece of information or something i'm misinterpreting that would make sense of what is being said in the guide. Please have a look at it for yourself, I should have posted that link in the OP to begin with. Apologies for the lack of supporting material...

I'm afraid I don't think I can't help you with this one, I understand where they're getting the whole oscilating frequency thing in relation to the functional characteristics of springs and how dampers affect these but the rest is a bit more in depth than I've ever felt necessary to know

 

[Litchi]

No idea, but considering that the app is free I don't see why it wouldn't be.

Yea, you were right 👍

 

[TurnLeft]

Here is a dropbox link to a PDF version, the part i'm referring to begins on page 30: https://www.dropbox.com/s/y27pxwqvg7scnnt/GT6 Beyond The Apex.pdf?dl=0

Please let me know if what you are referring to relates to this.

First, thank you, I will read this as soon as I can.

I see everything as frequencies/waves/colors, must be the bad habit of an old musician. This might not be what is discussed in the manual but this is my view on tuning the suspension. The front and rear of the car each have a different frequency ( a musical note), if they are not tuned harmonically together it causes an unpleasant "sound" (like an untuned guitar) or in this case two parts of the car that don't work together. So the ideal would be to find that beautiful chord ( or interval ) that makes the car drive freely on the track. There are quite a few factors that are added to this equation; type of tire, track, total weight, weight distribution, spring rate, dampers, toe angle, camber. Power, MLSD, brakes will also have a word in it but at different times. I haven't found it yet, that perfect chord or I'd be playing it to a few Tuning Garages in this Forum.

BTW that PSN name looks familiar, just can't seem to remember where.

 

[Thorin Cain]

@TurnLeft is on the right track (Pun intended). It refers to the difference between the frequencies of the springs.

@DolHaus can probably explain this better, but I'll try.

When a spring is compressed and allowed to extend it will keep bouncing until all of the energy which is put into the spring under compression disipates. Different spring rates will bounce at different frequencies and this difference is what you should be trying to control. As far as tuning goes, the goal when setting your springs is to try and match up these frequencies to balance the car. So a car which has a heavier front than rear will require stronger springs at the front than the rear and vice versa to achieve this balance.

Remember though, that the dampers also play a part by controlling how quickly the springs are allowed to move. So your springs can be a little off balance and as long as the dampers are set to compensate for minor differences you should be fine.

It is similar in principle to what you know from your audio experience. Thing of the springs as the left/right balance between two speakers and the dampers as the gain for each side.

Hope this helps.

 

[AlexMk7]

I'm afraid I don't think I can't help you with this one, I understand where they're getting the whole oscilating frequency thing in relation to the functional characteristics of springs and how dampers affect these but the rest is a bit more in depth than I've ever felt necessary to know

No worries bud! I have a thing for the theory behind everything and tend to overthink stuff a lot, that's my curse (and blessing in a way). Anyways thanks for giving it a shot

First, thank you, I will read this as soon as I can.

I see everything as frequencies/waves/colors, must be the bad habit of an old musician. This might not be what is discussed in the manual but this is my view on tuning the suspension. The front and rear of the car each have a different frequency ( a musical note), if they are not tuned harmonically together it causes an unpleasant "sound" (like an untuned guitar) or in this case two parts of the car that don't work together. So the ideal would be to find that beautiful chord ( or interval ) that makes the car drive freely on the track. There are quite a few factors that are added to this equation; type of tire, track, total weight, weight distribution, spring rate, dampers, toe angle, camber. Power, MLSD, brakes will also have a word in it but at different times. I haven't found it yet, that perfect chord or I'd be playing it to a few Tuning Garages in this Forum.

BTW that PSN name looks familiar, just can't seem to remember where.

Man that's a cool way of thinking about it I'll keep it in mind! Yea your ID looks familiar too, small world I guess Thanks for taking the time to read and trying to help!

@TurnLeft is on the right track (Pun intended). It refers to the difference between the frequencies of the springs.

@DolHaus can probably explain this better, but I'll try.

When a spring is compressed and allowed to extend it will keep bouncing until all of the energy which is put into the spring under compression disipates. Different spring rates will bounce at different frequencies and this difference is what you should be trying to control. As far as tuning goes, the goal when setting your springs is to try and match up these frequencies to balance the car. So a car which has a heavier front than rear will require stronger springs at the front than the rear and vice versa to achieve this balance.

Remember though, that the dampers also play a part by controlling how quickly the springs are allowed to move. So your springs can be a little off balance and as long as the dampers are set to compensate for minor differences you should be fine.

It is similar in principle to what you know from your audio experience. Thing of the springs as the left/right balance between two speakers and the dampers as the gain for each side.

Hope this helps.

I understand what you're saying. Different springs have different natural frequencies (depending on their constant and respective sprung mass) and you should try and get all of them to vibrate at the same frequencies (in theory) by adjusting the damping ratios. However, I think you should have a look at the section of the guide i'm referring to as it relates more to how a single spring would react to different excitation frequencies (in this case road input, being the second vibrating system I was referring to) than the difference in frequency between different springs (as the different springs on a car don't directly cause each other to vibrate). I could be completely wrong though (that's why we're here!), so correct me if I am. Thank you for your input!

 

[Thorin Cain]

Your not wrong. It is the road which causes the vibrations in the springs, any small bump, ripple or dip in the pavement will set the springs in motion. The springs and dampers must be set in such a way that the tyre remains in contact with the pavement when this happens. This is where you need to balance the springs, as @TurnLeft said, in harmony (Nice analogy bud!) so both the front and rear wheels maintain contact.

You will find a section on dampers which has this illustrated in the app (or you should, it's been in the last two books that PD have done with their games. If not, I'm sure @DolHaus has the same diagram in his General Tuning Guide. (Would post the link bit I'm on my phone and it's pain.)

Edit: I've not read the pdf yet but I did download it, thanks for the link. I'll check it out later. I understand what you were referring to in the previous post and have seen the explanations and various formula in another book on-line. I'll try and find it later and share it if you wish. but for now it's bed time.

 

[Thorin Cain]

Hey @AlexMk7, here's that other file I found. Hope it can be of some use to you.