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Easy and effective low frequency fix

MY-Y

Active Member
Mar 4, 2020
1,477
1,798
MD
I have solved the low frequency issue with my car. I had a 41 Hz standing wave that would come and go. It wasn't good. If the hatch bumpers are loose, a crazy subsonic buffeting occurs. I'm talking about the annoying rumble that is still there when the bumpers are properly adjusted.

To keep it brief, I placed my phone running the "spectroid" spectrum analyzer on my dash. I then went aound my car, thumping different spots with my hand to see which area(s) caused a 41 Hz resonance. Bottom line, pretty much all of the low frequency is from the hatch. Center glass and center of the metal has resonances at 47 and 50 Hz. The corners where the upper bumpers hit are the 41 Hz culprit.

I made a temporary rigid stop from wood and Epoxy putty to verify that the harmonic could be eliminated, and it can. I then spent a whopping $1.98 on two PVC plumbing pieces, my Epoxy putty, and flat black spray paint for a permanent fix. With the temporary blocks, I knew the exact height needed. I used my sander to shorten the PVC pieces to make the original squishy rubber bumpers ridged at the right length.

You can see the 41 Hz honor- look at read peak line when I thumped the hatch above where the upper bumpers were mounted.

Screenshot_20210715-152345_Spectroid.jpg

Making the temporary rigid stops.
20210716_175055.jpg

Resulting temporary stops.
20210718_131835.jpg

OEM stops with shortened PVC caps, sanded to same length as wood/Epoxy stops. Note, these are shorter than I had my OEM stops set to. These caps had to be hollowed out a little to fit over the rubber stops. Friction probably would have held them on, but I put a bit of Epoxy putty to hold them to the plastic turn collar just to be sure.
20210718_173927.jpg




20210720_164222.jpg

Final product - painted stops are rigid and look OEM. The foam board I'm holding was put inside the hatch above the stops. I don't think this was needed. The bottom stops still need to be adjusted to hit.
Screenshot_20210629-092643_Spectroid.jpg

Irritating 41 Hz rumble before this fix is shown above.
Screenshot_20210802-071631_Spectroid.jpg

The 41 Hz is GONE. Every now and then, it is back for a couple of seconds, but 99% of the time, it's gone.

The 47 and 50 Hz sounds are not annoying to me. If I feel inspired, I may make rigid stops for the bottom two.

Bottom line... after careful analysis, I have made my car much more enjoyable for very little cost.
 
Last edited:
I have solved the low frequency issue with my car. I had a 41 Hz standing wave that would come and go. It wasn't good. If the hatch bumpers are loose, a crazy subsonic buffeting occurs. I'm talking about the annoying rumble that is still there when the bumpers are properly adjusted.

To keep it brief, I placed my phone running the "spectroid" spectrum analyzer on my dash. I then went aound my car, thumping different spots with my hand to see which area(s) caused a 41 Hz resonance. Bottom line, pretty much all of the low frequency is from the hatch. Center glass and center of the metal has resonances at 47 and 50 Hz. The corners where the upper bumpers hit are the 41 Hz culprit.

I made a temporary rigid stop from wood and Epoxy putty to verify that the harmonic could be eliminated, and it can. I then spent a whopping $1.98 on two PVC plumbing pieces, my Epoxy putty, and flat black spray paint for a permanent fix. With the temporary blocks, I knew the exact height needed. I used my sander to shorten the PVC pieces to make the original squishy rubber bumpers ridged at the right length.

You can see the 41 Hz honor- look at read peak line when I thumped the hatch above where the upper bumpers were mounted.

View attachment 692156
Making the temporary rigid stops.
View attachment 692157
Resulting temporary stops.
View attachment 692158
OEM stops with shortened PVC caps, sanded to same length as wood/Epoxy stops. Note, these are shorter than I had my OEM stops set to. These caps had to be hollowed out a little to fit over the rubber stops. Friction probably would have held them on, but I put a bit of Epoxy putty to hold them to the plastic turn collar just to be sure.
View attachment 692159



View attachment 692161
Final product - painted stops are rigid and look OEM. The foam board I'm holding was put inside the hatch above the stops. I don't think this was needed. The bottom stops still need to be adjusted to hit. View attachment 692164
Irritating 41 Hz rumble before this fix is shown above.
View attachment 692166
The 41 Hz is GONE. Every now and then, it is back for a couple of seconds, but 99% of the time, it's gone.

The 47 and 50 Hz sounds are not annoying to me. If I feel inspired, I may make rigid stops for the bottom two.

Bottom line... after careful analysis, I have made my car much more enjoyable for very little cost.
To be sure I understand... The fix was to stiffen the middle adjustable bumpers attached to the hatch to the length you determined to be the best. Meaning that even when properly adjusted the bumpers have too much give and there is booming present. Does one need to do the intermediate step of making extensions to the fixed stop on car or could one measure the length of the adjustment on the adjustable bumper when adjusted to not be able to remove a sheet of paper? Then make a cap to take up that slack? Thank you - May Hears Hurt and this limits my driving of an otherwise fantastic car.
 

MY-Y

Active Member
Mar 4, 2020
1,477
1,798
MD
It seems reasonable to start with setting the modified ridged bumper to the length as you suggested. My intermediate step was to test my theory about this solving the 41 Hz resonance. I suspect setting the ridged bumpers to the OEM length will be a bit too long though. The OEM ones are pretty soft and compress fairly easily. It's easy to tell if they are too long - the hatch won't close on its own if they are too long. Sand and test a few times should work.

The PVC caps are a bit too small inside to fit over the OEM rubber extensions without sanding the inside some. I also sanded the flat end some to thin it some. This let me have a little more sleve to grab on the rubber extension. The OEM rubber extensions are set to the minimum height for this mod.
 
Last edited:

Pianewman

2021 MYLR VIN 88,XXX, Rd/Wh, 12/20 delivery
Supporting Member
Oct 28, 2020
2,536
2,230
Fort Worth
Mission accomplished! Brilliant solution.

Now, for your next assignment, if you choose to accept it: The HVAC rumble, which, when it occurs when the car is stationary (ie CAMP MODE!), is REALLY annoying! There HAS to be a way to isolate whatever is making that rumble (compressor?)
 

MY-Y

Active Member
Mar 4, 2020
1,477
1,798
MD
Mission accomplished! Brilliant solution.

Now, for your next assignment, if you choose to accept it: The HVAC rumble, which, when it occurs when the car is stationary (ie CAMP MODE!), is REALLY annoying! There HAS to be a way to isolate whatever is making that rumble (compressor?)
I'd try to solve that problem, but I don't have it. I checked camp mode at different fan speeds, no rumble for me. My car is a 6/20, which is when they first started adding the compressor cover.
Screenshot_20210824-073419_Spectroid.jpg
Screenshot_20210824-073404_Spectroid.jpg
Screenshot_20210824-073345_Spectroid.jpg
 
It seems reasonable to start with setting the modified ridged bumper to the length as you suggested. My intermediate step was to test my theory about this solving the 41 Hz resonance. I suspect setting the ridged bumpers to the OEM length will be a bit too long though. The OEM ones are pretty soft and compress fairly easily. It's easy to tell if they are too long - the hatch won't close on its own if they are too long. Sand and test a few times should work.

The PVC caps are a bit too small inside to fit over the OEM rubber extensions without sanding the inside some. I also sanded the flat end some to thin it some. This let me have a little more sleve to grab on the rubber extension. The OEM rubber extensions are set to the minimum height for this mod.
Thanks. Two questions
1. On the bodied ridged bumper. Is it the stiffening that seemed to help or did you need to lengthen the bumper
2. Hatch catch. I tried to lower the hatch catch. I loosened the torx screws but there was not much play. I may have lowered 1mm. Than did not help with ear pressure more than my unmodified bumper adjustment and did not make it harder to close the hatch. Would you suggest grinding the hatch catch screw holes to allow me to lower this.
 

MY-Y

Active Member
Mar 4, 2020
1,477
1,798
MD
1. It is the rigidity that helped. I tried making the original design bumpers longer to the point that the hatch wouldn't latch without pushing down on it. That didn't stop the resonance.
2. Personally, I wouldn't bother trying to lower the catch by grinding the holes. The ridged bumpers solved the issue for me. I fiddled with lowering the catch a while ago. If I recall correctly, the plate that the screws go in to moves a little when loosened and bumped with a rubber mallet. The catch itself has tapered holes that match the screws - no play there when tightened.
 

cab

Active Member
Sep 5, 2013
1,102
1,242
Grapevine, TX
I ended up doing a similar fix a few years ago in my Model S. I tried the PVC, but it was so stiff that it transmitted other harmonics so I settled on stiff rubber dowels (much stiffer than the S' soft rubber...which is a lot softer than the Y I think).

See post 78 in this thread:Pressure Buffeting - Has anyone experienced it?

While I'm sad to see the issue is there in the Y, I am glad the fix (or partial fix) is similar.
 
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cab

Active Member
Sep 5, 2013
1,102
1,242
Grapevine, TX
@MY-Y How tight are your new "adjusters" against the base now - say with the "paper" pull test (put a piece of paper on the stops, shut the hatch and try to pull them out. Is it so tight it will tear the paper or can you still pull the paper out with a heavy drag?

In addition, it looks like your PVC caps are touching the plastic hexagonal part of the factory adjuster - forming, effectively, a rigid structure with only the rubber "core" providing isolation. Is that correct?
 

MY-Y

Active Member
Mar 4, 2020
1,477
1,798
MD
@MY-Y How tight are your new "adjusters" against the base now - say with the "paper" pull test (put a piece of paper on the stops, shut the hatch and try to pull them out. Is it so tight it will tear the paper or can you still pull the paper out with a heavy drag?

In addition, it looks like your PVC caps are touching the plastic hexagonal part of the factory adjuster - forming, effectively, a rigid structure with only the rubber "core" providing isolation. Is that correct?
Paper rips with the paper test.

The rubber core does nothing but provide a convenient way to have the plastic stop screw into the hatch. Here's another pic of the stop to clarify. The rubber screw threads and plastic hex nut are the OEM stop. The motley looking junction is epoxy putty and the bottom is the shortened PVC cap. The original rubber stop is at the shortest setting and is inside the PVC cap.
20210903_165700.jpg
 
Just as another data point, I'm considering ordering a 2nd Tesla, the M3 SR+ (seems like a good deal). I test drove a 2021 M3 AWD today, and here is its Spectroid output. The residual ~50 Hz from the center of the hatch flex is noticeably absent on the M3. Maybe I'll make the center stops rigid too.
View attachment 704861
Did you eventually get chance to do same on the center stops? I am curious to see the result …
 

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