cam.in.head Posted March 12 Share Posted March 12 (edited) hi all . heres an interesting question . ive had my cav for nearly 40 years and over the years its had various repairs underneath as they all do and regular painting and wayoyling . what i seem to have noticed is that the car has slowly but surely got noisier over the years "body boom wise" and i have come to the conclusion that every coat that gets put on makes the metal theoretically thicker and lowers the resonant frequency. this is why i think it has become more boomy. i am thinking of stripping every bit of the underside back to bare metal , redoing some of the repairs as or if found nesesarry and then recoating with just a primer and texture coat rather than loads of coats as if is now .it lowering the resonant frequency makes sense as ive done similar to bass speaker cones o tune them to the cabinets with notable results . obviously stipping the underside completelyis a lot of work or should i simply add more to whats already there to continue to lower the frequency to "bring it out the other side" so to speak ? any thoughts or experience on this please. Edited March 12 by cam.in.head 1 Quote Link to comment Share on other sites More sharing options...
Mike. Posted March 12 Share Posted March 12 (edited) I completely stripped the underside of the Manta back to bare metal, but the engine was out, front wings off, subframes and running gear off, gearbox out, brake & fuel lines off then mounted on an A frame. Couldn’t imagine trying to do this without being on an A frame. Definitely a big job but worth the effort if you finish with Gravitex or Raptor or similar. Edited March 12 by Mike. 1 Quote Link to comment Share on other sites More sharing options...
®evo03 Posted March 12 Share Posted March 12 Would sound deadening on the inside affect this more than what's on the outside? The factory fitted sponge backed padding isn't really a great idea, due to it absorbing water, and holding it. It's fitted to most cars even up to early 2000's for some. I am experimenting with yoga mats, cheaper than dynamat, and they are absorbent resistant. Fitted to a car, but not a manta. Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 12 Author Share Posted March 12 its got sound mat all over it .under carpets,in doors and boot floor too. made a difference to outside noise but not the boominess ! Quote Link to comment Share on other sites More sharing options...
Jessopia74 Posted March 12 Share Posted March 12 1 minute ago, cam.in.head said: its got sound mat all over it .under carpets,in doors and boot floor too. made a difference to outside noise but not the boominess ! Was the deadening mat (sticky to panels) replaced after the repairs? The sounds mats absorb the sound, but without the deadening mats the floors are giant percussion instruments that the foam under Matt will have trouble with Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 12 Author Share Posted March 12 the original hard baked on stuff that was on the floorpans wasnt replaced as such with identical but had the self adhesive sheets that look like liquorece stuck on . if i do go down the path of taking the underside to bare metal i may redo the floorpans internally anyway. first plan when the weather warms up a bit is to try some foam sheet under all the seats and boot sides. reason i thought of this is once i carried a pile of foam cut to size cushion inserts for my house sofa on the back seat and the car sounded super quiet ! 1 hour ago, Mike. said: I completely stripped the underside of the Manta back to bare metal, but the engine was out, front wings off, subframes and running gear off, gearbox out, brake & fuel lines off then mounted on an A frame. Couldn’t imagine trying to do this without being on an A frame. Definitely a big job but worth the effort if you finish with Gravitex or Raptor or similar. yes i was thinking gravitex. not too fussed about doing it all on axle stands with drill and wire brush. il do one side and our lass will help with the other. couple of weekends should see it all off. just didnt want to do it if it doesnt make any differnce ! Quote Link to comment Share on other sites More sharing options...
Mike. Posted March 12 Share Posted March 12 (edited) The biggest advantage for me is that I’m able to clean the underside with a sponge or chamois just as quickly as I would wash the top side, I’ve even been known to give it a quick polish as well, that way I can keep a close eye on the underside as nothing is hidden by the heavy factory underseal that could hide corrosion behind it. the wire wheels on a grinder removed the factory underseal easily but it came off like chewing gum then you reveal a factory undercoat/primer stuff before the bare metal. Edited March 12 by Mike. 2 Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 13 Author Share Posted March 13 ive been watching a youtube channel called " yorkshire car restoration" they strip the underside of most of the cars they work on and it helps reveal stuff you wouldnt always see straight away and can be attended to better. Quote Link to comment Share on other sites More sharing options...
Jonathan Pounsett Posted March 13 Share Posted March 13 On 12/03/2024 at 17:25, Mike. said: I completely stripped the underside of the Manta back to bare metal, but the engine was out, front wings off, subframes and running gear off, gearbox out, brake & fuel lines off then mounted on an A frame. Couldn’t imagine trying to do this without being on an A frame. Definitely a big job but worth the effort if you finish with Gravitex or Raptor or similar. I did it with a needle gun with the car on axle stands - I looked like a coal miner. Not a job I would tackle ever again. Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 13 Author Share Posted March 13 if i strip it i will start with the central tunnel area up to the inside of the chassis legs and see how easy it is . then work from there ! Quote Link to comment Share on other sites More sharing options...
Trooker Posted March 13 Share Posted March 13 On 12/03/2024 at 11:01, cam.in.head said: hi all . heres an interesting question . ive had my cav for nearly 40 years and over the years its had various repairs underneath as they all do and regular painting and wayoyling . what i seem to have noticed is that the car has slowly but surely got noisier over the years "body boom wise" and i have come to the conclusion that every coat that gets put on makes the metal theoretically thicker and lowers the resonant frequency. this is why i think it has become more boomy. i am thinking of stripping every bit of the underside back to bare metal , redoing some of the repairs as or if found nesesarry and then recoating with just a primer and texture coat rather than loads of coats as if is now .it lowering the resonant frequency makes sense as ive done similar to bass speaker cones o tune them to the cabinets with notable results . obviously stipping the underside completelyis a lot of work or should i simply add more to whats already there to continue to lower the frequency to "bring it out the other side" so to speak ? any thoughts or experience on this please. I’d be tempted to try a decent recorder/mic get someone else to either drive or operate the equipment and record the ’boominess’ to properly ascertain the worst range of frequencies and see where the highest levels/amplitude is before considering stripping the car. Hopefully you’d identify which panel(s) are the culprits, or if it’s actually bleeding through from the boot. You should be able to pickup a Zoom H1 or a Tascam DR-05 or similar off eBay for under £50. Perhaps couple one of those with a shotgun mic designed for a DSLR like a Rode VideoMic would be helpful. You can always relist them when you’re done. Audacity is an open source DAW that has an audio spectrogram view. If you import the recordings to your computer and play with filters and eq in Audacity you may find that by listening back a few times through decent headphones or speakers you’ll more naturally have a ah-ha! Moment. Anyway, just an idea rather too late in the evening! 1 Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 14 Author Share Posted March 14 hey thankyou for taking the time for the detailed answer . and yes it may be bleeding through from the boot ( or hatch in this case )what i will try first before abything is stuff the area full of foam cushions and see if thst changes anything ! 1 Quote Link to comment Share on other sites More sharing options...
plumster Posted March 18 Share Posted March 18 (edited) When I completely stripped the inside of mine I replaced the black sticky stuff with stick on mats, in more places than the original factory stuff... But, to be honest with a stainless exhaust fitted I don't think it makes a lot of difference. I do wonder where the voices are coming from when I come off the motorway..... its usually the radio that I haven't been able to hear 😄 Edited March 18 by plumster 1 1 Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 18 Author Share Posted March 18 yeah the stainless exhaust would not be an option for me . im aiming for quietness all round . roadnoise on one of my cavs has decreased significantly since fitting some uniroyals . very soft tread. and also trying a curved exhaust tip seems to make a small difference too . just looking for some foam to try the next experiment with ! Quote Link to comment Share on other sites More sharing options...
Trooker Posted March 18 Share Posted March 18 (edited) I suspect that foam will do no good at all, even high density acoustic foam as it does nothing for the lower frequencies. In fact it may be interpreted by your ears as sounding worse because if the higher frequencies I.e. 800Hz+ are absorbed/dampened then it can feel as if the background bass sounds are louder when there’s less treble noises around. You may be experiencing this phenomenon already with your sound mat everywhere. What does the stereo sound like when you’re sat still with the engine off? Does the bass tend to feel a bit boomy? If you still want to experiment with absorption something like Rockwool semi rigid would be better behind your back seat https://insulation4less.co.uk/products/rockwool-rwa45-1200mm-x-600mm?variant=31690154704949 however if we go back to your original concerns it’s actually about panels resonating so best to stop that happening in the first place hence weird bits of roofing felt & tar melted onto the inside of car doors to stop the whole panel becoming a large narrow band ‘speaker’ Your repairs and uniform coats underneath isn’t stopping the resonance like the rectangular irregular patches of bitumen or whatever it was that appeared random but stopped waves building up across the panels. Just a few thoughts 😊 Edited March 18 by Trooker 1 Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 19 Author Share Posted March 19 with the car parked with engine off the stereo sounds great . nice smooth bass from the rear ones (6x4) but the bass is cancelled out once the engine is started or you are driving which i was thinking low frequency resonance reacting /cancelling the bass in the music. Quote Link to comment Share on other sites More sharing options...
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