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Sound deadening

Discussion in 'Tuning, Styling and Performance.' started by philchave, Aug 11, 2017.

  1. philchave

    philchave Senior Member

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    Evening to you.
    For 9 years I had an S280 (2001) petrol which had double glazing and sound deadening that would rival a sound studio.
    I fancied a change to something younger, so I swapped if for an S320 CDI (2007).
    It's still very quiet, but I'm guessing, as it's a diesel, the engine is naturally noisier anyway.
    The sound deadening is not as good in this model.

    I was pricing up some sound deadening quilt at Halfords (like the stuff we used to glue to the bonnet and stuff in the doors of our Fords in the old days), when I thought better of it and decided to ask on the forums first.

    Any of you have a great way to make the car a little, or a lot quieter? Have you done this before? What worked best? Is there a kit available that would make the noise situation better?
    I plan on driving it, so leaving it in the garage is not an option, ok? :)
    Thank you very much for any advice
    phil
     
  2. Frosty149

    Frosty149 Senior Member

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    Someone is gonna say earplugs!
    But you've peeked my curiosity and brought back some memories!
    Tyre choice can have a profound impact on road noise btw:rolleyes::)
     
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  3. Craiglxviii

    Craiglxviii Senior Member

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    NVH (Noise, Vibration & Harshness) is a really complex subject and just adding extra hood insulation won't work. For patrol ==> diesel, the most difference is felt through the dash bulkhead and so the best thing to do is to apply heavy/ dense material there. Automakers use bitumen sheet as it's rather dense.

    That's all rather hard to do at home, I know, what I'm getting at is that just sticking a piece of Halfords quilt under the hood won't do much for what you want it to.
     
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  4. umblecumbuz

    umblecumbuz Senior Member

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    As Craig. And the principle of diminishing returns comes into play.

    As we all know - add 200mm roof insulation to your house and you get a big improvement in heat loss. Add another 200mm, and the additional improvement is much smaller. Etc.

    Sometimes, especially on the bulkhead/firewall area, a small hole will let in a large amount of sound. Worth checking all bulkhead areas where wires, cables etc pass through. Even a cracked or misplaced grommet will allow plenty of noise to enter the cab.

    I took great pains to sound deaden our family runabout - seats out, carpets up, door cards off - and it made a noticeable difference. Problem is, I now have tyre roar, and can'tget rid of it.
     
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  5. Craiglxviii

    Craiglxviii Senior Member

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    You can reduce it, by adding insulation to the wheel arch liners...
     
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  6. C350Carl

    C350Carl Senior Member

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    Having done this on 3 previous cars (granted not a Mercedes but the process is the same) I can tell you that unless you are prepared to spend around £750 - £1k AND have the correct trim tools to remove the trim, you will not get the effect you desire.

    There is no wonder one piece material solution. If you look at how something like an S Class is soundproofed you will see it is made up of 2-3 layers of material. Usually a bitumen type material (as Craig has said), followed by acoustic matting and, depending on location in the vehicle chassis, some sort of foam. Then you have different glass, rubber seals around the doors etc etc.

    NVH is hard to stop and you also add weight to the vehicle in doing so.

    I will link the stuff i have used in the past. I haven't looked into it for a while so don't take it as this is the best. When i did it a few years ago it was one of the best at the time.

    You start off with something like this which you apply to all the doors and any large panels in the car you can get access to. I did this on 3 different Octavia's (1 saloon and 2 estates) estate and I spent around £900 each time. I also used 4mm stuff not 2mm:

    https://www.silentcoat.co.uk/collections/silent-coat/products/silent-coat-2mm-mat-volume-pack

    When I did it I removed all the interior trim including seats, carpet, door trim, complete boot trim, pillar trim and roof lining. So the car was just a shell apart from the dash. Sounds daft given what I stripped out but it was too involved to remove.

    I then applied a layer of the damping mat to every metal surface. This stuff makes the panel sound like knocking on a piece of wood rather than metal. It's hard to describe without demonstrating but it reduces the vibrations through the vehicle.

    Once that was done I then added this stuff to all horizontal and vertical surfaces (using glue to hold in place) apart from the roof.

    http://store.secondskinaudio.com/lu...d-vinyl-closed-cell-foam-1-sheet-24x54-9sqft/

    After that I then added this to the rear 3/4 panels, doors where it would fit, under the carpet and under the rear seats. I also added it to as much as I could access behind the dash from removing the glove box, stereo and air vents.

    https://www.silentcoat.co.uk/collections/sound-absorber/products/silent-coat-absorber-35

    For the roof lining and places where the 35mm stuff wouldn't fit I used this which is identical except its 15mm thick rather than 35mm

    https://www.silentcoat.co.uk/collections/sound-absorber/products/silent-coat-absorber

    After that I refitted all the trim and moved to the engine bay and fitted this to the underside of the bonnet and as much of the bulkhead area as i could physically get at ( I did remove as much stuff from the engine as I could. I also removed the factory installed wheel arch liners on the outside of the car and fitted this before putting the liners back.

    https://www.silentcoat.co.uk/products/silent-coat-noise-buffler-20

    I never measured the difference so I can't tell you in decibels how much the noise was reduced. If i was to put an educated guess on it i would say it reduced the overall noise in the car by around 50-60%. In real terms it was a very noticeable improvement and was always commented on how quiet the car was (especially for a Skoda! :D) when I had any passengers who didn't know what i had done.

    Each time the process took me 3 lonnnng days (about 12hrs a day) to complete. Probably because I was being overly cautious. It also added about 120-150kg of weight to the vehicle. Although I never had a noticeable reduction in fuel consumption. At best probably lost 1-2mpg but it's not something i could quantify given too many variables of traffic, weather, road conditions etc etc.

    But unless you are prepared to do this yourself (or pay someone the labour rate to do it) then you won't achieve a dramatic effect.

    If you want to reduce the NVH so that you can notice it then your best bet is the boot area, wheel arches and under the rear seat bench.

    I may still have some pictures somewhere of when I did this. I will see if I can dig them out and if I do find them I'll post up.
     
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  7. Craiglxviii

    Craiglxviii Senior Member

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    I'm speaking with a little authority in this area as I'm currently doing a systems analysis of NVH performance & interactions between parts. Cars (road vehicles) have:

    Two NVH functions (engine, road).
    Four NVH characteristics (absorption, isolation, damping, sealing).

    Different materials are used in each area for various performance interactions. Heavy layer felt in the carpet for example increases absorption, polystyrene blocks under the carpet to prevent your feet touching the floor metal. Baffles along the inner wing prevent booming. Bitumen meltsheets increase damping performance. Foam strip aids in sealing.

    What Carl did was very belt & braces (and ofc no holds barred open wallet vs OEM :D) and it basically added absorbtion and damping to all drumming (metal skin) surfaces. What no one can do, without a test rig or full vehicle CAD and FEA, is to determine which panels give the most NVH contribution (and at what engine speed, road speed, road type...)

    Here's an interesting one for you. The A class does away with the hood insulator altogether in favour of two constrained- layer meltsheets. These are bitumen pads with a thick aluminium foil layer on the outside face; vibrations enter, hit the aluminium: air boundary and bounce back, almost entirely cancelling out the incoming vibration (think of two opposing sine waves merging to form zero).
     
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  8. C350Carl

    C350Carl Senior Member

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    If you're going to do something you may as well do it properly. Go big or go home as they say. :D
     
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  9. Craiglxviii

    Craiglxviii Senior Member

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    :D

    When I pulled out the seat squabs on the 215 I was surprised to see heavy layer foam under everything- pretty much in the way you've described.
     
  10. 00slk

    00slk Senior Member

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    Years ago I did something similar to a Triumph Herald, completely stripped the interior including the dash and sound proofed the bulkhead, floors and inside the doors........Why?? Because I wanted the car to be as quiet as the 2 year old Rolls Royce Silver Shadow I had the use off for 2 weeks. Once I had glued carpet felt to the bulkhead and entire floor pan I went to my local upholsterer to get the best sound deadening carpet to fit to a car. It was a real mission to fit, it was very thick and firm to spread into tight corners but I got there in the end. The wiring behind the dash was unable to go back on the soft clips so had to cable tie most of it, I then had to find longer bolts so the seats could be bolted back in. I used good door opening rubbers from a boot surround from a modern car so the Herald doors closed solidly.
    The end result was quite remarkable, I had eliminated most of the door rattles associated with this type of screwed together car and the road noise was a lot quieter too, especially from the engine compartment :cool:
    Would I do it again........Bliming heck yer :D
    Though it was never as quiet as the Shadow :(

    Just thought I would add this piece of useless past activities :p
     
  11. OP
    philchave

    philchave Senior Member

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    Thank you all very much for all these great ideas, especially C350Carl whose post must have taken quite some time to put together. I am grateful to you all.
     
  12. umblecumbuz

    umblecumbuz Senior Member

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    All great info!

    So, what do I insulate the plastic wheel arch liners with?
    I often pressure wash the undersde of my cars including the wheel arches, and the shopping trolley I mentioned earlier still has dust on the top of the plastic wheel arch liners (the opposite face to the wheels), which suggests that I don't need to be too worried about any sound deadening material getting wet.

    What's the best? I'd like to do it as an experiment.
     
  13. Craiglxviii

    Craiglxviii Senior Member

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    OEMs use something that looks for all the world like a piece of the cheapest sleeping bag you've ever seen. You don't need to cover the whole thing, either, you only need a piece around 6 x 8" located near the top of the arch. It's for sound absorption, so an sort of sticky-backed fibrous or heavy felt material will do the job.
     
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  14. C350Carl

    C350Carl Senior Member

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    Or use the stuff I linked further up which is also used in the engine.

    Because I’m OCD I covered the same area that the wheel arch liner covered.

    But as Craig said you probably wouldn’t need to do the whole arch.

    However from experience I would say do from the base of the wheel arch nearest to the interior of the car to about a quarter of the way past the top of the wheel arch.

    You’re trying to block out road noise in the wheel arch as well as NVH. So you need to block it from that portion as that’s the nearest to the cabin.

    If you have a look at the wheel arch lining on something like an S-Class you’ll normally see that portion has a felt type lining to the wheel arch and the front portion is plain plastic, if it’s not all completely felt. Never actually looked at an S Class wheel arch. But on the ŠKODA Superb that’s how they used to do it and that does have very good soundproofing from the factory.

    Easiest way to explain it is that the sound sort of travels the same way you expect water spray to come off the wheels. Bit of a crude way to explain it but that’s sort of how the noise travels.
     
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  15. C350Carl

    C350Carl Senior Member

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    As an example. This was the wheel arch liner on my vRS. It was actually the wheel arch liner from the L&K Octavia (top of the range Octavia in terms of standard kit and comfort)

    At the time of taking these I was doing a tutorial for changing the turbo discharge pipe.

    But as you can see around 3/4 of this is the fabric material over the actual plastic liner. However I placed the silent coat noise buffler stuff behind it (hadn’t done it at the time of taking the pics as I was still modifying the car power wise).

    [​IMG]

    [​IMG]

    [​IMG]
     
  16. Craiglxviii

    Craiglxviii Senior Member

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    I wish I could post what I'm doing at the moment but it's all under NDA. Shame really as there's a number of very helpful diagrams.

    Imagine a simplified plan view of the car. Draw a line from the front and rear edges of each wheelarch to the centre point of the driver's seat base. You'll end up with a squashed X shape. That is the pathform that radiated tyre noise takes (well, to each seat, but it's the driver we're primarily concerned with). Now, imagine that in three dimensions so you get a height vector as well as length and breadth. The portion of the wheelarch liner that gets felt pads is that which, when viewed from the hub location, points towards the driver's head. So, the location can (and dependent on OEM, may do) change dependent on RHD/ LHD and also model spec/ grade- VAG for instance have different levels of NVH pack applied dependent on grade. The top and bottom grade Golfs are something like 8dB average apart.

    Now take your view of the driver's seat from the hub and widen your view angle to cover both front seat headrests. Where that angle intersects the plastic wheelarch liner (wheelhouse) is where the felt pad needs to be applied. NB this is for absorption not damping, so we're after felt/ carpet and not dense material).

    Now go to the wheelarch itself, that is to say the body metal inside of the plastic wheelhouse we have just NVH'd up to the nines. This has an issue whereby vibrations from the engine, and from the tyres rolling over the road, can set up and cause all sorts of nasty harmonics. These can be perceived as sound or vibration in various body panels- side doors are notorious for picking this up due to their large drumming surface. So we have to either damp out (easy) or prevent (hard) standing harmonics from forming in those arches. Easiest way to do this is to fit bitumen pads usually on top/ inside-facing of the arch. The precise location will vary model to model, engine to engine (and tyre to tyre too, which is why changing tyres can have such a dramatic effect).
     
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  17. C350Carl

    C350Carl Senior Member

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    So basically what I said for positioning :p
     
  18. Craiglxviii

    Craiglxviii Senior Member

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    Kind of. Just "not quite" enough to be different to what you said :p
     
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  19. umblecumbuz

    umblecumbuz Senior Member

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    Armed with all that info above I will experiment.
    I have a bunch of heavyish bitumen pads (actually Norwegian roofing shingles made of bitumen and strongly self-adhesive).
    With a heat gun they will deform to more or less any shape you apply them to.
    Will report back when done.
     
  20. Craiglxviii

    Craiglxviii Senior Member

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    Those are pretty much bang on the money for what the carmakers use for damping on body metal.

    For absorption of sound under the plastic wheelhouse, you'd need something like carpet.
     

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