Great post Acolyte! Or is that -Acolyte? I should have trademarked the leading hyphen...
Yes, I agree about the imaging as you describe with the speakers pointing downwards - it can work well, as it may equalise the distance for the left & right speakers from the driver's seat. Also, the stuffing behind the speakers has the effect of making the speakers behave as if in a smaller enclosure - which in the hollow space of the dashboard is probably what you want.
Smaller enclosure, not ported = less volume, that would explain why my 12" sub in a very small sealed box was not very successful - that and the fact the 164's boot is rather well sealed. Luckily my 10" Carbon-Fibre sub is dual-voice-coil and the boot of the Uno is far from sealed...
Now, soundproofing. Where to begin?
The basic theory is sound-deadening, where a material is added to the sheet steel to absorb vibrations. A thin bitumen-type material will attenuate high-frequency sounds (in theory) because it changes the resonant frequency of the steel to which it is applied. A thick, soft material will reduce low-frequency noise, effectively creating a barrier (like the earmuffs when you use a lawnmower). The best technique is usually a sandwich, with the thin material against the steel and then overlayed with the thicker, softer material.
If we start by considering the soundproofing installed by FIAT... (it won't take long)
- On the more deluxe models (e.g. 70SL) there is a rectangle of bitumen self-adhesive sheet applied to the inside of the door skin. This does not need to cover the whole area. The main effect is that if you flick the outside of the door with your finger, there is no tinny 'clang'. Closing the door therefore sounds better.
- On all models, there are similar squares in the floorpan, though some Mk1 base models do not have squares in the rear footwells. These bitumen squares are then overlayed with a green fluffy underlay (looks like recycled clothes).
- Similar fluffy material is applied to the firewall and front floor, but with a thick bitumen layer on the outside. I think the idea of this is to provide a 'barrier', though I am surprised that the bitumen is not against the steel (probably arranged this way for durability reasons).
- On the metalwork that forms the rear strut towers, there are specially-shaped bitumen sheets. This is interesting because so far, we only saw the bitumen applied to large, flat areas which tend to 'ring' like a bell. You would think that small, curved sections of steel would not resonate as easily. Yet, FIAT have obviously spent the money to install sound-deadening there (also in the spare wheel housing).
- The underside of the bonnet, on most models apart from early Mk1 base models, has a black fibrous pad similar to the firewall on all models (inside the engine compartment) which on Turbo models is foil-covered to reduce heat transfer. The sound insulation attached to the bonnet is probably not that important for noise levels inside the car.
And, that's about it.
So, where do you start? Invest in four or five large 'squares' (about 50cmx50cm) of the self-adhesive bitumen. Car stereo shops sell it. I think it's about $16/sheet (65 Rand?) Not cheap - so I came up with a cheaper solution - 'underseal' in a can, to 'glue' offcuts of flooring vinyl in place. It works nearly as well and costs only a quarter the price...
Improve the deadening in the doors (it's probably fallen off anyway), fit a foam sheet to improve the 'seal' of the door trim card.
Take out the carpet. You'll see a large number of oval/round holes in the inner sills, extending up to the door hinge area and across the back of the rear footwells in front of the fuel tank. Sometimes, in basic Uno models, you can hear fuel sloshing around when you come to a stop in traffic, so there must also be quite a bit of road noise getting though into the floor. Solve this by covering all the oval/round holes with the bitumen sheet (maybe after spraying in some anti-rust wax!) - a hot air gun is essential to mould the sheeting into place.
Under the carpet, use fairly dense underlay material if you can. Car upholstery shops sell this. Unlike FIAT, you will be able to cover the whole floor area up to the seat rails. It is not expensive (1.8m x 1m will be about $20 - R80). Local experience will tell whether the stuff will rot (and stink) if it gets wet. It is worth fixing any water leaks that you know of... My experience is that this underlay by itself is not terribly effective against noise but in conjunction with the bitumen deadening and sealed holes, it helps. It also gives the carpet a nice soft feel...
Inside the boot, there are more holes - which probably allow the sound from the large rear-quarter panels to get through. I think you should start with the material that FIAT applied and work outwards. That is, any flat areas like the boot floor should also be 'deadened' since they are obviously going to pick up vibrations from the suspension, the same as the strut towers. You may like to place some underlay under the boot floor/carpet.
I think that the roof would benefit from having some bitumen sheeting applied. The headlining tends to not keep intimate contact with the roof as the years go by. I'm sure when it was new, it was reasonably effective. Again, there are various holes in the metalwork which could be sealed up.
The heater chamber (under the windscreen) seems to be a big sounding-box to me. I think that lining it with bitumen sheeting (as standard in my 164) will possibly reduce resonance, though it may be more worthwhile to work on the actual bulkhead itself to reduce sound transfer from the engine bay. Again, the standard soundproofing is usually sagging away from the metalwork. And under the dashboard, where the top corners tend to fold back on themselves. Perhaps invest in some Ados contact glue and apply some underlay to any gaps.
The FIAT Stilo shows an interesting approach to reducing tyre noise. There is a furry, carpet-like material applied in the wheelarches! Yes, on the outside! I don't think this is necessarily a good idea for the Uno (though black carpet on the plastic wheelarch liner may be OK!) The space behind the liner could perhaps be deadened with some heavy application of the underseal in a can mentioned before. Foam or underlay would not be wise behind the liner because of the obvious corrosion trap.
Once you start soundproofing, you may become aware of particular 'noise areas' that warrant further attention. For example, in my Uno it sounds like the passenger's door is slightly open at all times. This will lead you to holes in the weather-stripping, loosely-fitting windows, gaps around wing mirrors etc. which can all be sealed up. Sometimes it helps to remove the weatherstripping and tap the spot-welded flange outwards, evenly with a mallet, to make the seal tighter.
Plus of course you will need to eradicate various squeaks and rattles from the seats (grease the rails) and the dashboard - take apart and at the fixtures apply silicone grease, pack in foam rubber, or possibly do what the more up-market manufacturers do and install 'squeak and rattle' tape. This is basically a thin fibrous tape, usually black cloth, applied along the edges of plastic pieces to avoid grinding/creaking contact. Masking tape will do in a pinch.
Right, there's a few of my thoughts
Also consider buying more expensive tyres next time you are up for replacements, though I am not familiar with 'Nexen' and maybe they are already top-stuff?... I know that the big manufacturers (e.g. Michelin) spend a lot on reducing noise, and it makes quite a difference. The profile is working against you, though... ever wondered why luxury cars usually have 60-profile tyres?
-Alex
