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I wonder if anyone has added sound deadening to interior of their cars, while like the Lotus music, I would like to reduce it a bit. Perhaps I can put something under the carpet in the footwell, Any advice would be welcome.

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I replaced the plastic sheeting behind the door cards on my S3 with Dynamat, a couple of years ago,  it made a little bit of difference but not as much as I was expecting. I think you really have to do the entire cabin from top to bottom to get a substantial reduction in road noise.


Normally Aspirated - and lovin' it!

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I tend to remove any sound deadening material on my classics. The more dramatic the better for me.

Lotus can leak (as do many older cars), so ideally pick something that is easily removable or find a waterproof product. 

The Excel has rubber, backed with foam, that was stuck to the floor-pan at the factory. Nightmare if water ingresses. 

Woolies and many others offer a variety of options. www.woolies-trim.co.uk 

Justin 

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I'm planning to use a self-adhesive open-cell acoustic foam followed by a self-adhesive visco-elastic membrane (Tecsound SY50 ALU).  Basically a modern version of what Lotus fitted to the Excel.  The main drawback is weight.  Colin is right though - you really need to do the entire cabin.

Pete

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I thought sound deadening like dynamat worked by changing the reasonant frequency of the panels by adding mass. So some panels need it and some don't 

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I'm going the whole hog and soundproofing every inner surface with soundproofing mat from 

https://www.nkgroup.co.uk/

It is thin, flexible, easy to cut and very sticky

They also door thicker material for floor pans and another for under bonnet surface

Brian

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I’ve done a lot of research on sound proofing as I have a Land Rover defender. I also studied acoustics as part of my degree. You need. To use a combination of materials. Dynamat types help to stop panels resonating and acting like a drum as someone else said adding mass. Foam cell like materials help to kill road noise Ie sound waves. Good door seals etc will also help. Just plastering a car in layers of dynamat is not the best. You need to do it scientifically as it works and will save materials. 

Thete are some hints on the singer 911 build videos, private jet builds are a good source of info as well. 

One of the most effective materials I used on the defender was a sticky backed closed cell foam that is used on commercial generator housings. Another good product is lizard skin it’s made up of paint and micro glass beads. You can make your own with house paint and beads from model aircraft building,  spray it on. One mix is 80% paint 20% beads for sound suppression. The other is 80% beads 20% paint, the glass beads dissipate heat. 

Hope this helps, it’s an area I’m really into. 

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Interesting Chris!

Can you clarify whether closed cell foam is as effective as open cell foam at suppressing sound waves? I used a layer of closed cell foam with a layer of mass loaded vinyl on my bulkhead and transmission tunnel, but have since read that, although waterproof, closed cell is not so effective.

The major issue I have is in suppressing noise - e.g. exhaust resonance - at source, as no amount of sound deadening will deal with this. I've had some success in lining the chassis with heatporoof sound deadener where it sits next to the exhaust, as I believe that, being relatively thin sheet steel, it can resonate to the frequency of the exhaust. My next trick is to attach lead weights to different parts of the exhaust to reduce a resonant frequenciy at around 2500rpm (I use the Lotusbits stainless exhaust system and manifold). I'm also going to renew the air intake hose with a silicon hose and try to line it with a thin layer of foam rubber - as I believe was oroiginally done at the factory - to reduce intake roar.

Cheers, Richard

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Hi 

I think the thing with closed cell foam is that it’s more ridged therefore transmitting more noise. But of course it’s waterproof, you really need to use a combination of products in different areas. There is a lot of smoke and mirrors in soundproofing. Basically hard surfaces act like a drum skin transmitting  sound waves. Mass stops that, ie shifts it’s frequency. Soft foams etc change what the air/ sound waves have to move through therefore killing some frequency. In a vehicle there are obviously extra complications from wheel/ mechanical noise. Also the design of a vehicle some act like a funnel driving sound into the vehicle. Modern designs try to overcome that. 

ill be honest with you never looked into exhaust resonance. But that would depend  on material used for exhaust hence different sounds and also the way the gases flow through the pipe work. Hence the valves on Aston’s to make it sound sporty etc... Same with the intake.

You have got me thinking now! I’m really into this part of vehicles. 

Just read up closed cell foam is better at absorbing low frequency sound. 

 

 

 

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Amateurs built the Ark

Professionals built the Titanic

"I haven't ridden in cars pulled by cows before" "Bullocks, Mr.Belcher" "No, I haven't, honestly"

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This is an interesting thread not least because lotus was experimenting with anti-noise in the early 80's, i think, to quieten things down but not adding extra weight. the research got abandoned since the antinoise would be played through the car stereo and canceling out the sound wave at your eardrum by having a sound wave from the speaker coincide at your ear with a sound wave from the engine was very, very difficult. you could of course just where noise cancelling headphones. 

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Regards the playing through the stereo, I have a feeling there are a few manufacturers who do this, Bose do it.


Amateurs built the Ark

Professionals built the Titanic

"I haven't ridden in cars pulled by cows before" "Bullocks, Mr.Belcher" "No, I haven't, honestly"

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My wife's 2015 Honda Accord uses the standard sound system to generate cancelling waves, my rather sensitive ears can now and then detect it at work. Chris makes some very worthwhile points, to which may I chime in agreement on the value in decoupling sound transmission paths. Some years back a well informed mate quite successfully advised another in the acoustic isolation of his man-cave, largely by way of suspending the finished interior wall rather than tacking on to structure in the conventional manner. I'd stroll up alongside the place, fashionably late for no particular reason, hearing just about nothing of the music and whatnot going on within. With intent to lay on a respectable effort in noise mitigation as my Esprit is completed it seems both simple mass dampening ( eg Dynamat ) and mass loaded vinyl can be used in stacked form, where the MLV carries one or more layer of dampener in partial suspension from the structure. There is a great deal of fertile ground to plow in Lotus noise control as even the backbone chassis panels are themselves capable of remarkable resonance. Yet to hear of anyone trying dampener on the chassis but I shall likely have a go.

Cheers   

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I've used a visco-elastic membrane and open-cell acoustic foam on my chassis - where the body fits closely.  Only just got the body back on, so cannot comment on how effective it is!

This is the foil-backed membrane - Tecsound SY50 ALU

 

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Pete

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