924Board.org

[Scorpio]

What are key areas to focus the sound dampening material in?.



im using a mixture of products including

http://www.secondskinaudio.com/viewproduct.php?id_product=355#tab5

Second skins- Damplifier pro on both sides of the firewall with

Thermal block over the damplifier pro on the engine side

Damplifier pro throughout the car including floor, door panels..behind rear speaker panels, above and behind rear wheen arches..

Accoustic foam on the floor with extra thin layer of felt

Will add around 10-15kg all up...but should be a very comfortable ride.

Any specific areas that need more sound deadening?

eg exhaust drone...roof....rear boot etc?
_________________
1979 NA
MS1..EFI..
GARRETT T25 TURBO
BILSTEIN SHOCKS
GT BASED CUSTOM BODYKIT

Brisbane , Australia
Think mean think fast
all youll see is
my Porsches Arse!!!

[leadfoot]

Wouldn't bother with the engine side covering, just use it under the dash

You basically have three areas when talking noise into the drivers compartment...
engine - firewall primarily under dash
road - comes through the floor
exhaust - through the trans area and back compartment, around rear wheel wells.
work out whats loudest from what your hearing and isolate from there.
Jaycar also had some pretty good acoustic noise mat IIRC

Energy in the form of sound waves are destroyed (in this case a good thing) by density and variation of material. There are other methods/ slat panels, resonators etc but are often space dependand for low frequencies.
The more varied types of density and material i.e layers of rubber/wood/plastic/fiberglass...in different thicknesses with consume this energy far more effectively
So the rear carpet/rubber/acoustic treatment material/bitumen actually does a fairly good job of this in the first place.
There are other approaches but they often require space... resonators are another approach, if you wanted to you could build a false floor above the rear compartment angling back from the lock to the back seat.
Line this with your foam and it would serve to trap broad spectrum frqeuncies.
I like the mat approach because if you make it as a removable item it won't affect you on the track.

If you're trying to reduce the noise of a modified exhaust the best way is to use the 2 x baffled muffler and a resonator setup similar to the N/A,
when I first went to the stainless 2.5" system with a single straight through muffler it put out nearly 122db... concert sound stuff...

A good starting point for those that have I phones is to get the real time analyser app, or if you want to go old scool pc a real time analyser and a microphone.
Sit in the car and measure the noise frequencies recorded. Then go to
http://www.sengpielaudio.com/calculator-RT60Coeff.htm and select the material of choice based on the frequency and the coefficent being as closest to 1 as possible.
i.e if I had a problem of 4000Hz I could use .99 2" thick fiberglass but I certainly wouldn't choose .02 marble tile as my material.
and yes for those that noticed the acoustic tiles ... yes the one's with the contours on them would knock out all those unwanted noises provided you lined them on the roof of your car.
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[Scorpio]

Interesting stuff stu I wanted the engine side damper also as a heat shield as there is alot of wiring etc on the firewall also don't want heat coming through MLB angled acoustic tiles on the roof why the roof ? Are you talking anechoic chamber style ? Wouldn't that just stop echo within the car ? Don't see myself doing a slanted floor, just about to download that app, this message has been typed on my new I phone four ! It's sweet
_________________
1979 NA
MS1..EFI..
GARRETT T25 TURBO
BILSTEIN SHOCKS
GT BASED CUSTOM BODYKIT

Brisbane , Australia
Think mean think fast
all youll see is
my Porsches Arse!!!

[leadfoot]

frigging I phones...bah I says....
when they can fetch me a coffee and a paper on a sunday morning THEN i'll be impressed....
haha
probably just me changing gears by listening to the engine... got shift light??

the contoured foam can be used in many more applications, anechoic chambers are for recording studios and testing labs... dual reduction of absorbtion and resonance trapping like in the pletes of heavy drapes (i.e helmholtz / muffler design) there's also diffusion technicque to stop the standing waves principal or bouncing around between parallel walls, the reverse of speaker design, which are design to help promote this effect to boost speaker diaphragm excursion.
don't you just love physics... this is old school stuff with the event of line arrays it's all changed to the point you need to be a friggin scientist to operate a sound system...
server rooms, home theatres, noisy environments etc are also examples, they can trap and reflect sound waves, the acoustic foam you're probably using is similar to stuff used in speaker cabinets or wall cavities and is used for it's density/absorbative coefficient properties.
The addition of this to your roof is because it is the largest chamber in the car, and all the frequencies you're hearing are bouncing around in it, reduce these flying around and you won't hear them, also placing them on the front and back glass defeats the purpose of having eyes....
P.S yes the ceramic compound you were looking at will help reduce firewall temps, ducting the air properly through the engine bay will also do the same thing. Just remember if you stop the heat from entering one part it will inevatably find it's way into the next part along.
A friend once removed an inch of the top lip of the firewall allowing air to flow over the top of the motor and out past the windshield and claimed he got a 15 degree underhood temp reduction from this. food for thought.
Stu
_________________
1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

[ideola]

A surprising amount of noise is allowed into the cockpit area by the torque tube tunnel, and particularly the hole for the shift lever. All the little bits that Porsche put there make a BIG difference in noise ingress, including the rubber boot that fits under the leather boot.
_________________
erstwhile owner of just about every 924 variant ever made

[Scorpio]

[Smoothie]

I drove mine a bit without the rear (boot) carpet, rug, and sound deadener in place during the bodywork-repaint saga. I can tell you that stupid levels of transaxle noise pass through there with inadequate sound insulation..
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox