I'm not quite familiar with the science and mathematics of waves a whatnot, particularly when it comes to sound. ( Some of you may have noticed, I'm nearly deaf! )
But I was wondering if anyone had an idea of how loud, in some measured form, the exhuast is on our cars? With a 3" straightback?
You see, since I still have not put my carpet and much of my interior back, (from the SwapTober Project) I'd like to throw down some sounding foam ( I work for Grainger, remember. ) so that I could run a nasty exhaust, yet still have a conversation with my passenger, or listen to music at decent
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*snicker* decibles. (Pun intended.)
But my stock exhaust with the muffler chopped off and a cherry bomb clamped on, an intercooler wedged against the firewall, desnorkified and K&N filter is still quieter inside the cabin than my parents 96 Mazda Protege, competely stock.
My guess would be somewhere in the low 80's max for decibels with a rude, loud exhaust. Some of the auto reviewers list bB for rtested cars at cruising speeds, around 70 mostly. Remember is a log scale so 80 is 10 times louder than 70.
I have a dB meter here at work for measuring machine noise so as to monitor safety. They are fairly cheap.
If you want to attenuate noise, the best way is with dual-density materials. Both heavy and light. By that, I mean heavy mat applied to the big metal panels (stuff like Dynamat). High density materials attenuate low rumble noise like road noise and low exhaust burble. Luxury cars use lots of this which is why the road rumble is so well damped.
High frequency noise is attenuated by low density materials like foams.
If you pull up the carpet on many cars you'll find dual-density stuff under there, a heavy rubber layer which is loaded with barium sulfate to make it heavy, bonded to a foam which makes the carpet soft as a bonus. I suspect you can find this material but it might be expensive.
In the old days they used tar-based rollstock stuff which was stuck to the metal panels. This stuff cracked and caused rust and has been replaced by plastics. I have had many a headache from pulling up that old tar stuff with a heat gun and scraper, in confined spaces.
professor wrote:In the old days they used tar-based rollstock stuff which was stuck to the metal panels. This stuff cracked and caused rust and has been replaced by plastics. I have had many a headache from pulling up that old tar stuff with a heat gun and scraper, in confined spaces.
are you talking about the nuclear gorilla tar stuff found in mk1 vw's and the like? that stuff is horrible.
professor wrote:... I have had many a headache from pulling up that old tar stuff with a heat gun and scraper, in confined spaces.
Me too, Ha ha.
I just put a Helix 3" stainless turbo back on my '91 SS and its pertty loud, its got no cats, a center glasspack resonator and a big glasspack can at the rear... you could drop a tennis ball in at the bellmouth and it would shoot out the end (Hmm... sounds fun, now how could Irig that up, lol).
At steady freeway cruise (75mph) there is a bit of a low drone but you dont have to talk loud to get over it. Steep uphill or heavy throttle bring out the monster. Truthfully its just a hair to loud for me, I may cut off the silly 4 1/2" tip and weld on a 2 1/2"... dont know yet.
On the up side... the tone of the pipe is simply beautiful, very low and a great growl. Power is up across the board, turbo spools faster and the engine breaths better in the top, widened the useable power band quite a bit. And seems to have picked up a mile or two per gallon in fuel economy.
Gary
No matter how broke I am... I always seem to find two cents.
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) so that I could run a nasty exhaust, yet still have a conversation with my passenger, or listen to music at decent 
