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I'm not sure what the test and instrument setup was back in 1989 when they got 71dB. For my own rough reference, I just held my IPhone at chest level near me, and used the same IPhone, same location, to get the before and after readings for swapping to the new wheels/tires. The delta was a about 10dB quieter at 70mph, and this, to my ears, represented a big improvement in comfort for me.
Though, it is still not yet 71 dB. I'm inclined to go after the other rubber bits first and maybe save the option of installing sound dampening if I still need it after.
I'm not sure what the test and instrument setup was back in 1989 when they got 71dB. For my own rough reference, I just held my IPhone at chest level near me, and used the same IPhone, same location, to get the before and after readings for swapping to the new wheels/tires. The delta was a about 10dB quieter at 70mph, and this, to my ears, represented a big improvement in comfort for me.
Though, it is still not yet 71 dB. I'm inclined to go after the other rubber bits first and maybe save the option of installing sound dampening if I still need it after.
From your avatar, it looks to me like you have much larger than the 16" wheels that came stock. Wider tires and/or tires with thinner sidewalls tend to be louder. If you are trying to compare your car to the stock test, you need to be running 225/50-16 tires on all four corners.
The avatar shows my '88 with the new wheels /tires. The Panamera 18s with the Ventus v12s are much much quieter (~10dB) than the stock 16s with Yoko ES100 (rears@50%) that I recently had on it. I really love the new wheels. I like the look of CIIIs too.
My 87 S4 still has the stock 16s with some brand new GY Eagles that came with it and they are a lot noisier than the Panamera 18s/v12 combo too. (I'll be looking for better tires/wheels for the '87 once I finish sorting it out)
I wonder if the slightly higher mass of the 18s helps noise, or maybe it's all in the tire selection/condition.
It's interesting that for you the lower profile tires are actually quieter. What PSI are the 225/50-16's pumped up to? Could it be that the insane 44psi spec for the rear tires was really for reducing interior noise?
I started out the 18s at 36 psi all-around because they are wider 8J & 9J. Surprisingly, this has also, in addition to quieter, proven to be a softer and more comfortable ride than the 16s at stock pressure.
Update: My average decibels on my '88 (per I-Phone app Decibel Ultra, held chest level) are now about 55db idle, 70db @50mph traffic, and about 75db@ 70mph traffic, on an average road (not new asphalt). I know the I-Phone is not the best instrument to use, but as a baseline the noise was mid-80'sdB on highway!!
I want to thank you for posting this App and the information in here.
I downloaded it and tested how damn loud my car is. Bald tires and everything else and the noise level was bouncing between 82 and 88. I'll be getting new tires next week so I'll report back how much that drops the sound.
Another test tonight:
(Disclaimer - again, this is just using an I-Phone App, subject to some variables and just for a rough reference)
To see the effect of mileage on noise. I took the noisy 16s with ES100s and put them on my '87, which has 100k less miles that the '88. The '88 has about 168K and the '87 about 71K miles; however, the cars were built in the factory within about 5 months of each other, and both are basically stock with no mods, and no suspension rebuilds/refresh other than new Boge shocks for the '88).
'87 w/ noisy wheels and tires:
Idle (no tire noise) 60dB vs 55dB for '88
50 mph w/ traffic 80dB vs. 83dB for '88
70 mph with traffic 83dB vs. 85 db for '88
The '87 was about 5dB noisier at idle than the '88, even though it has less mileage. I attribute this to the refreshing I've been doing on the '88's engine, which is now silky smooth at idle and at speed, and the 88 has relatively newer motor mounts. The '88 engine is quieter in the cabin, but this is much less of a factor once at road speed, when road noise is the more dominant factor.
At road speeds, the '87, with 100k less miles than the '88, was about 2-3 dB quieter with the same wheels/tires. Maybe this is the effect of mileage on the cars noise level (rubber bits, insulation, etc.). This was not a big difference in noise, but still apparent.
So, considering the same tires and wheels, it appears mileage does have an impact, but not as big as I thought it would be.
I sit around 80-83Db..70mph ...measured with the Android app....X pipe..high flow cats..and RMB...dynamat in the doors and rear wheel arches stuffed. Also have a noisy wheel bearing i think.
Thats also on a grooved concrete freeway with these on...
We are all using the 'A' scale on our audiometers, right?
IIRC, apparent sound pressure doubles every 3dB on the "A" scale. So saying that "I sit around 80-83Db..70mph" is a pretty big range. Same applies to the differences between the OP's early and late cars with different mileage, with 2-5dB difference measured.
My car is about the quietest stock 928 I've driven in. Seems like all my 928 buds have RMB's, x-pipes, headers, big noisy tires, etc. So maybe my references are skewed a little. Guess I need to try the iPhone app so we are comparing Apples to Apples, so to speak...
I'm running Yokohama AVS Sports on 17" wheels, and they're much, much quieter than previous Bridgestones.
I need to replace driver door seal which is really only source of irritating noise as it's right by my ear! It's the original, and I can see the window is not a great fit at the top rear where the seal has sort if widened out whereas it's tight fit to glass on passenger side
BMW dealers sold a great rubber care product (looked like vasolene) you'd work it into the door seals working the flat profile back to shape and it would make a good seal again. Not sure if Porsche offers the same product but it really does restore them.
If your noise is tire related a cheap noise insulation material:
My tires are loud too and new, i cut in one piece, lightweight 1/4" thick duct insulating wrap to place under my hatch area carpet. Put it under my floor mats too, It quieted things down significantly, can't be seen and weighs nothing. If you need to know the exact product PM me i can find out for you.
Hmmm.... Downloaded the Phone app but it uses the "C" scale. Gotta go find out how that relates to the "A" scale. I used to know this stuff. Can't remember half of the stuff I've forgotten.
So the dBC scale used in the iPhone app is a better indicator of true sound pressure levels. The A scale is tailored to indicate what the human ear perceives to be the sound pressure level. The ear is more sensitive to 2-5kHz sound than to sounds above and below that window. So the A scale responds more to frequencies in the spoken-voice range, effectively derating sounds like the thump-thump bass from that hotrodded Corolla with the deaf kids in it.
With Google and Wikipedia, we are all little Einsteins so long as we have a smartphone handy.
This is an old thread, but not dated info. Ive been working on cabin noise reduction, as ive been working on the interior.
Using industry dbA readings, on a real meter (my iphone is wildly higher than this thing reads no matter the weighting) compared to a real meter:
Off/Idle conditions were at work parking lot, with well, obviously some ambient noise, but very little...no major roads nearby.
Driving at 65Mph on a surface (not highway) road...it is a long 3lane wide expressway...worn slurry coated asphalt, ~67dbA, I saw 65s, I saw 69s...not a consistently smooth road.
02-20-2013, 08:14 AM
475hp/460lb.ft
