I'm wondering what everyone else saw for db sound in different parts of the cab before installing sound deadening. My car reads about 68 in the speaker corners, 69 in the luggage area and at the bottom of the luggage area 71. In the front seat, and doors 65. and 67 at the floors. Under dash is same as doors 65. If you have recorded the db's in your car before or after the sound deadening material. Also I was going 55 mph on relatively smooth road.

 

Omg! Really! It's a sports car!! Not a luxury sedan!

 

The whole car is noisy. Most of us end up putting the deadener on the ENTIRE inside of the car, including the doors, storage compartments in back, footwells and the floor. And you most likely will not be able to hear the dash speakers. Just experience talking here.

 

OK so maybe I didn't make myself clear. This is the third corvette I've owned, so I'm not surprised about the noise, and I'm not new to the car building scene. My first car was a V8 Vega in high school, and my last car was a factory five Shelby Cobra I was just wondering if anyone else monitored their car before and after the sound deadening. I've already purchased the sound deadening material and have the interior halfway torn down, so there is no deciding on if to do it or not. I also purchased some rubber treatment for the doors and t-tops because they are making a lot of noise.

 

About 100 with the side pipes and the windows down.

 

OK, I will jump back in after I understood what you are asking. I do not know of anyone who made the effort to take decibel readings at various locations in their C3. I also have a C6, and when I was putting sound deadening material in it, I did not come across anyone who took those readings in that car either. For the C6, the process was the same as the C3; Just put it everywhere. On the C3 it was a bare cabin, in the C6 I removed all the carpeting front and back but did not do the floors. Great improvements in both, although the C6 was quiet to start with. Not the C3. Good luck on your project.

 

With the tops off, windows down, and sidepipes, my son and I were able to have a normal conversation with budget headsets.

The tiny amount of insulation I added dampens the pinging from rocks flung by the rear wheels. I didn't want to add too much weight, though.

 

Hey, HEY HAAAY, My name's Richard Petty; can you speak Up ???

 

Just pulled the luggage area wheel well carpet out and someone went to the effort to take all of the padding out and install new carpet. No wonder it sounds loud, no padding or anything under the carpet and not the kind of carpet that has padding built into it. Just thin carpet.

 

I am curious to see where this goes. Interesting data you collected so far. I'm considering doing the same baseline test on my 73 survivor.

 

Sounds like you picked the wrong car.

BTW, my Hooker Max-flos sound wonderful.

 

badhcraft,
I checked all the obvious things. No rust, new dual exhaust, new tires, excellent paint, interior all there and looked ok. But then like anything once you get into it you find things that were done wrong or skimped on. So, I think I picked one in good condition, and I bought it one year ago so I'm still fixing things to make it personal to me, and I'd like to say almost finished but are we ever finished? like maybe a new 383.I don't know what's in the engine now but it's not stock, just not a 383 yet.

 

I didn't mean that there was anything wrong with the car, just that you may have been expecting something other than a noisier than usual 50 year old car.

 

bashcraft,
Thank you for clarification. The two corvettes that I previously owned, 72 and 75 were quieter so yes, I was expecting a slightly quieter car. When I started taking the carpet out to put sound deadening in I found out why. It's because someone had taken all sound deadening out and there was only thin carpet. My last sports car was a Shelby Cobra from Factory Five which had no top and side pipes that you could touch sitting in the car. didn't do a db test but it was really loud. Kept it for 10 years meaning fun outweighed the loudness. When I finish installing sound deadening it will be a little bit more civilized and a little bit more like the other corvettes I've owned.

 

OK, sound deadening and insulation as well as carpet is all in. Also new clamshell seats replaced stock seats. The rear corner speaker area was 68 and now is 66-67 ish. doors were 65 and still 65 because I didn't do them yet. The floor area was 67 and now a solid 65. The upper luggage compartment area was 69 and now 68. The bottom of the luggage area by the three storage doors was 71 and now 69. Both tests were on the same road driving 55 mph and my wife took the readings while I drove the car. So, it looks like 1 to 2 dbs lower everywhere except for the doors but then I haven't done those yet. What we noticed a big difference was the floor and center console area is noticeably cooler now than before. I wish I had taken temps before and after. I really thought it would make a larger sound difference than it did but it's done and did make some difference to the positive. I used 50 ml of sound deadening and 1/4 inch insulation. So, if you were to use 80 mil of sound deadening and maybe 3/8 insulation you might get another db lower. I will do the doors when I get some more door parts in and then I'll do the sound db on them and let everyone know but I'm expecting 1 to 2 db lower like everywhere else. My muffler is against my tire carrier so after I put my new headers in I'll have the muffler shop adjust to they don't touch. I'm thinking there is some noise from them transferring into the cab area and hopefully it will lower the db. Also, I'm getting a lot of noise from the t tops so new plastic and new weather strips and new adjustments. I'm making good progress and soon it will be more enjoyable to drive, because I don't like noises that should not be there.

 

Op;
Since no one else has weighed in, I will.
I am a science guy and love this stuff.
My Corvette is in a 1000 pieces, but I have tested my daily.

What are you using to measure sound level?
A decibel meter that only gives you one number is of limited value.
I use a free app download for my Android phone called audiotool.
It uses the phone speaker.
It can measure db in different ranges, gives a frequency graph, and can generate tones as well.
Those features are very useful.
But since it uses the phone speaker, it may not be all that well calibrated, and your and my readings could differ.
But it does not really matter if your and my peaks match, it is the peaks that truly matter.

61db, ( db(A) = A weighted) does not really sound too bad to me.

My house reads a low 29dB (A), the library 35 db,mostly AC, my parked car 42, that goes up to 44 with the engine running, 71dB at 2000 rpm cruise, and 80 dB at W.O.T. Your meter will likely vary.

This is a 2008 Caddy CTS, manual trans, with magnaflow mufflers, You can definately hear them, They purr mostly, but growl pretty good at W.O.T.
I mention it is a Caddy because when I had to remove the carpet to drain the water from a leaky sunroof with plugged drain, (duh), I discovered the floor carpet has about 2 inches of high density foam. When it had stock stock mufflers you could not hear the engine, at all. I like the current muffler purr. Magnaflows on a C3 are a little louder, but not by too much.

The Graphs tell the story of the low frequency muffler resonance.
As a former musician, high frequencies are very directional. Low ones are not. It would make zero difference you placement of the meter for measuring low frequencies, just like subwoofer placement barely matters.

FYI it takes 6-10 dB to double the sound volume.


Car parked engine off. All the peaks are at about the same level, so you can not hear just one. It sounds like white noise, almost invisible to your ears.


Engine idling, muffler resonance is at 102Hz at 650 rpm idle. 44 dB in parking lot. This is only 2dB than no engine at all, and you can definately hear it purr. This 102 peak is near 6-10dB higher than the rest, The rest all blends together and sounds like white noise. The purr barely stands out, because it is not quite twice as loud, but it is there. Maybe 50% louder than the white noise.


Car at 60 mph, 2000 rpm cruise in 5th gear, 71dB significantly louder than at idle. Noticeable engine / exhaust purr at 2000rpm at 123Hz. This purr is very noticeable, but not loud. It is about 65dB vs a background of other freq at 50dB, about 15dB louder. So it does stand out as twice as loud as the rest of the car. If I cut the engine, that peak does go away, but the overall dB only drops a couple dB. If I had my druthers, I would cut that back a little to 6-10dB louder than the background.


Wide open throttle at about the same rpm, sound level jumps to near 80dB. Roughly twice as loud. My wife will stop talking and pay attention to the outside. LOL
Radio fades into background. Engine noise raised the background level a little from 50 to 55dB, but the 123Hz exhaust doubles in volume, as it jumps from 65 to to 80dB, that's more than double as loud as before. The engine is now 25dB louder than the background, and totally dominates what you hear. Four times louder than the background. As the engine revs that peak climbs higher up into the 250-300Hz at high rpm.

So my Magnaflows generated a moderate drone at 2000 rpm at 70 mph cruise in 6 gear. I originally only had one set and it sounded like a porsche race car. Waay too loud. I now have 2 sets (4 mufflers) and that cut it down quite a bit. If I wanted to soften the peak some more, or eliminate it (I do not) I could use a J-tube on the exhaust to target that one problematic freq, and then it would just dissapear at cruise. I did do just that on another car.

So that is the exhaust reverberating in the pipes themselves. Body panels will also resonate at a certain Hz and if that happens to be the same as the exhaust, you are really in for it. That would double the volume, again. When a panel vibrates, it is like hitting a drum head.

My Caddy is really quiet in that regard, the doors go "thud" etc.

If you find another peak, that is NOT the exhaust, and the Hz does not move higher and lower as you rev it, you can go looking for it.
Tap a suspect panel, lightly, like a drum stick. Measure the sound frequency. If it matches the one you have driving down the road, you found the source of your reverberating panel. Add some sticky tar sound deadener to it, or support the center in some other way, like ribs, and that will change it's resonating freq. Shorter equals higher pitch, and gets you out of the trouble zone. Check it again with a tap and measure. Make sure none of them resonate near the exhaust zone.

The exhaust drone zone is 100 to 250Hz.

Door panels are large enough to really act like a big drum head, and give off low freq. Test them, and dampen them. Most flat sheet metal panels have creases in them to stiffen them. Glass panels do not.
Test any other big flat panel with lack of curves or creases.
On a C3 I would suspect the top & bottom of the storage compartment especially.

Hmmm...my body is empty and on a body stand.
I might need to do some reverb testing before I put it back together.....

 

Thanks, that's some deep testing you've done. I think as long as I keep testing my car with my meter it will be relative. My exhaust is really loud and against my tire clamshell holder, so I'm thinking it may be transferring noise into the cab. This will be fixed next week at the muffler shop. then I'll do the doors and replace the t top seals and adjust them. When we took the measurements, it was at the same speed and about 2500 rpm, on the same road, and my wife pointed the microphone at the same areas at the same distances and even the same tire PSI. All this was the same before and after the sound deadening and insulation. What matters most to me is the difference from before I did all that work. so I could tell other people the difference it made in my car. I think the rattles and squeaks when fixed will make me happiest. I can deal with the noise, but the squeaks and rattles must go.

 

I agree the exhaust is the loudest.
And if it is touching something that will vibrate loudly.

Your and my meter likely will not match. Because mine is not calibrated.

The free audio tool app can still show you the spectrum analysis and how badly your exhaust "sticks out".

Are your using a dedicated dB meter?

 

Yes, I'm using a dedicated dB meter. I forgot to say yesterday that I appreciated all of the new dB stuff you posted. It will benefit the group to know there is better technology out there to work with.

 

I just got back from the muffler shop and the pipe on the drivers side was against the frame and the muffler was against the tire carrier on both the drivers side and passenger side. I can tell a big difference in the lack of noise resonating into the cab. I have not done a dB test yet because they found the plastic trim piece that goes around the rear window inside is really lose and rattles when you rev the engine or hit a bump. That will get fixed tonight. Then when the parts get in I'll put new rubbers on the t tops and adjust them. If my wife is available we will do another dB check.