After doing sound deadening on my Fit (see https://www.fitfreak.net/forums/2nd-...-step-1-a.html), reako was suggesting to compare DB reading against the stock Fit. Finally borrow a DB meter. Here is my testing condition and measurement:

- Sound deadened Fit Sports M/T with stock Bridgestone Turanza EL470 at 33 psi
- DB meter with passenger holding on the laps with mic facing forward.
- Wet road with light drizzle (typical Seattle weather)
- DB meter from Radio Shack: Digital-Display Sound-Level Meter - RadioShack.com
- DB meter at A weighting (500-to-10,000 Hz)

Test Result #1

- 60 mph on freeway to work on average road surface; 71 to 75 db; most of the time around 73 db
- 40 mph on local road; around 64 db

Test Result #2 (Compare with 2004 Passat)

- 60 mph on a smoother surface freeway
- sound deadened Fit: 68 to 69 db
- stock Passat: 65 to 66 db
- loss by 3 db

If any of you have a db meter and would like to compare with my sound deadened Fit, please post reading.

 

a lot of factors go into db meter...diff placement of the meter will cause 1 db off or so
even if it just an inch different
and the way the sunvisors are placed can cause a difference too
i know cause i looked into spl competition and read up on tricks to get a higher db

and diff db meters are not always accurate..so even if someone has a db meter...results wont be accurate...BUT it stil always good to look at

=)

 

However! You can get pretty accurate with other spls. Intake and exhaust for example. As long as you are outdoors, in a relatively quiet place, you can get good spls. In normal conditions sound degrades at a rate of 6dbl everytime you double the distance. If everyone measuring spls agrees to do it at a set distance in those conditions, we can get relatively close. I have a db meter in North Texas,and would love to have spls to add to dyno charts on stuff. I want a quick Fit, but I also have to be able to take my wife around without her getting embarased.

 

oh, and considering where an engine makes all of the noise (at the top of the tach) I would suggest a weighting as you used above. We really aren't going to be bothered by the low notes given around idle, and the only notes toward the high end of the spectrum would be harmonics, which again arent going to be too big a deal

 

Reako’s conditions and measurements:
*All conditions that differ from vwli are underlined/bold.

- Fit Sport A/T with stock Bridgestone Turanza EL47Z at 34 psi
- PRM intake
- Driver holding DB meter 2’ above e-brake lever- mic facing forward
- Dry road – older 2 lane highway
- DB meter from Radio Shack: Digital-Display Sound-Level Meter - RadioShack.com
- DB meter at A weighting (500-to-10,000 Hz)

Test Result #1 – Using “A” weighting:

35mph - 63 dbA
40mph - 65 dbA
55mph - 67 dbA
60mph - 69 dbA

Test Result #2 – Using “C” weighting:

40mph – 85 dbC
60mph – 88 dbC


Trying to figure out why mine measured so quiet…

• My test highway (typical curvy 2-lane highway 55mph speed limit) may be smoother than yours.
• My engine (A/T) may turn fewer RPM than your M/T at 60mph.
• I did try to keep out of the throttle when measuring (PRM intake growl adds db’s)
• Maybe test yours again when the roads aren’t all wet?

Anyway, as 713_fit touched on a bit, the human ear may be more sensitive to specific frequencies which your sound deadening knocks down – meaning even though the overall db readings may not differ by a large margin, the frequencies that remain after sound deadening are not as bothersome/noticeable. Regardless, with the level of sound deadening you added, I would expect at least a 5 dbA drop across the board – this is likely the case, our readings are likely skewed by one of the endless environmental variables that may interfere with these type of tests.

Most importantly, this was fun! I can take some more measurements down the line, or perhaps try a different db meter some day. Let me know if you want to complete any more testing, and thanks for posting up your results! +1

 

I understand that it is very difficult to do a true db comparison between reako's and mine. However, I was truly disappointed about losing 3db to my co-worker's Passat. We were measuring it under the same condition. I was hoping that my sound deadened Fit would kick the VW behind.