# Experiment on Road Noise during Commute



## XEagleDriver (Apr 15, 2010)

*QUESTION:* What is the average, low, and high dB sound levels experienced during my one hour commute from home to work and does this pose a long-term risk to my hearing?

*DISCLAIMER:* This is a quick look generated out of personal curiosity, providing only antidotal data and not a scientifically supportable exploration of the subject. My intent is to generate thought and discussion on the potential of typical commute road noise as a source of risk to one’s hearing.

*EXPECTATION:* Windows up, sound system off, cabin noise is moderate (~80db) and therefore not a risk.

*METHOD:* Drive my normal ~1 hour commute to work and record the average, low, and high dB levels on a Samsung Galaxy S5 Sport cell phone running the Android app “*Sound Meter*” by *Smart Tools Co*. I quickly experimented with cell phone orientation and placement and found no significant difference in the readings. I settled on putting the phone on top of my right thigh, microphone pointed aft (attempt to further limit any impact of a/c fan noise).

*CONDITIONS:* The vehicle is a 2015 Camaro, V6 engine, 2LT trim, Rally Sport (yes, it is one sweet ride :R ) with windows rolled up, a/c fan speed set to 3 (out of 12), and sound system off. The commute is ~40 miles on both Interstate, United States and South Carolina 2-lane highways/roads; specifically I-77 South for 6 miles, I-20 East for 6 miles, SC-268 for 8 miles, US-601 for 9 miles and US-378 for 11 miles. I drove at the speed limit to speed limit plus 5 mph (nominally 35-65 mph). A/C fan speeds below 4 did not appreciably increase the cabin noise levels (a fan speed of 12 increased the dB by several points).

*RESULTS:* Average dB was *99*, low value was *74*, and high value was *107*.
*OTHER OBSERVATIONS:* Speed was not the driving factor (pun intended) in cabin road noise; road condition was the most significant factor. Increasing from 35 to 65 mph only changed the db readings a couple dB. Whereas going from a smooth road to a lousy road increased the readings about 6dB. Specifically, SC-268 is a lousy, noisy road (visible cracks) in comparison the recently repaved US-601 is a much smoother and quieter road (speeds on each road were the same). On the Interstate, passing semi-trucks and pickups with over-sized tires did cause noticeable short peaks in noise levels, the other passing vehicles did not.

*CONCLUSIONS:* Without nitpicking the preciseness of the app’s data, it indicated to me a there is the potential for long-term hearing damage since my exposure is nearly 2 hours/work day. I had not expected my commute to have as high an average dB as indicated and will begin using hearing protection to help limit exposure (like I did when flying fighter aircraft).

*FOLLOW-ON RESEARCH:* Conduct a similar test with sound system on playing typical content at my preferred listening levels and I will probably hate the results this provides. :rolleyesno:

Cheers,
XEagleDriver


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## NBPk402 (Feb 21, 2012)

You could rip the whole interior out of the car, and put sound dampening in. I did that on my last car and it made a noticeable difference in noise.


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## Kal Rubinson (Aug 3, 2006)

What you need is a cumulative spectrograph to determine the frequency distribution. I suspect that most of the energy is in the low frequencies to which we are less sensitive. The scale you post does not state what the spectral content of the "noise" is but is probably based on wide-band noise and road noise is heavily weighted.


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## XEagleDriver (Apr 15, 2010)

Ron,
Don't know if I have the stomach to dismantle the interior on a new car; but for arguments sake what was the approximate cost to outfit with dampening material?

XEagleDriver


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## XEagleDriver (Apr 15, 2010)

Kal,
Your comment on low frequency content tracks with what I heard; most high dB travelling sections were inconjunction with noticable low frequency road rumble.
- Does your comment imply low frequency sound is less damaging to human hearing for similar dB levels?

Cheers,
XEagleDriver


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## NBPk402 (Feb 21, 2012)

XEagleDriver said:


> Ron,
> Don't know if I have the stomach to dismantle the interior on a new car; but for arguments sake what was the approximate cost to outfit with dampening material?
> 
> XEagleDriver


I did it a few years ago... I think I spent a few hundred, and it took a weekend (we even did the headliner which was the hardest part). You could do the doors, and floors without too much trouble at all. I think a Shop would charge about a grand to do it. If you want to give it a try...buy enough to do your trunk and do that first. The trunk is very easy to do. 

The nice thing about doing it yourself is you could spend the afternoon doing the doors, and interior panels.... Then the following weekend pull the seats, carpet, and the factory insulation and install the new dampening. Then you can see what it does, and do it when you want to and not have the car down for more than a day. When I did mine I even put small pieces in the door in the area the window rolls up and down in.

Or you could get some friends to come over and have a party afterwards. :T


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## Talley (Dec 8, 2010)

I have a SPL meter (not a phone) and record noise inside cab at around 88db driving down the road at 75mph in C weighted mode and switch to A weighted mode it drops to 65db.

The issue is the lower frequencies.

There were many times in C weighted mode that the peaks where 95-100db yet I could still clearly talk and would not have to scream.

OSHA says 85db average over 8hrs via "A weighted" mode.


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## XEagleDriver (Apr 15, 2010)

Talley said:


> I have a SPL meter (not a phone) and record noise inside cab at around 88db driving down the road at 75mph in C weighted mode and switch to A weighted mode it drops to 65db.
> 
> The issue is the lower frequencies.
> 
> ...


Talley,
Thanks, I also have a SPL meter and will replicate the experiment with C and A weighting. 
- I do not know what weighting the phone uses, but suspect it must be C, given the data and that when travelling with my wife she does not have any issues giving me advice (my selective hearing is another story).

The OSHA numbers are more comforting, assuming a government agency got it right for once! :heehee:

Cheers,
XEagleDriver


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## Talley (Dec 8, 2010)

XEagleDriver said:


> Talley,
> Thanks, I also have a SPL meter and will replicate the experiment with C and A weighting.
> - I do not know what weighting the phone uses, but suspect it must be C, given the data and that when travelling with my wife she does not have any issues giving me advice (my selective hearing is another story).
> 
> ...


well the exposure dramatically reduces the tolerance when the DB goes past 85. I think it's some 105db then your limit is only like 30 minutes for the entire 8hr day. I work in the petrochemical industry so hearing conservation is a key priority. 

the consensus is the lower frequencies can be tolerated to a higher degree (not much). 85db at 20hz is not as damaging compared to 85db at 4k which is where the ear canal typically resonates. 

We are most sensitive in the 1000-4000k range and the higher frequencies are typically what we lose naturally with age. I typical male above 65yrs of age will not hear beyond 5-6khz where a male of 18 will hear all the way out to 18-20khz... 

that is if they don't take care of the ears. I wear hearing protection when mowing/triming etc for anything loud I wear it.


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## Wayne A. Pflughaupt (Apr 13, 2006)

Talley said:


> OSHA says 85db average over 8hrs via "A weighted" mode.





XEagleDriver said:


> The OSHA numbers are more comforting, assuming a government agency got it right for once! :heehee:


I’ve always felt the OSHA’s PEL for noise was way too lenient. Turn off your sub and run a pink noise signal through your system, and turn it up to 85 dBA. It’s hard to imagine listening to that for 8 hours a day wouldn’t result in eventual hearing loss. :huh:

Regards,
Wayne


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## tonyvdb (Sep 5, 2007)

XEagleDriver said:


> *QUESTION:*
> *RESULTS:* Average dB was *99*, low value was *74*, and high value was *107*


Wow, your Camaro's interior is really noisy. I only get around 70-75db average in my van driving mostly freeway to and from work using audio tools on my iPhone And it never peaks over 80db.


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## XEagleDriver (Apr 15, 2010)

tonyvdb said:


> Wow, your Camaro's interior is really noisy. I only get around 70-75db average in my van driving mostly freeway to and from work using audio tools on my iPhone And it never peaks over 80db.


Tony,
It turns out the van is probably not quieter than the Camaro, but rather the iPhone App is a better SPL tool than the Android app I used.

*REPEAT WITH SPL METER:* On today's commute, I drove the same route and used the same method as previously stated, except I used a *Radio Shack SPL meter* (picture below) set to *A-Weighting* and *Slow *response as Talley suggested and the SPL (dB) readings were as follows:
- On the Interstates at ~68 mph readings of *70+/-2 dB*; 
- On smooth 2-lane Hwys at ~60 mph readings of *68+/-2 dB*; 
- On rough 2-lane Hwys at ~66 mph readings of *72+/-2 dB*.

This analog meter does not capture highest/lowest values or calculate the overall trip average like the cell phone, but from what I observed the lowest was 60dB when standing still and the highest was ~76 dB when travelling over bridge seams at speed.

These values tracked much closer to what I was hearing, basically a quiet cab with audible pavement noise in relation to road quality.

I did toggle back and forth between A-Weight and C-Weight, as well as Slow and Fast response:
- C-Weight read a lot closer to the cell phone readings, but still reported ~10 dB less than the phone.
- Slow versus Fast did not appreciably change the peak readings, just the amount of needle movement.

*CONCLUSIONS:* 
1) The phone app is C-Weighted and also inaccurate reading about +10 dB high (basically a toy).
2) The noise levels in the car most likely do not pose a significant risk, as they are well below the OSHA A-Weight standards Talley contributed.

Cheers,
XEagleDriver


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