Expert: Harriet B Jacobster, Au.D. - 7/2/2008

Question
QUESTION: Hi,

I have a relatively loud car and I'm a little concerned about my hearing. I bought a RadioShack sound level meter that has both an "A" and "C" setting. At freeway speeds on the "A" setting my car is about 70-75 dB but on the "C" setting it's closer to 95 dB. I know that 70-75 dB is generally considered a safe level and that 95 dB is around the threshold for problems. I also know that dBA measurements filter out lower pitch sounds more. This makes sense to me, my car has a low pitch drone from the engine at freeway speeds. I also know that dBA measurements are considered the technical standard for workplace sound level safety, but there is some question of it's appropriateness.

I guess my question is: Should I be worried about my hearing? I'm considering investing in some insulation for my car but it's very expensive and time consuming to install.

Thanks so much for your time!

ANSWER: Hi Mark,
This is a good question and I had to think a while.  The dBA scale is more closely akin to human hearing than the dBC scale. However, at louder levels, they are roughly equivalent.  Safe is considered around 80-85 dBA, so at 75 dBA you are right at the borderline.  However, this doesn't mean that listening to 75 dBA of sound will NOT hurt your hearing.  Over time it could still do a lot of damage.  Then, add to this your stereo system and you're probably pushing it to the max.  Therefore, if you are asking me, should you worry about your hearing?  I would.  I would rather err on the side of caution in this case.  After all, isn't your hearing worth the price of insulation?  In the long run, I can guarantee you that a pair of hearing aids is much more expensive.
Hope this helps.
Harriet B. Jacobster, AuD
Board Certified in Audiology

---------- FOLLOW-UP ----------

QUESTION: Hi Harriet,

Thanks for the reply, as a follow up question, I understand that the dBC scale
measure more towards the lower pitch. When I start the car up and it idles, I
can barely hear it, I hear a very very low rumble right on the edge of my
hearing but the dBC scale goes nuts, registering at about 80 dBC. Is this
sound that I can barely hear damaging my hearing?

Also, what is the range of human hearing?

Thanks!

- Mark

Answer
Hi Mark,
Let me answer the easy question first. The range of human hearing is approximately 20 - 20000 Hz with greatest sensitivity around 1000-3000 Hz.  Now, your other question. I found an excellent resource for you: http://www.defra.gov.uk/environment/noise/research/lowfrequency/pdf/lowfreqnoise
Pay special attention to Chapter 7.  Apparently, even a short-term exposure to high levels of even low-frequency noise will cause a temporary threshold shift which apparently recovers rather quickly.  The problem happens when you are constantly exposed, it becomes harder for the ear to recover so your temporary shift becomes positive.  So, the question remains...how LONG do you listen to your car idle?  If only for a minute or two, I doubt very much this will have long-term effects.
Hope this helps.
Harriet B. Jacobster, AuD
Board Certified in Audiology