Grant Erwin wrote:
Anyone got a clean db meter they don't need and want to sell/trade? I
live about 100 yards from a large freeway that the state is preparing to
widen, and I want to take some sound level data to feed to their team
that's evaluating the need for sound wall height adjustment. Also, I
want to keep an "ear" on the sound intensity levels reached in my son's
band's practice space.

I know this isn't exactly on topic, but it's a damn sight closer than a
lot of the garbage I see lately, and I've been a regular on this NG
since the mid-90s.

Thanks!

Grant Erwin
Kirkland, Washington

The measurements you are planning to take for the freeway people are not
easily done with a common sound level meter. The preferred method is to
measure LEQ ,the time averaged sound level, over a 24 hour period.
Usually another 8 hour LEQ measurement is taken during hours of sleep
for a residential community and then combined. Also the weighting of the
measurement (A,B or C) has to be taken in account. Sometimes frequency
specific measuremets are also taken.

Here is a very basic prediction of sound level attenuation for a wall
separating a sender from a receiver, if the receiver is much further
away from the wall then the sender.
Height of wall squared /( wavelenght of frequency, times ,distance from
wall to sender). This gives a number which then is plotted on an
estimating chart.
For a calculation result of .5 the attenuation is 5 db
For a result of 1 the attenuation is 10 db
For a result of 2 its 12db
For 4 its 16 db
For 6 its 18 db
For 10 its 20 db
For 20 its 23 db
For 30 its 25 db
For 100 its 30 db, and that is the theoretical limit. In practice more
than 25 db attenuation is unheard of.

cheers
T.Alan