I went ahead and did the noise
measurements on my PM.
If you want to read a very detailed report, its here: http://www.builditsolar.com/Projects...oise/Noise.htm
But, the highlights are...
Did the test exactly per the test procedure in the first message of this thread.
Measured with both the
as well as with the best of the phone apps I could find form my Android phone (Noise
Meter 2.1). See below for more on the phone apps.
I did these with the windows closed, heater fan off, and radio off -- this does make a difference -- see below.
Forward microphone position:
Driving either direction at 60 mph over the about 1 mile stretch of highway I chose for the test, the noise
level with the meters positioned forward (midway between driver and passenger ears) was 71 db on the meter and 72 db on the phone.
This is a plot from the phone:
This is the test road -- good asphalt with chip seal -- pretty smooth.
Back Microphone Position:
Moving the meter support back to middle of cargo area and then repeating the 60 mph run on the same section of highway.
level as measured by the phone averaged 72 db -- so, only about 1 db less than the phone measured with meters forward.
Took some additional readings in the PM and also in our Honda Pilot.
Gravel road at 25 to 30 mph: 68 to 74 db
With PM stopped beside road
Engine off, fan off, radio off 40 db
Engine at idle, fan off, radio off 48 db
Engine at idle, fan at 1/2, radio off 55 db
Engine at idle, fan at full on, radio off 65 db
On the standard test section of highway at 60 mph 68 db
So, the Pilot is about 3 db quieter than than our PM conversion.
3 db is the smallest change that good ears can just detect, so, it says that the PM and Pilot should sound about the same, and they do to me.
It turns out that the phone app noise
meters are not that good.
This article http://blogs.cdc.gov/niosh-science-b...09/sound-apps/
tested a bunch of them (nearly 200 altogether) and only found 3 that read within +- 2 db of their lab meter. The lowest reading ones read as much as 20 db less than the highest reading ones for the same noise
level. This is a very large difference.
I think that this is a good reason to buy the $25 noise
meter from Amazon for the testing if you can. If you do use a phone meter, make sure to use the same phone meter for the before and after tests, and it may be that the difference between the two may still be useful even though the absolute levels could be off by quite a bit.
I am encouraged by the consistency and repeatability of the test, and I think that we can get some useful data if a few people will give it a try and get the before and after conversion measurements.
After doing this first go, I'd suggest that we simplify the test a little:
- Drop the measurement in the back of the van. Idea being that there will normally not be anyone back there while driving to hear the noise
- Just hand hold the noise
meter about midway between the driver and passenger ears. This is what I did on the Pilot measurements and it seemed to work fine -- the reading don't change a lot if the meter moves and inch or two out of position.
I do think that there is some benefit in using the Amazon meter -- it looks like its going to be be more accurate and more consistent than the phone apps.