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Discussion Starter #1
Hi,
A number of people have gone through the whole conversion process on their PM vans -- some have devoted a fair bit of labor and dollars to install noise reduction layers and some have done less on noise and some have done nothing on noise, but did put in insulation and paneling which reduce noise to some degree.

So, question is, does it pay to add the extra layers of sound proofing material over just insulation and paneling? And, if so, how much does it pay? And, which noise techniques work the best or offer the most bang for the buck?

This is a proposal for people who have not yet started their conversins to actually measure the before and after noise levels in a consistent way so that as people do conversions and measure noise levels we can develop a bit of a data base on what works and how well. This (I think) would be a big help to people trying to decide how much they want to put into noise reduction ?

So, here is a cut at a simple "standard" for measuring PM van noise:

Before:
1- buy a cheap noise meter. I've got this one [ame]http://www.amazon.com/dp/B00A13M9D2/ref=sr_ph?ie=UTF8&qid=1428457842&sr=1&keywords=noise+meter[/ame] for $25 it appears to work quite well and gets lots of good reviews.

2- Make a 4 ft high support for the noise meter that you can place on the floor of the van. This could just be a 4 ft long 2 by 4 screwed to a square of plywood to serve as the base -- or anything that will support the noise meter 4 ft off the floor.

3- Pick a section of road that you want to use to do the noise measuring. Maybe a mile of "average" paved road that you can easily drive the van over with noise meter before and after the conversion.

Do the noise measurements:
1 - Before the conversion -- mount the noise meter between the driver and passenger seats on the 4 ft high pedistal with the meter 2 ft back from dashboard. With an assistant to read the meter (or a video cam to record it) do the run on your standard road at 60 mph once in each direction. Note the weather, time of day, ... anything that might influence the measurements.

2 - Move the noise meter and pedestal to a position half way back in the cargo part of the van -- eg half way between the back of the driver/pax seat and the rear door. Repeat the same two 60 mph runs on your standard road section.

After the conversion, repeat the same measurement runs as you did before the conversion. Even better, repeat the noise runs several times as you (say) finish the bare noise treatment, after floor, after paneling, etc. But, the main thing would be to get the bare van and the fully treated van.

The difference in noise levels between the two runs gives the noise reduction for the noise reduction your conversion achieves.

Post your noise readings and the noise reduction materials you used as well as the type of paneling, insulation, flooring...

I have zero experience doing noise measurements, so if you have a better idea or improvements to the procedure to suggest, please do.

I'm an incurable engineer type, and this may be way over the top of what any reasonable person would do -- please feel free to say so if you think this is just too involved.

If people think this is worth doing, I can arrange to take the noise measurements on my van, but it would only be for the after conversion case.

Gary
 

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Save $25 and get a decibel meter for your smart phone. I use "decibel 10th" for iPhone a fee app from the app store.
 

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All that... that's exactly what I'm already planning on doing.

And in stages, as recommended. Empty. With completed floor structure. Full walls and ceiling. Then final conversion.

I've been using a decibel app for Android. Don't know its exact accuracy, but its precision seems good.


Though the whole process will probably take 6-9 months.
 

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I think it's a great idea, but the data will be very fuzzy.
Very few of us will buy a noise meter. We can use the same apps, but then still we have different phones so not sure the measurements will be comparable. Also the road surface makes a huge difference. It would be easier to just put the phone (or noisemeter) in the center low console.
Most of my noise reduction is already in place, so I can't do a before measurement.
I'm installing decibel 10th on my android phone, I'll take some measurements sometime. ZZyz what app do you have?
 

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Great idea, I was doing similar. Don't really care about the noise much because my hearing is poor but I was curious how much the noise would be reduced from empty to completed. I used an app and measured driving down the road. Won't be very accurate because I am not going to reproduce similar conditions as your plan will. I'll post for what it's worth
Oh, no noise reduction materials, just insulation
 

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Great Idea!

I'm in:)

I have no experience either on noise measurements, but it seams like you want to isolate the instrument from any noise/vibration that the support arm/2x4 might induce. Bungee seams to be what recording studios use for suspending micro phones.

I would be even more interested in the effectiveness of insulation methods and materials.

Cheers,

Dave
 

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Noise levels

Count me in,

I have already taken the first reading in my 159" high roof PM. The methodology I am using is as follows:
1. I travel the same road,distance, and speed (about 5 miles @ 65mph). 2. I use an iPad laying on the passenger seat with an external mike extended to a position between the rear wheel wells at a height level equal to the top of the wheel well. 3. I do about 4-5 screen captures during the trip.

That said, the results of my first readings were 73.4 db on the A-weighted scale. The noise app that I use is SPL PRO and is available on the Apple store @ $7.95. I did a lot of research b4 buying and this seemed to be the best for my needs. They may have an Android version.

I am by no means a noise/sound engineer, however I do have a little working experience from my days in the Health and Safety Environment industry. This leads me to taking what I consider a practical approach. My advice ---No analysis/paralysis. Get close to the noise source for the readings.Using the A-weighted scale is most important as it most closely relates to what we hear. Don't be discouraged by small number reductions. A 3-5 db reduction cuts the noise in half

I will use three layers of material to insulate and dampen noise in the interior.Next week I will be installing the first layer of insulation and will take readings afterwards. I look forward to sharing the results
 

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Discussion Starter #8
Great -- looks like we will get some measurements.

The smart phone noise meter looks good -- had not thought of that. I've downloaded the Smart Meter Pro on my Android and it even appears to have a way to save plots of values. I'll check it against the Amazon one when we get back home.

Agree that things like road surface make a lot of difference -- will have to see how good the data look.

I'll do the measurements on our van next week and post them.

Gary
 

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Discussion Starter #9
Hi,
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/Vehicles/PMRV/Noise/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 $25 sound meter I bought 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.

Results:
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.

Noise level as measured by the phone averaged 72 db -- so, only about 1 db less than the phone measured with meters forward.

Other Readings:
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

Honda Pilot:
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.

Noise Meters:
It turns out that the phone app noise meters are not that good.

This article http://blogs.cdc.gov/niosh-science-blog/2014/04/09/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.

Simplified Test:
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.


Gary
 

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My iPhone App (decibel 10th) has a calibration screen so if you think of a repeatable sound and distance (since sound attenuates with distance) we could calibrate to your Amazon meter and have comparable measurements. Short of that, sound reduction may be more important than an absolute measurement. I am amazed you got readings within 3 dB of the Pilot. dBs are on a logarithmic scale so even though we can hardly tell the 3 dB it is much less sound power. Doubling our perception of a noise is considered to be 10 dB.
 

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Discussion Starter #11
My iPhone App (decibel 10th) has a calibration screen so if you think of a repeatable sound and distance (since sound attenuates with distance) we could calibrate to your Amazon meter and have comparable measurements. Short of that, sound reduction may be more important than an absolute measurement. I am amazed you got readings within 3 dB of the Pilot. dBs are on a logarithmic scale so even though we can hardly tell the 3 dB it is much less sound power. Doubling our perception of a noise is considered to be 10 dB.
The idea of a standard noise maker that people could set up easily to calibrate phone meters would be really helpful. Have not come up with anything yet -- anyone else have an idea for a standard noise source?

Gary
 

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The idea of a standard noise maker that people could set up easily to calibrate phone meters would be really helpful. Have not come up with anything yet -- anyone else have an idea for a standard noise source?

Gary
We all have the same horn? Could use that, from a specific position and distance...

Might aggravate a neighbor while doing it though...
 

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Standard Noise generator

Noisemakers are available at this site:

http://mynoise.net/NoiseMachines/trafficNoiseGenerator.php

You can select from many types of noise. This is probably as close as you can get to arrive at a standard level of noise for calibration of Smartphone/software sound level meters.

Instrument hardware sound level meters use hardware calibrators (costing 150+). They fit over the mic and emit a constant tone. Definitely not practical for your suggested coordination of efforts.

I used traffic noise from this site and recorded it on a voice recorder. When shopping I hold the recorder behind a material to see if it has attenuation values. Spot checking and using only my ears as a measurement tool.

Personally, I am working on reducing the existing levels of noise in my van by starting w/ a measured untreated level and recording the difference when changes are made. I will use all of the same variables, such as speed, road ,etc.

I will share the results.
 
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