Sound measurement (traffic noise inside)

[FrankT]

I live on a busy road.  The traffic noise is becoming a bit unbearable.  All noise reduction renovations are expensive, so I plan to start with one room and measure the effect of each change.

I've search the forum and people recommend the NTI tools which are way to expensive.

My plan is to us a PC with USB ADC (behringer umc404hd) to record 24 hours of information and then post-process the results. 

I'll use one channel to record audio with a microphone (ECM8000).

Is there any point recording the output of a sound level meter?  Can I calculate what a sound level meter indicates from raw audio data?

For the other channels, I was thinking of recording window, wall and ceiling vibration, either using a cheap analog output accelerometer, or a vibration sensor (like https://au.rs-online.com/web/p/vibration-sensors/0285784/).  This will be recording at audio frequencies, max 44kHz.

Is this useful information to record?  Is there anything else worth monitoring?

For results, will the area under the audio graph (absolute amplitude vs time) give an equivalent to a sound level meter?
Can I do the same with FFT results to show sound levels at different frequencies?
I'm thinking I can do similar with the vibration results.
Is there anything else I can extract from the data?

Thanks for any input.

[coppercone2]

Well to get good data, make sure you use good anti aliasing filters.

Also, learn which kind of filter you want to use, if you want accurate impulse response you will want a different type of AA filter then butterworth topology.

A sound level meter will probobly give you a RMS output. You can calculate RMS values from FFT data, or you can measure them with another instrument, theoretically RMS values might be a bit more accurate and the electronics are simpler/cheaper/possibly more stable, but for something like dampening a room to human hearing levels I would not worry.. the accuracy is low. If you were interested in doing something like dampening a precision mechanical/laser laboratory from noises and vibration obviously the answer would be different, but if its a human dwelling you don't need to worry about it too much.

Also, RMS is a bit easier to calibrate, but I think relative levels are adequate for your task.

The data collected using non-microphone sensors may be interesting to investigate things or form useful models, but ultimately you are interested in what you persieve with your ears, I think the microphone is the sensor most similar to your ear drum. Those sensors are more for making sure machinery is not destroying itself etc, since it is actually telling you what is happening to the metal (i.e. how much energy is in the vibrations of the structure of the machine) rather then how much energy is being coupled into the air (which is what you end up hearing).

They might however be interesting to use for lower frequencies (i.e. like if your bed rumbles when a truck drives by, using a accelerometer connected to the leg of the bed might be more useful then trying to use a microphone).

Look up how an oscilloscope measures RMS digitally to understand how the various values are calculated.

Doing your own FFT works well, but the main problem is input amplifier noise and dynamic range. The ideal instrument for this situation is known as a dynamic signal analyzer which is a special instrument that works like a FFT spectrum analyzer (and often has a Voltage/Time interface like an oscilloscope), but it is designed with good anti aliasing filters, only goes up to some KHz (maybe 100KHz) and has an excellent noise floor, dynamic range and various useful measurement functions built in.

I think you will be interested in the 'waterfall' function for doing this kind of testing.

But again, you will want to research good anti aliasing filters for connecting your own sensors to ADCs, they are important, especially for FFT.

[jmelson]

One thing I have found is that TINY air leaks around windows can let in a lot of high frequency noise, like tire noise.  Sealing up these little leaks makes it quieter inside.  It also makes the house more efficient to heat and cool.  It is harder to do much about the low frequency stuff, like the rolling boomboxes that annoy us.

Jon

[coppercone2]

I recommend the new generation loctite expansion foam for this task (nice and white too not that old yellow shit). Commonly sold in home depot for like 6$

It is 4 times more dense. Also, wooden windows (like anderson) and rockwool acoustic dampening insulation made a difference for me, when I was remodeling a room.

Rockwool is real nice shit, even the thermal one is pretty nice.. it's pretty dense, more fire proof and healthier for you then fiber glass. And I found that I did not get all itchy and shit after using it, and cutting it is easier then fiber glass, especially with a serrated knife.

Also, make sure the sheetrock is lifted off the floor and foam is used to bridge the gap, not shitty walls that wedge the floor boards against the sheet rock. And using a softer glue to connect the molding to the floor will help. I don't know about the ceiling/wall interface, I just wedged it, which was probably a bad idea, but for some reason all the contractor videos on you tube focused on the floor/wall gap and said not to leave a gap between the ceiling and the wall. The main thing I notice from this is quieter walking.. but you might want to research a wall/ceiling gap as well.

Stiffening up the floor boards also helps, with some nails. I was able to do these things and have satisfactory results (I thought I was going to have to put fucking rugs on the wall before, to prevent annoying shit like lawn mowers waking me up in the morning. I did not do this in a scientific way, I decided to remodel for mainly electrical and thermal reasons and decided to follow best practice when it comes to acoustics, coincidentally thermal/acoustic design is similar for comfortable living.

[coppercone2]

And A major thing I noticed was that when I was laying in bed I did not hear people walking in the hallway or when they were walking down the basement stairs. The walls were basically plastered into the floor before, so I think the basement steps were conducting directly into my bed. And much much much less creepy crawlers appeared in that room since the renovation (centipede etc). I think this is because the rockwool basically sealed the void in the wall pretty completely.

It might be a good idea too to put silicon feet on the bed to limit coupling.

[FrankT]

Thanks for the replies.

Well to get good data, make sure you use good anti aliasing filters.

I'm really only interested in lower frequencies, probably under 1kHz.  (most spikes I see are around 125Hz).  Do I need a hardware filter if I am recording at 44kHz?  Will software filters work, or a simple hardware low pass filter?

The data collected using non-microphone sensors may be interesting to investigate things or form useful models..

I was thinking the vibration sensors would give an indication of the structure borne sound.  My first improvement will be replacing the 3mm window glass with something thicker.  If there is a measurable change, I can then look at the walls and ceiling; currently single sheets of plasterboard - the ideal wall seems to be resilient channel with 2 layers of plasterboard with a sound deadening compound (greenglue) between.

I thought I was going to have to put fucking rugs on the wall before, to prevent annoying shit...

I've been reading "Master Handbook of Accoustics" which has a lot of information about Reverberation, absorbtion, and modal resonances.  But that seems to focus on sounds that are already in the room, not stopping it from entering.  Do these techniques (rugs, etc) help?

One thing I have found is that TINY air leaks around windows can let in a lot of high frequency noise, like tire noise.  Sealing up these little leaks...

Slightly off topic, but can sealing up these gaps too much make my room air tight?  I'm think of the story* of the guy with a bad diet who died in his sleep from breathing his own farts.




* the story appears to be fake.

[coppercone2]

I don't know about the rugs actually blocking noise or reflections, it was just gonna be a half assed experiment done as triage that I seemed to avoid.

As for air leaks, I read that during the reign of Saddam Hussain certain people got word of a gas attack (maybe during the iran iraq war), and taped up their houses really secure, and they were found suffocated. I don't know if its a cover up possibly. I typically leave my windows cracked because I think I get less head aches from fresh air. It seems my headaches have improved in the summer when I switched from a window AC to one that blows air out the window.

If you are replacing a window I think a better option would just be to measure room noise after doing so. It will probably faster and more efficient to measure perception.

someone else will probobly explain aa better then me, but it should be analog. You still have aliasing error but it will be attenuated (you would need a perfect filter).

maybe put some material over the window and seal it tight to see what will happen before you buy a new window lol

[coppercone2]

http://www.dspguide.com/ch3/5.htm