This may be a bit silly, but you could try a seismograph.[br]
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Bass is such a low frequency that it has a physical impact, such as bouncing you and your chair around.[br]
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If you get a seismograph, and have it recording when neighbor comes home, it can paint a very real and clear picture of the amount of physical movement that his bass is causing. A few calculations could then be used to prove the volume that it is producing in your home. http://eqseis.geosc.psu.edu/cammon/HTML/Classes/IntroQuakes/Notes/seismometers.html[br]
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Even if you do not want to buy (or cannot afford) a professional seismograph, it is fairly cheap and simple process to make one. This is a dedicated project resource for exactly that purpose: https://raspberryshake.org/ (though you can find many other resources for other ways and things to use to make one).[br]
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You can program it to record along with the date and time. A clearly documented recording that the house is stable for hours, then neighbor comes home and shakey-shakey. I think a few weeks would be more than enough to document conclusively the affect that his bass is having. [br]
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Additionally, there is ample research and many studies on the affect that seismic activity has on construction and architecture. If you do not live in an earthquake-prone area, your home is probably not built to withstand such things. Meaning landlord's case would be improved as he could have an inspector likely document structural damages, especially if located in/around the garage area where the car comes, as a result of the negligent behavior.