I want to know what will be the average dB of a band playing in a garage, it's not fully isolate but it cut the sound a lot when we are outside the garage. In our town the law say that between 7AM and 10PM the limit for a steady sound if 55db and in the night it's 50db
The house is about 20 feets from the garage and with the windows open we barely hear the drum or bass.

If I ask that it's because in we had the visits of cops 2 times in 3 weeks because of neighboor calling them because of "excessive" noises.
And what make me laugh about that, is that both time they came here at around 3PM in the afternoon, like if we are disturbing a lot of people at that time of the day.
From what they say, we are playing often and for long period of time, but me I'm playing mostly on weekend (we never had problem on weekend) since I'm working, and my friend is playing around 10-15 minutes 2 or 3 times a day between 12PM and 4PM, I think we have played one time after 8PM.

The worse thing is that last saturday evening me and my girlfriend were outside and we were hearing a drum playing 3-4 houses from ours, so perhaps the neighbor that doesn't like "noise" s not able to judge from where the sound is coming and he always think that it's frommy place... and the cops this afternoon said the only have our adress so that's why the immediatly came here even if it can be from another house.

So what do you think of that? I know for sure that we won't stop playing because of one stupid neighbor that doesn't have the guts to at least come here talk about it, and I will perhaps try to get a db meter and see what the sound is like from outside the garage

Scoop some garbage bins for egg cartons - and hang them all around to absorb the sound and you should be fine. As far as at what level do you have the sound going on - I'm not sure the police would know the difference between 50 or 60 or whatever. They would just swing by as soon as there is a complaint and land you on a shit list if it happens often, which you said is already happening.

Instead of buying a db meter buy yourself a police radio scanner and see whenever the police is called into the area about noise and shut down everything and play video games in the garage and say the neighbor is crazy

Well, I'm not sure of the regulations in your particular area, or how they are enforced.

Places I've lived: it doesn't really matter about specific decibel levels, or stuff like that. The bottom line is, if a neighbor complains about the noise, the police will come and ask you to stop. This is a major reason I moved to a more rural place. I don't want to bother anyone, and I certainly don't want to stop playing guitar when I feel like it

The actual decibel amount doesn't mean jack squat, if somebody complains, and the police agree that it is indeed loud, you're gonna get dinged. The cops aren't going to show up with a meter and say "Well sorry ma'am, they're only playing at 50dB, kindly fuck along now".

you can try putting some foam pads in your garage across from your amps, im pretty sure that should break the sound significantly, but i may be wrong.

Well the first officer told us that what he was hearing was decent, and he will not stop us from playing, that's just annoying to have the police showing up for almost nothing, I'm pretty sure they have better thing to do.

But I really like the idea of getting a radio scanner and doing something else when they show up

...did you try talking to your neighbors? maybe ask them what exactly bothers them and when is a bad time in particular? i admit they're being pretty fucking lame just calling the cops and not saying anything to you, but sometimes you've gotta kill 'em with kindness and courtesy. go and actually TALK to your neighbors and try to work something out. they do have a right to peace, but you also have a right to use the space allotted to you for your own purposes. even the cop said they wouldn't stop you, so the only risk you run by continuing to play is pissing your neighbor off more. if you take the time and initiative to go and talk to them you might be able to nip this in the bud before it becomes a huge hassle later. this seems like it would be the obvious first step...i'm curious as to why you haven't mentioned doing so.

as for soundproofing, we use mattresses at my house to pretty great effect. granted, we play in our basement which is much easier for soundproofing. a garage is tricky because it's above-ground and the walls are often rather thin, so you'll have to do a good amount of work to make sure it's even worth doing. don't bother with egg cartons...they really aren't worth your time and effort to get because they don't really cancel a whole lot out. i would say focus on getting some mattresses or thick, padded blankets to hang from the walls. bass traps in the corners can also be helpful, but thick padding on the walls will do a lot to absorb the higher frequencies from cymbals, guitars, etc. bass traps would help to reduce the bass rumble outside, but realistically you're going to be hard-pressed to fully soundproof a garage if you aren't trying to make it into a pro studio. if you REALLY wanted to do that, the professional way (as I understand it, at least) is to build an insulated room-within-a-room, but that's generally out of your average person's budget.

in all, don't let this dissuade you from playing! your best bet is to talk to your neighbors. if they prove to be obstinate assholes, then demand that they bring a decibel meter to see if you're actually breaking the law. if not, perhaps the cops will tell your neighbors to kindly fuck off and stop wasting their time.

Well we ask our 2 closest neighbors, those that have their home not that far from my garage, one said they are ok with it (it help that my friends know them) if it's not too late in the evening, the second one was suspecting that we were playing music, but wasn't sure and said it was ok with her cause she's only hearing a little sound when she's outside, and nothing in the house.
The first cop told us that if ever the neighbor complaint again, he will try to arrange a meeting with us to talk about it, but he didn't want to say who it was.
Yesterday, my girlfriend ask the 2 cops that show up why the person that complaint doesn't come talk with us, and they said that it seems she's afraid, so I might just wait for another visit from them, and ask them to bring me to that place to talk with the person.
I can understand that perhaps they have another way of life (working during the night, being sick and need more sleep, etc) but if they just don't tell us, there's no way for us to know it

If you have a smart phone, there are actually apps that let you listen in on dispatch channels around the world. Can't be impossible to track down your local area. Kind of depends on how your local jurisdiction
"talks" though, they may have codes instead of plain speak, though that shouldn't be impossible to decipher.

My drummer have an iphone, will ask him to check that

haven't read through this yet, but if there are any windows, it's a good idea to just get old roadside mattresses to cover them while you're rehearsing. It works...

Hell, cover the door, even, until you leave... make it totally hot and claustrophobic and miserable in there. It should help in the creative process, too.