the topic returns like a boomerang, I can see that there are still various superstitions, let's put it together again:
The drawpieces dampen minimally - if someone thinks they are muffling - it is only to the extent that they distract - there is no echo, so you can, for example, play quieter and hear yourself. the overall effect is that there is less noise. They suck - not very durable, light, so they will fall off the wall because you will always catch them, etc.
In order to prevent sounds from penetrating outside, you should dampen with mineral wool at least 10 cm - and preferably thicker - on a frame (because something has to hold it, and cover it with e.g. carpets - because the mineral wool "dusty". and even on Allegro below PLN 10 per meter.
The garage is 3 m high? Are you sure? usually below 2.50 ...
Unfortunately, so that the sounds do not penetrate to the outside, they have to be muffled very carefully. If you leave the door open, 90% of the work is for nothing.
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It is different if you just want to improve the acoustics inside so that it is fun to play. But in such an arrangement, I advise against the extrusions, but I recommend all kinds of rugs, blankets, tapestries, sheets - what can be found among the family, etc. In fact, each element (carpet, carpet) improves the acoustics in relation to the non-damped one. You cannot, of course, exaggerate - because then the sound is muffled. You have to hear it by ear if it is all right.
If you do not have rugs from your family, you can buy the cheapest carpet, the so-called "renovation" - about 5 zlotys. performs similar functions to a carpet, and much more aesthetic - (because, for example, my rehearsal room looks like a genghis khana yurt)
The polystyrene is of no use when it comes to the rehearsal room.
Quote: Will an ordinary 1 cm thick mat be able to soundproof such a room if it covers one wall?
Are you crazy