If you're looking to make a speaker sound better in the door one needs to completely adhere (do not spot glue here) the material to as much of the metal door surface as possible inside the door. Use the recmonded Adhasive and the Acoustic tape where needed. Do not use a substitute glue as many adhesives and tapes will hold initially but after a few weeks will lose the adhesion to the Acoustiblok Membrane. The object here is to create significantly more mass in the speaker enclosure (in this case the door). The speaker mounting should be as airtight as possible. We suggest to compelete sealing with Acosutic Sealent. It is of course imperative that after all your speakers are installed you verify polarity. A simple 9 V battery touched to each speaker wire at the amp connection allows you to visually see the cone move in or out. There is of course much more sophisticated equipment for doing this as well.