all alpine setup?

I am using, if I say good... will you buy immediately?

u can see my signature.ur question too general.yes alpine do produce some audiophile grade model(like f1) if u can afford it. in my opinion based on my setup alpine w520e+processor-quite good, alpine type r speaker-average, alpine pdx1.1000 amp-average

ill take door sound proofing:

when your speaker resonates/vibrates (the mid bass, when theres bass kicking in), it will travel through the door. more often than not that will cause unwanted vibration/noise and it will pollute your sound reproduction.

sound proofing helps reduce or even completely eliminate that.

another example is engine firewall/hood or bonnet sound proofing:

engine noise? minimal or gone.

what do u mean by yi yi oh oh sound? sound proof is to prevent unwanted noise cause by vibrating car parts. like quazacolt said. but its not solution to all noise in your car.if the noise come from ur foldable rear seats, sure sound proof wont much help.

put some good comp like morel etc at ur front speaker, play it loud and you know what i mean