The performance of rear deck speakers gets affected due to high air pressure waves generated by subwoofers. I discussed with Bro STJ about installation of these cups ... according to him, he wanted to check whether these isolation cups would result in limited air volume for speakers to function. It would be decided when I visit Lahore and get it tuned by Bro DrShaggy.
Yesterday I went to Rawalpindi and bought a pair of spacers for 6X9 speakers. Such spacer boxes are used by taxi drivers for installation of speakers over a rack when the space is limited by a CNG cylinder.