I knew about the lack of spring support...forgot that you have to have a SSF.I haven't had a chance to look up the Sony owners manual.But in speaker setup should be the crossover. Have absolutely no idea how you would ever hear voices from anything out of the .1 on any AVR. Even if set up...
According to the DIY subwoofer...the Blaupunkdt you bought lies outside what is recommended for Transmission Line, where the other one fits.
But...an 18" Transmission Line is HHHUUUUUGGGGGEEEEE anyway.
Message Robert_J directly. He's the resident guy here.
But...
Sealed is the way to go. Providing a port means the sub is "dead" below the port...unless you EQ it(which if you EQ it to make up for the port...why have one? However you could design a Transmission Line...that is a different...