-db level of subwoofers - explanation please

[tfraser]

I am in the process of choosing two 10" drivers for a diy sub. One is Scanspeak ScanSpeak 25W8565 01 £119
https://secure.wilmslow-audio.co.uk/acatalog/Wilmslow_Audio_Scan_speak_Drive_Units_19.html
and Stryke SB10 at $149 plus I don't know how much carriage; could be out of the question.

Using WinISD freeware program I can see that the Stryke has -7.69db at 20hz and the Scanspeak has -12.16 at 20 hz.

What does this mean folks. Is it a big difference, big enough to order the one from the states?

[Ramius]

From the help section on WinISD-

...The purple line is the -3dB (or half-power, or cutoff) point. This line represents the frequency at which the usable bass output of the box "runs out of steam". Any frequencies below the intersection at the -3dB point simply won't be reproduced very well by the box...


A couple of excellent DIY guides that explains subwoofer design (a good read)-
http://www.diysubwoofers.org/
http://www.audioc.com/diy/Information/submanual/sub_manual.htm


What about going for a vented enclosure?
It's is probably preferable for home cinema duties.

Cheers