Note- I had one of these older NSD subwoofers. It stopped working after more than a few years and I contacted SVS about fixing it. They stated they would not fix it because it was an older model. I am not sure if it was because it was DC’d or not.
BTW I live in Ohio... where they were making the sub. So I offered to bring it to them in my SUV and pick it up to avoid any shipping if they would fix it. They stated it was not an option. I ended up selling it in a garage sale because I did not have time to turn it into a DIY project.
SVS wanted me to but a new sub from them. Nope.