You can't just buy an "adapter" to fix this problem...lol.
The active subwoofer has a POWER AMPLIFIER built into the cabinet! Thus you just feed it a low-level audio signal and it amplifies it and drives the subwoofer's speaker.
The passive subwoofer requires an EXTERNAL POWER AMPLIFIER of about 150 watts RMS or more to drive it. You can't just feed an unamplified signal to it. You must connect a POWER AMPLIFIER between the receiver and the subwoofer to provide the power to drive the speaker. It does not have its own amplifier; that is why it is called "passive". The box contains nothing but the speaker.
Since an amplifier is likely to cost several hundred dollars, you would probably be better off getting a suitable powered subwoofer.
You could either use your old one or buy a new one.
The Polk PSW505 may be a much better powered subwoofer than what you have, and Amazon is selling it for under $200, which is a very good deal.
Edited by commsysman - 11/28/12 at 4:00pm
Originally Posted by letsgoflyers81
I just purchased an Onkyo HT-S3400 to replace my aging Onkyo HT-R8230 (Radioshack version of HT-S570). The one downside is that the older system has an active sub and the new one is passive. I was hoping I could use the old sub so the receiver could direct its power to the other five speakers without having to share with the sub. However I noticed that the old system as a single RCA connection to the sub and the new one uses regular speaker wire just as with all the other speakers. That got me thinking, could I just use or make an adapter to go from RCA to speaker wire? My concern is if the receiver would be sending current to the sub which is designed to get its power from AC. Is there a problem with this scenario or should I just use the new passive sub?