Can an active subwoofer be connected to a receiver designed for a passive subwoofer? - AVS Forum
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post #1 of 9 Old 11-27-2012, 10:28 AM - Thread Starter
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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?
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post #2 of 9 Old 11-27-2012, 12:10 PM
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You can buy an adapter to convert from speaker output to RCA output, typically they are used in car audio where a head unit does not have low level outputs. It might work, and for the $10 for a converter could be worth a shot.Just go to Wal-Mart and pick up a 2 channel LOC. Will be in the car stereo section.

For the record, I have no idea if this would work in the home. But I don't see any reason why it would not work either.
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post #3 of 9 Old 11-27-2012, 12:13 PM
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My initial thought would be no because of the power requirements between an active and passive sub. The S3400 might not be able to detect a "modified" sub output as well.
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post #4 of 9 Old 11-27-2012, 12:20 PM - Thread Starter
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Yeah I know the adapters exist, and that it'd be physically possible to connect the sub. My concern is over the power and if the receiver will try to power it even though it gets its power from AC. I wouldn't mind spending the $10 to see if it works, I just don't want to risk damaging something in the process.
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post #5 of 9 Old 11-28-2012, 08:31 AM
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Quote:
Originally Posted by letsgoflyers81 View Post

Yeah I know the adapters exist, and that it'd be physically possible to connect the sub. My concern is over the power and if the receiver will try to power it even though it gets its power from AC. I wouldn't mind spending the $10 to see if it works, I just don't want to risk damaging something in the process.

The receiver sends power to the passive sub via the speaker wires (say 25V), your older receiver simply sent a much smaller signal via the RCA (say 1V) to the active sub, that was then amplified by the sub back up to 25V or whatever it happens to provide. When you add in the adapter, you are taking that higher voltage (25V) that the new receiver is sending (the receiver still thinks it is sending it to a passive sub), the adapter converts that back down to a low voltage (1V), which your active sub reads, and amplifies back up again to 25V as if it were still connected to your old receiver.

The only thing I can think of is that you might want to try to find out the RCA voltage of the old receiver, it may be very low, and if you then send your active sub 4v, instead of say 0.5v, you could run into potential issues. In car audio you would just turn the amp gain down, but I am not sure if your sub has a gain knob.
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post #6 of 9 Old 11-28-2012, 03:51 PM
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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.




Quote:
Originally Posted by letsgoflyers81 View Post

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?
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post #7 of 9 Old 11-29-2012, 07:44 AM
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Originally Posted by commsysman View Post

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.

This is exactly what the adapter I am talking about does, it takes a high level audio signal, and converts it to a low level audio signal for use by an amplifier. Typically they are used in car audio when someone wants to add an external amplifier to a stock head unit that does not have any low level outputs.

Now, I am not sure if it would work successfully on a home theater application, but in theory I don't see why it would not. It takes the high level signal from his amp, converts it to a low level signal to provide to the active subwoofers amplifier. Ultimately though his new receiver will still be sending the high level signal to a sub, just via a converter to an amplifier, so it is still splitting its power to all the channels.
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post #8 of 9 Old 11-30-2012, 10:21 AM - Thread Starter
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Thanks, but I'm not looking to buy additional equipment other than inexpensive adapters if necessary. The system I just bought was only $180, and I can't afford to spend substantially more. The passive sub is actually good enough for my application, but if it was a matter of spending a few bucks to convert speaker wire to RCA and I'd get better sound from the old sub I would have done that. It looks like that's not the case, so I'll just use the new system as intended. Thanks for the help guys.
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post #9 of 9 Old 11-30-2012, 01:06 PM
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Quote:
Originally Posted by letsgoflyers81 View Post

Thanks, but I'm not looking to buy additional equipment other than inexpensive adapters if necessary. The system I just bought was only $180, and I can't afford to spend substantially more. The passive sub is actually good enough for my application, but if it was a matter of spending a few bucks to convert speaker wire to RCA and I'd get better sound from the old sub I would have done that. It looks like that's not the case, so I'll just use the new system as intended. Thanks for the help guys.

Your welcome, don't forget you can even try to sell your old sub in the classifieds to make some of the money back on the new system.
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