Passive and Powered? (1 Viewer)

[Matt Baldwin]

This might seem like a dumb question to most, but I will just throw it out there anyway.....

I have a 8" powered sub that is currently hooked up to my Yamaha 5660 reciever via a subwoofer RCA cable, I also have a 15" passive sub that currently is just sitting around. Does it make any sense to hook up this passive sub? With the LR speaker wires running to the passive and then out the front LR? With most or all of the bass going to the powered sub is it really worth it?

Thanks!

 

[Aaron Gilbert]

There are any number of reasons this is not a good idea. First off, is the 15" passive subwoofer a dual voice coil driver? If it is not, you'll only be able to send it the left or right channel, not both. And, since you will be modifying the output level of whichever satellite it's connected to, if you can't connect it to both, you're screwed. Now, you could get some giant inductors and capacitors and make a passive crossover (again, assuming it's a dual voice coil woofer). The coil would go in series with your passive sub, capacitors in series with the satellites. You'll need to know the impedance of each. If it's a dual voice coil woofer and you don't want to use crossovers, you can do that, but realize that you'll create two problems: First, the receiver will see an impedance no greater than four ohms, assuming your satellits and subwoofer are eight ohms nominal. If they are less, you'll come in even lower than four ohms. Second, and even more concerning, is that the subwoofer would receive a full range signal, which would make it ridiculously easy to localize in the room, and ask it to reproduce all manner of frequencies which it cannot do well.

Of course, the exception to this train of thought is that your passive subwoofer MAY have a crossover built in already, in which case it's no doubt a dual voice coil unit. If it has a crossover built in, then it would have four sets of binding posts/terminals, two pairs for the inputs and two pairs for the outputs. Is yours such a unit?

If it's a single voice coil unit with no crossover, my final suggestion would be to buy an amplifier for it, either external or a plate amp, then get an RCA Y-cable and use it along with your 8" sub. If the 8" sub really sucks in comparison, you could scavenge the amp from it's enclosure and put it with the 15".


Aaron Gilbert

 

[John Garcia]

Passive subs are really intended to use a secondary amp, not be driven off your receiver. Depending on how much power your receiver puts out, a 15" sub may draw too much current and actually degrade your performance or clip. If you are talking about a 15" passive assembled sub, you can pick up a cheap plate amp or an old receiver and power it that way, as Aaron mentions.

 

[Aaron Gilbert]

Oh yes, thanks for the reminder John, I totally forgot one of the most important points! Running both your front L/R and the passive subwoofer as full range off the same receiver channels would result in less power being available for your front L/R than before. How much depends on the current output ability of the receiver, as John noted. Also, there would be no way to adjust the relative level of the 15" subwoofer as compared to anything else, which could be very bad as a result of room placement and differing efficiencies.


Aaron Gilbert

 

[Matt Baldwin]

Thank you all for your help, I kinda figured would not be the best idea, and the passive sub does have two sets of hook ups two in two out. For now I think I will stay with the powered sub which I'm very happy with (Acoustic Research 8" bandpass 120watts) and maybe add another powered sub down the line.

Thanks again!

 

[Mike SJ]

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[John Garcia]

It makes perfect sense that a passive sub has speaker level outputs, since the signal it is being provided with must be powered - it would be more common to see a passive sub in an "inline" configuration. Most likely this sub has a built in passive x-over for the sub driver and a high-pass on the outputs, just like any other sub.