Need advice on a passive subwoofer

I might be in the need of a passive subwooofer in the near future. I won't know until I've broken in a new set of speakers. I've been advised that I should look for a passive sub with an impedence of 4 ohms. I don't need a homewrecker, just a musical sub to fill in whenever the need arises. A subtle sub will sufffice. I would appreciate any suggestions as I have no working knowledge of such a device. The speakers are down 3db @37hz and my room size is small: 15' by 11'. My price range would be up to about $500. Any suggestions would be appreciated
Why do you want passive? It only makes things more complex.
Why do you want 4ohms? That's usually disadvantageous since it will parallel what you now have.

On the advice of someone who knows my setup (a TAD Cayin TA-30 tube integrated), using a passive isn't that complicated at all: "first connect to 0 & 4, then connect the high driver '-' to the 4 tap, '+' to the 8 tap (double stuffing the 4 tap), using the entire output transformer winding in a semi-isolated manner. Its like having 2 amps in one". Or so I'm told. I've found that there is more than enough current (I used to drive Legacy Classics w/no problem) as long as the speakers are effficient. The speakers that I will be getting are 93db efficient. All I may need is a modest, musically accurate sub.
Have to agree with Kr4. Too much of a pill with a passive.

If the sub is too loud or too soft how will you integrate it - put a resistor in line - Yuck.

If you're that serious about it, look at some of the REL's that do a good job at line level, and you can adject whatever you need win its performance.
I've recently become a dealer for VMPS after having used their speakers for the last decade. Their passive subs are extremely musical and powerful not to mention bargains for the money. They come pre built or can be ordered as kits. Check out the reviews on and also check out the Vmps forum at Also I thoroughly understand why you'd want a passive sub as it can be much more versatile and you can use a much better amp than a plate amp.

Another option is to build your own. On the madisound and partsexpress boards there's alot of knowledgeable people that are very helpful. A sub is relatively simple compared to a multiway speaker and is fairly easy to build.

Not too many speakers in my opinion can do a truly thorough job without at least one sub. I run my speakers which are full range(Vmps RM 40's) with a sub. The Rm 40's are running full range and I've got the sub crossed over at about 45hz. Others do the same with similarly powerful speakers and there's a thread here with some info on that. Then there's people who don't care for bass as much as many of us. To me the bottom octave must be produced accurately and this means it must be well articulated, have power and weight. Best of luck to you.
If you can stretch your budget to about $600, you should definitely look at Outlaw Audio's subwoofer, which is a steal at the price. For more info, here's the link:
Thanks for understanding my question and for the advice. I'll check out the sites you mentioned.
Ha. So you are planning to add an amp/crossover and, in effect, make it an active sub. You should have said so.

Dear Nonoise: Makes no-nonsense to ask for a passive subwoofer.

A self powered subwoofer ( active ) has a dedicated amplifier that match with any single woofer parameter: impedance, damping, range frecuency, power, etc, etc..
No one external amplifier can match the characteristic of any subwoofer.

Please read the follow link:

Regards and enjoy the music.
No, I wasn't planning on adding a crossover and/or amp: as I stated in my initial post, I'm new to this and need advice and appreciate all the input I can get. I don't know where this will lead or how I'll end up implementing the sub. My goal is a symbiotic relationship w/my existing system with no 'seams' in the sound.
And Raul, thanks for the leads; I'll check them out.
Nonoise: You're welcome. If you want any more help just email me. I'm not a dealer for a living, sell only two lines and do it as part of my hobby. This is over thirty years I've spent doing this and so I figure I must love it.
Passive, sorta powered, no plate amps, build your own (better than factory (sure), crossover, no crossover.

Sure glad I bought my Revel where they had that all that impedance, damping, Q etc. figured out.

OK, I'm lost, nevermind.

One more time - if you go with a passive (as a passive - ie taking power from the main amp and routing above the crossover point to the main speakers), depending on efficiency it could be too loud, too soft or whatever. Your only potential to decrease the volume of the sub would be to put a resistor in the line to the sub, a yucky way to go.

If you're going to add an outboard amp to a passive sub, then you have - guess what - an active sub If you're going to do that anyway, then buy one where the manu. has already done the matching of all the characteristics mentioned above, rather than guess.

Why cobble something together and hope and pray that it works when manufacturers already have done the legwork?

The reason I mentioned the REL subs before is that they have a unique way of using high level outputs to combine with your speakers.