I am a little puzzled by this question. Are you proposing to use three subwoofers in a single audio system or build one cabinet to hold all three speakers? Do you plan to build your own cabinets yourself? More than two subwoofers in a system provides no benefits, unless the listening room is a large hall, while making bass management more of a headache. It is not so much how the subwoofer is powered, but how you plan to match it or them to the rest of the system. Most home theatre (HT) systems provide a single LFE (low-frequency effects) channel, so, unless you plan to install one subwoofer at each end of the front speaker group, there is no need for multiple subwoofers. If you are planning to use two subwoofers in this configuration, each should be amplified separately. You may still require an active lowpass (LP) filter in the subwoofer, with an adjustable low-frequency (LF) cutoff to blend the subwoofers into your system if your HT amp lacks bass management controls or if the controls are inadequate. Active filters are placed in the system ahead of the power amplifier. Some people use two subwoofers in conventional stereo systems to obtain better control of low-frequency (LF) dispersion in the listening room. This is useful where your main speakers lack deep bass response or the response is inadequate for a large room. If a subwoofer is used only to provide deep bass response (e.g., the bottom octave, 20 to 40 Hz), one is usually adequate, unless you have problems blending it into your environment. In this case, you may not require highpass (HP) filters on the main left/right speakers, as the subwoofer will pick up where the other speakers leave off. If an HP filter is required it would need to be passive, unless you use a separate preamplifier and amplifier or your amplifier has separate pre-outs, which would allow you to use an active HP filter. You will require an active LP filter on the subwoofer, with an adjustable LF cutoff. Once the subwoofers have been constructed and installed, you will need to blend them into your system. This can be a very time-consuming process. Locating one subwoofer can be difficult, particularly if it is a reflex design that uses room characteristics to obtain optimum results. Installing two may force you to blend them with one another, as well as the rest of the system. Direct-firing sealed enclosures have an advantage in this regard, as their position in the room can have less effect on the results. If you intend to use three separate subwoofers on one system, you will gain no benefits over using one or two. Some companies mix all of the dialog into the centre channel, so intelligibility is far more important than LF response. Besides, little LF information is carried in the centre channel. In addition, trying to blend three subwoofers into the small space occupied by an HT system would be quite difficult and you could end up with a muddy mess. If these are car speakers that you are intending to use with a home system, I would recommend selling them and purchasing a single subwoofer. Many of these include the amplification and filtering required to blend into the room. A decent subwoofer can be purchased for US$500. However, the subwoofer still has to match your existing system and room characteristics. If you plan to put three speakers into one enclosure, you must wire them in series, not in parallel. Few amplifiers can deal with a 2.7 ohm (nominal) output impendance, which will dip to under 2 ohms at different frequencies. Such a cabinet would be very large and more difficult to blend into the listening room. If you are a would-be speaker builder, there are a couple of publications on the market that are very helpful: - "The Loudspeaker Design Cookbook", V. Dickason, sixth edition, Audio Amateur Press, 2000. - "Testing loudspeakers", J. D'Appolito, first edition, Audio Amateur Press, 1998.

this ones easy,get a 1ohm stable mono amp,wire the subs in parallel.if u build the box,make sure you use 3/4 mdf and screws,and get the inside air space right........thats it!!!