The Tube2 (tm)

My second custom sub for my Civic is a high-performance isobaric ported tube. It's still in its prototype stage, clearly showing the simple carboard tube construction. All that is necessary to finish the enclosure is some automotive carpeting.

The drivers are two identical 5.25" woofers mounted face to face in a 6.5" OD 22" long tube. They are wired out of phase, so that as the inboard woofer moves outward, the outboard woofer also moves outward (wiring in phase would result in them canceling each other and zero bass!). The drawback of this type of mounting is that the two woofers only have the sensitivity of a single 5.25", since the cone area is only equal to one woofer. So why mount them like this? Isobaric mounting results in a smaller enclosure and lower distortion than a single woofer would offer. The nonlineraties in both the motor (magnet) and suspension are effectively linearized, lowering 2nd harmonic distortion. The motor strength is doubled for the cone area, and the suspension non-linearities are cancelled. The doubling of the motor strength allows the use of a smaller enclosure, which was necessary for this application. The result is that these two little woofers can handle more power mounted face to face, than if they were mounted seperately. Believe it or not, these things play loud. I've blown many minds with this cutey. They are not as loud as my 1500GTi was, but trust me, they play loud enough. My body and ears think the Tube2 (tm) also has a lower f3 than the sealed box 15 did, which made me very happy.

One of the secrets of this tube playing loud is the flared port tube. The port is designed with an inner and outer flare. The curvature of the flare was properly engineered to allow very high air velocity with very low turbulence. This port was designed to work with an 8" woofer, so I have plenty of port area for my little 5.25s. No huffing and chuffing, and no changing of the system tuning due to port compression!

Now why did I go to all this trouble to make this little subwoofer tube? Check out the picture. Yes, the tube fits under the dash and partially behind the center counsel. Acoustically this works great. The bass always seem to be coming from the front of the car, not the rear. This really helps the imaging and staging. It does take away a little bit of foot space. But, my 5' tall co-pilot doesn't miss it even on long trips. The carboard tube and port are very light, so the entire subwoofer weighs about 8 pounds. The woofers are behind the center counsel, so the majority of the weight is centered in the car. And the weight is very low to the ground. When I call this a "high performance" subwoofer, I'm not only refering to how it good it sounds, I am also stating that since it is light, it doesn't hurt the high performance acceleration and handling of the car!

Some of my taller friends get a little cramped on long trips, so I added a second set of wires in the rear. With the bungy cords, I can move it from the front to the rear in just a minute. It actually booms more because of the corner loading effect. Its noticable that the bass is coming from the rear, though. Sometimes I like that it booms more, and sometimes I like it in front with the solid front imaging foundation. Depends on what disks I'm spinning. Perhaps the answer is one in the front AND one in the rear?!?!

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Last update: 11-28-97