The suggestions for the dorm bass-shaker wiring so far all have a slight problem. The problem is that the bass-shakers will not get equal power delivered to them from the amplifier.
In one example drawn in an earlier post, with two 8 ohm groups in series with a single 4 ohm driver, the single shaker will get HALF of the power of the amplifier, the other 4 will split the other HALF of the power between them. (In other words, they each get 1/16th of the power) Now, it is true that the impedance presented to the receiver is great, but the difference in shaking between the chairs will result in a rather poor implementation. (in my opinion)
The situation is even worse with the drawing of 9 shakers (three sets of three) in series with 1 shaker. Now we have 1/18th the power to most of the shakers, and half in the other.
A better solution would be to deliver EQUAL power to each of the shakers. I can only think of three (easy) ways to get there. None are perfect. One is outright bad.BAD - NOT RECOMMENDED
Wire 5 of the drivers in parallel to the left channel of the amplifier, and 5 in parallel to the right channel. This would result in an impedance of somewhere .8 ohms. (that connection results in less than one
ohm impedance and will probably harm the output transistors in most amplifiers if run at any volume)BETTER
Wire 5 of the shakers in series. 5 x 4 ohms results in a 20 ohm load. Connect it to the left channel, wire another 5 in series to the right channel. The disadvantage of this is that the amplifier will not nearly deliver as much power output (only about a third actually) as if it had an 8 ohm load, it will be an easy load for the amplifier. If things shake enough... you are done.BETTER - and what I would try first
Take 5 of of the shakers and wire them in series. Do the same with the other 5 shakers. Each set is 20 ohms. Parallel both sets and connect them to ONE channel of your amplifier, leaving the other channel unused. The series-paralleled sets will result in an impedance of 10 ohms and allow your amplifier to deliver most of its rated output. and each shaker will get the same amount of power.BEST
Take up a collection at your dorm... buy two more shakers. You should be able to find a pair for about $30. (NOW you have 12 shakers) Find two more chairs and invite two more friends... have them bring the popcorn/drinks. Then, wire three shakers in series, connect them in parallel with another three in series and connect the six to one channel of your amplifier. This will be a 6 ohm load and your amplifier will probably drive it easily. Do the same with the other 6 shakers. Connect to the other channel of the amp.
Amplifier (one channel illustrated)
[+==-] = bass shaker
You do not have to go crazy keeping track of polarity of the shakers. It does not really matter since each is on a different chair. (And if you can tell that your dorm-mate's chair is moving/vibrating upward when yours is moving/vibrating downward, you are probably sitting too close...) It is different when you have multiple speaker cones all trying to move the air in the room. Then, you want the cones to all be moving in the same direction at the same time, and polarity matters. With shakers, you will not be able to tell.
At least with this wiring scheme, all the seats are vibrating the same amount and the amplifier is seeing a reasonable load.
Edited to fix drawing and description....