I have previously looked into some commercial tactile transducers (see post 2 if you don't know what one is ), and during that research I found a few sites where people had made their own. I made one as a site suggested... blew it up (my fault... level on amp was wayyyy too high)... made another... (still good ) and then a third (which worked even better). The third one I wised up and actually thought a bit before I put it together.
Here are two pics of the basic design that I made from the pics from other sites.

The idea is pretty basic. You cut out the cone from a speaker (the bigger the better - preferably with a large strong magnet too), and replace the cone with a strap of steel. This strap is connected in the center to the middle of the speaker, and on either side of this a piece of wood is attached. The wood is attached to whatever you want to shake. This system uses the mass of the speaker itself- it vibrates and is limited in excursion by the steel. I used a 2 part epoxy to join the washers and bolt to the speaker. These don't make any sound themselves, but do a very respectable job of shaking a couch.
This design has a few drawbacks. The first is that the response is not very sharp- a bass hit will take noticeably longer to die out than the note from the sub will, and the fidelity of the vibration is low. The second is that it is very difficult to align the remnants of the speaker cone with the bolt to glue it in.


To that end, I came up with the above. Very similar to the first (and second) attempts. This time I left two strips of cone in place to keep the voice coil aligned when I was gluing in the bolt (visible in top pic). I also left the dustcap of the speaker on and coated it with epoxy to reinforce it, as opposed to cutting it out and then having to use washers to bridge the space. (hard to tell because of all the dust on it- but it's actually hard and shiny when clean). I also added in another steel strap - this made the response much more accurate, a lot closer to 'hi-fi' shaking .

Basic (very) Definition:
A tactile transducer is a device that creates vibrations. They're usually fed from the subwoofer out on a system and respond to low frequency effects (not so cool if voices shake your couch..). If you've ever had your subs up really loud and felt everything shake - it's the same feeling. But the great part is you don't have to crank everything up to potentially harmful levels to achieve the same effect. And when you do crank it up high- it feels like you've got another few 15" subs working. They're not a 'one note' device either, they can respond quickly to input and change in frequency. *feel free to help out with this definition- it is by no means comprehensive
This is how I have mine attached to my couch.

I have two C clamps which hold on the black bits of wood to a strong structural element along the back of the couch. It is sturdily built, so this isn't a problem. Another solution is to block up the couch several inches, and clamp the board to one of the crossmembers underneath it. I am powering this with one channel of an old stereo amp (only ~75watts). This is more than enough to shake the whole couch with the volume at ~40% of max.
I have a pair of polk RT3000Ps for my front speakers.

They have dual longthrow 8" subs with a 300w amp in each tower. Dual 8"s are equivalent to a single 12" in terms of cone area, but are more responsive due to smaller cone size. The pair of these can shake the couch with no help from the transducer, but require a moderatly high volume level (somewhere around 90db according to my meter). With the transducer on, it seems like the volume is up- but without the ear pounding. I use the LFE pre-out on my receiver to drive the amp for the transducer.
The speaker I used came out of a 80s era speaker which had a blown midrange and tweeter. Now it's a vital part of my theater experience - it adds a visceral impact to movies which just subs can't quite touch. Plus, if you have the speaker and spare amp of some kind lying around... it'll cost about $15 (and that's if you get the nice epoxy )

Very nice. I have seen similar ones where they cut the frame away from the drivers for more direct contact. I like it!

For someone who isnt looking to mount woofers on their couch, you should look here.

SJ

SJ - Thanks for the pin - I think enough of us probably have old speakers lying around that it's pretty good info. I do recall seeing one with the frame cut down... as I recall that particular one used a wider sheet of metal, and required a bit more metalwork than hacksawing a steel strap from the hardware store Do you know if cutting down the frame provides a significant advantage..?
I don't suppose that you have one you could slap together? I don't have any other shakers to compare with, and am very curious how the home brew model stacks up against the aura shakers (especially since they have a much smaller and easy to work with form factor). Not to mention the good price at partsexpress...

do you think these things would work on my simulator. i experimented with putting a pc base speaker under the seat but it wasnt powerful engh to feel, but these look like they might simulate engine vibration quite nicely.

twisteddman - I think one of these would certainly do the trick. If it is shaking something small like a chair or loveseat - it should be more than enough. I've enjoyed the added emphasis with any low frequency effect- explosions, gunshots, the standard action movie fare I would bet that engine vibration (provided it is low enough frequency) works just as well. Gl.

how many of these does on need on an average couch?

I have one on a couch (standard size as far as I know) which also has a hide-a-bed in it. It's a pretty heavy couch. I only have one attached to the back- and it does a pretty good job.
Two would probably be a better idea- that would make more shake overall, and tax the transducer less, leaving more headroom. I just didn't have another speaker around to cannibalize

What are those motors called that are in the game controllers? For a more compact space, like a computer chair, the motors seem like they would give the same amount of vibration at a lower wattage. And you could hide them better.

hehe this reminds me of an old project i had before i moved to my own apartment, did the same thing and i can say the effect is VERY immerse

i watched a submarine movie and had 2 old 18" attached on the backside of my couch just as you have and they were powered by an old sterio 2x 70W and it was enough =) no "HIFI" signal needed since u hardly hear them anyways.. and those wondefull subwoofer-testing sink-bomb-scenes will shake ya good that's for sure. It tricks yer ears into thinking there's (just as mentioned) like 8 subwoofers all over the place just pounding -TRY IT! its an easy mod to those old speakers u got layin around =)

PS: try it with an old 8" or something it'll give the same effect under that livingroom chair =) dont haveto go big to get the effect.

I have an 8" 600w, but the suspension is starting to tear away from the coil. If i used rubber adhesive would it be ok to use? or should i get another speaker? Its tore about halfway around the coil.

Hey!!!! Im new here...Im just wondering ...What width and thickness straps did you use for this project? I want to build one for my computer chair. Thanks a bunch!!! Regards, Galaxy