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Like many home theater owners, I wanted to take the movie-watching experience beyond just sights and sounds. I enjoy generous amounts of low end bass in both music and movie soundtracks, so I knew that adding bass shakers to my theater seats was a must.
Bass shakers (a.k.a. "butt kickers," "seat shakers," or just plain "shakers") are more accurately referred to in home theater parlance as tactile transducers. Essentially, they act like speakers that don't make any noise. When normal speakers vibrate, they move the air and send sound toward the listener. When tactile transducers vibrate, they do so sliently, but pass the vibrations to whatever they are mounted to.
In my case, I had attached a Clark Synthesis TST429-Platinum tactile transducer to the base of each of my 12 CinemaTech Valentino motorized recliners. I wired the transducers in series and powered then with two AudioSource Amp Three 150 watt x 2 channel amplifiers in monobridged configuration, so that each amp delivered 400 watts (that's approximately 66 2/3 watts for each chair for those who are keeping score). I then connected the amplifiers to the Subwoofer 3 output on the back of my Sunfire Theater Grand III pre-amplifier, so that every time a movie soundtrack sent a signal to fire the subwoofers, that signal would be sent to the amplifiers, which in turn pass 800 watts of power to the transducers, which transduce (which simply means to "convert energy") the power into vibration, then pass that vibration to the chairs, which then pass that vibration to the backside of the viewer sitting in the chair, which then causes the viewer to yell "WOW!"
Well, at least that's the intended effect. After my first installation attempt, however, I determined that the "WOW" effect wasn't big enough. Sure, the seats would shake along with the subwoofer sounds, but what I really wanted was my fillings to shake loose every time there was an on-screen explosion.
Initially, I considered the traditional brute force approach: MORE POWER (argh, argh, argh). Since the Platinum versions of the Clark Synthesis transducers are each capable of handling up to 135 watts continuous and 400 watts peak power, and since I was currently only sending slightly less than 67 watts of power to each of them, one solution would simply be to purchase bigger or additional amplifiers and pump up the wattage flowing to the transducers. With each AudioSource amp costing around $400, this would amount to an $800 upgrade.
A more elegant solution was brought to my attention by a post on the AVS Forums that discussed the merits of Behringer's Ultrabass Pro EX1200. Designed for pro-audio users, this unit generates musically consequential subharmonics that can be set to either one or two octaves below the lowest frequencies present in the original signal. Based on waveform analysis, the generated tones harmonize perfectly with the original sound, giving you big, fat low end. The product is targeted primarily to dance clubs and other applications where massive additional bass is required.
Since my transducers are rated to handle frequencies all the way down to 5Hz, I decided that simply sending them frequencies that were 1 or 2 times lower than the original signal might give me the violent shaking I was looking for without the need for any additional amplification. And with a street price of less than $80, this wasn't just a more elegant solution to my problem, but a massively cheaper one, too! And since the Ultrabass has adjustments to control the range of frequencies it outputs, I knew I wouldn't destroy my transducers by sending them potentially damaging frequencies.
When the Ultrabass unit arrived, I used a custom-built balanced XLR cable from WickedCables to connect the subwoofer XLR output on my Theater Grand III to the Channel 1 input of the Ultrabass (the two subwoofers in the theater were unaffected by this upgrade, since they were directly connected to 2 of the subwoofer RCA outputs on the pre-amp, and therefore wouldn't receive any synthesized frequencies). I then used a ¼" male jack to RCA female connector to connect the Ultrabass' Channel 1 output to a high-quality RCA interconnect, which I connected to the right channel input on the first AudioSource amp. Finally, I used a second RCA interconnect from the Line Out Thru connection of the first amp to the second. With everything connected, both amps were ready to receive the lower synthesized frequencies. After setting the knobs on the Ultrabass to limit the high and low frequencies being produced, it was time to test out my $80 upgrade (with the connectors, it was actually closer to $100, but still a relatively small budget project).
I selected the 1 octave option on the Ultrabass and popped in the Armageddon Criterion DVD to watch the opening meteor shower scene, which contains a non-stop assault of loud explosions and rumbles. The result was astounding. So much so that for the first time, I actually had to turn down the gain on my transducer amps because there was TOO MUCH vibration. Pleased with the result, I next watched the hotel demolition scene of Ocean's Eleven and felt like I was sitting inside the hotel as it tumbled to the ground. A smashing success!
In addition to simply more vibration, however, I've enjoyed this upgrade because I also have more control over the vibration. I can control how much they shake as well as what frequency range is sent to them, which allows me to can block harmfully low frequencies that would damage the transducers, and eliminate high frequencies that would otherwise make the seats vibrate with normal on-screen dialogue. I have mine set to just go when low frequencies are sent to the speakers, but when they go - they REALLY go. That type of control of the transducers is essential to tricking the viewer - even if just for a spit second - that they are in danger of an explosion, car crash, earthquake, or any other type of movie-based rumble.
I now enjoy a much more "moving" experience as I watch action sequences, but the bypass option on the Ultrabass allows me to
disable the synthesized frequencies if I feel the need to not feel the extra vibration. For less than $100, it's an upgrade I
highly recommend to anyone looking for a little extra kick in the pants from their shakers.
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