Sensurround

[AndyC]

I was watching Earthquake recently, and it got me thinking about the old Sensurround audio system from the 70s. It occurred to me that although the name goes hand-in-hand with Earthquake in my mind, and has since I was a kid, I didn't actually know what it was. I just assumed it was some early surround sound system. So I did some reading, and it was much more than that. For working within the limitations of audio technology at the time, it's pure genius. I'm sure there must be somebody on the board who has seen a Sensurround film in the theatre, and can describe it. As I understand it, even the sound systems in theatres today can't duplicate the effect.

Theatres installed arrays of gigantic, specially-designed subwoofers, tuned for bass all the way down into infrasonic frequencies. They hooked these up to huge amplifiers. And since film track audio didn't go that low, they used a rumble generator. This thing used a few logic chips to generate a pseudo-random mishmash of low-frequency noise. Two of the audio tracks on the film carried a series of tones that fed into a controller that activated the rumble generator, controlled the amps, and even routed some of the film's audio to the big subs. The result was earth tremors that not only had a fuller sound and bass you could feel, they actually shook the theatre. Grauman's Chinese Theatre had to install a net to catch falling plaster, and a couple of cities banned the system because their building inspectors thought it could potentially cause structural damage.

Sensurround was developed specifically for Earthquake, but it was further refined and used in a handful of films - Midway, Rollercoaster and the theatrical release of Battlestar Galactica. Then it vanished, because it really wasn't all that practical. The equipment was expensive, it took up potential seating space, and it didn't lend itself to multiplexes at all, what with the effect working almost as well on people watching a different movie next door.

What is most surprising is that the electronics of Sensurround are not that complicated. Anybody could build the rumble generator with a few bucks worth of parts. The controller is more challenging, but could probably be greatly simplified with today's microcontroller technology. I'm sure you can guess that I'd really like to have a go at making a more modest version of it. Maybe do a screening of Earthquake for the community. The real obstacle is that only theatrical prints of the movies have the Sensurround control tracks. The Earthquake DVD claims to have alternate 2.1 "Sensurround" audio, but that is, by all accounts, a lame gimmick.

As I understand it, the only thing that comes close is watching Earthquake in a gaming chair with vibration motors. I wonder if a room-sized rumble generator could use that type of controller, and take its cues from the DVD audio itself. Hmmmm.

[The Burgomaster]

I saw EARTHQUAKE in Sensurround.  It wasn't a big deal.  A lot of bass and you could feel some vibrations from the sound.  Today's digital surround is far superior.  Other movies such as ROLLERCOASTER and MIDWAY were also released in Sensurround, but many theaters just showed them with normal sound.  Sensurround tended to disrupt movies people were watching in next-door theaters.

[The Burgomaster]

. . . and had I thoroughly read all of your initial text, I wouldn't have repeated most of it in my reply!  But anyway, Sensurround really didn't live up to the hype.  It was like sitting in a room surrounded by speakers with the bass cranked up.

[Jack]

You can just get a very large subwoofer for your home and create pretty much the same effect.  Something like this:  http://www.edesignaudio.com/product_info.php?cPath=2_41&products_id=606  Put that in a medium-sized living room and I'm sure it would put any theater experience to shame 

It all depends on the audio track on the DVD though - you're not going to get randomly generated frequencies like that Sensurround system.  I've got as fairly good sub and it can certainly shake the house if you crank up the volume during the avalanche scene at the beginning of The Cave or something like that.  I find very few movies actually make good use of the Low Frequency Effects channel though.  Mostly just rumbling which doesn't do a good job of enhancing what you're seeing on screen.  If you hang out at the home theater forums like AV Science you can find a list of movies with exceptional LFE tracks.

[Flick James]

I saw Rollercoaster in Sensurround. Wow, Andy, I haven't thought of Sensurround in a very long time.

It was pretty cool. Yes, I had heard of it, and as a kid I was excited because you were supposed to be able to "feel" the movie more. It did it's job in that regard.

[AndyC]

Burgo's description of Sensurround sounds like what I would expect to hear if somebody filled a room with high-powered subwoofers - too much bass. Still, I have to admire the ingenuity of it.

I wonder if Sensurround installations were ad hoc affairs, made to fit the space and the budget of each location. The description I've read of the system, as designed, sounds like a lot more than most theatres of the time could accommodate, in size and cost. I can't see theatre sound in the 70s being to the same exacting standards of something like today's THX systems, and if it was created specifically for Earthquake, it must have been installed pretty hastily by a lot of local audio techs. Could be that Sensurround worked better in some places than others.

The problem I can see with creating the effect (or at least what it was supposed to be) at home, is getting the low frequencies at high power, without it sounding like crap. The output of most subs drops off sharply below 40Hz. It's getting those sounds down in the range that you feel much more than hear, getting them strong and clear, that's the challenge. And then there's the question of whether those frequencies are even contained in the DVD audio. Being pretty much outside the range of human hearing, as well as the capabilities of most audio equipment, I can't see good infrasonic sound being a priority. Still, I think it's possible to do on a budget.

The new rotary woofers show a lot of promise. Fans with blades that change their pitch to reproduce extremely low frequencies. Haven't heard one yet, and the cost is prohibitive, but the idea is intriguing.

[AndyC]

I saw Rollercoaster in Sensurround. Wow, Andy, I haven't thought of Sensurround in a very long time.

It was pretty cool. Yes, I had heard of it, and as a kid I was excited because you were supposed to be able to "feel" the movie more. It did it's job in that regard.

As I understand it, there were about three generations of Sensurround, with each being more refined. Rollercoaster, I think, used the second generation, where they eliminated the sound generator and added noise reduction and a few other tricks. I can imagine it sounded better than Earthquake.

[trekgeezer]

I  remember seeing Midway in Sensurround and thought the opening scene  of the B24s taking off was quite impressive, but when they got to the bombing it was just too loud.

[RCMerchant]

I saw EARTHQUAKE in the 70's but our ancient theater didn't have Sensurround.
Notice how some kids drive around in their car with the bass so high you can hear it thumping a block away? I caught a ride from work one day from one of these kids-my heart felt like it was going to burst. Very uncomfertable-and I've been to speed metal concerts!

[Jack]

Most of the better subs have a fairly flat frequency response down into the 18hz range.  You're looking at around $400 and up though.  Here's the chart of mine for example



It's an Elemental Designs A2-300, which was only around $300 at the time, but I see they're $415 now     It did knock a picture off the wall while I was watching Silent Hill last night   

I'm sure that's the way to go to get the effect you're looking for.  If you really want to feel the whole room shaking, and for there to be the possibility of structural damage, you'd need to spend more money though.  It depends on the size of the room - the bigger the room, the more cubic feet of air you've got, and the more power you need to move it.  Or put something like the A2-300 in a small room like a bedroom. 

You can also get these things called a Buttkicker http://www.thebuttkicker.com/ which produce vibrations down well past the range of human hearing.  You bolt them to the floor under your chair or sofa and they shake.  From what I've heard from people on the home theater forums they seem to work pretty well.  It still depends entirely on the soundtrack of the DVD though - if there's not much sound down there, it won't produce anything.  And having sound below the range of human hearing to impress the .01% of viewers who have a gigantic home theater setup isn't a big priority with most movie producers unfortunately.