Six Foot Speaker Shakes Buildings To Their Foundation

In the first scene of Back to the Future, [Marty McFly] visits the unoccupied laboratory of [Doc Brown]. Seeing an 8-foot-tall speaker connected to a huge array of amplifiers, [Marty] immediately turns on the amps, plugs in an electric guitar, and promptly destroys the amps and speaker while being thrown across the room. This scene must have been a huge inspiration to [Dan] and [Kyle]; they decided to replicate this gigantic speaker for the 2011 UW-Madison  Engineering Expo.

A speaker is a remarkably simple device – they’re usually just a coil of wire, a set of magnets on an iron frame, and a cone. [Dan] and [Kyle] wound hundreds of feet of copper wire around a fiberglass frame for the voice coil, used 8 and 10-inch steel pipe to secure the magnets, and pop riveted two sheets of polycarbonate together to form the cone. The result is a six-foot-diameter speaker in an 8x8x2 foot enclosure.

A speaker this size is only good for one thing: a ton of bass. The speaker can reliably reproduce frequencies from 5 Hz to 50 Hz, frequencies that are better felt than heard. There’s a video of the speaker in action after the break, but we’re pretty sure the best way to experience this insane device is in person.


43 thoughts on “Six Foot Speaker Shakes Buildings To Their Foundation

      1. Sometimes just building what’s in your head is better than copying what was in someone else’s head.

        I did this for a college project, and only AFTER it was done and graded, did I look up patents on it. I found out it was patented and used by NASA 17 years prior. Oh well, there goes my great business idea… but I got the A+++ and it was all mine!

      1. It’ll play up to about 1kHz but it rolls off above 50Hz. We did have a guy playing bass on it and it sound pretty nice. (We used that as a cool down technique after playing Crystal Method and reverse chirps).

  1. You can see the polycarbonate deforming under the low frequency stresses. They really should have used a stronger material. Carbon fiber composite would probably have been best, but that may be too expensive. Glass fiber could probably work.

    1. The polycarbonate was donated and thus free. The code deformation was improved greatly later by adding a port. The problem with the initial test was that the air in the box was too stiff.

    1. 300,000 watts of ACTUAL RMS bass would equal out to something like 2500 amps assuming single pole, 120V power. Obviously, most commercial rigs are 3 phase at probably 208 or 480 but I doubt that most concerts truly need that much power. A lot of times, the “big speakers” are just props.

      1. While you are correct that 300kw does seem a bit high for all but the largest sound rigs, I’d like to point out that big speakers that are only props are typically found on the stage, not actually as part of the PA.

        I wouldn’t think it’s impossible to find a show with 300kw of audio (I typically work with 200-300A/3ph services for audio, including stage power).
        If you were running something like a Crest 9200 at 2 ohms, you’d only need about 50 of them to hit 300kw.

        That said, higher power doesn’t necessarily mean better sound- things will typically sound much better with a 4 or 8 ohm load than at 2 ohms (but will consume more power at 2 ohms)

  2. That’s freaking awesome! The box does seem a bit small though. They should’ve left the back open and then pushed it up against a doorway and used a classroom as the box :D

  3. over 120 years ago there was a scientist and his assistant playing with the below human hearing frequencies.
    After one experiment there was only the scientist, the assistant was imploded when caught in one of the troughs of the sound wave.

  4. The real question isn’t “dB” but dB/W. I’d love to stick that in a horn.

    Back in the ’70 I saw a styrofoam cone 36″ driver made by JBL for service in a church organ. The cone was tapered and 6 inches thick at the voice coil.

    And @Bob, if you believe that, I have a toll bridge you can buy real cheap.

  5. Lets here it for electron guns, you know you are going to miss them when the CRT disappears. Unless they return in a more awesome application. Interesting but I don’t often open paint to doodle using the mouse, much less feel like stretching my arm across the desk to use a desktop touch screen monitor

  6. Did anybody see the movie “cliffhanger” in a good theatre? They messed up the sub-20Hz part of the spectrum on that movie. The opening scene with the heli hanging above would’ve been great with a 5Hz subsonic bass going through the theatre.

    When I saw that movie, the theatre proved it had good audio with the ads and previews before the movie, but when the movie came in all subsonic sound was gone. :-(

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