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A few years ago I started going to the monthly London Critical Mass bike rides. Quite often other riders would bring along sound systems, ranging from a couple of speakers on a rear rack to large trailer mounted systems that needed a tandem to tow them! After one particularly memorable Mass where I spent most of the evening behind one sound system playing really cool stuff, I decided to build my own. My first effort (christened SoundWave by my teenage son) was OK, but I felt I could do better. This instructable documents the construction of my second system, christened BeastBox (OK, he's a Transformers fan).
First off, I must say that the design of BeastBox owes a lot to a sound system called Son of Pedals, the designer of which put up a very helpful web page . Without that one page of notes I guess I would have got there in the end, but it would have been a lot harder! I'll refer to Son of Pedals and that one page of notes throughout this Instructable and to save time I'll just use SoP.
BeastBox is a trailer mounted sound system that can just about be towed by a reasonably fit person on a mountain bike. It weighs 54kg and will play seriously loud music with proper gut-thumping bass for 3-4 hours. I borrowed a sound meter from work and clocked it at 120dB(A) at 1m, not bad for something that runs off torch batteries :-D
Someone shot some video of the March 2011 Critical Mass ride and caught me a few times along the way. The guy kindly let me edit the footage and I have uploaded a new video showing just the clips of BeastBox to give an idea of the sound level. The part at 1:30 under the bridge was very loud - you can hear it is overloading the camcorder's microphone!
I have used it on a number of Critical Mass rides and a few other cycle events in and around London over the last 6 months. I nearly always get a few people asking how it works, what it runs off, where I got the plans etc. and a friend of mine suggested I write an instructable for it. This is my first Instructable so I'll welcome any comments, good or bad!
First off, I must say that the design of BeastBox owes a lot to a sound system called Son of Pedals, the designer of which put up a very helpful web page . Without that one page of notes I guess I would have got there in the end, but it would have been a lot harder! I'll refer to Son of Pedals and that one page of notes throughout this Instructable and to save time I'll just use SoP.
BeastBox is a trailer mounted sound system that can just about be towed by a reasonably fit person on a mountain bike. It weighs 54kg and will play seriously loud music with proper gut-thumping bass for 3-4 hours. I borrowed a sound meter from work and clocked it at 120dB(A) at 1m, not bad for something that runs off torch batteries :-D
Someone shot some video of the March 2011 Critical Mass ride and caught me a few times along the way. The guy kindly let me edit the footage and I have uploaded a new video showing just the clips of BeastBox to give an idea of the sound level. The part at 1:30 under the bridge was very loud - you can hear it is overloading the camcorder's microphone!
I have used it on a number of Critical Mass rides and a few other cycle events in and around London over the last 6 months. I nearly always get a few people asking how it works, what it runs off, where I got the plans etc. and a friend of mine suggested I write an instructable for it. This is my first Instructable so I'll welcome any comments, good or bad!
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Signing UpStep 1It's all about efficiency
A sound system loud enough to dance to needs more power than you can generate by pedalling so you have to rely on batteries to carry your energy around with you. Batteries are HEAVY so you need to be as efficient as possible to get the maximum volume and play time from the limited stored charge you are carrying. The bass driver soaks up the majority of the power because to create decent bass you basically have to shove large volumes of air back and forth so the bass driver and its cabinet is the most important factor in the design.
Like SoP, Beastbox uses a 6th order bandpass box for the woofer. This is a two chamber enclosure with the driver mounted in the dividing partition. Each chamber is tuned to a different frequency so that the effect is to get a big bass boost at those two frequencies and some boost over the ones in between. The frequency response comes out a bit lumpy but you get a 5-10dB boost which makes a big difference.
The other important factor is the amplifier(s). The obvious choice of amplifier is some sort of car audio unit. My first sound system used a second hand car amplifier and wow, did it get HOT! All of that heat is wasted energy so an efficient amplifier was a priority. Fortunately you can now get Class D amplifiers which are much more efficient than older units. Until recently you could only get Class D bass amplifiers but there are now full range Class D amps which cover the complete audio range. Beastbox uses two Class D amps, one for the bass and one for the midrange and tweeter.
Like SoP, Beastbox uses a 6th order bandpass box for the woofer. This is a two chamber enclosure with the driver mounted in the dividing partition. Each chamber is tuned to a different frequency so that the effect is to get a big bass boost at those two frequencies and some boost over the ones in between. The frequency response comes out a bit lumpy but you get a 5-10dB boost which makes a big difference.
The other important factor is the amplifier(s). The obvious choice of amplifier is some sort of car audio unit. My first sound system used a second hand car amplifier and wow, did it get HOT! All of that heat is wasted energy so an efficient amplifier was a priority. Fortunately you can now get Class D amplifiers which are much more efficient than older units. Until recently you could only get Class D bass amplifiers but there are now full range Class D amps which cover the complete audio range. Beastbox uses two Class D amps, one for the bass and one for the midrange and tweeter.
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I noticed a purple, trailer mounted sound system on a Y-frame.
Brilliant instructible BTW.
I'm composing a fun Critical Mass chant to sing with the Critical Mass Choir when the batteries run out...
!D