The basic stuff:
rear bike rack
mp3 player with belt clip/holder
small wood screws
mount from an old bike light
mp3 player cable and speaker cable
4 bolts around 3" x 5/16" (80 x 8mm) with 8 washers and 4 nuts
about 2' (70cm) of wood around 1" x 5/8" section (25 x 15mm).
if you want 2 speakers instead of 1: a piece of plywood to mount them on
The key components:
Speaker (1 or 2)
The key to this project is efficiency
. Home and car sound gear is not designed to be efficient or light - it just isn't a concern in those applications. Low efficiency means you need lots more power to make the same amount of sound, and lots of power means a big heavy amp and a big heavy car battery. An efficient speaker can produce 5x the sound volume from the same amount of power. An efficient amplifier is 2x better than a standard one, plus its far smaller and lighter.Efficient speakers:
PA and DJ speakers are the best place to look for efficiency. Auto and home speakers are usually poor. Large speakers are nearly always more efficient than small ones - this is one of our real tradeoffs because large speakers also weigh more.
The smallest speaker I recommend is the Gemini RS-308
, you can get that at Amazon and other places for $70. It fits into a milk crate and weighs 15 lbs.
For the current project I used a somewhat larger Behringer S1020, I got it from parts-express.com
for $100, it weighs about 20 pounds. American Musical
has a lot of speaker choices too.
Go MONO! Stereo doesn't make a lot of sense when you are riding around on a bike. Using one larger speaker you get will more sound and less weight than two small ones, and its less work to mount it.
How big a speaker can you fit on a bike rack? The speaker in my project photos has a 10" woofer, most models with a 10" woofer are about this size. The Gemini 8" speaker is quite a bit smaller, it fits into a milk crate that you might already have on your rack.
Hacker Tip: Occasionally I've seen hackers try to use a bare speaker cone with no box to save weight. Do not do this! The box of a speaker is critical to its ability to create sounds. When you get rid of the box you lose most of your sound output.Efficient amplifiers:
For amplifiers there is really only one choice: a Tripath-based amp, sometimes called a T-amp, Class-T amp or Digital amp. These ultra-efficient wonders are inexpensive but obscure. T-amps are available in a couple of different sizes. parts-express.com
sells the 10 watt DTA-1 for $45 and it includes a built-in battery holder. It runs at full power for 4-6 hours on 8 rechargeable AA's - wow!
On Ebay.com there are several vendors with higher power T-amps. For a 20 watt amp I recommend the TA2020 amp from ebay seller indeed-hi-fi-lab
. It's only $20 and is very good quality with durable construction. indeed-hi-fi-lab seems to have 2 variations called the "Tripath TA2020 Mini Cute Class T Amp Amplifier Ipod MP3" and the "NEW Class T Amp TA2020 Amplifier Tripath Chip TA 2020". Rest assured the one I bought is the "mini cute" type, but the other one looks equally well made in their photos.
The larger T-amps don't include a battery holder, you will need to supply an appropriate 12V battery. 12V "SLA" type batteries are very inexpensive, and also easy to find at recycle yards. For a new one try batterymart.com
. A 7.0 Ah capacity should last you all day and costs $20. They also have a nice charger
for $15. Amazon has these batteries too.Much more details about speakers and amps I have tested
if you need it.