Big John said:
Hi Adrian,
Yes, it does sound like a fun project. But putting it together may not be
all that easy. I'll try to give you some info to get you started.
First, what speakers you use and how you connect them will make all the
difference. There is a lot to it, more than I can post here. Several years
ago I purchased a copy of "Building Speaker Enclosures" by David Weems at
Radio Shack. It wasn't expensive. This book goes over how speakers work,
the different types of drivers (woofer, midrange, and tweeter), speaker
impedances, cross over networks, how to connect speakers electrically, some
info on amplifiers, L-Pads, and a lot on the design of the speaker
enclosures. I hope Radio Shack still carries it, but if not try Amazon's
used book section. I'm sure you can find it or a newer edition. Read this
book first - it will save you a lot of grief.
Second, a car battery may not be the best choice to power your system.
They weigh a ton, but there is another problem - car batteries are not
designed to be deeply discharged. If you discharge a car battery below
about 80% of it's capacity on a regular basis it won't last very long. Car
batteries also like to stay in the vertical position. My advice here is to
try gel cell batteries. These look like small car batteries, but they can
be discharged more deeply. They don't spill if you turn them on their side
and, for your application, will probably be much lighter. A lot of
electronic places carry them including Digikey and All Electronics. Some
automotive stores carry them in a plastic box, complete with a charger, for
jump starting cars and portable applications.
As far as what to use for a CD player and amplifier - why not just use a
decent after market car stereo with a CD player. They're made for a 12 volt
system and you can get a fair amount of power out of one. They're also
designed to handle a fair amount of vibration - which is good for a portable
player.
This is a big project for a beginner, but you'll learn a lot.
Good Luck,
Big John
I built such a device many years ago using standard car stereo components.
There was a cassette head unit connected to a CD changer and a small
amplifier (150W IIRC) driving a 8" woofer/tweeter speaker set. This was all
powered from a normal car battery. It was constructed from 12mm MDF divided
into 3 compartments. The battery & audio components in the centre section,
then approx 1 cu.ft of sealed space on either side for each woofer. The
tweeters were surface mounted. The whole lot was weighed in at about 80lbs!
As loudness rather than sound quality was the goal, also wow factor when you
get this thing out at BBQs etc
I didn't spend too much time calculating
optimum speaker box volumes etc. It sounded pretty good, and it was LOUD,
plus it was somewhere to sit if you didn't have enough chairs
If I were to do it again I would use plywood instead of MDF to save weight,
also the previous poster's suggestion of using gel batteries is a good one
but they are a lot more expensive than car batteries. Besides, I got a whole
afternoon's use out of a smallish car battery which is probably long enough
before the police are called.
Try to get the most efficient car amp & speakers you can. This will maximise
the volume and battery time. Don't worry too much about having loads of
speakers, especially woofers as you need big amps and therefore lots of
current to drive them. A pair or two of good quality 6*9s will probably be
fine. Just position the thing close to a wall if possible and this will give
you a big bass boost for free.
I wish I'd taken a picture if it...
