Sam Bond wrote:

I want to build a portable amplifier for a musical instruments used indoors and
outside for incest (or morris dancing). As far as I can find, commercial ones
are rather expensive and wouldn't stand the odd shower of rain.

I've come across a couple of 40watt Pioneer 3 cones speakers and a "booster"
amplifier (2 * 100w, might be a bit dodgy if I'm not careful with the levels).
The amp actually has a couple of 600mv inputs so until it's working I shan't
bother with a preamp.

The question, really, is how to box the speakers. All I can find by Googling
seems to be hi-fi, large-ish adn not designed for out use.

I was thinking of shelf type chipboard (it seems rigid and comes foc from the
garage) as MDF is rather too heavy. The odd thing about most of the guitar
amplifiers I've seen are open backed, but most but not all of the bass
amplifiers are closed! I don't want a big box I have to carry it, the
instruments and the battery! The speakers are only 5" in diameter, so how small
a box can I get away with? Do I fill it with furry stuff? Do I stick a hole or
even a "port" in it?

Any help gratefully received!

Sam



First of all, what are you amplifying?

If its an electricguitar the amplifier is more specailsied than you
think, being anything but 'flat' response wise, needing about 10mV
sensitivity, 2mV is better, and an input impedance of 2M ohm ususally.

None of these will be available on teh car booster.

In addition, the loudspeakers that are used for cars are usually totally
inappriopiate for guitar use. They will blow.

You need something like a celestion 10".

On the other hand, if you are miking up acoutsic stuff, its a different
strory, but again 2mV sensitivity is required.

Give me some more details and I'll advise. I used to design this stuff.