Need help building a speaker.

[Paul Lee]

What parts would I need to build a speaker within a small water proof cylinder box. 5x6.5 by 1.25 im doing a project for tech ed.

 

[Audioguru]

Build a speaker? You mean to put together a magnet, a moving coil and a cone?
Or do you want to make a sound system with an amplifier and a tiny speaker?

The tiny speaker in the tiny box will sound awful.

 

[FuZZ1L0G1C]

By 'cylinder box' I gather you mean a short length of pipe, plastic jar or similar.
As wise sage AG stated this will sound cr*ppy.
A hollow tubular enclosure will produce a strong resonance 'honk' at a certain frequency.
However, you can slightly improve response by loosely filling the enclosure with batting (BAF wool).
If the height is 1.25 (flat box) you'll get no bass (tinny sound).
Does the tech ed project score points on sound quality, and budget (or tech ed issue) limit you to a small driver?
If so, try a bigger rectangular box, say height 3.5x diameter of driver, with ratio 3:2:1. ( H : W : D ).
To reduce tinniness and drag out any lows, try a non-polarised audio-grade cap across the speaker terminals.
Roll-off f (Hz) vs raw cap value = 1/((2*pi())*C) or 1/((2*pi())*Hz)

 

[Audioguru]

To reduce tinniness and drag out any lows, try a non-polarised audio-grade cap across the speaker terminals.
Roll-off f (Hz) vs raw cap value = 1/((2*pi())*C) or 1/((2*pi())*Hz)

You neverconnect a capacitor across speaker terminals because it will be a dead short at high frequencies to the amplifier and the amplifier might be destroyed if it does not protect itself by limiting the very high current or muting itself. The high frequency levels will not be reduced anyway unless the amplifier limits the capacitor current because the amplifier has an extremely low output impedance (0.04 ohms or less) and has plenty of negative feedback.

 

[duke37]

If the speaker is to work at a decent depth, then the container will need to be made from strong, heavy material. This will need a high power to vibrate it and the water which it is coupled to.