volume control through pot

hey, just had a question. has any1 ever tried to adjust volume with a potentiometer before? well im still in high school and in the morning, listening to the announcements is brutal. the announcers talk soo damn loud and it PO every1 even my physics teacher. Well since i usually mess with electronics, i was plannin to help my science dept with turning down the volume on the single speaker inside the room. I opened one of them already and the speakers are 8Ohm max 20watts. any1 know what a good pot size is to use? or what i can use to cut back the volume just a little? hoping it can be cheap to do. thanks for any input.

Did you see a transformer in or behind the speaker or mount? is it 70Volts just using an 8 ohm speaker? No transformer: L-pad Radio Shack $10 With transformer, might be able to change the x-former tap.

i did actaully. It was fairly small but it didnt look like it did much. Well this is a PA system we are talkin about. any more info would be great.  

If you have a transformer in there, there will be an input and an output. On the input side, it will be marked with a voltage rating, (I'd leave it alone, though, as you don't want to mess with the overall impedance that the PA amplifier is seeing) and possibly have more than one tap - if so, it'll probably be marked 0V - 70V - 100V or something like that. On the OTHER side, there will be (or SHOULD be) taps marked with wattage... 1, 2, 4, etc... This side, you can move. If you are already tapped at the lowest wattage, you are stuck with adding a resistor or a pot. If you decide to use a pot, get one that is rated the same power or higher than the tap used on the transformer. Connect the common tab on the pot to the wire connected between the common tap on the x-mer and the negative on the speaker. Cut the OTHER lead, and the wire remaining attached to the transformer, connect to tab 3 on the pot. The last wire goes to tab 2 on the pot - the wiper. If the speakers are horns, then you will be hard pressed to really reduce the output much... Those things are PAINFULLY efficient, as you have alraedy discovered. If you'd like to just put in a fixed, permanent resistor network, to adjust the output, check this page for resistor values, and how to wire it up...It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

hey haemphyst, if i can take a picture of it, can you help me? Im plannin to help out my teacher and the whole science dept. For some reason, our science dept is THE LOUDEST compared to other rooms and its irritating. btw its not a horn, just a normal 8ohm speaker with a transformer on it.

Sure... post one or a few up!It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

I, too, would like the solution to this very problem. My situation is the same. Once tedmond loads up the pics (or even if he doesn't), perhaps you can help us both with the right pot and wiring arrangement. I see in your reply that the jist of the solution is there but I am a visual person and sure would appreciate a diagram showing the hook-ups. Thanks.