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Amplifing a PA system.

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shuluke

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I installed a small PA system in a car for a friend. He says its not loud enough, any ideas of how to increase the sound. I was thinking of a small car amp, hooked to a speaker that can take more power than his 15watt speaker can now. If anyone has a diagram to make another PA system using Radioshack and other stores parts, that would be greatly appreciated as well. He wants it to be heard even when people have their windows up. In his car, a Lexus, he cant even hear if his PA system is on.

Thanks

Shuluke
 
At some point you have to decide on how much power you want and if it's more than the speaker can take you'll need to replace the speaker. How loud is enough is something you'll have to determine. It would help to know how much you are delivering now so that you have a place to begin.

Keep in mind that power needs to increase logrithmically with expected loudness. Simply put - it takes a large power increase to produce a modest increase in loudness.

You might experiment with a boom box or other audio systems of known power levels to get an approximation of what it would take. Note that if intelligibility is important then testing with voice frequencies is important. Attenuation of vehicle components is quite frequency selective and likely goes up in frequency.
 
Ok, another question then is, how can i find out how much i can draw out of the circuit?. I didnt make the PA system, he bought it off of Whitney something catalog. If i just added a bigger speaker, it wouldnt change much, becuase the circuit only lets out so much power. But if i connected the output of the circuit to an amp and then connected that to a higher wattage speaker, it would be louder no?
 
You really need to tell us what you are trying to do, PA is short for 'Public Address' - which isn't really relevent in a car!.

As regards amplifier power, basically (and honestly) a single ended amplifer can give 4 watts, and a bridged amplifier can give 16 watts - both feeding 4 ohm speakers. For any more than that you require an amplifier with an inverter to give more than 12V.
 
Its a PA system for a car. When you talk in the mic, it puts it on "loudspeaker". Like a cop car. I was thinking of a car audio amplifier, which can go up to excess of 1000 watts. Not that big for this project, maybe a 100 watt amp. I think thats what ill do. thanks for the help. No one has diagrams on how to make one though?
 
Hi Shuluke,
A 30W re-entrant horn PA speaker is VERY loud with only a few watts. It looks and sounds like a megaphone. A 12V simple bridged amp IC will give its 8 ohms about 8 Watts.
If you increase the volume to where you can hear it in a car with closed windows, then you will deafen pedestrians and people in cars with their windows down. If you can hear it in your own car, then you will probably create feedback howling. In some PA systems, you record your message then play it back to the PA system to avoid feedback.
 
shuluke said:
Its a PA system for a car. When you talk in the mic, it puts it on "loudspeaker". Like a cop car. I was thinking of a car audio amplifier, which can go up to excess of 1000 watts. Not that big for this project, maybe a 100 watt amp. I think thats what ill do. thanks for the help. No one has diagrams on how to make one though?

The specs on in-car amplifiers are massively exaggerated, as are the speakers - a '1000W' car amplifier is probably only really 100W. If you ever use a proper amplifier to feed in-car speakers you are very likely to destroy them at only a fraction of their specification.

Anyway, aside from that, as already suggested you use a horn speaker for this type of PA application - these are many times more efficient than conventional speakers, and a simple bridged 12V amplifier (16W into 4 ohms) should be plenty loud enough. To get more than that you have to get a great deal more complicated, using an inverter to increase the power supply voltage (which is what the higher power in-car amplifiers do).
 
Yeah, Nigel.
Car audio spec's always leave out the missing decimal point. "Peak or Maximum" power is simply doubling the numbers of true RMS power. Then when it is turned-up to produce awfully distorted square waves, the "peak-to-peak" power is simply quadrupling or octupling the true numbers. "Music or Dynamic" power is rated just before the power supply sags. Etc.
If you ask the manufacturer, they might admit that their power rating is correct, but only for a millisecond, before it blows-up!
 
Ok, so ill tell him, we cant really make it louder, because it could cause feedback, and if not that, then it will get more complicated having to use another car audio amp.

I have an amp rated 2400 watts peak, and it has been bench tested at 989watts RMS. Thats alot of power RMS. I turn the gain to about 50%, and wired it mono to one subwoofer, so the amp sees a 4ohm load, which ive tested to be 103dB on the front windshield.

Ok so i have another question then. I want to make a circuit and hook it to my car, so when the doors of the car close, there will be a voice that says "Welcome, put on your seatbelt please". But i have no idea where to go to even start this project. I think i would have to hook it to the circuit that turns on the dome light when the door opens, but im not sure. I could even put a button on the door panel so when the door shuts, it sets the circuit off, and it talks. Any ideas would be greatly appreciated.

You guys are very knowledgeable, thanks for all the help.
 
shuluke said:
Ok so i have another question then. I want to make a circuit and hook it to my car, so when the doors of the car close, there will be a voice that says "Welcome, put on your seatbelt please". But i have no idea where to go to even start this project. I think i would have to hook it to the circuit that turns on the dome light when the door opens, but im not sure. I could even put a button on the door panel so when the door shuts, it sets the circuit off, and it talks. Any ideas would be greatly appreciated.

There are various audio recorder IC's available, these generally record something like 20 seconds of audio. You could simply record your message on one of those, and trigger it from the interior light switches on the doors.
 
shuluke said:
How would i exactly do the triggering? Thats the part that im confused with?

It's just a single pin on the chip, you simple take it high or low (depending on the design) and it plays back the sample. You first need to get the recorder part working, then sort out it's actual triggering.
 
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