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Technical info on speakers

Hello guys. I've made a simple audio board by following the instructions provided by the "Arduino Waveshield" homepage. Only changed one part (the audio amp) but it works flawlessly.

Now, i'm using a 1W audio amplifier, and i have an 8ohm 0.5W speaker. I'm not too satisfied with the volume, as i'd like it louder than it currently is. Options are:

1) Change amp, find a more powerful (more watts) one. Problem is i'd like to stick with my 5V supply, and most powerful amps i've seen require a larger power supply, except some that only come in QFN though (i'd like mine in DIP, because i'll eventually have to solder it in a protoboard)

2) Change speaker. Now this second option is the main focus of this post. The previous Amp i've mentioned supports 8 ohm speakers, and i've scavanged a few speakers from around my house, problem is they are rated at 4 ohm. Can i still run it by placing a 4ohm resistor in series with it. Is this gonna "change" something (well, amp should be fine as it will have it's 8ohm load...but i guess that means less output)? Second question: what does the Wattage rating on speaker actually mean? From the very very basic knowledge i know P = I * V or P = V^2 / R ....so ok, we got the resistance, but how can we determine the wattage without knowing the supplied voltage?

 

Thank you :=)

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I screwed around with homemade amps myself for a while with results I was not happy with. In the end, I simply bought a set of USB powered laptop speakers and gutted them. Everything I needed was already there, they run at 5v, and don't sound half bad. Goto ebay --There are plenty from Hong Kong that are dirt cheap and pretty good.

I kinda followed your advice. I found an old pc speaker lying around my house so i decided to use that one. It was rated 4 ohm / 5W. You can really hear a HUGE sound difference when using this speaker. I then also found another speaker rated at 4ohm / 3W, slightly less loud the the 5W one. 

But i wonder....where does the extra energy to make the 5W speaker louder than the 3W one come from? The load (4 ohm) is the same, so....

Thanks for the tip CTC!

PS: the TDA amplifier clearly shows an 8 ohm load being used in the example schematics, but it doesn't get hot with 4 ohm  loads so i think it's fine. I've also read about a guy using 2.7 loads with the same amp who says it has run fine for 2+ years.

You need to distinguish between electrical power and the acoustic power of the speaker. The Watt parameter of a speaker is normally the electric power. But the efficiency is very low (a few percent). Efficency and sensivity are the parameters to distinguish between the "loudness" of different speakers.

Here is a nice calculator to play aroud with these values. PC Speakers are at the lower end with an efficency of 0,1..0,5%,

It's a TDA7052. I've also tried the LM386 but it's less powerful than the TDA.

LM386 I assume?