I assume the answer is yes but underpowered.  thought I would ask

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It is fascinating and almost counter intuitive.

On one hand, an amplifier pushing 2.5 watts to an 8 ohm speaker is squirting 0.5 amps down the wire, an amplifier pushing 250 watts to an 8 ohm speaker is squirting 50 amps down the wire.

I = √(W/R)

(amps is the square root of the ratio of watts to ohms)

{ 0.5 = √ (2.5/8) }

you would think a speaker that can handle 50 amps of current would practically ignore 0.5 amps since its only 1%.  Sort of like trying to jump start your car with 8 AA batteries, right voltage, not nearly enough amps to move anything.

on the other hand, 8 ohms is 8 ohms is 8 ohms whether it is 8 feet of 40 gauge wire in the voice coil, or 80 ft of 30 gauge wire, or 800 ft of 20 gauge wire. If the amp puts out 0-9v on a 8 ohm speaker then it puts out 0-1.1 amps.

On the other hand, power and volume are not linear to each other.  100w only sounds twice as loud as 10 watts.  The electricity is confined to a wire, but the sound has to fill a 3-D space.  sort of like doubling the height-length-width of a water tank means it takes 8 times as much water to fill.

hmm, seems I've turned into Zaphod Beeblebrox, time for a pan galactic gargle blaster.

I think your math is a bit off, 250 Watts at 8 ohms is about 5.5 amps. Still the point you made is valid in that the power, spl, and volume are not linear.

Here is a link to an easy to understand write up on all this sort of stuff for those who want to know a little more.



JL's equation is right but he must of hit a wrong button when entering the numbers. 250w/8ohms is 31.25 so the square root of that is 5.5 amps.


Yes...except an amp doesn't produce ohms LOL

0.5 amps, not 0.5 Ah (amp hours is used to rate how long a battery runs at nominal design current)

an amplifier is rated at wattage, the combination of volts/amps it can put out without burning, which depends on how many ohms the speaker has.  more ohms in the speaker, less amps from the amplifier, less ohms in the speaker, more amps from the amplifier, short the speaker wires for zero ohms and the amplifier burns.

yup I goofed, forgot to carry the 2, lol

I remember getting bit but not killed by a speaker cabinet wire, 5 amps 50 amps BIG DIFFERNECE, thanks

All I can say is  I'm glad I didn't know all this years ago when I started to build & just wired some up   I guess its the old no rules thing 

It's not that it won't work but it may not work to everyone's expectation. Loud enough for one person might be too soft for another. I'm sure this particular amp and speaker combo work fine or Gitty would not be selling them. Not sure about how it would work with car speakers. Have you or anybody tried this with a car speaker yet? Would be interested in how it turned out.

I can see the appeal of building your own amp but I have a Blackstar Fly 3 battery powered amp that is awesome and is only $59


Wayfinder, to answer your question up above...you would use the Ohms rating of the speaker that you are using. But remember this does not mean that using a 4 ohm speaker is going to double the watts compared to using an 8 ohm speaker unless you have a very good amplifier.

What is the reason you are wanting to know the current draw? It isn't really very useful.in the long run. 


As a point of reference, my little Blackstar mini amp is a 3 watt amp and runs on 6 AA batteries, The Batteries last a pretty long time, The speaker is a 3 inch but not sure if it is 4 ohms or what. I suspect it is probably 4 ohms.

I bought the Blackstar wall wart for it and it is rated 6.5 volts at 1.5 Amps.


MicroCube Stereo Portable gives you two 4" speakers...

2 x 4 = 8

It is simple math, but it seems to work.

You can use the Line Out to drive a homemade speaker cab, ya know...oh, and yer math is worng...

PiR2 = 3.14159 x 4 (not 16; r=2 fora a 4" spur) = 12.56636 x 2 = 25 sq in

8" spkr

3.14159x16= 50 and change

Yes, an 8 has double the surface area, and therefore moves more air.


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