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

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If a CD of Seasick Steve sounds OK through a car speaker, it should work well enough.

A guitar cabinet specific speaker has design considerations for desired shaping/distorting the sound, and can take being pushed past its design power rating a little farther without damage, but unless you are Slash you can probably live with not turning it up to 11.

The CBGitty offered amp board by artec is rated to put out 2.5W of power on an 8 ohm speaker, pulling 0.5 amps.  I couldn't find the spec sheet, but nearly every one of these has one that states output power for both 4 ohm and 8 ohm speakers.  Back of the envelope calculation say that if you put a 4 ohm speaker on it (or a pair of 8 ohm in parallel) you will draw 0.8 amps, which will probably be fine.  Though if you have a pair of 4 ohm car speakers, wire them in series to get 8 ohms.

The speakers should be rated for more watts than the amp to avoid burning the wiring or tearing the cones.

just to experiment on how close they have to be, We tried a hotone nano 5w mini amp head with a 200w 4x8 guitar cabinet and it blew us away how much volume it gave and how good the sound was.

The watt rating of the speaker has nothing to do with the sound volume out of the speaker. What you need to look for is the sensitivity rating in SPL in db. Most home speakers are in the 87 to 89 db range. Car speakers are usually a little less. Pro Audio are very efficient and are normally in the high 90 db range and even up over 100 db.

The SPL rating is usually measured at 1 watt amplifier output and at a distance of 1 meter directly in front of the speaker. 

Matching the watts of the amp and the speaker is not only not necessary it is not desirable either. The speaker watt rating is the max you can continuously drive the speaker without damaging it. The watt rating of the amp is how much continuous power the amp can deliver. 

So the only thing to worry about is having the speaker rated higher than the amp. Even then you are OK as long as you don't turn it up too far.

I Googled the spec sheet of the amp chip used in the Gitty amp board and from what I recall it didn't look like it would drive a 4 ohm speaker very well. I'll try to find it again and post a link.

Another issue with these cheap amp boards is that the output ratings are spec'ed at 10% THD which is pretty noisy. That is also at the max voltage for the chip so anything less and the wattage drops off quickly.

Russ

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.

https://geoffthegreygeek.com/amplifier-power/

Russ

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.

Russ

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

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

Russ

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. 

Russ

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.

Russ

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