I know nowt about stereo’s do sorry if I sound dumber than usual. I may be replacing a 4 channel stereo on a boat (so 12v) with a 30w 2 channel amp.

Boat currently has 4 smallish speakers, can I connect them to a two channel amp?
I presume that instead of getting 30w each the speakers would get 15w?

It doesn’t quite work like that as you need to consider the resistance and load of the speakers on the amplifier as that will also alter the power available to the speakers.

Is there any reason you haven’t got a 4 channel amp instead of the 2 your opted for which would be more suited?

If you wire them up in series you’ll double the impedance (AC resistance) of the speaker’s load on each channel; in parallel you’ll halve it. Your amp will (should) have some sort of guidelines / spec as to what’s supported. Going outside that could kill the amp. RTFM.

You want twelve volt and four channels….why aren’t you down Halfords looking at car units?

Edit: Cougar is right about the impedance which is important

Boat currently has 4 smallish speakers, can I connect them to a two channel amp?
I presume that instead of getting 30w each the speakers would get 15w

Strangely enough no, if you connect the speakers in parallel you will lower the total resistance (measured in ohm) for example if you connect two 8 ohm speakers in parallel the amp will “see” a load of 4 ohm.

The power rating of an amp is always given with the expected load in ohm. So it would be 30w at 8 ohm with say 0.1%THD (THD = Total harmonic Distortion) at 4 Ohm the same amp may output 60w but the THD will rise as well. essentially you will get the same power delivered to four speakers as you would two, but at the cost of quality of sound.

Some amps can cope with this fine, some cannot. If you are not going to push the volume to much, most modern amps will be fine at 4 ohm. (assuming the speakers are 8 ohm) House hold speakers are usually 8ohm, and car speakers are usually 4 ohm. It will usually say on the back of the speaker.

Edited to add that you can usually halve the rated ohm, on any given amp with no problems, car amps are usually 4 ohm so most will run at 2 ok.

Cheers

Rubber Buccaneer +1

House hold speakers are usually 8ohm, and car speakers are usually 4 ohm. It will usually say on the back of the speaker.

And back in pre-digital Pro Logic days, surround speakers were typically 16 Ohm IIRC.

If it’s for a boat and therefore stereo is of little importance, and if the source is capable of a mono output, then you could daisy chain the speakers (2s2p) which keeps the impedance the same as 1 speaker. That’s how we used to do it for gigs, 2x 3kW mono amps and 2x 3×3 ST-12’s on each side.

Why 9 each side? Because that’s all you can draw from a single 13A socket without tripping it 😈

You want twelve volt and four channels….why aren’t you down Halfords looking at car units?

Because their 4 channel amps are £100 + when I can get one of these for £22 and it’s got bluetooth built in!

I’m not utterly convinced the existing stereo is dead, but the boat is 100 miles away, so I don’t want to chuck a load of money at something that may not been needed. The above would be a quick and simple fix without having to extract the existing system immediately (and it would give us AUX in for a portable DAb radio and bluetooth for streaming from phones).