Questions about using one speaker with a stereo amp

[ppataki]

I would like to understand what happens if I try to do the folllowings:

1.
Connect one 8 ohm speaker to one of the outputs (let's say left) of an amplifier that outputs let's say 2x10 watts at 8 ohm (and 2x15 watts at 4 ohm) - in that case would the amp be able to drive that single speaker with 20 watts or only 10 watts or somewhere in between?

2.
What if using the same amp and same speaker I connect the speaker to both outputs of the amp, like this:

Since I am not an engineer I would appreciate any educated comments
Thank you

 

[NiagaraPete]

Option 2 will likely kill your amp. Back in the day 70’s you would use the positive connector from left and right to wire the speaker mono.
I’m not sure that is good advice so don’t try it. Wait for more information.

 

[DVDdoug]

1.
Connect one 8 ohm speaker to one of the outputs (let's say left) of an amplifier that outputs let's say 2x10 watts at 8 ohm (and 2x15 watts at 4 ohm) - in that case would the amp be able to drive that single speaker with 20 watts or only 10 watts or somewhere in between?

10 Watts. Possibly slightly more depending the power supply. If the power supply is well regulated it won't change with the load. It's possible that the power supply voltage is a little higher with the lighter load of only one channel operating.

2.
What if using the same amp and same speaker I connect the speaker to both outputs of the amp, like this:

DO NOT DO THAT!!!

The "source impedance" of an amplifier output is very low. Impedance and resistance (both measured in Ohms) is "the resistance to current flow". If the resistance is too low you get excess current. (Zero resistance is a "short circuit".) The outputs will be feeding current into each other instead of feeding current out to a speaker and you'll get too much current and things can burn-up.

As a rule, it's OK to connect two or more inputs together but you should never connect two outputs together.

There is something called a bridge amplifier which as two opposite-polarity "hot" outputs and no ground connection to the speaker. Some stereo amplifiers are designed with a polarity switch to invert one channel internally, converting a stereo amplifier into a bridged mono amplifier. In this case the speaker is connected to the left & right + connections with no connection the - terminal. They aren't really + &- since audio is AC... The - connection is usually ground.

Bridging doubles the voltage to the speaker which means the current also doubles, and that gets you 4 times as much power. But the amplifier has to be capable of double the current.

 

[Vladimir Filevski]

I would like to understand what happens if I try to do the folllowings:

1.
Connect one 8 ohm speaker to one of the outputs (let's say left) of an amplifier that outputs let's say 2x10 watts at 8 ohm (and 2x15 watts at 4 ohm) - in that case would the amp be able to drive that single speaker with 20 watts or only 10 watts or somewhere in between?

2.
What if using the same amp and same speaker I connect the speaker to both outputs of the amp, like this:

1. Maximum amplifier output will be slightly more than 10W/8ohm (and 15W/4ohm).
2. No! NO!!

 

[ppataki]

Thanks guys for the answers, appreciate it!
I definitely won't try option 2 (and option 1 does not seem to have much sense either)

+ I assume that something like this would be a No-No! too, right?

 

[Chrispy]

Does the pre-amp/amp have a mono function? If not, will your source material be mono? Hard to add a second speaker?

 

[ppataki]

Does the pre-amp/amp have a mono function? If not, will your source material be mono? Hard to add a second speaker?

The source will be mono
Idea here would be if I get two of these stereo amps can I drive two speakers so I would get higher power vs using just one
So one stereo amp driving one speaker for the left channel only and the other doing the same for the right channel only

 

[antcollinet]

Thanks guys for the answers, appreciate it!
I definitely won't try option 2 (and option 1 does not seem to have much sense either)

+ I assume that something like this would be a No-No! too, right?

View attachment 227029

Yes - that is also a no-no. You've just shorted the + output to earth (probably) or to another low impedance output.

Either way you are going to release the magic smoke.

 

[Chrispy]

The source will be mono
Idea here would be if I get two of these stereo amps can I drive two speakers so I would get higher power vs using just one
So one stereo amp driving one speaker for the left channel only and the other doing the same for the right channel only

So you haven't chosen an amp yet? Like was said, driving one channel instead of two in a 2ch amp may give you a bit extra but it won't be significant. Just best to get a more powerful amp capable of two speakers if that's what you want. Some stereo amps can be bridged for higher wattage, but at the cost of lower impedance handling ability....but the manual would specifically need to confirm it can be bridged. Try playing around with this calculator perhaps http://myhometheater.homestead.com/splcalculator.html

 

[antcollinet]

The source will be mono
Idea here would be if I get two of these stereo amps can I drive two speakers so I would get higher power vs using just one
So one stereo amp driving one speaker for the left channel only and the other doing the same for the right channel only

No

You will not get more power driving just one speaker. (Not audibly more anyway)

 

[ppataki]

I promise this is my last silly question for today but what about something like this when having a mono signal (same signal is fed into both inputs)
Would this be like the equivalent of connecting the single speaker to just one of the channels? (yielding just slightly more output)

Thank you for your answers, again, much appreciated!

 

[Chrispy]

I promise this is my last silly question for today but what about something like this when having a mono signal (same signal is fed into both inputs)
Would this be like the equivalent of connecting the single speaker to just one of the channels? (yielding just slightly more output)
View attachment 227031
Thank you for your answers, again, much appreciated!

That would be the bridging I was referring to....the amp needs to be able to be bridged, tho (check the manual).

 

[ppataki]

That would be the bridging I was referring to....the amp needs to be able to be bridged, tho (check the manual).

No, it is not bridgeable (SMSL A1)
Using the calculator you provided actually even 10 watts/channel will provide me with 105dB peaks at my listening position so I might be OK with just one amp then....