There's a LOT to consider here...
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A "small" speaker is probably similar to what's in your TV except your TV is probably stereo and there might be separate tweeters for better high frequencies.
I'm probably "using" about 1 Watt when I'm listening to my TV quietly-normally. And that would be OK for "background music".
But when I turn on my surround-sound receiver and 15-inch subwoofers to watch a movie or video concert "the sky's the limit". But, I don't have it cranked-up all the way and I don't want to annoy the neighbors so I'm not using the hundreds of watts available.)
Doubling the power is +3dB which is "noticeably louder" but not tremendously louder. That's why you can easily get into the "big watts", especially if you want deep-strong bass.
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What you have isn't adequate for a "party" unless maybe if it's background music for a "nice classy" dinner party. But several people talking at the same time can get rather loud so you have to turn-up the music to hear it. And you'll probably want stereo.
For good bass you need to "move lot's of air". That means a big speaker/woofer, a big amplifier, and a big cabinet. Flat screen TVs (and laptops) usually have lousy bass because they have small speakers in a fairly-small cabinet.
Speaker design is complicated so this is over-simplified but the soundwaves from the back of the speaker are out-of-phase with the waves from the front so they tend to cancel-out, especially at low frequencies. The cabinet helps with that and a bigger cabinet means the speaker can move more freely without trying to compress the air inside as much. "Ported" speakers are "tuned" to phase-delay the bass waves from the back to reinforce the main waves at the tuning-frequency.
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The LM386 chip is more like 1W or less. (Check the datasheet for the actual chip.)
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Amplifier power is often limited by the voltage. (High power car amplifiers have a built-in voltage booster.)
It's the RMS voltage that's important. For example, with a "regular" single-ended amplifier (like the LM386) you can't more than 12V peak-to-peak. (In the real world you'll loose a little voltage because there is voltage drop across the amplifier circuitry.) That's 6V peak. The "formula" for RMS is 0.707 x peak so that's about 4V RMS. (You can use a factor of 0.354 X the power supply voltage, and a spreadsheet is handy.)
There a couple of ways to calculate power but this is handy:
Power (Watts) = Voltage (squared)/Resistance. Just remember that's RMS voltage.
So with the 12V power supply we can get about 2 Watts into 8-Ohms or 4W into 4-Ohms.
With a bridge amplifier where both speaker terminals are driven in opposite directions you get double the voltage for 4 times the power.
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Most modern audio is stereo (different sound coming from left & right). If you want to use a mono speaker the left & right signals should be mixed. That's easy to do in analog, it's easy to do digitally if you are doing your own digital audio processing, or it's pretty to make mono copies of your MP3s, etc.
But if you are streaming music with your phone through Bluetooth it might not be so easy, There MIGHT be a mono setting in your phone software.
