Decibels
Sound levels are measured in Decibels (db) In essence, our ears detect differences in volume level in a non-linear fashion. Our ears become less sensitive to sound as it increases.
Decibels are a logarithmic scale of relative loudness. A difference of approx. 1 db is the minimum perceptible change in volume, 3 db is a moderate change in volume, and about 10 db is an approximate doubling of volume.
To give you an idea of how this relates to real-world situations the following examples are listed:
0 db is the threshold of hearing
Whisper: 15-25 dB
Background noise: about 35 dB
Normal home or office background: 40-60 dB
Normal speaking voice: 65-70 dB
Orchestral climax: 105 dB
Live Rock music: 120 dB+
Pain Threshold: 130 dB
Jet aircraft: 140-180 dB
In order for one amplifier to reproduce sound twice as loud as another in Decibels you need 10 times more wattage output. An amplifier rated at 100 WPC is capable of twice the volume level of a 10 WPC amp, an amplifier rated at 100 watts per channel needs to be 1,000 watts per channel to be twice as loud. In other words, the relationship between volume and wattage output is logarithmic rather than linear. If a sound gets louder by 3 decibels or "slightly louder," it takes twice as much electrical power from your receiver or amp to produce that modest increase. Therefore, a 100-watt amplifier will produce sound only slightly louder than a 50-watt amplifier.
So remember the formula.
To double the volume you ten times the power (all things being equal)
So as you can see once you get above 2 watts, all things being equal for your bedroom amp, the perceived volume doesn't change much.
Stop torturing yourself. Buy yourself, a nice practice amp with headphones out like the Hog 20 or a Fender G-Dec. If you're going to busk then get the Pignose. Yes, and the Pignoses have a nice sound.