They say that the average human is sensitive to a 1db change, and I feel in a test environment that may be true. In practice, people are only realistically sensitive to about a +/-3db change in volume. 3db is pretty significant, but it takes between 3db and 6db of change for it to be truly evident in a musical context. Most solo's in an album are pushed roughly +6db, and pads or other background sounds are -6db relative to the rest of the media.
When you say 3db quieter when the sound is currently at 105db, it doesn't sound significant, but you have to think of things relatively. For most people, 60db-80db is how loud your entire life is. An average conversation sets around 70db. The average volume of a concert sets around 105db. So if those are the two extremes, we are talking about a 45db swing, of which 3db in change, either way, is pretty big.
In my experience, 3db has never been enough to make or break a gig. This means that if you need to reduce or increase the volume, you need a +/-6db change to have an effective difference. Now imagine being at a venue where the policy is 90db at FOH. if the band is already banging out at 111db ( I have mixed shows at 116db before!!!! so not far from imagination ), you really have a LOOOOONG way to go in order to get them within policy. Most bands WILL NOT tolerate a 6db change, let alone cutting their volume down by 2/3rds.
A 9db change in volume is considered a doubling or halving of the perceived volume level. So if a band is cranking at 110db, and they turned down to 100db, most of the world would perceive that as being half as loud. If they turned down to about 90db they would again be perceived as being half as loud as they were at 100db. So on and so on. So a 3db change is not exactly chump change. It is 33.33% of the way to being half as loud, or twice as loud.
How do guitar amps get so loud? The speaker sensitivity is the biggest help. If you double the power with the same speaker, you get a +3db increase in output. If you double the number of speakers powered by the same power as you had before, you also get a +3db increase in output. If you double the power and double the number of speakers, you get a +6db increase in output. This assumes free space loading ( imagine playing 100' in the air ). Now, most ALL guitar rigs are setting on the floor, which is half-space loading, which increases the output by +3db. So output compounds really quickly when you look at it from a mathematical perspective. A 50-watt amp powering a single speaker that has a 100db sensitivity, will produce about 118db in free space. Half space load that speaker by placing it in a box on the ground and you just passed 120db easy. Now place two speakers in a box on the ground and you are around 123db, then take another 2 speaker ( for a 4x12" ) and you are at an easy 125db of output. Reducing the output power to 25 watts, will only drop that total by -3db. use a 10-watt amp and you only drop to around 120db, and if you have a 5-watt amp, it would drop to around 117db. In reality, it would be a little lower than that due to other losses, and the fact that a 5-watt amp will not sound as clean as a 50-watt amp with the same relative volume. With each halving of power, you also lose -3db in clean headroom.
There is a significant amount of math that goes into why most bands don't/won't play at safe volume levels. Much of it is the snowball effect, ego, and attitude. If you want to hear yourself at X level above everyone else, and everyone else wants themself to be at that same relative level above everyone else, you can see how you just round robin into volume wars. If you have that mindset, that " this is my sound " so deal with it, that too often drives much of the volume wars, and then there are simply bands whose intent is to be rudely loud and obnoxious ( I was in a band that had that mentality for a while ). There is also a lack of understanding of the laws, the dangers, and the purpose of their volume. Some bands think that just because they are outdoors at the city fair, they can turn to 11 and it's cool, some play at a metal band night and think louder is better regardless of the harm it can have on themselves and their fans, some just don't even realize that many venues are pressured by the city with laws that limit how much volume can be had at X distance from that venue.
This is what is pushing the lunchbox amp craze I think. More bands are getting tired of lugging heavy equipment, getting hounded by sound guys, and being labeled as " that band ". Many are starting to become more practical, sensible and professional about their brand. There is also the fact that less and less venues will tolerate LOUD. Now if you can bring in a WALLLLLLLLLLLLLLL of amps and play at reasonable levels, you are a PRO,and you deserve to do what you will. Many can't pull it off.
