There is an equation for watts to decibels, given a sensitivity of x decibels, (1w/1m)! Wattage must double for each increase of 3db. See here and here for more info. So that sensitivity (SPL) score is a pretty crucial starting point for a speaker. Not that adding more amplifier watts is not impossible, just moderately costly. But then again, in the case of an amplified PA speaker with 700 watts peak (and 350 RMS) then you’ve a lot of power. By my calculations, taking a 98db SPL woofer up north of 122db, and a 110db SPL tweeter up past 134db – past the threshold of pain! Also, I’ve read that perceptively, humans believe +10db makes one sound twice as loud as another.
BUT distance from the speaker matters! On a ratio of 1/d^2, the sound gets softer the further away you are! If pumping 350 watts through that woofer gets us 122db, standing 52 feet away from it, it will sound just like it we only pumped in 1 watt at 1 meter = 98db. That’s still plenty loud.
It makes sense to me now why stage monitors are always like 100-150 watts. Even with all the noise on stage, you’re pretty close which means they’re pretty loud.
Here’s what that speaker system sounds like as the watts are increased:
| Watts | Woofer | Tweeter |
| 1 | 98 | 110 |
| 2 | 101 | 113 |
| 4 | 104 | 116 |
| 8 | 107 | 119 |
| 16 | 110 | 122 |
| 32 | 113 | 125 |
| 64 | 116 | 128 |
| 128 | 119 | 131 |
| 256 | 122 | 134 |
| 512 | 125 | 137 |
| 1024 | 128 | 140 |
| 2048 | 131 | 143 |
Contrast that with another system with a higher SPL:
| Meters | Woofer | Tweeter |
| 1 | 122 | 134 |
| 2 | 116 | 128 |
| 4 | 110 | 122 |
| 8 | 104 | 116 |
| 16 | 98 | 110 |
| 32 | 92 | 104 |
For reference, here is a reference table for decibels:
| Source | Intensity Level (db) |
| Threshold of Hearing (TOH) | 0 |
| Rustling Leaves | 10 |
| Whisper | 20 |
| Quiet bedroom at night | 30 |
| Quiet library | 40 |
| Average home | 50 |
| Normal Conversation | 60 |
| Busy Street Traffic | 70 |
| Vacuum Cleaner | 70 |
| Busy road | 80 |
| Diesel truck, 10 m away | 90 |
| Large Orchestra | 98 |
| Walkman at Maximum Level | 100 |
| Front Rows of Rock Concert | 110 |
| Chainsaw, 1 m distance | 110 |
| Threshold of discomfort | 120 |
| Threshold of pain | 130 |
| Jet aircraft, 50 m away | 140 |
| Instant Perforation of Eardrum | 160 |