Hello everyone. Today we will talk about how much power you need in your speakers. So a speaker has a value called a sensitivity rating. A sensitivity rating is a relationship between three factors. Decibels, the amount of sound pressure level, measured at one watt of power from your amplifier to the speaker at a distance, and all sensitivity ratings are comparable across all speakers. So you can determine just how much power you need to push through that speaker to achieve a specific volume at your listening position.
Decibels, in simple words, are a measure of sound pressure level and physical energy that our bodies have to handle. The higher the sound pressure level, the higher the dB, and the lower the amount of time we can expose ourselves to that energy before we begin to experience pain or hearing loss.
Setting a target
Because TV shows and movies and music are dynamic, and they have moments of very low quiet and moments of high energy, what we are going to do is target a range where we calibrate our system to get that dynamic, but we are going to be safe for the amount of time that we’re going to be listening. For most people watching a movie, that’s about two hours, so 85 to 90 decibels of energy for that prolonged exposure will be safe. So that’s the number we will target; ideally, 87 dB will be our target.
Relationship between decibel output and power
Now let’s look at the relationship between decibel output and power for a speaker sensitivity rating of 90 dB at 1 watt at 1 meter. If we double the wattage from one to two watts, we add 3 decibels of output to 93 decibels. Every time we double that power, we add another 3 decibels, so at 4 watts, 96, and at 8 watts, 99 decibels of output.
Distance matters
Now 99 decibels, as we just discussed, is a lot of sound pressure level, but keep in mind that it measures at a one-meter distance from the speaker. Your listing position will likely be three to four meters from your speaker.
Well, how does the distance relate to sound pressure levels?
As we double it on that sensitivity rating, we remove six decibels of energy from the system. So if it’s at 99 decibels at 8 watts at 1 meter, at 2 meters at the same power, it goes back to 93 dB, and at 4 meters, it goes back down to 87, which is our target.
The difference in sensitivity rating
From speaker to speaker, that sensitivity rating will be different, and if we keep your listening distance, the same will require either more or less power to achieve the same decibels at that listening position.
Example
For example, an 87-decibel sensitivity rating speaker will require twice as many watts, while a 93-decibel sensitivity speaker will require half as much wattage to achieve the same listening level at your listening position. Hopefully, the details in this article will help you figure out how many watts you need for outdoor speakers.
