I spent a bit of time running the numbers to see about how much amplifier power matters as part of a FB post. I thought some folks might find it interesting and may be able to correct me if I'm incorrect in my quick assessment. I appreciate any feedback and comments.
Here are my thoughts on power and what I call speaker efficiency falsehood:
Speaker efficiency is commonly measured by applying 2.83V (assumes 1 W with an 8 ohm load) @ 1KHz @1 meter measured on axis. The current works out to be .35 Amps btw.
For a speaker with a nominal 8 ohm impedance and an efficiency rating of 88DB:
- +3DB requires 2x power, +10DB = 10x power. So let’s say we want to achieve an average (not peak) of 94DB (pretty loud). You would need 4x the power = 4 watts. For 104DB you’d need 10x = 40 watts. And for 107DB you’d need 2x = 80 watts.
- Now take into account the sweet spot distance to the speakers. Using the SPL to DB calculation and using our 88DB efficient speaker (measured @ 1 meter) let’s say our listening chair is 4 meters away = -12DB reduction. So now 80 watts yields 95DB (107DB – 12 DB for distance).
- There are other variables like efficiency gain via 2 speakers = +3DB depending on proximity, decrease in efficiency via room treatment (especially absorption) , speaker phase swings and voice coil impedance changes over high power / high temps, and other factors.
However here’s the biggest flaw I see in speaker efficiency and required power estimates: When is the last time you played a song that is a 1KHz tone? Music is incredibly complex spanning ~20 – ~20KHz simultaneously and often in bursts with dynamic swings. So all the calculations and resulting power estimates above are mostly meaningless because they are predicated on the signal equating to one frequency (and a fairly high frequency at that). Woofers are notorious for drawing significant current and are primarily excluded at 1KHz, so IMO you need much more than 80 watts to achieve 95DB @ 4 meters. Based on impedance and phase graphs for many speakers I’d take a swag and say you need 2x the average power to avoid compression, clipping, etc. For peaks I'm sure significantly more is required. And that, IMO is why power matters.
Here are my thoughts on power and what I call speaker efficiency falsehood:
Speaker efficiency is commonly measured by applying 2.83V (assumes 1 W with an 8 ohm load) @ 1KHz @1 meter measured on axis. The current works out to be .35 Amps btw.
For a speaker with a nominal 8 ohm impedance and an efficiency rating of 88DB:
- +3DB requires 2x power, +10DB = 10x power. So let’s say we want to achieve an average (not peak) of 94DB (pretty loud). You would need 4x the power = 4 watts. For 104DB you’d need 10x = 40 watts. And for 107DB you’d need 2x = 80 watts.
- Now take into account the sweet spot distance to the speakers. Using the SPL to DB calculation and using our 88DB efficient speaker (measured @ 1 meter) let’s say our listening chair is 4 meters away = -12DB reduction. So now 80 watts yields 95DB (107DB – 12 DB for distance).
- There are other variables like efficiency gain via 2 speakers = +3DB depending on proximity, decrease in efficiency via room treatment (especially absorption) , speaker phase swings and voice coil impedance changes over high power / high temps, and other factors.
However here’s the biggest flaw I see in speaker efficiency and required power estimates: When is the last time you played a song that is a 1KHz tone? Music is incredibly complex spanning ~20 – ~20KHz simultaneously and often in bursts with dynamic swings. So all the calculations and resulting power estimates above are mostly meaningless because they are predicated on the signal equating to one frequency (and a fairly high frequency at that). Woofers are notorious for drawing significant current and are primarily excluded at 1KHz, so IMO you need much more than 80 watts to achieve 95DB @ 4 meters. Based on impedance and phase graphs for many speakers I’d take a swag and say you need 2x the average power to avoid compression, clipping, etc. For peaks I'm sure significantly more is required. And that, IMO is why power matters.