This tool lets you calculate the sound pressure level (SPL) at the listening position from a single loudspeaker.
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Calculate the SPL at a known distance with a known amplifier power
Why Do Some Speakers Sound Better With More Power?
Speakers have an electrical impedance they present to the amplifier which is often not quite what is advertised (note all speakers are a 4 or 8 ohm load, so the value is often rounded) and can vary quite a bit. On top of this, each speaker has a sensitivity factor that denotes how easy they are to drive. This used to be measured in SPL/w/1m – so sound pressure produced by 1W at 1m. This is now changing to SPL/2.83V/1m – which is a more accurate measurement that good designers are adopting.
Some designs are highly sensitive and will produce >90dB of sound driven by 2.83V at 1 meter, while others are quite hard to drive, at <85dB sensitivity. Give this a read if you’re interested in more detail: Loudspeaker Design: Engineering vs Marketing
Keep in mind that the dB is logarithmic, a 6dB increase in measured sound pressure level (SPL) reflects a perceived doubling in volume, but a 3dB increase requires a doubling in power. More on that here. This means the difference between 91dB sensitivity and 85dB sensitivity is the difference between comfortably driving a speaker with a 5W SET amp and needing a 150W amp. When someone says a low powered class A amplifier drives inefficient speakers with ease, you need to define inefficient (because chances are the speakers in question are not *really* that inefficient), and also question the ears of the reviewer. There are a few speakers that are notoriously hard to drive (Apogee, Thiel) and no matter what some reviewer says, will sound like hot garbage when fed with moderate power.
I feed my ATC SCM19’s which are 85dB sensitive with a 1500WPC amp. I likely never use this kind of power, but when listening at higher levels, transient (momentary) power demand can be much greater than average power demand. That sudden kick drum hit might require 10X the amplifier power for a fraction of a second, and if the amp can’t deliver that – it will not reproduce the transient as accurately. This is much more common for low frequency transients, so home theater nerds like me are very concerned about amplifier headroom (excess power for these situations). Here’s a good summary on that topic: Dangers of Using Small Amplifiers
Damping factor is typically higher in amplifiers with higher power output, but is not a result of power but output impedance, wire length and the speaker’s impedance or load. I think many folks hear tighter bass and assume it’s damping factor at play, which is not like always the case.
Ultimately, tight bass (removing acoustics from the equation) is a function of controlling the moving mass of the transducer. This is the result of the electrical ability to put the brakes on a woofer that is already at peak excursion and bring it back to a resting state. There are a ton of ways amp designers try to do this, but in general you’ll find the best engineered amps typically have this consideration in common.