markoveter wrote:Yes, very clear, thank you!
But, could you better clarify this?
KaiS wrote:The power amp needs some amount of it’s power to eliminate the energy stored in moving membranes, and load and unload components in the x-over.
So, if you leave the power amp a little bit of headroom you will be rewarded with a cleaner sound.
A real world scenario:
Imagine the amp just pushed the speaker’s woofer membrane with 200 Watts of power outside, because the music (e.g. a bassdrum punch) asked for it.
The very next swing period of this same bassdrum sound is much smaller, as the real sound is decaying fast after the beater had hit the drumskin.
The typical woofer is much less dampened than a drum, so it tends to, once pushed, oscillate on for several periods.
98% of the energy the amp had pushed into the speaker is stored there in form of mechanical energy, in compressed or decompressed air inside the housing and the spring-effect of the woofer’s suspension.
Only 2% (real figures) is converted into sound (10-20 % at best in a very big horn speaker).
OK - now for this next much smaller swing of reproduced drum sound, the amp has to use almost the same amount of power (think 180 W) it had used to push the woofer in the 1st place, to stop it from moving now, plus some extra amount of power to correctly form the next wave-part.
So for real, the amp can at worst only deliver 1/2 of it’s nominal power into a speaker to produce music.
The other half is needed to eliminate the energy from former music events stored in the speaker.
This is specially true for most class-D amps, as they don’t have too high current capability margin, maybe just 50% extra.
They might run of of steam (current) earlier than their specs might suggest when driving a real speaker, not just an artificial resistive load used for the specs measurement.
On the other hand some designers like Mark Levinson built amps that have ten or twenty times the (steam) current capability they would need for their nominal power - these don‘t have problems being driven almost full scale.
To make the life of an amp even harder, the behavior of a speaker is “complex“, which just means the voltage and the current are not synchronous.
A lot lot of amps struggle if this a-synchronicity (phase angle) is too big, because their control mechanism, called NFB - negative-feed-back, has a limited capability to handle this.
This capability is called “phase margin” and typically ends at +/– 180° the latest - voltage and current full anti-phase.
If you now force an amp into it‘s power or current limit on such a complex load, it will completely loose control on the speaker, resulting in momentary very nasty distortions.
If all this sounds bad and problematic to you, don’t worry:
Practically, with a 400 W amp, your neighborhood’s tolerance to sound might be the real world limit - usually somewhere in the 1-figure watts region, which every amp can handle easily.
All clear now 
?
Very happy with the decision I made!
