NB,
I apologize if my comments below are already understood, but thought I'd put this out there for members that may still have some questions relating to amplifier power needs versus transducer ratings.
In the real world, audio music\soundtrack playback can\does generate up to
+10db of dynamic headroom peaks. In the case of the Sierra 2's, if your playback levels are averaging 87db with 1 watt of power, then you will need 10 watts of clean power to safely cover the musical peaks (logarithmic facts state 10db=10X power). Thus you need an amp that has a "clean 10 watts of power output"! In this scenario, the dynamic musical waveforms are smooth and unclipped with S2 playback that has natural and clean dynamics as per the genre of music.
Continuing with the Sierra 2's (in the real world), their maximum continuous unclipped power rating of 150 watts means that your sustained maximum S2 playback levels will only handle "15 continuous watts" of amplifier power, which still yields 150 watts of unclipped, clean dynamic musical peaks! At this point if your power amp has a clean continuous power output per channel of 150 watts, the theoretical musical output of the S2's would be 98.5 db, with 108.5 db of CLEAN, UNDISTORTED Musical Peaks...all is good!!!
Dave also rates the S2's as being able to handle maximum short term peak power of 300 watts. Assuming your amp is rated for continuous clean 300 watts per channel, then the S2's could (during
short duration playback levels), give clean dynamic peaks of 111.5db!!
As Dave has clearly stated, amplifiers pushed
past their clean power ratings, [such as when attempting to cover the +10db of headroom to cover real-world musical peaks], DO go into extreme waveform clipping distortions, generating tremendous heat in the driver voice coils that quickly can destroy the speakers. I've seen it happen in tweeters and woofers...Not Pretty!
If music playback starts to sound harsh, strained or fatiguing, probably a good indication that the amp is being driven into dynamic peak distortions...turn it down or you may end up needing to replace drivers!
Again "in-the-real-world", driving speakers with low powered amps can quickly create a Much Greater Risk of damaging (blowing) speaker drivers due to entering into clipping amplifier waveforms while attempting louder playback levels. Matching, or slightly exceeding the max clean power rating of the amp to the speaker rating goes a long way to enjoying your HT or Stereo for a much longer time. Either way, still be cautious of maintaining "Clean Amplifier Peak" playback levels!
Hope this was clear and possibly helpful,
Ted