Hi all,
A few comments: Dantana, one of the many virtues of titanium and aluminum-dome tweeters is that the metal dome itself serves as a heat sink to dissipate heat from the voice coil (along with the ferrofluid). Consequently, metal-dome tweeters are able to produce higher sound levels with much less distortion than silk or cloth or poly-dome designs.
Incidentally, during my many years on listening panels at the National Research Council, for my work reviewing speakers for the magzine I edited (Sound&Vision Canada), we kept various speakers, good and bad, as "anchors" for use during double-blind tests. These sonic anchor speakers were mixed with the actual models under test, partly to confirm our own listening consistency and to provide a range of rankings. (In some tests where there were several models that were "similarly good," we sometimes had to have a real clunker in there just to remind us of how bad some brands really are!). What is amazing is the consistency of the rankings of the same anchor speakers over many years by different listeners, even down to the tenths of a point. These were driven hundreds of hours, and the frequency response curves never changed a fraction of a dB, nor did the listening test rankings, so that relegated the notion of speaker break-in to the status of myth. If the loudspeaker's characteristics changed over time, these changes would show up in the measurements and also in the controlled listening tests.
A comment as well on heat dissipation: Years ago, Kef used a popular T27 tweeter with a phenolic dome (it was used on a pair of audiophile favorites, the BBC monitor (LS3-5A), built by Rogers, Kef and other Brits). Under high volume conditions, this speaker's frequency response curve changed quite dramatically. After experimentation, Dr. Floyd Toole discovered that the T27's dome tweeter began to melt from heat and actually changed shape at high volume, so its dispersion traits changed. When you lowered the volume, the dome resumed its original shape! That's the only instance I can recall of a speaker's response changing in measurable and audible fashion in almost two decades of listening tests.
Speaker break-in is another one of these faddish notions promulgated by high-end niche magazines, which at their core are fundamentally anti-science.
Speaker break-in is a psycho-acoustical phenomenon where your ears and brain adjust to a different set of speaker dispersion traits that energize reflections and room modes in different ways.
Regards,
