I’m sure this is for me but it’s habit. Just a preemptive “how many subs do you use” thing. I’ll try...
I am using 5 subs in my small HT room and I never felt the need to say 7.5.4.. No I did not direct that appeal to you, but to all
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Dealers, professional reviewers, followed by hearsayer (surely unintentionally..) have already successfully popularized the misnomer type of terms such as RMS Output power, or even just output "power" in "watts", speaker "efficiency", when it should have been stated in VA, or Current (A, i.e. amperes) at a specified voltage and the load impedance and most often sensitivity instead of efficiency (though efficiency is a correct term if meant as such). It may seem trivial, but the realities is, that's how so much misconception, misunderstanding and confusion were originated from influential people taking shortcuts instead of educating the public in the beginning.
In comparison though (say to the "watts" and "rms power" things), the term .2, e.g. 7.2.4 is actually quite understandable and acceptable and I have never said anything against it. That's because it at least serves the purpose of letting people know there are two subwoofer outputs that are not two, but one discrete channel but are in fact two discrete outputs electronically/electrically speaking. It is when I see the use of 7.3.x that I think it may be time to saying something about it, but obviously I am saying it with due respect..
Sorry I digressed, it does not really belong to this thread.