Az- I don't see what the big deal is. You argue from never having tried one.

I 1st tried without one. My system sounded "good" to me at that point.

I then got one, and *much preferred* the results after I had calibrated. Better imaging between any 2 speakers, better panning of effects between speakers etc.

I then used it to do such things are properly set the phase between my subs and mains. You can't argue with that one, because it's a simple comparison of the level of the sub alone, the mains alone, then the sub + mains. The latter must be higher than either of the former. I tried many time to do this by ear with the signals on Avia, VE, S&V, and I was always wrong.

Also got a BFD parametric EQ to mellow out some of the room induced peaks with my sub. Again, it sounds better to me with these changes than without. But you have never compared so you are arguing with theory that in theory (!) does matter, but in the real world, your "variables" don't influence the measurements enough to give you a *worse* answer with an SPL meter than without.

And as far as the SPL meter getting worse results at lower freq, that is true. However, the sub signals that are on test DVDs or even most pre/pro-receivers are still random white (or pink) noise (can't remember which) just at lower freq. So because of the *range* of freq that is included, the error is still less than 5 dB or so. That is *still* way better than most people can do by ear. Especially since the ear is less senstive to low freqs than higher.

You can still say, phooey on yooey, I've adjusted my sub by listening to a mix of movies and music to get the level I like. That would *still* be the last step I would suggest. Just that you'd be changing from a known reference point.