Re: Need more head room, long, narrow room
If you get a speaker up higher and tilt it down so that the speaker is aimed at or near the back of the listener area then due to affecting the distances involved and off-axis effects that can typically provide more even front-to-back coverage. If you tilt the speaker too much then you may get the scenario you note with increasing levels up front and decreasing levels in back, but that is not what is being suggested.
Think about it, if you take the furthest listener from being some amount off-axis with the speaker pointed straight out to their being on-axis with it tilted down then you are increasing the level the furthest listeners receive and that is often more of an increase than the associated change up front. When you raise the speaker and tilt it down you also typically direct more of the speaker's output at the listeners and less at the walls and ceiling.
This is the concept behind flying speakers to get better coverage, get the speaker up higher to minimize the difference in distance, and thus the losses related to those distances, from the speaker to the various points in the listener area and then tilt the speakers down to use the speaker pattern to compensate for any remaining differences in distance and loss. All while trying to keep the majority of the speaker energy directed at the audience where you want it and reducing the energy aimed at the ceiling and walls where you usually don't want it.
A 10dB crest factor is reasonable, but it could range from 20dB+ for some very dynamic music to 3dB or less for heavily compressed music.
