Bill Fitzmaurice

Damping absorbs midrange frequencies that will otherwise reflect back to the cone at various angles of phase, causing response peaks and valleys. The back is the critical place to apply it, but for best results all the surfaces should be covered. It may not make a major difference, but it's so inexpensive there's no reason to not do so.

That's one option, but you don't need 50 meters. You should be able able to find the same polyester batting in a useful size at fabric shops, it's used for pillows and furniture upholstery.

Indispensable.

The E140 was rated at 200w. The problem with pairing it with the 2515 is that their T/S specs are wildly different. As for sealed versus ported, with sealed you give up about an octave of low frequency extension and take a huge hit on excursion as well. Besides that neither the JBL nor 2515 have specs that work well sealed. The net volume of the cab is probably closer to 200L, so by no means is it too large for two fifteens.

Add another Eminence, then it needs proper porting and damping. With the exact interior dimensions I can provide the porting information. There may be another issue as well. For a number of years their inputs were marked red negative, black positive, which is the opposite of how the Eminence are marked. If that's the case it would explain the farting.

Not exactly the Royal Albert. 😉

I was referring to the dispersion of the woofer, not the high frequency element. One of the main shortcomings of many twelve and fifteen inch loaded PA tops is they tend to cross over to the HF element at too high a frequency, which should be no higher than 1.2kHz with fifteens, 2kHz with twelves. Those that do get it right tend to be in the upper price range.

An eight loaded top is sufficient for pub gigs, provided the woofer is of high quality. The same applies to eight loaded subs. The trick lies in knowing the quality of the woofer, as manufacturers are loathe to reveal what they're loaded with. Eight loaded tops are less directional, as the angle of dispersion is inversely proportional to the size of the cone/radiating plane . As to throw, the inverse square rule applies to all driver sizes. The advantage to 'stick' systems is they have very wide dispersion on the horizontal plane, due to the smaller driver sizes, along with narrow dispersion on the vertical plane, due to the taller radiating plane. That aims more sound into the audience, less at the floor and ceiling. The disadvantage is most use woofers too small to do the job, at an unjustifiable price. A very good arrangement is a 2x8 top, which can give output equal to a 1x12, with wider horizontal dispersion and narrower vertical dispersion. The same applies to 4x6.5 inch tops. But those are few and far in between, as their advantages are very much unknown to the average user.

Darwin enters into it as well. The human ear is most sensitive in the frequency range of the human voice, the midrange, critical for communication that can be heard over background noise. That's especially important when the wife is calling you to dinner. Men who couldn't hear her calling were in big trouble when they finally showed up back at the cave, leading to a highly shortened life expectancy. As for damage, we are most likely to be hearing damaged by high level midrange. That's the reason why 'A' weighted sound level measurements, which filter out highs and lows, are specified for acceptable industrial noise levels. Most of us have experienced this. It's why after playing a set at high levels it seems like the volume has gone down, in response to which we turn it up. That can be a vicious cycle. Ask Pete Townshend, although his response is likely to be 'Sorry, mate, I didn't hear the question.' 🤫

That's one, University of Salford is another. That was quantified by Bell Labs, which invented the dB, as in deci Bell.

That works, it's called the Sub Crawl. https://www.audioholics.com/home-theater-connection/crawling-for-bass-subwoofer-placement

Wall placement gives not only up to 6dB more output, the equivalent of doubling the sub count compared to well away from the wall, but also eliminates reflection cancellations. Uneven room response is seldom an problem in typical pubs and small to medium sized clubs. Every room is different, so experimentation is key to find the best spot to place them. Where you'll usually get the worst result is below mains, so that should be avoided whenever possible.

On that subject fluid dynamics are often used to visually display sound wave behavior.

He fails to mention wall loading subs, which gives higher output. Not all venues can take advantage of that, but most can, and as sub output is omni-directional they can be placed to either side of the stage.

There are many branches of Physics, and some can be detrimental where understanding acoustics is concerned. The main obstacle for most, irrespective of their level of education, is realizing that sound waves and light or radio frequency waves are totally different in how they function. Light waves in particular are easy to comprehend, because you can see them. There is almost nothing intuitive about how sound waves work, and even at the post-graduate level there are few courses of study available. One very good source is here: https://blog.soton.ac.uk/soundwaves/