Bill Fitzmaurice

Normally I'd agree there, but...the SP212 isobaric configuration means that while it has two twelves it only has the output of a one twelve. A proper 212 will give the OP what he needs, save the SP212 for those gigs where it's enough on its own.

A few items of disagreement. First off, he loaded that cab with replacement Celestions, so what the frequency response is one cannot say. Second, most of the power with electric bass is in the 2nd and 3rd harmonics, so when you play a 41 Hz open E what's mainly there is 82 and 123 Hz. By and large a speaker f3 of 50 Hz is sufficient, even for drop tuning. The SVT 810 f3 is 58 Hz. And lastly where hearing yourself is concerned that's mainly in the upper midbass through the midrange, roughly 200 Hz to 2kHz. As for "In terms of the angled / stacked speaker cabs, I’d have to disagree in my experience. The only times I’ve done that I’ve hated the sound - too harsh and right behind my head." when you aim the cab at your head rather than your calves you hear what the audience hears. If you don't like what you hear neither will they. The EQ should be set so that it sounds good on the speaker axis, not 30 degrees or more off axis. To remove the room from the equation I always walk out onto the dance floor for sound check, adjusting the EQ so that it sounds good there. If that results in less than optimal tone on stage I live with it, I'm playing for their enjoyment, not my own.

If this hasn't been a problem in the past then it wasn't your gear, it was the room, although a 4x10 arrangement doesn't help. You'd be better served with a pair of 2x10, stacked vertical, to get the upper drivers closer to ear level. At the very least your 4x10 should be tilted back and/or elevated, otherwise the directional mids that are the source of clarity are passing by you unheard.

They are.

More than a few DIY experimenters have turned that hobby into a lucrative profession. Included in that list: James Lansing, Paul Klipsch, Edgar Villchur, Henry Kloss, Conrad Sundholm, Thomas Danley and Alex Claber, and if I may, myself. All of got into speaker design because they were dissatisfied with what was available commercially and thought they could come up with something better. Audio design in general, and speaker design in particular, has always been advanced by the work of amateurs, unimpeded by corporate politics. Villchur's example is perhaps the best. He had a Masters degree in Art History. He got into audio as a radio repairman while in the Army in WWII. That piqued his interest in audio, which he followed up on after the war. When he came up with the idea for the acoustic suspension speaker he shopped it to all the major players. They all said the same thing, that if his idea had any merit that their own engineers would have already done it. That was circa 1950. Undaunted, Villchur built a prototype of his new speaker out of a plywood box. The dimensions of the face of the box were taken from a picture frame that he had hanging in his house. His wife, Rosemary sewed the pattern for the flexible surround out of mattress ticking. After proving his concept to himself, if not others, he and his student, Henry Kloss, proceeded to create their own company, Acoustic Research, in 1954. In 1966 AR’s loudspeaker sales represented almost one-third of the entire market. Not bad for a couple of tinkerers.

As one who does both commercial and DIY designs I have to disagree. One major advantage to DIY is being able to build designs that are labor intensive without concern for the cost of the labor. There's a reason why high end outfits like Danley Sound Labs get top dollar/quid for their products, and it's not just the cost of the components, it's also the cost of the labor to build them. A DIY build of a sophisticated design can easily match the performance of a high end speaker costing $5k at a fifth that price or less. Where commercial has the advantage of economy of scale is in the low to midrange price range, but even there DIY can still be the better route. You can buy a simple ported or vented box or you can build one for the same price but loaded with premium drivers, whereas buying a commercial one with premium drivers would raise the cost considerably. Now that's not to say that all DIY designs are gems by any means, I see cringe worthy junk all the time. But to be fair I see plenty of cringe worthy commercial junk too. Maybe not in the $5k range but certainly in the $500 range. And lest I forget...well, I did actually...DIY doesn't have expenses for marketing and distribution, office staff, accountants, lawyers, offices and factories, the guys on the loading dock...it's a long list that all contribute to the price you pay.

Zero. 😮 http://hornresp.net/ While it's called hornresp it will do horns, transmission lines, and direct radiators both sealed and ported. https://xsim.software.informer.com/ The only catch is you need Z and FRD files, but those are available for most drivers. Cost of the software is no issue. Learning how to use it is the hard part. Where going active is concerned there are full DSP plate amps at reasonable cost. Even if you go DIY with the amp the cost of DSP to go with it is about 10% of what it was 20 years ago. Not that I'd recommend trying to design your own for a one off build, the time it takes to acquire the skills required ranges from months for simple designs to years for complex designs. But there's no shortage of plans available from those who have done the work.

'Tis puzzlement for sure. If they have the chops to design and build good bass cabs they have the chops to design and build good PA cabs. On the flip side: The same absolutely applies to bass cabs.

You'll get the best results with four round ports 8cm diameter 15cm long. The rattles indicate insufficient panel to panel bracing.

To paraphrase Disraeli there are lies, there are damned lies, and there are specifications. 😮 No eight inch driver can take 650 watts continuous mechanically. No eight inch driver in a direct radiating enclosure can produce 126dB continuous. This is an example of the marketing department writing a cheque that the engineering department can't cover. Yes, most companies play the same game, but that doesn't make it any less dishonest. 🤥

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/