Bill Fitzmaurice

Players, not necessarily. But speaker designers should know better. Sadly not all do. 🙄

For best results the mains must be out front, lest they feed back into the mics. The subs should be close to a wall, for boundary loading and to prevent boundary reflection sourced cancellations. If you have two or more subs they should be placed either together or at least 16 meters apart, to prevent phase sourced cancellations. This also isn't new by any means, but it is almost universally unknown by consumers, and therefore ignored by consumers and manufacturers alike.

The detracts from the interior volume of the cabinet. Not a good idea when most commercial bass cabs are undersized as it is.

Once again, with feeling: The watts don't matter.

Mains should seldom, if ever, be mounted above subs, but that's a PA issue, not electric bass. Leo was a very skilled machinist, but acoustic engineering wasn't in his wheelhouse. He did recognize the need for tilt back legs on his cabs, though, a feature curiously absent on other brands.

The loudspeaker engineering community has known this since the late 1940s. Neither Leo Fender nor Jim Marshall were loudspeaker engineers, so the blame for poor electric instrument speaker designs that persist to this day can be attributed to them.

Isn't that a dual channel amp?

Run each cab off its own power amp. I won't bother getting into the whys and wherefores but the watts don't matter.

Maybe she preferred Entwhistle? Or Sir Paul? 🙄

Crossing above 80Hz is usually the better option with all but high end PA, as typical portable PA tops don't go much below 100Hz, if at all. There's no reason for subs to go below even 35Hz with music. Below 30Hz is home theater territory.

At what frequency to cross over to the subs depends on how low the tops go before dropping off in response and/or output capability. Finding out where that frequency is usually requires experimentation, as it's not a spec provided by most PA manufacturers. 'What other folk are doing' should not be a consideration.

I doubt if you need a sub based on your audience capacity. Home audio subs won't work, they lack the sensitivity/output to work for PA.

It does not, at least where maximum volume is concerned, which is usually limited by the driver excursion. With no changes to the knobs the four ohm cab will be perhaps 3dB louder. However, all it takes to get the same excursion, and therefore the same output, from the 8 ohm cab is a slight twist of the volume knob. If the amp is rated well below the power rating of the speaker, like by half, then you might, might, get 2 dB higher maximum output from the 4 ohm rig. It might even be slightly audible, but that's it.

That's a common misconception. You do get higher output per volt, but there's no such thing as a free lunch. You also lose current headroom in the amp. People tend to look at the higher amp power output into 4 ohms as opposed to 8 ohms and assume that's a good thing. It's not, because that higher power output is obtained at the cost of higher current draw.

You can't have the one without the other, but in this case the current level is far too low to be of any consequence and has no influence on the result.

While on the subject: The reason speakers are very inefficient, on average only converting 2% of the electrical energy they receive into sound, is impedance, specifically the impedance of air, which is very low. 8 ohms doesn't sound like it's a high impedance source, but it's a lot higher than air, so nearly all of the energy put into a driver is lost as heat. A horn loaded speaker acts as an acoustical transformer, just like the output transformer in a valve amp. The horn raises the impedance of the air mass that the driver operates into, increasing efficiency as much as tenfold.

Current doesn't determine the signal level, voltage does. Input impedance doesn't affect the signal voltage flowing in the cable. Losses occur when the amp input impedance is too low, not when it's too high. When the amp input impedance is less than some ten times the output impedance of the bass what's known as loading occurs, which results in signal loss. https://www.electronics-lab.com/article/input-and-output-impedances-of-amplifiers/ This being the case the higher the source impedance the higher the input impedance must be. Power amps tend to have an input impedance around 10k ohms, because the consoles that plug into them have an output impedance of 600 ohms or less. Instrument amps have an input impedance of 100k ohms or more, because passive pickups have an output impedance of 5k ohms or higher.

You don't need a new cab, you need new wheels. 😊

Those sites are useful, but they only scratch the surface of speaker design. They're the equivalent of the first day's lecture in a four semester course at University of Salford.

Even with identical drivers a sealed cab and ported cab will have totally different low frequency response and displacement limited output. You may be able to get a useful result, if you've got the engineering skill to pull it off, but otherwise it's a shot in the dark.

If they don't have a crossover that assigns different pass bands to different drivers they weren't truly designed to be mixed, advertising claims notwithstanding. I've yet to see definitive objective data that says otherwise.

Like he said. 115s in general don't add any low end to 410s, and they have lower sensitivity and maximum output. That said, where 410s are concerned the Orange OBC isn't exactly stellar, being loaded with entry level Eminence Beta 10 drivers. I'd be looking at replacing it, rather than trying to augment it.

He may have claimed to be a sound engineer, but he was not. That's the Myth of Wave Propagation, see my previous post above.

A pair of 210, vertically stacked, is a good option, but IMO the best option involves spending the least, which is the case if you tilt back your 115, perhaps with a touch of lift as well, which you get from a number of stands.

Your ears are to either side. They're quite capable of hearing midrange coming from behind you, which is a very good thing in the event that said midrange is the breathing of a Sabre Tooth Tiger. That's not a major concern today, but it was when our hearing evolved to become what it remains. I don't care to have my rig in front of me, if only out of 56 years of habit. It just doesn't feel right. Floor wedges are placed where they are because they have to be to prevent mic feedback. Where the OP is concerned since the 115 is what you have tilt it back, by whatever means, so that the center of the speaker is aimed more or less at your head. If you need more output then you'd want to stack a second identical 115 on top. As for the 410, it's the worst possible speaker configuration, unless one of the vertical banks of drivers are low passed. AFAIK the Barefaced Four X 10 is the only 410 with that feature.