Bill Fitzmaurice

Those mains are intended to be used with subs to handle the lows, so without subs they probably wouldn't do. Assuming they're up on poles you don't have ground reinforcement,while you do have floor bounce cancellation of bass, which makes the situation even worse.

I've seen it before, though I can't recall on what.

+1. By and large you want to high pass the bass in the PA around 150-200Hz. That way the directional mids and highs get dispersed throughout the room by the PA, without adding lows that the backline amp will usually provide enough of. The exception would be a very large room.

Power has nothing to do with it. What determines cone excursion, which determines sound pressure level, is the amp voltage swing. A SS amp will deliver the same voltage into any impedance load, so when you add a second identical cab both will realize the same excursion. That gives a 6dB increase compared to just one. The halved impedance load results in doubling of the current draw, which results in the doubling of the power draw, but it's the doubling of cone excursion driven with equal voltage that gives the increased SPL.

Pickups are like speakers. If they had flat response they'd all sound the same.

It comes from amp voicing, which is response adjustments independent of the EQ not user adjustable.

Channel strips are designed to have flat response with the knobs at zero, otherwise they'd never pass muster in a studio. Most bass amps are designed to have a pleasing tone with the EQ at zero according to the preferences of the B testers, but with different basses, speakers and personal taste what usually prevails is the preference of the actual designer. An exception is valve amps with the classic Fender tone stack EQ, which not being active is incapable of flat. That was of no concern to Leo Fender. He didn't care what the response looked like, he just wanted it to sound good. The consensus is that he succeeded. https://robrobinette.com/How_The_TMB_Tone_Stack_Works.htm

Mixing a 115 and 410 is always a bad idea, no matter what advertising may say to the contrary.

That's up for interpretation, but in any event the thermal power rating doesn't say how much power a cab can actually make use of. It's like asking how bright is a 100 watt light bulb. That all depends. Incandescent? Sodium? Florescent? LED? We can get the real information we need on a two quid light bulb package but not on a speaker that costs upwards of a hundred times or even a thousand times that. 🙄

Most active EQs have similar plots. It doesn't show what's happening elsewhere in the amp. As to what sounds flat, you have to take into consideration both the coloration added by the speaker and the effect of equal loudness. Once you do so it's impossible to say that a particular amp sounds flat.

That still doesn't guarantee flat, as most pre-amps have some degree of pre-shape. Besides that, speakers aren't flat. Chances are if you did get truly flat you wouldn't like it anyway, as flat sounds quite sterile. I've never understood why anyone would want it flat.

If they were the same drivers in the same net cabinet volume per driver with the same tuning then all three 12s would have had the same output. Your experience shows the downside of what can happen when they're not.

The notion of using a low impedance load to 'get all the watts out of my amp' is intrinsically flawed. It assumes that what determines how loud you can go is power related. It's not. While power is part of the equation so is the speaker frequency response, sensitivity and cone displacement. There are 8 ohm 1x12s that will go louder than 4 ohm 2x10s, so unless you have the exact specs on your current speaker and any that you're considering, which isn't likely as most manufacturers don't provide them, side by side testing is the only way to know if a change is worthwhile.

They may all be 32 ohms, as is the case with the SVT, so one must be sure of it.

It was intended for use along with a TNT amp and cab as a bi-amped low frequency/high frequency rig. Another example: https://reverb.com/item/21762989-peavey-2x8-100w-powered-bass-bi-amp-cabinet-late-1980-s-early-1990-s

We've all been through this identical question.

My advice is don't double post. 🙄

Absolutely correct. The second cab will increase both sensitivity and maximum output by 6dB. That's the equivalent of quadrupling power. Chances are the 350 watt amp will deliver all the power the drivers can handle. It's the rare twelve that can make use of more than 175w before running out of excursion capacity. OTOH the number of twelves that can take 500w without exceeding their excursion capacity is small, and they're PA subwoofer drivers, not electric bass drivers.

I've been trying to call my local paint supply store but can't get a dial tone on my phone. 🙄

Awaiting the first person to ask 'What's a blackboard?'

This is a proper tweeter for electric bass: https://eminence.com/collections/bass-guitar/products/bgh25_8 Don't be thrown by the 25 watt rating. That's for the actual power in its passband, which is on average only 8% of the full system power. All tweeters used to be so rated, but it became too difficult for people to comprehend that of a 300 watt program perhaps 25 watts goes to the tweeter. In the cabs where I specify this tweeter I use a 4th order high pass filter that doubles its power handling.

You can't do that. BTW, the usual reason for blown tweeters is that the crossover is dodgy, and does not provide adequate protection from low frequencies. They also tend to use cheap tweeters. You may be able to upgrade it, but no one can say how without knowing what's in there for both the tweeter and crossover.

Not really. The product of cone area (Sd) and excursion (Xmax) is displacement (Vd), which combines with sensitivity to give SPL. To further complicate matters driver size, and in the case of multiple drivers layout, affects dispersion. There are no short and sweet rules of thumb, other than always use the same drivers in a grouping, and always have that grouping vertically aligned.

If your amp is 2 ohm capable a BF Super Compact. That gives the option of running 1x12, 2x12 or 3x12 depending on the gig.

This is a case where 1+1 equals 2, so long as the drivers are identical and the box net volumes and ports are identical.