Bill Fitzmaurice

Placing subs close to walls can realize as much as 6dB higher output, from spatial loading, compared to well away from walls. It also prevents low frequency cancellation. When the distance from the sub to the wall is 1/4 wavelength the reflected wave meets the original wave 180 degrees out of phase, causing a response dip as much as 24dB deep. Another problem with subs under mains is the creation of a power alley with dual stacks, where the sub outputs alternately reinforce and cancel each other across the sound field. The only way to prevent that is to either place them together or to separate them by two wavelengths. At 40Hz that's almost 18 meters.

One can't overlook the fact that this particular arrangement was invented by Bose, a company that has always placed form ahead of function. The rest followed suit because it's easier, and far more profitable, to give buyers what they want rather than to educate them to the benefits of better engineered alternatives.

How do you know? The knob position doesn't reveal the amp power output, nor does anything else. With a low voltage input signal the knobs could all be wide open and yet the output -10dB or more from rated output. With a high voltage input the knobs could all be at 9:00 and yet the output +6dB over rated output. I once blew a 200 watt EVM-15B with a 50 watt amp when I hooked up a pink noise generator for testing. I didn't realize that the generator was cranked, so when I turned it on the voice coil blew in less than a second.

In terms of placing the subs beneath the tops they did get it wrong. It's a convenient arrangement, but you can't wall load the subs and place the tops out front at the same time when you do it that way.

The early bass cabs that were open backed might not have benefited from being sealed, as they used generic musical instrument drivers which were guitar oriented anyway. Besides, they could give a good tone, they just couldn't go loud. Play just about any Beach Boys recording and you're probably hearing Carol Kaye playing through an open back Fender Super Reverb.

Pushed to clipping it can probably deliver 800w into that cab. Amps are rated at low THD. At high THD they can easily deliver twice their rated power, if not more.

Sealed designs are simple compared to ported. The advantage to sealed is that they're hard to mess up, so long as the drivers used have the right specs for sealed. It just so happens that the right specs for sealed are high Qts, which are what's usually found with inexpensive drivers, so if you're going to use an inexpensive driver just stick it in a sealed box and you're good to go. Ported cabs work best with lower Qts drivers, which also tend to be more expensive, so if you have a more expensive drive it probably needs to be in a well designed ported box for best results. Ported goes lower than sealed when done right. What you don't want to do is to put an inexpensive high Qts driver in a badly designed ported box, as the result will usually be a boom box. When you hear people complain about ported speakers being boomy it's usually because they had a cheap driver in a bad box. Like most generalizations it's not true. The Ampeg SVT, for instance, was made sealed because that's what gave the best results with the high Qts drivers that they used. They could have made it ported and probably would have if they were able to find low Qts 32 ohm drivers, but none were to be had in 1969. Damping factor is a non-factor other than in extreme cases that are very rarely seen. http://www.cartchunk.org/audiotopics/DampingFactor.pdf

You're not wrong, but also not entirely correct. Most of what's heard form electric bass is midrange harmonics, not low frequency fundamentals, exaggerated as the ear is most sensitive in the midrange. Therefore the comb filtering is happening where it's most audible. Then there's the matter of horizontal dispersion, which is halved when drivers are so placed compared to vertically aligned, and here again that halved dispersion occurs primarily in the midrange that's critical to intelligibility.

The problem is that assumption is incorrect, in a few ways, the most obvious being that speaker impedance, and as a result current and power, isn't a constant with respect to frequency. That's why neither amperes nor watts are used in SPL computations. Volts are, being unaffected by the load impedance, and being linear with respect to cone excursion. See paragraph above.

Try plugging your headphones directly into the SansAmp. You 'll need a stereo to mono converter plug to get it in both ears.

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.