Bill Fitzmaurice

That wouldn't tell you which wire was which. If anything the white wire is probably chassis ground, assuming there is a chassis ground. Being an older amp it most likely has a chassis ground, but that's not the case with many micro amps. Quite right.

Discussing driver size is like hitting yourself upside the head with a hammer. It feels really good when you stop. 😉

So 2022 starts off with deja vu, and not in a good way. Getting sucked in this time I am not. 🙄

Anything Marshall. What with the pandemic lots of gear has made its way into pawn shops and onto EBay, so prices should be down. For instance: https://www.ebay.co.uk/itm/255281994107?hash=item3b6ffe197b:g:aGUAAOSwNZ9humOJ

That. While the tops need to go to the left and right front the subs can be stuck out of the way, because on the one hand their output pattern is omnidirectional, while on the other not directionally locatable.

It's easier to hear the sound of the cab up close more like what's heard at a distance when there's no short ceiling or side walls on the stage. Those can cause boundary sourced low frequency null zones close to the cab, killing the lows if you're standing in one of those zones. Those zones go away the further you are away from the cab, explaining why the lows can sound much louder out in the audience than on the stage. This phenomenon lead to the myth of wave propagation, the notion that a wave can't be fully heard until one is a certain portion of a wavelength away from the source. Like most myths it was a seemingly plausible explanation for an observed result arrived at because the true explanation was unknown.

There's a big difference between the 3dB sensitivity increase you said was realized from each boundary and the 6dB that's actually realized. You're not going to get any increase by putting a cab on the floor compared to your chart because your chart already reflects the result with floor placement. I didn't mention flush mounting because it's not pertinent to this discussion. Placement some distance in front of a wall does not lead to comb filtering. It does result in an Allison Effect response notch, which I could have put on that chart, but that would be making things more complicated than necessary for this particular thread. What matters as far as boundary loading is concerned is that it will not turn a well executed ported cab into a boom machine, nor will turn a thin sounding sealed cab into a low end monster. Most of the inherent characteristics of both will be maintained, but they'll be louder, which is seldom a bad thing. Just by being louder they'll seem to go lower, as that's part and parcel of how our hearing works.

The boost is greater in the lows. That's not the same as only in the lows.

Your chart is half-space, so it already shows response on the floor. Moving it close to the wall puts it in quarter-space, which adds as much as 6dB of axial sensitivity. It does so over a broad pass band, not just in the lows. Most speaker modeling software can't model the difference between different space loadings, but HornResp can. This shows the difference between quarter-space on the darker upper trace, and half-space in the lighter lower trace. You don't get just extra bass with wall loading, you get extra everything. The effect is the same with ported and sealed cabs, so wall loading doesn't make a sealed cab work as well in the lows as a ported cab. It just makes both work better closer to the wall than away from it.

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.