Bill Fitzmaurice

On 22/01/2022 at 06:56, mybass said:

Speaker design and tech has probably moved forward in some areas quite a bit.

Not all that much in the last 15 years. The last significant tech change was to neo magnets, which allowed improvements in excursion without sacrificing sensitivity, and as a result higher output than previously possible. Most of the major alterations that neo allowed came circa 2004-2008. There have been further refinements since then, but nothing earth shaking or trouser flapping. 

The BF displacement is 250cc. Markbass? Who knows? Where bass output is concerned it's just like horsepower from an engine, there's no replacement for displacement.

There are tens that can handle a lot more, but to do that they sacrifice midrange response, so they're typically used in subwoofers or designs with separate midrange drivers. On the flip side guitar tens that will go into high distortion with only ten watts are common.

5 hours ago, Tdw said:

Thanks, I thought that might be the case. I don't suppose you've any idea about x max for the barefaced and the te 10 inch drivers?

The BF ten has 250cc of displacement, indicating around 7.5mm xmax, which is very respectable. I don't see it handling less than 225w. The TE driver is an unknown commodity. It supposedly uses an Eminence Neo Ten, but they make at least four different varieties, and that doesn't count OEM variants.

They're just examples of how far apart drivers can be in their mechanical capability, which is defined by xmax. By no means are these differences rare. One of the most ubiquitous drivers is the Eminence Beta 10, and OEM versions of it. Orange uses it in their OBC 410. It reaches xmax at 40w at 80Hz, where the output demand for electric bass is at its highest.

3 hours ago, acidbass said:

Maybe from a scientific perspective it isn't 'correct' but to me what's correct is what sounds good

When you have one driver that can only take 50 watts before reaching its mechanical limit and another that can take 500 watts before reaching its mechanical limit you don't need a scientific background to see that it's a bad pairing. It's not about being correct, it's about being logical.

Don't mix different cabs. If they're not identical, most especially if the drivers aren't identical, you're creating a weak link in the chain scenario.

31 minutes ago, jay42 said:

 in my mind if I went for 4 Ohm cabinets I could utilise full power from the amp

Divest that notion. It's the rare cab that can make use of more than half its rated thermal input power before running out of the mechanical ability to use it, so the oft mentioned quest of 'getting all the watts out of my amp' is right up there with the search for the Holy Grail or an honest politician of things not worth the effort.

Cabs don't hiss, or create any other noise. They will reproduce hiss and/or noise present in the signal chain, which starts with the pickups and ends at the amp output jacks.

What you'll end up with is a blown 4 ohm resistor. If you must use a second cab make it identical to what you have now. If your amp won't handle a 2 ohm load you'll need a break out box to series wire them.

4 hours ago, BassmanPaul said:

It's how I would have wired it but I would have performed a battery test to verify which terminal is the positive on the driver.

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. 

Quote

If you only use the combo on its own i.e. without an extension cab then it doesn't matter which way round you connect it.

Quite right.

1 hour ago, Dan Dare said:

Aw, go on Bill. It will be entertaining.

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.

16 hours ago, Phil Starr said:

OK now move into a gig. Put the cab on the floor and the bottom end gets a 3db boost, back against the wall another 3db.

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.