Bill Fitzmaurice

2 hours ago, Rubbersoul said:

Can I add a cab rated for less wattage, say 150W, without too great a risk of blowing it up?

Chances are you can't find one, not that it matters. Cab ratings are thermal, and next to meaningless. What matters is the mechanical displacement, how much air the driver cones can move without creating high distortion or suffering physical damage. You can find out the displacement if you know what drivers are being used and have their Thiele/Small specs, but cab manufacturers are loathe to reveal that. Barefaced does, with good reason. They boast as much displacement as anyone, more than most. It's the main reason why they're held in such high regard. https://barefacedaudio.com/pages/how-speakers-move-air-volume-displacement

K12H-200TC

3 hours ago, orangepeelneil said:

I've seen these speakers being advertised as guitar speakers as they have lots of headroom.

If the xmax spec is 2mm they have more headroom than most guitar drivers, the Greenback is 0.7mm, but the rest of the specs if similar to the K12H-200TC aren't well suited to guitar. I'd be very wary, as even the BN-12 300S has only 2.5mm xmax.

My concern about the K12T-200 is xmax. I can't find specs on it, but the K12H-200TC xmax is only 2mm. That's half what I'd consider the minimum acceptable. It results in a real world mechanical power limit of 25 watts. One can only speculate if the K12T-200 xmax is that short, but given the age of it and knowing Celestion came very late to the party where real bass specific drivers are concerned I wouldn't want to assume otherwise.

1 hour ago, Sparky Mark said:

Some also seem reluctant to stray from this noon position as if it is sacred and any adjustments equate to a compromise or corruption of a pure tone. 

IMHO those who have that attitude have no idea what a 'pure' tone is and would be shocked to see the measured response of their rig. No component has flat response, starting with the bass, ending with the room where it's being played. If tone controls weren't meant to be used they wouldn't be there.

Maybe it does, maybe it doesn't, but since the speaker doesn't have flat response it just doesn't matter. The amp probably has an EQ pre-shape as well, most do. Where EQ is concerned set it where it sounds best via trial and error. When it sounds good it is good.

The 2x8 ohm will be 6dB louder than  1x8 ohm. That's from the combination of 3dB additional sensitivity from the halving of impedance and 3dB additional sensitivity from the doubling of cone area. It will also have 6dB more maximum output, as the Vd (displacement) is doubled. That makes it 3dB louder at the same volume setting as the 1x4 ohm, and 6dB higher maximum output than the 1x4 ohm.

There's a saying in automobile circles that there's no replacement for displacement. It applies to speakers as well, because loudspeaker cones are pistons.

The 4 ohm will be 3dB louder, as the cone of the 4 ohm driver moves further with the same applied voltage. However, where maximum output is concerned they're the same, as both have the same maximum excursion. It just takes more voltage into the 8 ohm to get there, which takes only a slight increase of the volume knob, say from 5 to 6. Not from 5 to 10.

He has a point. If one driver is sufficient to provide all you need, or ever expect to need, for output then 4 ohms has its advantages where the amp voltage headroom is concerned. But 4 ohm tens and twelves are rare, because 2x cabs are far more common, and manufacturers aren't going to make many 4 ohm drivers when most of the demand is for 8 ohms. The exception is fifteens, which are more commonly offered in 4 ohms because most fifteen users only need one.

28 minutes ago, BassmanPaul said:

Didn't we go through all this before they kicked me off TalkBass? LOL

I quit going there before they could kick me off. Maybe it's different now, but ten years ago it was one of the worst moderated forums I've ever come across.

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especially when some of our better educated and more experienced posters dumb things down into lay terms;

IMO anything that can't be said in a paragraph using non-technical language is a waste of time for all involved. KISS isn't just the name of a band. 😉

9 minutes ago, DGBass said:

I've been down this road experimenting on a one cab solution with a 4 ohm and 8 ohm version of the same driver, in the same cab, with the same (class AB) amp and the same bass plugged in. It did in my experience make a noticeable difference running at 4 ohms      

It will, but it has nothing to do with power, everything to do with voltage. The amp puts out the same voltage into any load. (A good thing that is, because the actual impedance isn't a constant, it varies with frequency, so if this wasn't the case every frequency would be at a different level.) If all else other than impedance is equal, which it never is, with the same voltage applied the cone of the 4 ohm driver will move further than the cone of the 8 ohm driver. This results in a 3dB increase in output. There can be tone differences as well, because all else isn't equal, including but not limited to inductance and moving mass. As for the perceived increase in dynamics at high levels, that's also voltage related. An amp's dynamic response suffers when it's pushed close to its voltage output limit. Using a lower impedance driver gives more voltage headroom from the amp, which gives better dynamic response. This begs the question 'why not always use low impedance drivers?'. The answer is that the lower the impedance the higher the current draw, which can create its own set of problems. 

22 minutes ago, StingRayBoy42 said:

Me stupid think more watt mean more loud  🤪

Not your fault, industry fault. What makes speakers go louder is increasing the voltage output of the amp. Watts never should have been used to define amplifier output, or speaker capacity. But they were, and now we're stuck with it.

1 hour ago, Sparky Mark said:

Aren't these used when someone (guitarists mainly?) is wanting to get the power amp over-driven tone but at a lower volume?

Yes, with a valve amp, so that the output valves can be pushed into hard clipping while keeping the voltage to the speakers low so that they're not too loud and not overpowered. Tom Scholz sold one, and I believe Marshall did as well. Useful as that is on guitar it's not what I'd want to use with electric bass.

4 hours ago, StingRayBoy42 said:

Is there a cheap and simple way to get the full 500W of power into my one 8 ohm speaker?

There's no point. Power and decibels output are only indirectly related.

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Is there such a thing as a 'fake' 8 ohm speaker that I can plug into the other speaker output?

It's called a power soak. Using one is akin to driving with your parking brake engaged so that you can get all the horsepower out of your engine. 🙄

Is that a reference to the women? Or the livestock? 😁

On our side of the pond they had to remove the grass and install artificial turf on the University of Vermont football field, to stop the cheerleaders from grazing during halftime. 🙄

I managed to get a decent level from my Bassman, when I played it through eight twelves. 😳 This was the 60s, when the average twelve had only 1mm xmax. Today it's not hard to find a 212 that has 450cc displacement. The 212 Bassman/Bandmaster/Twin Reverb loaded with Jensen C12s had 80cc. They also had Fs of 112Hz, so going low wasn't in their wheelhouse.

It's the same cab as the 50w Bassman, so it's marginal. The drivers aren't bass specific, they're generic musical instrument drivers. They sound OK at low levels, but that's about it. A Twin is OK for recording, again at low levels. Carol Kaye, possibly the most recorded bassist of all time, mainly used a Fender Concert 410 in the 60s-70s. . If you've heard the Beach Boys you've heard that amp.

4 hours ago, JapanAxe said:

99.99% of the time I would agree with you, but the Barefaced 4x10 etc have low pass filters on one side to prevent phase cancellation.

True. I mentioned the concept to Alex way back before he started his company, it's called a 1.5 alignment, and he eventually employed it. It's not just to prevent comb filtering in the highs, it also improves horizontal dispersion in the mids.  But a pair of 2x10 vertically stacked also has the advantage of getting drivers up higher so you can hear the mids better when close to the cab.

Not that I recommend it, but if you connect the terminals of a 9V battery, the small type, with a screw driver you'll get a small spark. Do so with a 12v car battery and the screw driver will suffer serious damage. It can even get arc welded to the terminals. The difference is due to the ampere capacity of the two. Consider a taser. They run at 30 to 50k volts. They tend to be non-lethal because they have very low ampere capacity. A static shock you receive on a dry winter day can be an upwards of 75,000 volts, but the current is so small that all you might feel is a slight annoying zap. Like most electricians I seldom bothered to turn off the breaker to swap out an outlet or switch, and as a result got zapped dozens of times over the years. Smart? Maybe not, but that's what we do. I once stuck my finger in the wrong place in a Fender Bassman and got the full 470v. Unpleasant, but not injurious. Still, that experience educated me to the value of using a bleeder resistor to drain the caps before messing around. 😳

Leave it on the road case. Whether you go with a second Midget or some other cab with multiple drivers you want them vertical, not horizontal. It sounds better that way, to you and to the audience.

Not necessarily lethal, and it's not the voltage that kills, it's the amperes. Still, getting zapped with even 450v isn't a pleasant experience. One thing to do is to turn the power and standby switches on, with the amp unplugged, before removing the chassis from the case, especially the standby. When the standby switch is off the power supply caps will hold their voltage for a long time. With it on they'll discharge, albeit slowly.

Clean everything with contact cleaner, including the pots, tube sockets and tube pins.

Don't do anything until you get the cab and at the very least post the pictures. The Delta 12LFA is a subwoofer driver, best for electric bass when mated to midrange drivers. The BN12-300 is unsuitable for electric bass, at only 2.5mm the xmax is far too short. As for OEM versus Eminence branded, when Eminence creates a new driver they test a number of variations. The ones that test the best are the ones that end up being sold under the Eminence brand name. I've seem some OEM Eminence that were pretty good, but I've seen some that were pretty bad. That includes one relatively well known manufacturer's version of the Delta Lite II 2512. 🙄

Post a picture of a driver. Also post the exact dimensions of the cab. The only way to know what will work well in any cab is via loudspeaker modeling software, which allows for reverse engineering.

A harsh tweeter is an indication of high THD, which can be sourced by the amp and/or the tweeter. When it's the tweeter the usual reason is a poor crossover, which allows far too much low frequency content to reach it.  The only thing most manufacturers go cheaper with than the tweeter is the crossover.

3 hours ago, asingardenof said:

 I've done noise assessments to determine if noise barriers are required adjacent to motorways, but that was relatively simplistic (albeit I'm sure the formulae were developed by some serious boffins at TRL who smoked pipes and suchlike) compared to modern acoustic modelling methods.

That's one of the most basic calculations. Where the barrier is at least one wavelength high sound is reflected back. Where it's less than one wavelength high sound goes over it. One wavelength at 100Hz is about 3.5 meters, so reducing transmission above 100Hz isn't difficult. One wavelength at 50Hz is about 7 meters, so reducing bass is impractical.