Bill Fitzmaurice

[quote name='Twincam' timestamp='1499040406' post='3328808'] Is it not better to achieve a given output using more gain and ask less of the power amp. [/quote]How are you 'asking less of the power amp'?

It doesn't matter if you achieve a given output level with the gain low and volume high or the other way around, the power will be the same.

[quote name='FinnDave' timestamp='1499025942' post='3328709'] I started playing in the 70s, when the accepted standard was a cab rated at double the potential output of the amp. [/quote]In those days real bass drivers were few and far in between, most being generic 'musical instrument' drivers, ie., guitar drivers. They had very short excursion, so you needed lots of them to run clean in the lows. The first rig I had that was capable of running a clean low E with my 50w Fender Bassman was a pair of 4x12 Kustom columns, which had a thermal rating of 150w each. Much has changed since then, mostly with respect to the excursion capability of drivers. For instance, the 50 watt Jensen P12 was often loaded in 2x12 Bassman cabs. Its excursion (xmax) was 1mm. In real world terms that limited it to perhaps 10 watts in the lows before running out of excursion. The xmax of the average twelve inch bass driver today is 5mm. That translates to over four times the power handling before running out of excursion.

[quote name='FinnDave' timestamp='1499018391' post='3328632'] Personally, I would never plug an amp into a cab with a potentially higher output than the cab could handle. Any accidental tweaking of the volume knob could be catastrophic. [/quote]You should get into the ring with a believer in the myth of under-powering, see who wins out. The fly in your particular ointment has to do with the fact that a volume knob position isn't an indicator of how much power the amp is putting out. That depends on a number of factors, starting with the frequency response and output voltage of the pickups, the gain structure throughout the signal chain, EQ boost or cut, speaker impedance with respect to frequency, and so on. Even with the volume knob dimed one set of circumstances can result in the amp running at perhaps a quarter of its rated output, while another set of circumstances could have the amp clipping with the volume control at noon or less. There's a lot of wiggle room with respect to what will work. Having the amp rating anywhere between 1/2 and 2x the speaker rating is probably safe.

[quote name='pawleep' timestamp='1498928691' post='3328071'] was wondering myself if the qes, qts and power; 200 vs 400 rms (deltaPro) are really that much different? [/quote]Different from a driver that was on evilbay four years ago? If I said so it must have been, but that listing is long gone into zombieland, as was this thread until you did an Igor on it.

[quote name='Osiris' timestamp='1498738725' post='3326717'] I want to be sure that it isn't going to be too overpowered that it could potentially damage the Mesa cab before opening my wallet. [/quote]Does it come equipped with a volume knob? If so no worries.

That's called lumber core plywood. It's not as stiff or stable as regular plywood.

[quote name='EliasMooseblaster' timestamp='1497874581' post='3320988'] they've actually specified "due to restrictions, guitars are all DIed, no amplifiers." [/quote]They should spin some CDs with a couple of blokes playing air guitar.

[quote name='EliasMooseblaster' timestamp='1497872428' post='3320957'] I've recently been offered a slot on a gig where we've been told expressly not not to bring any amps at all [/quote]That's OK if there's a house backline, and the gear isn't junk. I'd certainly want to know before booking it. They should have a printed handout of what's there.

If an engineer gives you a DI to be placed before the amp an alarm should go off. Either he doesn't care about duplicating your tone in the PA or he's technically ignorant. The guys who know what they're doing and care how you sound will DI post-preamp if they can, and will mic as well, the one for the lows, the other for the mids and highs. Imagine what would happen if they expected a guitar player to go to a DI in any way, shape or form.

[quote name='Jack' timestamp='1497284450' post='3317029'] Hit them with plenty of input volume. [/quote]+1, that's the only time a valve will act all that much differently. IMO valves in the pre are only effective as a sales tool. The real 'magic' of valves happens when they're in the output stage.

[quote name='Freddie75' timestamp='1497052015' post='3315632'] Looking to upgrade the driver to 300/400 watts (8ohms) so it handles the pairing better. . [/quote]Higher thermal power capacity doesn't necessarily translate into higher output capacity. In some cases it can be less. If you need more than what the one RS212 will do your best best is to add another RS212, not a 112.

[quote name='DIYjapan' timestamp='1497001664' post='3315182'] 12mm or 15mm? [/quote]Properly braced 12mm is all you need. [quote]bagends look rugged as heck and they are thicker 18mm not 15mm. [/quote]Commercial cabs tend to use 18mm, because lower labor costs make it less expensive to build barely braced or unbraced 18mm than well braced 12mm. Besides, they don't have to haul the cab but once to the loading dock for shipping. The sweat equity invested in building a lightweight cab is repaid every time you lift it.

Damping doesn't take up acoustical space.

If designing speaker cabinets was easy everyone would do it. Just to complicate matters further, it looks like you're using WinISD Beta, or perhaps an old version of Alpha. I can't tell which from the photos, as they're too small to make out details, and in any event I haven't had either of those for quite a few years, so I have nothing to compare to. You should be using WinISD 0.7.0.950. http://www.linearteam.org/

Of the three I greatly prefer the green. The white will be boomy in the midbass and weak in the lows. What they don't show is response above 200Hz. That you can only find by comparing the charts on the Eminence data sheets. The Delta 12LF will be weak in the mids. You also should be looking at the SPL chart, not the transfer magnitude chart, which doesn't take into account sensitivity. For comparison this is the measured response of the 2512 plus tweeter in my Simplexx 12: You can see the midbass hump is slight, so boom won't be an issue, and the low end is stronger as well. You're also missing two charts that are of equal importance to the SPL chart, the maximum SPL chart and the rear port velocity chart. The port velocity chart, which needs to be calculated at the maximum power of the driver, tells you how large the port area must be to keep port velocity below 20m/s to eliminate port noise. Too much area isn't good either, it makes the port longer and therefore the cab larger for no reason.

Panel to panel braces can be made from whatever is handy. There are no flexing forces exerted on them, only compression and extension, so stiffness isn't required. When I use spline braces, only if there's no place to put a panel to panel brace, they're plywood, at least and inch and a half wide, because they do require as much stiffness as possible.

[quote name='Marty Forrer' timestamp='1496374873' post='3310886'] With all due respect to Mr Bill Fitzmaurice, I have just built a Greenboy Fearful 12/6 from scratch, not a kit. I have pumped 500 watts RMS of double bass signal (huge transients and organ re-arranging bass) and have no problem with the spine bracing. I will be stone deaf before I hear any rattles or vibration. Each to his own. [/quote]With all due respect, I've done extensive testing of both, in the same cab configuration, side by side. Panel to panel bracing is at least four times as effective as spline bracing, with less weight. Modal analysis bears that out, but I prefer to rely not on analysis alone. Your results may be acceptable, but unless you have built both configurations you have no basis for comparison.

I don't know about Linden, but American Basswood is too lightweight for speaker cabinets. It's considered a junk wood, not suitable for construction or furniture. It doesn't even burn well.

[quote name='Chopthebass' timestamp='1496070973' post='3308520'] I remember having a better experience at this venue with my two Jack 12's[/quote]Probably because the Jacks are much more sensitive in the lower mids than commercial cabs, and those lower mid frequencies are above the band width where null zones occur.. [quote]My GK cabs are the wedge shaped ones, so if I angle them will the crowd still hear them ? [/quote]They'll hear the lows that you don't. The mids and highs, maybe not, especially as they have rather poor dispersion in the mids and highs to begin with.

[quote name='Jack' timestamp='1496059700' post='3308428'] It's electrically the same as having a thicker cable, so if anything your amp would have a minutely easier time of it. [/quote]If anything the lower resistance of dual cables would lower the overall impedance load, and that might make things harder on the amp. OTOH if the cables are undersized to begin with the lower resistance could lessen insertion loss, and that would ease the load on the amp, so it could work either way. Then there's the scenario if the amp has dual power amps, ala the Ashdown Superfly for instance. Plugging both into a single cab with parallel jacks could fry a 'Fly. I don't know what the LM III configuration is, but the possibility for damage does exist. [quote]after having some numpty at a gig borrow my gear [/quote][i]That's [/i]the source of the problem. If I do let someone sit in I have one rule: don't touch the amp. If they don't like the way it sounds that's their tough luck for not bringing their own gear.

You were standing in a null zone. http://billfitzmaurice.info/forum/viewtopic.php?f=10&t=999 Moving the cab and/or your position can help. Since you can't hear lows when you're in a null zone it's critical to have the cab either elevated or tilted back so you can hear your mids.

[quote name='DIYjapan' timestamp='1495931610' post='3307648'] most people on here are recommending tube ports. [/quote]I didn't. You may find these threads interesting, including the builder's choice of finish: http://billfitzmaurice.info/forum/viewtopic.php?f=30&t=24323 http://billfitzmaurice.info/forum/viewtopic.php?f=13&t=24354

[quote name='Jus Lukin' timestamp='1495819948' post='3306897'] Money- no longer worth it's weight in burgers! [/quote]I'm sure they're no longer like that. The reason: credit and debit cards. Before the barriers went up fast food joints were easy marks, and cash heavy, as that's what everyone paid with. Nowadays cash is a thing of the past. Banks were less likely to be robbed, having armed security guards. You never saw Ronald McDonald packing heat.

[quote name='Jus Lukin' timestamp='1495817800' post='3306874'] I seem to remember drinks and tickets​ were dispensed through a hatch- perhaps the missing part of the rectangle housed the office and storeroom! [/quote]Years ago in some of the seedier sections of New York City, and I'm sure other cities as well, there were bullet proof perspex dividers over the counters at McDonalds and other fast food shops, where the orders were passed through small revolving doors. Banks in the same neighborhoods had less security.