Bill Fitzmaurice

I doubt any of them has the slightest clue what they're talking about. What they're actually referring to is that using two cabs sounds better than one. That's the case 99 times out of 100, and it has nothing to do with the impedance load, everything to do with the increase in sensitivity when you use more than one cab. How many of them did side by side comparisons of the same amp with two 4 ohm cabs and with two otherwise identical 8 ohm cabs? I bet you couldn't find a single one of them who's understanding of how a speaker works goes beyond 'you plug it in to an amp'.

It doesn't run best at 2 ohms, it's just capable of running at 2 ohms, and running at 2 ohms doesn't maximize anything other than current draw, which isn't a good thing. You're wasting time and money going to 4 ohm cabs.

Chances are there's an open coil in one driver, but those four may be series wired, so when one won't pass signal they all stop. You'll need to pull and test the top four drivers to be sure.

Pretty much nothing, as specs only concern low frequency response, while what most refer to as tone comes from the mids and highs. You can use the SPL charts on driver data sheets to see the mid and HF response, but it does you little good if you don't know how what you see translates into what you'll hear.

The captain of the Titanic said pretty much the same thing when he ordered full speed ahead, in an iceberg zone, at night. Needless to say he was not prepared for the worst case scenario. It's one thing to emulate another captain, James T. Kirk, by boldly going where no man has gone before. But this particular voyage of discovery was completed by Theile and Small right around the same time that Kirk's first foray was, circa 1969. The OP has no need to reinvent the wheel, no matter how hard one tries it will always be round.

That's worst case, and would take a very large hole. Still, there is a science to this, and if you don't understand it don't mess with it.

Using all the maths etc. you can get it right the first time, and for that matter determine if it's worth doing at all. You'll also know why a small circular hole is probably a bad idea.

Paraphrasing a quote I saw in Speaker Builder Magazine many years ago, there's a thousand ways to make a ported cab. This is one of them. I shy away from claims of magical never before achieved results that aren't accompanied by hard data. That's especially the case when I see advertising blurbs like this: providing 600 watts of full range sound . Sound isn't measured in watts.

It won't work as well as standard construction. For instance, how do you fit the front and back?

I can't say without seeing the specs, but there are at least four that are more significant than impedance.

Again, you might get a better result with a different driver, but you may not. Before you can fix something you have to find out if it's broken. That means finding the specs and frequency response chart for the original driver, which amp manufacturers are loathe to reveal. That said, the drivers in most combos tend to be low end, and a pair of low end tens or twelves will work better than one low end twelve. They wouldn't work better than, say, an Eminence 3012HO, but drivers of that ilk aren't found in combos.

A driver upgrade may be possible, but you'd have to know the full set of T/S specs of the original to make that determination. As for a 212 versus a 112, the 212 will almost always sound better, no matter what the drivers are. For that matter virtually any two cabs together will sound better than either alone. That's a basic property of how speakers work. As for this: Changing from an 8 ohm to 4 ohm load will have little, if any, effect. Many factors can result in an improvement, but impedance is seldom one of them.

That's not true. In the same 2 cu ft ported cab tuned to 45Hz or in 2 cu ft sealed the Beta 12 and BP122 have virtually identical low frequency response. Neither will have very good low frequency sensitivity in a sealed cab, because it's a sealed cab.

Using a midrange driver with a BP122 isn't a bad idea, using a Beta 12 as a midrange driver is a very bad idea. It's not about response, it's about dispersion, and the midrange/HF dispersion of a twelve is horrid. That's why guitar cabs beam. The right tool for the job is a six or an eight.

It could be a microphonic tube. Gently tap on them with a pencil to find out.

[quote name='chris_b' timestamp='1509963042' post='3402835'] All TC RS cabs are 8 ohm. [/quote]There's a reason for this disclaimer: [i]As long as you use TC cabinets, most of our amps can actually handle 3 cabs simultaneously. [/i] The reason is that they're not 8 ohm cabs, otherwise their amps would be able to handle any three 8 ohm cabs. In BGM issue #6 they measured the RS210 and RS212 at 10.54 Ohms and 11.54 Ohms respectively.

[quote name='Zummerbass' timestamp='1509898054' post='3402414'] Do I get a PC 210t [/quote]If you like what you have but need it louder add another identical cab. [quote]Or another RS cab? 115 or 212. Heavier but well matched. [/quote]Well matched cosmetically, but otherwise, no. To be acoustically well matched is to be identical.

Speakon connectors are made in two, four and eight-pole configurations. The two-pole cable connector will mate with the four-pole panel connector, connecting to +1 and −1; but the reverse combination will not work.

[quote name='discreet' timestamp='1509643382' post='3400573'] I think you're right - you have the knowledge BIll, how about a short post on driver substitution and I'll get a mod to make it sticky? [/quote]I'd only do so if the topic was locked. Back when I still frequented talkbass they asked me to explain how driver phase response affects mixing cabs. It turned into a complete clusterf*ck when the usual bunch of idiots decided to fill the thread with Luddite nonsense. If the topic had been locked, or if the mods had done their jobs and cleared out the detritus, it wouldn't have given me one more reason to leave there. Lesson learned. To do it right would take a fair amount of time, which I'd only invest if I was assured that it wouldn't turn into an endless debate.

I think the need for a sticky that explains what it takes in terms of the tools and knowledge required to successfully substitute drivers is long overdue.

The 2510 has more xmax. Low Qes chokes off bass response, 0.30 is as low as you want. But don't expect miracles, 17L is less than half what you need for best results. Long wavelengths at high levels don't come out of small cabs.

Since you have the specs on the original you just need to match those within 10% to determine if another driver is compatible, except for xmax. At 2mm it isn't even mediocre. 4mm is the least you should consider. I'd use the 2510 myself. As for the 3010MB the Qes of 0.21 rules it out as a bass driver.

You would not high pass higher than 50Hz, and it would have to be an active filter, not passive. The Thumpinator is one example.

[quote name='TheRev' timestamp='1509176748' post='3397111'] I have used cabs (usually 4x10s or 8x10s) at festivals where the notes all seem to run together, with the result that I can't really hear what I'm playing.. My 4x5 sounds clearer and more articulate to my ears [/quote]That can be chalked up to the better upper midrange response and dispersion of the smaller drivers. It's why some cabs are now made with larger woofers for the lows and smaller midrange drivers for the mids. PA and hi-fi cabs have used that arrangement since the 1950s. Bass cab manufacturers, and bass players, are slowly coming around.

The cone diameter isn't the same as the frame size. Even with the same frame size the cone area, T/S spec Sd, differs from driver to driver. There are some fives where four of them will have the same, or even more, cone area than some tens, but by and large they won't.