2x12" Cab Build

[Phil Starr]

Hi all, I had a recent request from @police squad for help with a 2x12 design.  I've started to do this via PM but thought other people have asked for similar designs and people might like to follow the design process.  Basically it involves me asking a series of stupid questions to home in on exactly what he is going to try to achieve. Then I run computer models and ask more questions to home in on what I hope will be his best speaker. Anyway this was his initial question

 

On 22/07/2025 at 15:45, police squad said:

Hi Phil

I hope you're well and hope you don't mind me messaging you direct

 

I've just bought an Ampeg V4B 100 watt valve amp

The matching cab weighs a tonne but looks very nice, sites under the head etc

 

dimensions are Dimensions (WxHxD): 610 x 635 x 406 mm

 

what I was wondering is, do you have any designs similar and would some eminence S2012's sound good (as I have a pair in my garage)

 

TIA

martin

[Phil Starr]

Hi Martin,

 

I've had a quick look on the Eminence website and these speakers look like they would work in a 50l cab or 100l for the pair. They are very high efficiency and have Eminence's typical midrange peak so good for creating an old school sound. Eminence used to offer cab designs for all their speakers but I can't find them as they have re-built their website. The designs may still be there of course. In performance the basslites will be very similar to the ceramic magnet Beta12-2A as used in dozens of commercial cabs so you'll end up with something sounding like TC/Markbass etc etc. Not exactly, but in that sort of ball park If you are a valve man you'll probably be looking for that sort of sound rather than FRFR anyway so they could be a great match.

[Phil Starr]

Hi, I've put in the speaker parameters and run a quick check. Get ready for a blizzard of graphs. The first thing is that these speakers are underdamped, basically the magnets/motor systems are small giving a very 'American' approach to bass. The sort of warm/bloated sounded you might expect from Ampeg  To get lotsof deep bass extension and a flat response they would need a huge cabinet. This is a pair of them in a 100,200 and 300litre enclosure

 

The one in bold is the 100l cab which is roughly the size you are planning. The 300l cab gives you output down to roughly 33Hz -10db and the flattest response but you wouldn't want to fit a 300l cab into a car never mind carry it. However you probably wouldn't want that much bass anyway in a gig situation. I just want to show you the choices you are making

 

[police squad]

I never realised how complicated cab design could be

I'm trying to save a bit of weight over the Ampeg SVT212 which is 30Kg and as stated in my original message, I have a couple of Eminence neos I'd like to find a home for

[Phil Starr]

1 hour ago, police squad said:

I never realised how complicated cab design could be

I'm trying to save a bit of weight over the Ampeg SVT212 which is 30Kg and as stated in my original message, I have a couple of Eminence neos I'd like to find a home for

That's my fault, I'm a details person and I just assume everyone is as fascinated as I am about loudspeakers. I'm a riot at parties 😂 

[Phil Starr]

OK a bit of a recap. on our discusion so far. This is the cab Martin wants to copy but he won't use the horn driver so we are leaving that out. I suggested that he would be better with a taller cab and putting the two 12" drivers in line to improve dispersion and the audibility on stage. Anyway this is the cab we are 'copying' 

 

[Phil Starr]

You could go for this shape

 

[police squad]

10 minutes ago, Phil Starr said:

You could go for this shape

 

it depends how tall it is I suppose

[chyc]

This is going to be an interesting topic!

 

So is the brief that you like everything about your Ampeg SVT212 except the weight?

[JPJ]

Sorry for the thread hi-jack, but I started to build a vertical 2x12 some time ago, then became impatient and bought a Vanderkley 2x12 that came up local to me. As a result, I have a professionally pre-cut plywood carcass ready for assembly sitting in my loft, along with two of the desirable Faital Pro 320 speakers from the Basschat 1x12 cab design if anyone is interested. 

[police squad]

36 minutes ago, chyc said:

This is going to be an interesting topic!

 

So is the brief that you like everything about your Ampeg SVT212 except the weight?

I haven't got the ampeg cab, only the V4B

I have other cabs to use but I have these neos that I'd like to use

[chyc]

1 hour ago, police squad said:

I have other cabs to use but I have these neos that I'd like to use

Understood. From what I can see the S2012s would make for a very potent rig, and if the cabinet is built around the dimensions of a V4B that would sit on top, yeah that would look pretty nice as well.

[police squad]

Yep agreed

I just tried it thru my mark bass cl115

Sounds epic with my HW4003

[Mottlefeeder]

11 hours ago, Phil Starr said:

Hi Martin,

 

I've had a quick look on the Eminence website and these speakers look like they would work in a 50l cab or 100l for the pair. They are very high efficiency and have Eminence's typical midrange peak so good for creating an old school sound. Eminence used to offer cab designs for all their speakers but I can't find them as they have re-built their website. The designs may still be there of course. In performance the basslites will be very similar to the ceramic magnet Beta12-2A as used in dozens of commercial cabs so you'll end up with something sounding like TC/Markbass etc etc. Not exactly, but in that sort of ball park If you are a valve man you'll probably be looking for that sort of sound rather than FRFR anyway so they could be a great match.

I have copies of some of the Eminence designs.

David

Basslite_S2012_cab.pdf

[Phil Starr]

This is interesting, it's the measured response curves of the SVT212. Obviously ignore the top end because we won't be using a tweeter but the bottom end shows a similar roll off to your speakers in a 90l cab, It rolls off really quite high from 150Hz but also quite gradually so it is around -10db @ 50Hz.  There's a big drop in everything at around 1300 Hz, which I'm guessing is the crossover. The red line is the response straight ahead and the colours are off axis. You cvan see how much the mids are lost off axis and this is increased because of the sideways displacement of the speakers. You get quite a lot of off axis fall off anyway due to the size of the 12" drivers but the cab is over 600mm wide so it's like having a 24" driver rather than a 12. Above 2,000Hz you are looking at the response of the horn which isn't relevant if you are building a tweeterless cab.

 

I'm not a purist in these things, if you've tried the SVT and love the sound then you can build something like a horn free SVT. Without a horn the off axis problems will be worse but if you tried it with the horn turned off and still liked it then that's clearly somethign that doesn't worry you. If you want a cab the same width as your amp but with the speakers in line then you can do that too and it will be slightly easier to hear yourself on stage.

 

[Phil Starr]

10 hours ago, Mottlefeeder said:

I have copies of some of the Eminence designs.

David

Basslite_S2012_cab.pdf 237.02 kB · 3 downloads

Thanks David.

 

Martin @Mottlefeeder managed to find them too. The "small vented cab" is 45l and to 55Hz for a single driver. My first guess was to use a 90l cab tuned to 50 hz which is the approximate volume of the Ampeg cab we are copying so in this case it's reassuring to know I've come up pretty much with the same design as Eminence. It may even be that Ampeg knew of this design when it developed the VB212 but to be fair there are only so many sensible solutions for any given driver.

 

[Phil Starr]

OK one last thing to bring everyone up to date, @police squad asked about a sealed cab. Once you have the speaker's mechanical and electrical properties loaded into WinISD it's a matter of seconds to model a range of cabs so I sent him this: The purple line is the sealed cab, the red line is a 90l cab and the blue and green lines are for 200 and 300l cabs. I actually quite like the sealed cab, it has the flattest response and -3db is around 75Hz so all the second harmonics of a 4 string bass will be accurately reproduced and Eminence also have this design which they describe as "ultra clean" which is probably a very fair description of how this would sound. However you can see how much bass is lost compared with the three ported cabs and the bass hump at 100Hz will also warm up the sound and add a bit of thump which is what Martin wanted. I'd had the other two cabs there to play with different cab volumes to see if I could squeeze a bit more bass out of the cab. The 300l cab in green has a whole lot more bass and a flat response but 300l is an absurd size for a cab if you have to transport it. I'm only showing this to demonstrate that all cabs are compromises of practicality cost and sound and I suppose to say that I did look to see if there were any advantages to a slightly bigger cab.

 

 

 

Edited 1 hour ago by Phil Starr

[Phil Starr]

At this point we have a design brief ready and the parameters are loaded into the computer so now it is simply about tweaking the design. I'm looking for a roughly 90l cab for two Eminence Basslite 2012's, the shape will be determined by the needs of the user so now all I have to do is tweak the design and see what I can squeeze out of the cab. I'm starting out by looking at the tuning. I've bracketed my 50Hz tuning in blue with 60hz tuning in red and 30hz tuning in green.  I'm quite liking 50Hz tuning. Theres a 2db hump of extra bass at 100Hz which will warm things up a bit and give that old school thump. 60 hz increases the hump to 3db which I would find intrusive and would be hard to tune out. 30Hz tuning gives a flatter response and a slower roll off (but from a higher frequency) but is more like the measured bass response of the 2x12 Ampeg SVT cab. This is down to Martin's taste I think, so the question is: 

 

In your face bass warmth, Ampeg like gradual roll off from fairly high up or a compromise somewhere in the middle? 

 

Before you choose there's another consideration, how does this load the speaker cones and will this affect power handling?

 

 

 

[police squad]

I'm still thinking to stick with the ampeg sound. All the people that have the rig love it.

So there must be something in their cab design that gives the classic sound

I've tried the V4B thru a small Mark bass 1x15 and that ampeg sound and grind is there in spades

so if their cab enhances the amp, so be it I think

[Phil Starr]

So this is the excursion of the speakers at 300W. The horizontal red line is where the excursion starts to distort. If the excursion reaches 0.09 (9mm) the speakers will be damaged and eventually stop working. You can see the lowest excursion is at high frequencies and at the tuning frequencies of the ports 30,50 and 60hz in this case. The only tuning that runs into distortion at high power is the green/lower tuning. They all go into damage levels below 40Hz/bottom E at full power but it's a lot lower in the lowest tuning. Even if you are reading this and have no intention of building a cab it's worth knowing that this shaped curve is the same for every ported cab and your bass cab almost certainly can be forced into damage mode at low frequencies!!!!

 

However don't panic. There is almost no fundamental coming out of your bass pickups. they are placed well away from the middle of the string and that reduces deep bass. Most of us don't have amps that go down to 40hz without rolling off either. There isn't any reall evidence of a lot of broken Ampeg VB212's or any other cab of this type. For me this graph shows that any of the tunings will work without issues but it's not a bad reminder of using an HPF if you have one.

 

 

 

[Phil Starr]

8 minutes ago, police squad said:

I'm still thinking to stick with the ampeg sound. All the people that have the rig love it.

So there must be something in their cab design that gives the classic sound

I've tried the V4B thru a small Mark bass 1x15 and that ampeg sound and grind is there in spades

so if their cab enhances the amp, so be it I think

OK lower tuning it is, I'll have a look at tunings between 45 and 30 and base the design on that and flattest response.

 

Did you manage to take any internal measuremnts yet?

Edited 21 minutes ago by Phil Starr

[chyc]

4 minutes ago, police squad said:

I'm still thinking to stick with the ampeg sound. All the people that have the rig love it.

So there must be something in their cab design that gives the classic sound

Alex at Barefaced wrote a fabulous article on what gives a bass cabinet its bottom end sound. In it he describes that the classic tone that many people like is a bump in the 100Hz region, basically exactly as @Phil Starr has said!

 

https://barefacedaudio.com/pages/what-is-bottom/