Basschat 2x12

[Phil Starr]

4 hours ago, JPJ said:

Ok, so I’ve started to assemble the components needed to build the Basschat 2x12 and I will document the build here but before I do, two final questions for @Phil Starr - is there any advantage/disadvantage to:

 

1) adding the Basschat 1x12v3 crossover and high frequency driver to this cab?

2) splitting the baffle and angling the top half back at 10-15 degrees so that the upper speaker is not firing straight at the back of your legs (I seem to remember a Hartke speaker like this a few years back)?

Looks like @stevie and @Chienmortbbhave answered your questions. If you look at the crossover it has two parts. The one to the horn which matches it's output to a single bass driver, it wouldn't match the increased output from two bass units. The bass section doesn't match two units because the combined impedance would be 4ohms not the 8ohms it was designed for. You could do a version that John alluded to. A 112 and a 112T with the problems that he mentions that the 112 operating without a crossover would have midrange output that would 'interfere' with the carefully controlled midrange of the 112T. That's not to say that it might not sound nice, just that the sound would be unpredictable. If I wanted to go that route I'd build two cabs, one with the horn and one without. You'd effectively have the FRFR/hi fi sound of the 112TMk3 with the old school sound of the 112 with the possibility of increased output and a third sound when the cabs are combined. We never tested this but I'm like John/Chienmortbb on this, it might sound quite nice.

 

As to the port, well you could simply shift this to the central position but retaining all the dimensions of the cab I gave you. It would certainly help brace the cab. Personally I don't like the symmetry of that arrangement, with both speakers the same distance from the port any resonances would be likely to sum. Like so many decisions in cab design there are wins and losses to be made. You asked for a slot port but actually a round port of the same area would be better. Turbulence in the port causes chuffing at high volumes. You get turbulence at the edge of the port because the surface causes friction in the air movement. A round port has the minimum outside edge for a given cross section so reduces turbulence. That's why I don't like the narrow vertical ports some designs use and put the port on the bottom. It's also easy to construct that way.

[JPJ]

Thanks again @Phil Starr for your valuable input. Sorry for being the numpty here but you mention the 'edge' of the slot port causing turbulence. Would there be any discernible reduction if I rounded over or thinned the edges of the top 'shelf' of the port (the internal edges)? 

[JPJ]

On 25/08/2022 at 10:29, warwickhunt said:

I like the idea of 2) especially for those gigs where space is tight (most gigs) and you are standing close to your cab.  I assume the loss of (internal) volume due to the angle would need a rejig in cab volume/dimension.

So I dug out my logarithm tables and dusted off my school boy trigonometry and the impact of splitting the baffle and angling it at 15 degrees adds an extra 23mm to the overall internal depth of the cab. Allowing for constructing from 15mm ply and 30mm in front of the baffle, this brings the finished depth of the cab to 443mm which will accept my 19" racked amps very nicely. 

[Balcro]

20 hours ago, JPJ said:

Thanks again @Phil Starr for your valuable input. Sorry for being the numpty here but you mention the 'edge' of the slot port causing turbulence. Would there be any discernible reduction if I rounded over or thinned the edges of the top 'shelf' of the port (the internal edges)? 

The abrupt edges of all ports, round or rectangular, cause turbulence. There will be little discernible difference unless you  "round off" all 4 sides of a slot port. A tricky and time consuming process. With Phil's preferrred round port you do at least have the option of buying a flanged reflex port, such as this: - https://www.parts-express.com/Precision-Port-4-Flared-Port-Tube-Kit-268-352

The flares/flanges reduce the production of turbulence at the internal & external abrubt edges and may also smoothe/improve the velocity of air within the pipe.

They come with either single or double ended flanges ( flares ). When sizing the port length you only measure the parallel part of the tubes and ignore the flare/flange. In winISD v 0.70... , there is a setting under "Rear Port Air Velocity" for "End Correction" but in my version it does not seem to have any effect upon the port length calculation.

Whether you really need flares/flanges depends upon you're particular speaker design and the multitude of compromises needed to get the result you want.

[Phil Starr]

18 hours ago, JPJ said:

Thanks again @Phil Starr for your valuable input. Sorry for being the numpty here but you mention the 'edge' of the slot port causing turbulence. Would there be any discernible reduction if I rounded over or thinned the edges of the top 'shelf' of the port (the internal edges)? 

It's actually a very good question.

 

Yes in theory, but that little chamfer wouldn't probably be enough to be significant. There are plenty of successful designs that have compromised ports but which still work well without obvious problems. It's just one of many aspects of design where there is room for disagreement. @Stevie and I disagree slightly about this and works hard to avoid any chuffing in the ports. I'm more relaxed because it has never been an issue for me at a gig and I haven't noticed it when other people are playing. The reality is that there is very little fundamental coming out of the pickups in a bass guitar so designing for really high levels of those frequencies is like designing houses for a once in a hundred year flood. It might never happen but there are ways around it, you have to consider the odds and what the consequences would be if it happens. In this case it is a bit of distortion on the loudest deepest notes if the amp is right up and you are applying lots of bass boost. 

 

WinISD calculates the port air velocity and I did look at it, it's not perfect but I tried a range of port sizes for you and this is the biggest port that easily fits in your cab. Any bigger would reduce the chance of wind noise but would mean constructing a port longer than the cab is deep. That means either a folded port with other problems or changing the shape of the cab so your 19" amp would overhang. 

 

When we were discussing this Stevie was able to demonstrate chuffing at very low power in one of my older designs. This was with a test signal at 50hz and I think around 20W. That's alarming but I never heard any chuffing in use from that cab before or after that cab. That's the day we found that one big port is less prone to chuffing than four little ones. My ports still tend to be smaller than Stevie's but I'm now much more likely to use a single port and as big as possible. 

 

So there isn't an absolutely right answer to this, all designs are compromised and different designers worry about different issues. I'm not anticipating that this will be a problem for you.

 

[JPJ]

Just a brief update to keep the thread from sinking onto page 9 or lower. So this week, thanks to our own RichardH I have taken delivery of two pristine Faital Pro loudspeakers. But as fate would have it, I am in a really busy period with the day job with lots of travel (I am typing this from Riyadh Saudi Arabia) meaning I probably will not get to start the cabinet build until October. 

[nilorius]

I will not speak about the ohms, but i would choose and i did 2 separate 12'' cabs. It works better in all situations - transporting only one when needed, if two You can put it in your car in different positions and i don't thing 1 cab with 2 12'' would sound better than 2 separate 12''. I got myself 2 cabs with 12'' and have the power i need in different situations.

[Stub Mandrel]

I think two 1x12 makes a lot of sense if building your own as the extra cost will be much smaller than if buying commercial units.

[JPJ]

Thanks for comments @Stub Mandrel & @nilorius but I am really wanting a 2x12 single cab solution. I toyed with building two of the Basschat 1X12 designs, but settled on this design.

Build thread to follow 😎

[orangepeelneil]

@JPJ did you make any progress on your 2x12" build? 

 

I'm keen to build one of these myself and have a load of suitable ply. 

 

Thanks Neil 

[nilorius]

I own and prefer 2 x hd112 better than 212 as i can control the weight of my needs any time. Ohh, i allready explained that before, sorry.

Edited October 15, 2022 by nilorius

[JPJ]

Resurrecting this thread as I will be finally getting around to building the 2x12 in the next few weeks. I've ordered all the hardware today and will be starting the wood butchery in the next week or so. I will try to remember to photograph everything and get them up on here. 

[DGBass]

I'll be watching this thread with interest. My last 2x12 was an old TC Electronic BC cab with a pair of Eminence Beta 12A2 drivers. It was a very capable cab and reasonably easy to move around. And a fair bit of an upgrade from the original 250w handling. Coincidentally I was also interested in a wider sized 2x12 as bass amp overhang on narrow 2x12's was an issue for me. I've been working on a test project after acquiring a display Marshall 1960B cab for £50. These are the ones used by bands to make fake wall of sound stage vistas and apparently a legit sale item made by marhsall uk and normally retail for £200-£300. They come with a blank uncut baffle and no speakers so in effect it was a blank canvas. In all other departments they are proper legit Marshall cabs made from high quality blonde voidless 15mm poplar ply. I couldn't have bought the timber for the cab cost so it seemed a good way to experiment with a wide 2x12. 

The cabs are just over 5 cu ft empty so a bit less when the drivers are loaded. I've used the pair of Eminence Beta 12A2's that used to be in the TC cab and did a little bit of science to work out porting rather than have a sealed cab as most Marhsall's usually are. If my math stands up the cab should be tuned somewhere between 45-50hz which will hopefully suit the Beta 12A2's.

I'm currently at the audio testing stage and so far it is all good. The cab is hugely loud at even low amp volume settings and the low end appears to be massive, much more than the TC cab ever was able to deliver. It's clear and defined with no hint of chuffing or farting out and no unusual cab vibrations to speak of. Its also substantially lighter than the average 4x12 and with a set of better lightweight drivers could be even lighter. The cab is also braced front to back to stiffen it up which seems to help. The project has moved on a little from the photo below as damping is now installed. It just needs a bit more testing and despite its physical size, its easy enougfh for me to lift. I like it a lot and hope to use it next gig in a few weeks time.

 

   

 

 

semi finished 2x12 4x12. Speakers are rear mounted in typical Marshall cab fashion. it also runs at multiple impedances eg 4 or 16 ohm 500W, and 2x250W stereo @ 8 ohms a channel. No tweeters as thats not my thing. It was intended to be a loud rock cab from the outset and I will probably experiment a bit more with port tube lengths to see how the cab performs with different sizes using the Beta 12A2's.   

[nilorius]

I like better 2 x 112 than 212. Small gigs allow to use only 1 x 112 so it is more comfortable to travel. But the combination is my most loved and found. I use Hartke 2x 112 hydrive, but soon will change them to 2 Aguilar SL 112. One is allready ordered.

Edited May 27, 2023 by nilorius

[Phil Starr]

On 27/05/2023 at 00:26, JPJ said:

Resurrecting this thread as I will be finally getting around to building the 2x12 in the next few weeks. I've ordered all the hardware today and will be starting the wood butchery in the next week or so. I will try to remember to photograph everything and get them up on here. 

I'd completely forgotten about this cab. It will be great to hear what you think of it when completed. Good luck with the build.

[JPJ]

So today is delivery day for the hardware for this project, and first to arrive is the speaker grill material. This has always been the downside of my previous builds, the lack of a good quality metal speaker grill at an affordable price. So this time I’ve taken a punt on eBay and ordered this material from eBay seller “baby.m2009”. 1.2mm pre-painted steel 600x521mm at the cost of £18.99 a piece. Obviously one sheet isn’t big enough for the full cab but I have a cunning plan (actually two cunning plans) but more of that later 😎

[JPJ]

So the other two parcels containing handles, tilt back wheels, speakon connector, corners, feet, dish tray for speakon etc arrived today. Whilst I am a fairly experienced wood butcher, I do not have either the space or the equipment for handling large sheets of ply so I have gone down the route of having all my panels pre-cut to size and delivered. More expensive than just buying a sheet of 15mm voidless birch ply but it will save me considerable amount of stress and time and the end result will undoubtedly be better. 

And I’ve also totalled up spend to date (with just finishing materials to go) and the number is £577.28, which isn’t too bad for what will hopefully be a high end cab that will stay with me for a long time. 

Edited May 31, 2023 by JPJ

[Stub Mandrel]

8 hours ago, JPJ said:

So today is delivery day for the hardware for this project, and first to arrive is the speaker grill material. This has always been the downside of my previous builds, the lack of a good quality metal speaker grill at an affordable price. So this time I’ve taken a punt on eBay and ordered this material from eBay seller “baby.m2009”. 1.2mm pre-painted steel 600x521mm at the cost of £18.99 a piece. Obviously one sheet isn’t big enough for the full cab but I have a cunning plan (actually two cunning plans) but more of that later 😎

 

That would make a nice posh fireguard. Acksherley, I once made a speaker grille out of a fireguard...

[JPJ]

So, keeping this thread alive, the fourth and final (for now) parcel arrived today containing the pre-cut plywood panels. 
And I guess construction has technically started as I drilled the holes for the speakon socket in the dish plate the other night 😎

[JPJ]

Wood butchery started in earnest today before a rain shower and thunderstorm stopped play. 
Despite my plan to get all the panels pre-cut to size I somehow managed to over specify a couple of dimensions so it was out with the table saw 🙈

Deviating slightly from Phil’s original design, I’ve decided to have the port between the two speakers. This will help with the overall rigidity of the box as I’m making the port as a sort of hybrid of brace ‘L’ from the Mk3 1x12 design. It will also allow me to radius the edges to make a pseudo ‘horn’ look. 

Edited June 25, 2023 by JPJ

[paul_5]

Mmmm, freshly cut tree-meat 

[Rich]

Following with fascination.

[3below]

 

The game is up, you are really building  a cigar box bass, the parts are leaning against the shed?  In seriousness, following the build with interest (and a view to rig size reduction). 

[Bassybert]

Did you get any further with this build @JPJ?

[Marty Forrer]

A numpty enquiry. I've built cabs before but always just used the dimensions of a commercial cab as a guide. Is there a formula or a program for calculating dimensions when given a volume, eg: 50L with a depth of say 12" ? I'm struggling to get my aged, rock n roll addled brain around it.