12" Cab Diary Continued

[stevie]

I've given some thought on how to do the flat packs. To cut the assembly time, the panels need be machined so that they slot together with a minimum of effort and tools. That would make it quite a fun project, with most of the work being in fitting the t-nuts, corners and handles, and painting the box.

I'll be publishing a crossover layout on here for those who want to build the two-way and could easily supply a kit of parts. You would need to be able to solder though.

Could be interesting.

[Gottastopbuyinggear]

I’m still interested in making a pair.

[Jack]

Moi aussi.

[stevie]

Très bien, Jacques.

[BlueMoon]

Yes... Great stuff.

I've just read through the whole posting and would definitely be up to try making a pair of the Mk II's.

Thanks so much for all the ground-work you guys have done! 

[Pea Turgh]

46 minutes ago, Jack said:

Moi aussi.

G’day, mate. I’m Welsh.

[stevie]

No need to apologise, Pea. 😛

[converse320]

I'd be interested in having a go at this project as well if you go ahead with the flat pack guys.

 

[Fonkbass]

Following this thread has been great! I'm thinking of building the 2 way design with the Beyma and the P Audio..

Hows it going with the flatpack? 🤔

[stevie]

There should be some news next week.

[RichardH]

With the new lightweight option, obviously with the crossover the level of the horn will be set to match the 12", but I wonder whether a lot of padding has been needed to bring the level down.

Just thinking aloud whether a switchable padding level on the horn might be possible so you could add a second 1 way cab without the compression driver. 

[stevie]

Good points, Richard. The compression driver I'm using for the latest lightweight version is not ultra-efficient and doesn't therefore have a huge amount of padding. The system measures 98dB at 1 metre throughout the midrange, which is slightly better than most, with a tweeter of about 104dB sensitivity.

I'm not a big fan of adding cabs willy-nilly - even if they contain identical drivers, because you get cancellation and combing in the midrange, which varies depending on where you are standing. My preferred solution for a second cab would probably be just to roll the bottom cab off at about 500Hz with a passive crossover. That would double the power handling at lower frequencies (where it's needed) and change the sound balance somewhat. I'd need to experiment a bit with that.

One of the reasons for adding a second cab is to have a cab close to ear level so that you can hear yourself properly. That is definitely not necessary with this design. You can hear yourself perfectly clearly even when the cab's on the floor and you're standing right in front of it. I can't imagine needing two of these in a normal gigging environment either. One is certainly enough for me. But your mileage may vary, as they say.

 

[RichardH]

An interesting thought, Stevie re the 500Hz xover .

I was thinking about two cabs as am used to using a 2x12 and had envisaged building them so that the 12" drivers ended up placed vertically above each other (of course), but also so that they were as close as possible - so the bottom cab would in effect be upside down As I understand it (and to be fair I don't understand much!!), having the drivers as close as possible helps address any potential combing issues (though I think from memory with a 12" driver that would still, as you say be a problem at anything much above 1000Hz or so). Sounds like a second cab is a bit academic anyway, so that's all to the good! 

[funkle]

Fascinating. Just caught this thread. Stellar work here Stevie, Phil, and John 👍

I’d be very interested in a box that does it all...not great at the old DIY though. 

I’ve often thought the ideal cab would be loud enough to cope with a drummer, have a decent bass output (the significant 50Hz range output of the Thunderchild, Fearless F112, and the AER Amp One have become my standards of measurement here), be full range (the BF BB2 has the sweetest top end I have ever heard out of a bass cab to date), and weigh about 30 lbs.

Ideally it would be a combo as well. With DSP tweakery to maximise the benefits of the carefully designed system. Lol...

Closest I’ve ever seen to date is the MB Alain Caron high end combo. Never heard one in the flesh though.

I’m very interested to hear and see what a no compromises cab looks like. 

Edited November 24, 2018 by funkle

[funkle]

A quick thought. Is there a reason more cabs are not made out of aluminium, like the GK MB150 combo?

[LukeFRC]

15 hours ago, funkle said:

A quick thought. Is there a reason more cabs are not made out of aluminium, like the GK MB150 combo?

I remember a bassist friend years back having a 4*10 made of ABS plastic - there’s another guy making them out of flight cases on Facebook 

[Phil Starr]

15 hours ago, funkle said:

A quick thought. Is there a reason more cabs are not made out of aluminium, like the GK MB150 combo?

The answer is in the price. Aluminium is a light metal but even so it's way denser than wood so you have to mould /cast /extrude it into shape then use fairly complex techniques to make that into a cab. The machinery to work wood is cheap and simple too It's not all positive either, you can achieve a reasonable rigidity easily enough but metal is less self damping than wood so it sets up it's own design challenges. There were some interesting hi fi designs in the 80's that used honeycomb aluminium but they were very expensive, as is the MB150. Basically there are marginal gains for a large cost and that money might be better spent on other parts of the cab/combo.

[funkle]

Fair enough. The usual problem of engineering then. Lol

[stevie]

We resume our little story after the cab has had two coats of Tuffcab paint. Time to sort the grille out. I was fortunate enough to obtain an Ashdown 2x10 cabinet with blown drivers, whose grille proved to be an ideal fit. But first I cut some 15 x 12mm pine strip to make a grille support.

A coat of matt black paint, and I had this:

The observant among you will have noticed that the port is no longer grey. The grey port looks quite good in actual fact - it's distinctive - but I thought I'd paint it black anyway, as I had paint in my garage that was unlikely to be used for anything else. It worked fine, as you can see.

I did have to cut the grille to size with my ancient, trusty metal-cutting shears.

.

 

 

 

 

Edited December 8, 2018 by stevie

[stevie]

Since I last posted on this thread, there has been a change of plan on the drivers. I struggled to get the cab sounding right with the original horn and decided to revert to the P. Audio horn I'd used previously. I haven't given up on the asymmetric horn and may revisit it later.

However, as the design objective of this particular version of the cab is light weight, I thought that the combination of the P. Audio horn and a Celestion CDX-1415 compression driver would be a good choice. The total weight of the 12" bass driver, the Celestion compression driver and the P. Audio horn is just 3kg. Amazing! So even though we've used 15mm ply for the cab, a proper crossover, and a metal grille, the total weight of the finished product is 13kg. I'd call that a result.

It was difficult to get a decent photo of the compression driver with my cheap camera and flash, but it really is dinky - weighing in at just 250 grammes. It's not cheap, but it does have a 1.4" voice coil, and not a 1" coil like cheaper compression drivers.

[stevie]

The hole for the other horn proved to be slightly too big, but some fibreglass filler came to the rescue. In the drawings, which Ghostbass is very kindly reworking for us as we speak, the horn is located more centrally on the baffle, as that is acoustically the best place for it. I also decided to position it vertically to improve the dispersion to the player's ears when standing up close to the cab.

So - the handle is fitted and I've foamed the grille support.

This is what is looks like with the grille.

Although perhaps I should say, that's what it looks like under flash. So I took the cab outside and took some more pictures.

 

 

Edited December 8, 2018 by stevie

[stevie]

Pea Turgh did ask for lots of piccies.......

I think you'll all agree, this does not look like a homemade cab. The Ashdown badge probably helps here, but you can buy all kinds of badges on eBay for a few pounds (plenty of Trace Elliot, for example). So if you feel like putting a name on your cab there's nothing to stop you.

[stevie]

Before I go into the internals, the crossover and measurements, this is what I came up with for the inputs at the back. The two holes are two inches or so in diameter. They are bevelled just using sandpaper. In fact, I used a sander and some hand sanding to soften the edges all round the cabinet itself. Because poplar ply isn't as hard as birch, it's actually quite easy to do. You certainly don't need to bother with a router.

 

Anyway, I just cut a piece of scrap poplar to size and glued it inside the cabinet to cover the holes Then drilled two holes for the Speakons - and Bob's your uncle. Anyone building the cab can, of course, use a normal metal input panel - but this looks good, costs less, and more importantly perhaps, weighs less. Unless you absolutely need two inputs, I'd advise builders using this arrangement just to fit one, as linking the two Speakons can be quite tricky whether your crimping your connections or soldering them.

 

Edited December 8, 2018 by stevie

[LukeFRC]

1 hour ago, stevie said:

The hole for the other horn proved to be slightly too big, but some fibreglass filler came to the rescue. In the drawings, which Ghostbass is very kindly reworking for us as we speak, the horn is located more centrally on the baffle, as that is acoustically the best place for it. I also decided to position it vertically to improve the dispersion to the player's ears when standing up close to the cab.

So - the handle is fitted and I've foamed the grille support.

This is what is looks like with the grille.

Although perhaps I should say, that's what it looks like under flash. So I took the cab outside and took some more pictures.

 

 

It looks awesome - for those who have lost track... which driver is this? 

[fleabag]

I'll throw caution to the wind and say Beyma SN/112 ?