12" Cab Diary Continued

[stevie]

Thanks Luke! A fair bit has happened since I posted regularly on this thread. So it's not the Beyma, fleabag. It's the Faital Pro PR320. I think I mentioned it earlier in the thread. It's a more advanced (much greater xmax) version of the driver used by Bergantino in their CN cabs. So it has quite a good pedigree. Its power handling to weight ratio is outstanding.

[Chienmortbb]

The weight at 13Kg is really light. It does not quite get to Barefaced levels but it is not far away. To get lowered weihht we would have the use thinner play and then the bracing and complexity of the design are a real issue. 

You would not believe the amount of work,especially by Stevie, that has gone into this.design. I am still using the Beyma Version and that comes in at about 14.5Kg I will be fitting a Faital Pro PR320 soon. 

 

Edited December 8, 2018 by Chienmortbb

[funkle]

Beautiful work.

At the risk of being a tiny bit inflammatory...have you essentially made something pretty close to a Barefaced BB2?...although I have no idea how your compression driver compares. 

The weight is amazing. 

Edited December 8, 2018 by funkle

[stevie]

I didn't really set out to make something close to the Barefaced. We've equalled the weight of the Barefaced but have got there by a slightly different route. This design is a development of the first one in this thread but the design objective this time was high performance and light weight. The performance is similar to the system with the Beyma 12 and ceramic Celestion 1" compression driver, but it's much lighter - and obviously costs more.

In answer to your question, I believe the Barefaced BB2 uses a Faital Pro HF102 compression driver. Both the ceramic and neo version of the Basschat design use compression drivers with a 1.4" diaphragm - twice as much diaphragm area as the Faital. They are much better compression drivers for our purpose, but the neo Celestion we're using costs twice as much as the Faital in the Barefaced.

 

 

[funkle]

It’s great work Stevie. This medium doesn’t allow much nuance...I’m just interested that you and Alex have come to not dissimilar results, though the means differ in a few respects. 

How much would it cost to make one of these? (I’m interested but would have to probably pay someone to do it for me.)

[RichardH]

Looks like the compression driver can be had for around £60. Faital 12PR320 is around £130. A sheet of the poplar ply will set you back £75 or so I would guess (though that would make 2 cabs IIRC), then horn, crossover components, tuffcab and misc hardware another £60 odd. There will probably be shipping costs for getting the bits as well.

So very roughly it would be around £330 plus whatever someone charged you to make one.

[RichardH]

...that horn you're using looks like the P-Audio PH-170 (it's the only one I can see on their site that is that shape, anyway) - but that is listed as a 1" throat diameter???

[funkle]

How much internal volume is lost if fitting a handle that is inset? A la the Bergantino CN112?

[stevie]

I'd say those costings are about right, Richard, although I'd mention that the £75 for the plywood in our case covered the cost of cutting two cabs accurately to size. If and when we have flat packs in place, I'll try to sort out some special prices for the components.

As far as cost is concerned, I'd like to say two things. Firstly, the DIY concept behind these Mk II designs is not to save money. If you want to do that, buy a second-hand cab. However, if you compare the cost of a new Bergantino CN112 or a Vanderkley 112EXT, the Basschat cabinet is substantially cheaper, although admittedly you're never going to match the excellent finish of the Bergantino. More importantly, however, and this is my second point, it's technically a much more advanced design than either of those two.

So, build one of these if you want a compact high-end cab and enjoy the satisfaction of making it yourself.

 

 

 

[stevie]

Interesting point about the horn, Richard. Yes, it's the P.Audio PH-170. Time for a quick lesson on compression driver specs.

The most common type of horn/compression driver combination is the 1". That figure refers to the exit of the compression driver and the aperture at the beginning of the horn. There are also 1.4" and 2" exit compression drivers, which are less common and more expensive.

The other figure you see in connection with compression drivers is the voice coil diameter , which is normally (but not always) the same diameter as the diaphragm. The traditional voice coil/diaphragm diameter of a 1" exit compression driver is 1.7 inches. The best examples of these can be used down as low as 1.2kHz. There are two other, smaller diaphragm sizes in use with the 1" exit: the 1.4" and the 1". These are cheaper and don't go as low. Depending on the design, a 1.4" diaphragm is useable down to about 2kHz and a 1" diaphragm to about 2.5kHz.  Making the diaphragm smaller allows the manufacturer to reduce the size of the magnet and associated components and to reduce the cost of the product.

So you have to be clear what the figure is describing. There is a big difference between a 1.4" compression driver and a 1" compression driver with a 1.4" diaphragm. (1.4" exit compression drivers have diaphragms between 2.5- and 4-inches in diameter). It's not uncommon for manufacturers to (erroneously) refer to their 1" exit / 1.4" diaphragm compression driver as a 1.4" compression driver.

Edited January 25, 2019 by stevie

[stevie]

39 minutes ago, funkle said:

How much internal volume is lost if fitting a handle that is inset? A la the Bergantino CN112?

Not enough to matter.

The top handle is one of the problems I came across when gigging this cab, and I suspect this is what you're referring to. The feet on your average 500W compact amp aren't tall enough to raise the amp high enough to clear the handle. I've been using a piece of sponge under my amp to deal with this, but it's not ideal.

We could move the handle to the side to avoid this, but I find it easier to pick up and carry with a top handle - so I'm not too keen on that. Builders can, of course, do this if they like; that's one of the benefits of building your own.

The alternative is to use a different handle, and funnily enough, I have three of these Adam Hall handles on another cabinet in my garage that I was going to use on a larger design. <http://www.bluearan.co.uk/index.php?id=ADH34062&amp;browsemode=category#>  When I mentioned this to John (Chienmortbb), he decided to get hold of one and fit it to his cab. The round handle not only gives you the amp clearance you need, but according to John, it makes the cab easier to manoeuvre.

I hope this image is big enough. If not, have a look at the Eich cabs on the Thomann site.

The flat pack cabs will be cut for this round handle but the drawings we are publishing on here will leave the choice of handle to the builder.

[LukeFRC]

So that RCF speaker that folk in the FRFR thread are saying is pretty good has a :

• 1.4" Titanium Compression Driver, 4.0" v.c. Neodimium 

Which sounds like it’s pretty high end! 

[LukeFRC]

“Sounds like” as in “from the spec I imagine” .... I’ve not actually heard it! 

[stevie]

23 minutes ago, LukeFRC said:

So that RCF speaker that folk in the FRFR thread are saying is pretty good has a :

• 1.4" Titanium Compression Driver, 4.0" v.c. Neodimium 

Which sounds like it’s pretty high end! 

Exactly. The retail price of that compression driver alone is £225.

Edited December 9, 2018 by stevie

[RichardH]

3 hours ago, stevie said:

Interesting point about the horn, Richard. Yes, it's the P.Audio PH-170. Time for a quick lesson on compression driver specs.

The most common type of horn/compression driver combination is the 1". That figure refers to the exit of the compression driver and the aperture at the beginning of the horn. There are also 1.4" and 2" exit compression drivers, which are less common and more expensive.

The other figure you see in connection with compression drivers is the voice coil diameter , which is normally (but not always) the same diameter as the diaphragm. The traditional voice coil/diaphragm diameter of a 1" exit compression driver is 1.7 inches. The best examples of these can be used down as low as 1.2kHz. There are two other, smaller diaphragm sizes in use with the 1" exit: the 1.4" and the 1". These are cheaper and don't go as low. Depending on the design, a 1.4" diaphragm is useable down to about 2kHz and a 1" diaphragm to about 2.5kHz.  Making the diaphragm smaller allows the manufacturer to reduce the size of the magnet and associated components and to reduce the cost of the product.

So you have to be clear what the figure is describing. There is a big difference between a 1.4" compression driver and a 1" compression driver with a 1.4" diaphragm. (1.4" exit compression drivers have diaphragms between 2.5- and 4-inches in diameter). It's not uncommon for manufacturers to refer to their 1" exit / 1.4" diaphragm compression driver as a 1.4" compression driver.

Stupid me, of course - I have previously realised this distinction, but in the excitement of seeing the project moving forwards, I glanced over the specs a bit too quickly, just seeing the 1.4".

Look forward to seeing the crossover details... I have some spare inductors, resistors and caps, but sod's law says they won't be the right ones...

 

 

[stevie]

The crossover's done, Richard - I just haven't got around to drawing it yet. I should be able to do it tomorrow. Don't worry about the components. I can wind the coils and have stocks of all the other components. So you won't have to order from different suppliers and wait ages for delivery.

[funkle]

Nailed it Stevie re: handles. 

I have found it much easier to handle cabs with a large inset/flush mounted handle in general, as well as it being easier to stick an amp on top. 

The worst cab I tried to move with one of those leather type handles currently on your cab was the Bergantino IP112ER. It weighed 50 lbs and the handle clearly couldn’t hack it - had to be replaced because it had broken down from use - and it was a pig to move around with that little skinny thing. 

I love the idea of rolling our own cab with better components than anything out there. £330ish and labour for a top end cab is a sweet deal. 

[funkle]

Another tiny weight saving idea. Maybe...

Could be tricky for doing at home, but with a grill, it could perhaps be bent at the edges so that it acts as its own stand-off from the front baffle? Then no wood/foam etc is required on the front baffle to screw the grill in to?

[funkle]

Also. Put me down for a flat pack kit as well. If that wasn’t obvious already...

[Gottastopbuyinggear]

53 minutes ago, funkle said:

Another tiny weight saving idea. Maybe...

Could be tricky for doing at home, but with a grill, it could perhaps be bent at the edges so that it acts as its own stand-off from the front baffle? Then no wood/foam etc is required on the front baffle to screw the grill in to?

I’m not sure that it saved any weight but that’s how I did my cabs, and it gives a nice appearance. I have gasket tape around the rear of the folded edges and they don’t rattle or fall out, but are easily removed if you need to tinker.  Had mine made by speakergrills.co.uk.

 

[funkle]

Nice. 👍

[stevie]

Thanks for your contributions, guys. The reason I did the grille this way was because of the weight. An expanded metal grille is lighter than a punched metal grille. Because it is thinner, you need to support it all the way round to stiffen it up. I also put a small piece of foam on the top of the bass driver (you can probably see it if you look carefully) to support it in the centre as well. Ashdown used this grille material for some years and it doesn't rattle as long as you support it properly.

The downside is that fitting it was quite time consuming. Not only do you have to obtain and cut the grille support battens, you also have to glue them to the cab and then paint them. Plus you have to apply special thin foam to the grille support frame. I had a problem sourcing thin foam strip – so I removed the foam from the old Ashdown 2x10" cab and reused it. If you use normal thickness foam, it pokes through the holes and looks really amateurish.

With a metal grille from Speakergrilles, you simply put it in place and secure it with four screws. Done. But your cab will weigh about half a kg more. The last time I fitted a box pan-type grille was on carpet-covered speakers. So the carpet gripped the grille all round and rattling wasn't a problem. I'm not sure about painted cabinets, but Gottastop will know.

 

Edited December 10, 2018 by stevie

[stevie]

OK - next up is the crossover. I do the initial work in CAD, but that is followed by hours of plugging and unplugging components and listening. This is my little crossover corner after a hard session.

The first crossover I did looked like this:

I built it on a fibreglass PCB board I happened to have to hand. This is the crossover that John Chienmortbb and Phil heard when they came over for an afternoon's auditioning. However, I thought that I should try to simplify it a bit, and ended up with this one:

The good news is that not only is that crossover simpler, it sounds noticeably better. It has just eight components, which is excellent when you consider that it is a fourth order crossover with CD horn correction.

 

[stevie]

My next job is obviously to do a proper circuit board layout. For the time being, however, here is a measurement of the finished system. I'll post off axis and impedance curves another time - I did do them, I just didn't save them.

[stevie]

Here's the circuit for the crossover: