12" Cab Diary Continued

[stevie]

Here are a few photos showing how to assemble the LF section of the crossover. The circuit is the same as the one used for the Celestion compression driver version, but the values are different as I'm using different drivers. I also changed the layout slightly to cater for a larger coil. The method is the same, however.



First, place all of your components on the board and draw round them with a pencil. I'm using 6mm plywood, but you can also use offcuts from your cabinet. When you are happy with the layout, cut the board to size. Drill the holes for the wires. You'll need a couple of small drill bits, say 1mm and 1.5mm, and a larger one for your tie wraps and bolts (if you use them).



This is your bare board marked up and drilled. Yours will probably end up with too many holes like mine, but don't worry - nobody will know.



Cut the tag board to size and fit. I've used 2 stainless steel bolts and nylon lock nuts, but silicon sealant will also work. Next comes the large inductor. I've used a larger stainless steel bolt, nylon lock nut and stainless washer here (plus a few dabs of silicon) but silicon sealant with a couple of tie wraps will also work.



For the resistors, I used a special Everbuild heat resistant silicon, good to 300 deg. C, although you can use normal silicon if you wish.


Here is the assembled crossover. I'm not going to cut the wires and connect everything up yet, as I want to do some more testing, but wiring up the back should be straightforward now that you've got this far. I'll add a photo of the rear of the finished crossover when it's done.

When buying silicon sealant for this purpose, you need to go for a high modulus type. If you're on a budget, don't get the cheap one they sell in Screwfix, as is is not firm enough (low modulus). The Pattex one they sell in Lidl is perfect, however, and relatively cheap. You could also use the Everbuild Heat Mate silicon throughout. It costs £5 to £6 from builders' merchants.

Edited January 30, 2018 by stevie

[RichardH]

You beat me to it - still waiting for the components to arrive for the standard xover!

[stevie]

That's a bit of a long wait, Richard.

[RichardH]

They did warn that there was a lead time on the inductors as they don't hold stock. Should be here soon though....

[RichardH]

Their ears were obviously burning - just had an email to say the order has been despatched!

[stevie]

I'm looking forward to seeing how it works out.

[RichardH]

The crossover build commences!



I worked out a layout on paper first (following the layout in the PDF attached to the top of this thread - the only laying out was really seeing how large the components are and arranging them), then made a couple of cardboard templates the right size as decided by my paper scribblings.



I then transferred the hole positions to the plywood - I'm using 4mm as it is what I happened to have around - see later for cunning plans and clever tricks though.

Holes drilled - make sure you use some scrap wood underneath to keep breakthrough to a minimum. I then de-burred the holes with a countersink bit (just by hand, not with the drill), and some sandpaper.



Populating the LF crossover just to see how it all goes together - no silicone or tiewraps yet!






...and so to the cunning plans. Being jealous of all the bass builds where everyone gets to clamp things, I thought I needed an excuse to do the same - so... nurse? THE CLAMPS!!!

I have cut some strips of the same ply and have run them along the edge of each board. This serves two purposes - first it will give more "meat" to where the mounting screws pass through, and also will act as a standoff.
I have also added a little pad under where the connector strip sits so the screws that hold that in position have more to bite into.



This may or may not be a good idea, so watch this space!

Edited July 22, 2017 by RichardH

[stevie]

Using cardboard as a template is a great idea. The standoff strips are another good idea, allowing for some free space below the board for the wiring and tie wraps.

Edited July 23, 2017 by stevie

[tauzero]

Would it be feasible to wind your own inductors? Presumably you'd just need the right gauge wire and the right diameter former, and to know how many windings you'd need?

[stevie]

It's not as difficult as winding your own pickups, and certainly feasible for the adept DIY'er, but you'd have to invest in the wire and an inductance bridge at the very least. So it's probably not worth it if you're only making a few.

[Chienmortbb]

I made my crossover on a single piece of ply and think separate pieces are easier. Yours are both a bit tidier as I was in a real rush. As is to be expected I did have one problem with the crossover, a detached wire due to my rush to make the Bass Bash but it has been fine since I fixed it

I just thought I would update you on my experience. Externally the cab still looks good despite being in and out of the boot twice a week. There are a few small dings but the Tuff cab has not been pierced. As they are small dings they just look like the texture of the cabinet. I often sit on the cab at rehersals and there is very little vibration through the top.

I did a dep gig with Stevie's band recently and during sound check was asked to turn down. I was using my Ashdown MiBass 220. Like all those 200ish watt amps it outputs about 100 Watts into 8 ohms*. The idea behind the cab was to get better on stage dispersion and a one cab solution. It certainly does that. Whet is more pleasing is that the sound, out front seems to cut through with ease. I cannot see that with a more powerful amp ( still working on my 500 watter) I would need another cab although the rocker in me yearns for a stack....


So what are the pros and cons? Well as with everything, I would like it lighter. The SM212 has a ferrite magnet but is not unduly heavy. You could save a couple of kg by using a Kappalite 3012 but it would add £100 to the cost. Most other neo drivers will only save 0.5-1Kg. The Mk1 with no HF unit and no crossover would save money and weight but the sound would be different. How different is the sound? Maybe Phil and I can swap cabs for a while and we could see? The HF horn weighed about 1Kg and the crossover probably the same.

Would I use 15mm poplar ply again? Yes it does the job and is lightweight. Tough enough for me and easy to work with. 12mm would require more care and bracing and I am not sure there are any real benefits for the diy constructor.

I may well build a combo version next and (don't tell Stevie) but I might use electronic crossovers but I have to finish my amp first.

*It uses the Icepower 50ASX2 module used by GK and many others.

Edited July 27, 2017 by Chienmortbb

[RichardH]

I was going to ask about doing the crossover on one piece - I thought seperate might be easier to locate within the cab - especially as this is for Geoff's MiBass cab rather than the BC cab, so I don't know what clear space there is inside.

I would reserve judgement on mine being neater until I have finished!! Waiting for some suitable silicone to be delivered at the moment....

[Chienmortbb]

[quote name='RichardH' timestamp='1501152279' post='3342843']
I was going to ask about doing the crossover on one piece - I thought seperate might be easier to locate within the cab - especially as this is for Geoff's MiBass cab rather than the BC cab, so I don't know what clear space there is inside.

I would reserve judgement on mine being neater until I have finished!! Waiting for some suitable silicone to be delivered at the moment....
[/quote]It will be easier to place in the cab and easier to trace through if you have a problem. BTW where did you but the inductors?

[RichardH]

Got all the components from [url="https://www.hificollective.co.uk/"]Hifi Collective[/url]. They don't hold the inductors in stock, so I assume the lead time is to allow them to make up an order from the supplier to get them in. The only other place I found that has a wide range of inductors is [url="http://loudspeakerfreaks.com/"]Loudspeaker Freaks[/url] - AKA Europe Audio in The Netherlands. Some say they are slow to supply (though I have used them in the past and they have been fairly good).

Component price for a set of crossovers for the cab (using the 407 tweeter) came to around £22.

Edited August 2, 2017 by RichardH

[stevie]

Splitting the crossover in two has a number of benefits. It makes the layout easier to design; it's simpler to assemble; it puts distance between the LF and HF coils, and gives you more flexibility when deciding where to locate them inside the cabinet.

As far as weight saving is concerned, the crossover for the version Richard is making is about half a kg lighter than the more complex compression driver version (because of the size and number of LF inductors). You could also save nearly a kg by using the neo version of the tweeter or the neo version of the compression driver, although that would likely require some modification to the crossover.

You could save about 2kg by using a neo driver like the Faital Pro PR300 used in the Bergantino CN112 and Vanderkley 112EXT, or an Eminence Deltalight, although neither of those will go as loud as the Beyma and they would add another £50 or so to the cost.

By going neo, I reckon a version with a tweeter could come in at under 12kg.

[RichardH]

Just weighed the crossovers I'm building. 246g for the LF, and 139g for the HF.

[RichardH]

Crossover build continued....

Started placing the parts. I am using the Everbuild Heatmate silicon throughout.

I used a bead of silicone plus two small stainless self tappers to hold the connector block in place


Underneath


Gunging up the resistors


...all in place after the silicone has gone off


Testing time


The completed crossovers


Bottoms up!



A few top tips.
1 - Apply the silicone to the parts, put them in position with the leads pushed through the holes and then LEAVE it until the silicone has gone off. Don't start trying to bend/route/connect the wires as everything will start slipping around.
2 - You'll see that I initially put two tiewraps in place over the large inductor. This was not stable enough, so I had to add a third. Definitely plan for at least three tiewraps on the big inductors. I did not use silicone to hold the inductors down, though (as it would make a HUGE mess if you wanted to remove them!)
3 - Sometimes you will find that you can't dress the component leads to reach the place they need to go. Always make sure where leads have to join that you don't jus trely on a blob of solder - hook the leads round each other before you solder to ensure a solid and long lasting joint.
4 - Take your time and follow the signal path carefully. Double and triple check.
5 - Testing - I used Audacity to create some test tones, and had the crossover connected between my desktop amp and my (full range 2 way) speakers. I was therefore able to check that the LF crossover was rolling off the treble (you'll hear it dropping once you get above 2500Hz or so), and the HF crossover was rolling it off the LF signal below around 2000Hz.
6 - I used 4mm (maybe 3mm) ply. This means that fixing the connector block needed a bad underneath to give the screws enough bite. So you may want to use something a bit chunkier to avoid that hassle. The standoffs idea seems to be a good one though, and should make fixing the crossovers to the cab easier.
& - The carboard template trial was really helpful, too.

So - there we go - one pair of crossovers!

Edited August 4, 2017 by RichardH

[Phil Starr]

well done

[geoffbyrne]

I'd just like to thank RichardH for making the boards.

They arrived the other day & I mounted them to the cab yesterday.

Everything works as it should & I'm looking forward to running the cab at higher volume.

G.

[stevie]

Way to go Geoff and Richard! Have you now modified your Ashdown cab?

[geoffbyrne]

Yup, Ashdown is up & running. Totally worth it.

G.

[stevie]

Now that I’ve gigged the prototype, I’m ready to assemble a finished cabinet in our cabinet material of choice, 15mm poplar ply. Although I am now using different drivers to the ones we started out with, this doesn’t affect the construction of the cabinet. The bracing is slightly different, due to the fact that we want to get two cabs out of a single piece of plywood. However, the lessons learned in building the prototype will be applied here.

First, cut the figure-8 brace and glue in place on the back panel. I used a couple of screws to clamp it down, but my plan is to assemble the whole box without any (external) screws. Filling and sanding these can be a real pain. To assemble without screws will require some longish clamps, which I ordered from eBay. If you don’t want to invest in the clamps, there’s nothing wrong with using screws, but you’ll have to fill and sand the holes later.

The first problem I hit was that, despite my best efforts to drill the holes at right angles, the screws pulled the brace slightly off target. When I wiped the excess glue away, I noticed that there was a slight gap at one side. I quickly grabbed a couple of clamps to straighten it up. Phew!

Edited January 30, 2018 by stevie

[stevie]

The figure 8 brace connects the cabinet side walls together with the front and back, and is the most important brace in terms of overall rigidity. Now on to the second brace. This one can't be a figure 8 because it goes directly behind the driver. The idea is tomake it as close to a figure 8 as possible by cutting out a space into which the driver will comfortably fit. Then cut holes for air flow without weakening the structure. I'm using hole cutters because they're easy, but a jigsaw works well too. Mark it up first.



Then cut. I have rounded all the edges using a powerfile and sandpaper to improve airflow somewhat, but I expect it's not really necessary.

Edited January 30, 2018 by stevie

[stevie]

By the way, all of these panels were cut by the wood supplier according to the cutting list on page 1.

Now to glue our second brace into place. This was tricky, because the clamps pulled the brace in different directions. After a lot of fiddling, I managed to get it into position using four clamps. I was missing the obvious, however. I should have learned my lesson when I glued the first brace into place: you do not need clamps for the braces.

You will need some kind of right-angle guide when you're gluing the braces in, because keeping everything at right angles is crucial.

Edited January 30, 2018 by stevie

[stevie]

Second circumferential brace glued in place. One more brace to go. It's starting to take shape now.

That's my right-angle guide in the bottom left-hand corner.

Edited September 9, 2017 by stevie