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X2

x3

To repeat: this is a long term project. Due to me being selective on the drivers that I want and the prices I'm willing to pay. As well as fitting it in around other stuff in my life. And not having a pressing need for more speakers in my home.

I've knocked up a quick drawing in Freecad to get an idea of the general proportions and layout.
The bass bin will be 500mm wide by 800 mm high by 450 mm deep. The Altec 12" upper bass to lower midrange driver will sit in a cubic box above this.

Then the squawker horn and the dolly parton tweeter on top. These will need a frame to hold them in place.

As Rolf used to say; "Can you guess what it is yet?"

A bit of tracksawing later.


Early stage of my mortice and tenon batch production with 18" JBL woofer. In this photo I was checking where to put the middle bar for the front section of the chassis.

I'm now on the look-out for the sheet material to form the skin of the lower bass bins. My current thinking is that I'll go for 18mm birch plywood, mainly because I think that will be easier to get looking nice than chipboard.

I'm also starting to think about threaded inserts for bolting it all together and clamping the woofer to the chassis and front panel. I'm open to suggestion to what inserts to get and where to buy them from.

Edit: I've now placed an order for some BB/BB 18mm birch plywood sheets...

Been messing around with xsim for the crossover design.
xsim likes to be fed with .frd and .zma files. Which in my head I keep calling Freddie and Kurt Zouma files. They're numerical representations of frequency response and impedance charts.
The sort of information that tends to be unavailable for vintage drivers. So that for example for the Altec 414-8C's I used the data sheet for Great Plains Audio 414-8B's and made a guess at adjustments for my intended cabinet.
BTW the Great Plains chart looks suspiciously flat to me, in an "I'm a marketing document" kind of way.

For the EV 1823 I discovered that the type of horn used has a big effect on frequency response, to the extent that you'd think 2 different drivers were being used depending on the horn. I'm still on the look-out for certain horns I'd like to try with these drivers, but am not holding my breath for any attractive deals.

On my xsim diagram the woofer is at the top, tweeter at the bottom.

I have a pair of EV X36 crossovers that I got free with the 1823's. This is a 2nd order crossover. The X36 is shown in the bottom left portion of my diagram.
xsim indicates that I should reverse polarity on the tweeter to avoid a big suck out at 2khz, which seems to ring a bell as this being what they did back in the day with this type of crossover.
I'm expecting to mess around with a small bucket of resistors to L pad down the extremely efficient EV compression drivers.

I've also discovered that a protection capacitor for the 18" woofers is a bad idea as 1250 micro farads of capacitance won't be cheap, plus may affect the sound quality and amplifier stability.

Bass bin frame . At the time of this photo the tennons were a little bit too large for the mortices.


Left and right hand bass bin frames fitted together. Pre-gluing.


Birch plywood delivered.


BB grade plywood


First gluing operation for the frame. Home-made clamp from 2 pieces of spare floor joist timber and M12 threaded rod.


2nd gluing operation.

Track-sawing of the plywood panels for the bass bins next...
I've ordered 100 off M6 x 11mm zinc coated steel threaded inserts and 100 off M6 x 55mm long stainless hex headed bolts with washers.
I will also be making a threaded insert insertion jig.
And I'll also be knocking up something to help route out the circular holes for the woofers.

Just get a router trammel to do the circular holes. Had to buy a new router when i was doing pauls newest lenco, the bearings finally went in my hitachi after 20 years hard use (and a new random orbit sander because the wanky ryobi one i had packed up aswell..... wasnt even a cheap one).
Anyway... the quick replacement trend t7 i bought came with a beam trammel.
I also have a baseplate type trammel which i use with a small laminate trimmer type router.

You can make one easily by using one of the rods from the router fence, just a block on the end of one rod with a spike through it that sticks into the centre point of your driver hole, slide the rod in the fence guides in the router base plate, lock it down at the correct diameter with the adjusters and rout away

For the trammel, I will be making something like this:
https://www.thisoldhouse.com/house-one/ ... r-a-router
Out of 2 pieces of spare floorboard offcuts plus a long partially threaded M6 bolt, nut and washers. Plus a dab of wax for lower friction.
1 piece to mount the router on. 1 to go underneath to screw onto the back of the workpiece for control on breakthrough.
With me cutting the circles by making a shallow initial circle cut, then jigsawing out most of the circle, then finishing off with series of plunging cuts with the router.

My threaded insert insertion jig will be a chunkier version of this:
https://www.youtube.com/watch?v=PkLYRWnKs80

I've had another look at my crossover design. Current estimated cost is about £200 for the stereo pair, with about half that for the big inductor for the 18" woofer.

Track-sawing the side panels


Drilling the 6mm diameter hole for the insert insertion jig.


Insert jig ready for action. Made from floor joist off-cut, long, partially threaded M6 bolt, spring, 2 x washers, 2 x M6 nuts, with insert shown on jig.


Experimentation with inserts in plywood offcut. The lifting of the surface layers of ply is an issue. Partially resolved by investing in a 9.5mm diameter drill bit - the largest size (give or take 0.1mm) recommended for this size of inserts. Applying consderable downward pressure as the inserts are screwed in seemed to help a bit too. Chamfering the pilot hole didn't seem to help.


Pilot holes for inserts drilled in first panel.


Front panel bolted on. I was pleasantly satisfied that my pilot hole drilling accuracy was good enough.
I personally think that the birch plywood has a natural beauty to it.
This panel will have a 427mm diameter hole cut in it for the JBL 2241.


Photo showing how the panel is bolted onto the chassis with M6 bolts.

These photos are for the bass bins.
I'm intending the upper bass bins to be of similar construction, but smaller and simpler. With it being a 13" cube for the Altec 414's.
The midrange units and tweeters will just need a frame to hold them in the right place.

Next job is to drill loads more pilot holes and fit loads more inserts to get to the stage where the front and rear panels on both channels are bolted on. From there I can cut the side panels to size, and then the top and bottom panels.