TG "The Loudspeaker" Build (Sort of)

[MistyBlue]

I need to make the stands so I can transfer the mounting holes onto the bottom panels of the cabs. I prefer to bolt the stands on through the bottom birch ply panel using some T nuts set into the panel to make sure the cabs don’t come off the stands when moving them. Last time, I made some welded steel box section frames that I filled with sand, and welded on some fancy machined stubs in the four corners so that I could use either spikes or casters.

Using spikes ended up being a real pain, needing the whole structure to be blocked up to move them for doing the hoovering – completely impractical. I soon swapped them for casters which made no difference sonically but made manoeuvring them much easier. This time, I will simplify things and just mount the casters on the underside of the frame and forego the fancy machined stubs. I machined some M12 threaded ports for inlets for sand filling.

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[MistyBlue]

Now if only I could find that small funnel, I could fill them with sand……

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[MistyBlue]

Oh Crap!

Went down the lockup today to finish off the stands. I was happily using that funnel to fill them with sand and marvelling at the satisfying thud of a previously ringing metal structure being reduced to a dead lump when I discovered a leak. Not serious, but annoying nonetheless. Looking more closely, dumbass here realised that she had forgot to weld up behind the mounting tabs and the inside seam in the four corners – Doh!

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I then had to take action and weld up the offending areas, but the other member of the household stepped in and volunteered to do it as it being a tricky operation since they are more experienced at welding. It meant scraping off as much of the black (smooth) hammerite paint as possible before burning through the rest to get decent penetration. There were copius clouds of smoke (Yuk) and much swearing.

Compensation was offered later in the form of walnut cake.

[MistyBlue]

More woodwork today, cutting some of the panels for the crossover enclosures. These will sit on top the main cabinets. I had some 18mm plywood lying around that I have used to save space but used one of the offcuts of birch ply to form a base for them. I will veneer the 18mm panels with flamed maple like the other stuff I’ve built to match. I also have some quarter round pine to go on the top edges of the box to soften the look. I reckon I should be able to use some of the veneer softener I formulated a while back for my guitar building antics to bend the veneer around the pine while I glue and clamp it into place with some concave pine moulding matching the profile of the quarter round.

CrossoverEnclosureHFMountMockUp.jpg (155.64 KiB) Viewed 9676 times

The base also forms a plinth for the tweeter mount, much the same as I did last time like this:

2WaySpeakersHFMount.jpg (59.64 KiB) Viewed 9676 times

However, this time I will make the tweeter front mount plate interchangeable so that if I do decide to try different tweeter options, a new piece of birch ply can be bolted on from the underside of the base instead of like the permanently glued construction above. That one is adjustable on four bolts in slots to facilitate changing the waveguide and/or compression driver and play with time alignment. The underside has a layer of felt to prevent sticking to the cabinet top.

The sides I cut with a hand saw and stacked them in the machining vice and faced them in the mill to height all at once. I have made enough connection points to enable a 4 way passive crossover if I decide to do that, although I intend to have a 2 way active from the start between the bass and the rest of the system. It all depends on the final simulations in Vituix with a full set of measurements, and whether I can get the old Sugden A21 (an old series 2 with the teak sleeve I bought in 1995 and modified) or some other power amp I have lying around up and running while I build the MoFo for the bass.

XoverRearPanel.jpg (128.01 KiB) Viewed 9676 times

I am actually wondering if I have made the crossover enclosure too small in the above (top) photo. I want to make it large enough to take a full 4 way passive crossover and/or possibly a plate amp if I go that route at a later date. I am also trying to balance this against any possible changes to the HF section if we find that the compression driver is too fatiguing. We both sat down the other night and listened to the CD on the ROSSE WG trying it with different notch filters and filter slopes. With a notch filter, the sound really does clean up going from sounding that it could possibly become fatiguing in the long term on a brief listening test (probably means definitely fatiguing in the long term) to open sounding and hearing right through into the recording and being quite pleasing overall. Troels mentioned this when he dealt with CD on the XT1086 horn. The ROSSE WG we have peaks at a different frequency but confirms what he found, nonetheless. We both agreed that we should proceed with the original plan, as I had been having a bit of a wobble over the HF section now for a couple of weeks, hence the listening session. I have been looking on and off for other options for the CD during that time (inevitably driving the other member of the household up the wall) and have a shortlist of about 3 different options. However, none are particularly cheap, or without drawbacks.

On another topic, I recently tried out JLCPCB for the first time (late to the party, I know). Up until now, I have either milled prototyes on a small cnc engraver or used toner transfer / produce UV transparencies and etch them). I received the boards the other day and I don’t think I will be doing any more home PCB manufacture by choice again. I’m very impressed. I used an existing PCB design done by someone else, although I have some experience with PCB design software (TINA years ago and more recently Kicad) and used it as a test before having a go at doing the gerbers for some of my own stuff. Looks like I will be building a couple more measuring microphones to add to my growing collection soon……

[simon]

to JCLPCB. And others like PCBWay. It has to be very simple point-to-point now for me to bother, it's easy enough, and satisfying, to draft a PCB. And so cheap.

I'm interested in your veneering technique when you get to that bit. I haven't done any yet but must try sometime.

[MistyBlue]

Yeah, I couldn’t believe how cheap those PCBs were!

I’ll make sure to do plenty of pics during veneering, although the bulk of the surfaces will be of the birch. The flamed maple or sycamore are the bits like the ends of the panels and anything that is not “woody” like the curved cabinet edges (diffraction). I’ll get to talking about the construction of those very soon.

In the meantime, here is a guitar body I did several years ago. It looks like a solid flamed maple top on mahogany. The mahogany is solid, but the flamed maple is actually all veneer. The plastic binding (edging) that was originally on it was removed and replaced with veneer. It’s only when you look closely in the neck and pickup pockets when they are exposed, that it’s obvious that the maple cap is made from very thin veneer. There ended up being two blemishes by the potentiometer holes, but they are luckily covered by the washers. This is after about 30 coats of 2K lacquer, cut back and done with scratch remover on a polisher.

Although, for the speakers, I will probably cop out of such a mammoth finishing task and go for a simpler PU roller applied coating like last time!!

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[simon]

Impressive. In a way it's a shame to have covered up mahogany, but the maple looks great. I take it the body is flat rather than gently curved?

A big lump of mahogany can't have been cheap? Is it preferred for guitars, or just something you had laying around?

[MistyBlue]

Er sorry, I should clarify that this guitar was actually an off the shelf model (a Schecter Damien Elite 8 in fact) that was stripped of it's paint finish and modified with the veneer. I have a habit of doing this with the 8 string guitars (less common, usually they are 6 string) as it's easier and quicker to get what I want and I don't really want to get into building guitars from scratch. Dad was a luthier and I learned a lot of stuff about guitar building and tonewoods from him. Mahogany is a common tonewood used for guitars e.g. Les Paul etc.

The body is actually a carved top (curved) and I have tooling (a vacuum bag) to get the veneer to conform to the shape.

The guitar looked like this when it was purchased:

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[MistyBlue]

With the paint stripped back it looked like this.

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[simon]

Ah I see.

That's very light for mahogany.

[MistyBlue]

Yeah, that what’s I thought.

Highly likely its Okoume marketed as mahogany. Guitar manufacturers are starting to do this increasingly.

[MistyBlue]

Spent some time using the stands to line up and drill the mounting holes on the bottom panel of the main cabinets.

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I’ve taken on board Greg’s and Ray’s advice about using epoxy, but have stuck with the T nuts for the stands as I feel that they will need to be extra strong given the weight of the final cabinets. These are M10 which should be more than adequate for the job. I have routed shallow pockets for them to go in to make sure the bracing structure can be inserted into the cabinet as one piece without snagging on them.

EpoxiedStandMounts.jpg (80.8 KiB) Viewed 9285 times

Talking of which, I revisited the unfinished business regarding the rebate behind the midrange driver and did as Max N suggested. Feeling much better about the rebate around the rear of the midrange driver now.

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[MistyBlue]

I am a little reluctant to change out the T nuts for those inserts on the driver mount holes (I did actually order some to do that – they arrived the other day), but I don’t want to cause myself problems by trying to rework them. If I had my time again, I would have probably gone with the inserts. I will check the alignment with the drivers and if there is any issue, I will rework the T nuts, but otherwise I will just leave them alone and just smear on some epoxy to bond them onto the baffle.
I’ve also managed to get some more work done on the crossover/HF mount. These are the counterbored holes on the underside of the crossover base to take the M8 cap head bolts for the interchangeable HF mount plate.

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I’ve also decided to make the crossover box larger. The whole structure will look like this:

XoverBoxHFPlinth001.png (193.99 KiB) Viewed 9284 times

The front part which mounts the HF driver/WG will be interchangeable so this is something I will use the inserts on. Last time (although slightly different application), I milled a hole in the side of the ply and epoxied in a machined threaded right angle insert before veneering over it to conceal it.

2WaySpeakerHFWGClamps.jpg (41.43 KiB) Viewed 9284 times

[MistyBlue]

So…….after 6 pages of thread since I started – we now, finally, have some construction started!

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[MistyBlue]

Spent the last couple of days reorganising everything ready to start constructing the cabinets. The 2 way speakers have now taken the place of the wood store and vice versa. They are looking a little sad having been banished from the living room.

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Started to glue the internal bracing structures together. Now things are starting to pick up the pace.

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Couldn’t resist doing a dry mock up of the cabs.

H0ly Sh*tballs!

The last ones are big but these are really big – so big in fact for a second, I thought I had outdone myself. I had to go and recheck all the doorways to make sure they would fit through them. I was met by a disapproving “I’ve been mis-sold something” look by the other member of the household. The photo just doesn’t convey the size of it. One cab is as big as the Hartke bass stack (1x15” + 4x10”) and my large 1x15” guitar cab put together.

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