FORT – a… devlog?

Okay, so this has been long overdue, and as we now have a site we can comfortably post to again, it's probably a good time to fill you in on what happened since we posted the introductory post about the Free & Open Rave Technology project – which was over two years ago. _{fuckin hell…}

We haven't exactly been pouring endless hours into it, but we also haven't been sitting still.

If you have been following us on the fediverse since then, you might have seen occasional glimpses of the project not being completely dead.

To recap our original post about FORT, what we had at the end of it was:

• two 2-way speakers
  • these should have had pretty great kickbass if things went according to plan (they didn't)
• a DC car amplifier jerry-rigged to a PC power supply
• a complete and utter lack of bass 😭

A couple weeks after the initial post, we got ourselves a pair of Behringer BEQ700 DC bass equalizers – and they did noticably improve the bass output, but sadly not to a level we would describe as good. The overall sound was still very much muddy.

We also soldered together a little DC/DC stepdown circuit to drive the 9V EQs from one of the PC power supplies' 12V lines.

The yellow boxes are the equalizers.
And yes, those are "bass equalizers" as in "bass guitar".
Don't judge, it was cheap to try out, worth a shot and technically still progress.

The result was still marginally better than complete shit for indoor use and we used this setup for months without any failures – not that it failed later, but we did extend the setup, which brings us to…

As indicated in the original post, we went with the well-established THAM12 design, which came highly recommended by people in the local free rave scene. For the driver, we chose the Beyma 12G40, which seemed pretty similar to what Martinsson originally used when designing the enclosure.

We finally got around to the actual build in December 2022.

One complication that arose was that the workshop rental service one of the local hardware store chains offered, and which we used for the two tops, was discontinued. On one hand, this fit us well, as we weren't allowed to use the tools there ourselves – but on the other it made things decidedly harder.

For one, we haven't done a lot of woodworking since high-school, but that part is manageable – the bigger problem was the tools.

Using the resources at a hacker- or makerspace would technically have been possible, but it would also not only mean dragging all the materials through the city at least twice – it would also create some very hard time constraints, because other people want to use the same tools/space. Not doing this proved to be very much the right decision.

A bigger (likely the biggest) issue was our lack of knowledge about what tools to get. We figured a normal buzzsaw would be good enough if we combined it with a rail.

This turned out to be a massive miscalculation as the saw still had wiggle room upwards of a millimeter when clamped into the rail sled.

Additionally, while the buzzsaw we got can be fixed at an angle, it is pretty fucking inaccurate, with a barely readable scale and no notches or similar helping mechanism to set accurate increments. Especially the 3° angle needed in one cut to create the tapered horn shape in the enclosure was a nightmare to get even halfway right.

And a lot of the connections between parts are still entirely more glue than actual wood touching. Quite honestly, if the design didn't include braces that force it into the right shape, the entire construction would be massively off-kilter. This was also why we sawed and filed those braces by hand. It was the only way to get the needed accuracy.

We definitely learned our lesson and will get us a proper mitre saw before building any more enclosures, or other things where we want cuts accurate enough to cleanly glue them together for that matter.

It legitimately took us weeks to build this thing – but build it we did.

Was it worth all the effort? Abso-fucking-lutely!

It's an absolute beast – and we still don't know just how far we can push it, as our neighbors immediately started pounding on the door when we did a test-run barely utilizing a fraction of its capabilities.

Also the worst trip ever ¶

In the summer of 2023, we visited Camp++ and we brought the then-current iteration of FORT along – but not before adding a nice coat of paint and some cheap DIY grills to the speakers to add some protection from the elements.

The grills are just steel mesh cut and bent into shape that are screwed onto the enclosures. In the case of the tops, with some rubber furniture feet to force some distance so the 8" woofers have a bit of breathing room.

The final result at least looks pretty nice:

So we wrapped the speakers into a plastic tarp, strapped it onto a cart and crammed our backpack and another big bag full of hardware and set out for our train trip to Hungary.

The journey started well enough on the austrian side of the transport equation, with the train doors being just big enough to fit the cart and the staircase just the right height for us to still get it lifted up there.

But things fell apart pretty quicky upon arrival at the station in Hungary. The only way off the platform was a 5+ meter high staircase. No elevator, no escalator, not even a ramp. Just a big-ass staircase that was completely insurmountable with such a huge, bulky weight. We don't have the slightest goddamned idea how people in wheelchairs are supposed to deal with it – but given the overall state of hungarian politics, we're guessing they're not supposed to deal at all.

After contacting some people at the venue and waiting for about an hour, help finally arrived, but the staircase was still pretty exhausting.

And when arriving at the venue, the first thing we learned was that there were already no less than two professional-grade PA systems set up.

In other words, the entire fucking ordeal was a completely pointless exercise.

To make matters worse, we suffered from heatstroke for essentially the entire duration of the camp, making this probably the most unfun hacker event we've had the dubious pleasure to experience.

On the way back, we at least had some help, but also more complications as we not only had to deal with the bulky weight, but also heatstroke and the the doors of the train being too small to fit the cart.

Luckily, someone managed to convince one of the railway employees to open the wider door used for deliveries to the onboard bistro.

And of course, the same people had to be convinced again to let us out through that door in Austria.

We are not looking to ever repeat this experience. At the very least not when travelling with a group of less than 3 people – much less alone.

But at least we could do some field testing during the event – which immediately demonstrated that we chose the wrong tweeters, as the Beyma CP 16 proved to be extremely directional.

So, for outdoor use, we'll need to install tweeters with a wider cone.

We still didn't get to figure out the exact capabilities of the THAM12, tho. The reason here being that both, the PC power supply and the car amp, are very much underpowered for driving an 8Ω driver that can handle a continuous input of 500W.

We needed a bigger amp – not only for the subwoofer, but also to make sure our lack of bass in the tops wasn't caused by the lack of amp power, too. We wanted a known-good component that is actually intended to power 8Ω drivers (whereas most car speakers use 2Ω).

So now we arrive in the summer of 2024, when we had a good chunk of disposable money on our account and promptly ordered the biggest 4-channel amp Thomann had to offer and a parameterizable crossover to handle the frequency filtering for the subwoofer – both 19" components.

As both the amp and the crossover expect symmetrical/balanced audio via XLR, we also got a passive DI box to do the balancing.

The components in question are:

• TSA 4-700 of Thomanns in-house "t-amp" brand
• Behringer CX2310 V2
• Millenium Pocket DI 2

After waiting for about a month, the hardware finally arrived and… they work fine for the most part? Tho one of the amp fans sometimes sounds like its dying and we think the crossover might have a loose contact – we might have to go through the warranty process for that, but in the longer run, these 19" components should be pretty maintainable; especially Thomanns in-house stuff is apparently known for lending itself well to maintenance and hackery.

The important thing is that we can now pump up to 4x490W at 8Ω into our drivers – and while this might technically be 10W less than the 12G40 can handle, we're not exactly looking to go over 80% so we still have a buffer, lest we fry our drivers.

A notable downside, at least in the context of this project, is that this is all AC-driven – but the custom 19" DC amp/soundcard contraption we want to build is still years away and we absolutely needed a solution until then.

But what about the sound!?

Well… the sub is great, better than before even.

The tops… are still utter shite.

By this point, we had established that the amp wasn't what's causing the weak-ass sound on the tops. So we searched and read and read and searched, until we found this blog post on the site of Eminence, the manufacturer of the 8" woofer we use in the tops, and this is when we first learned about the EBP, or Efficiency Bandwidth Product. We don't claim to actually understand what the fuck this means, but – to quote the blog post:

"A parameter called EBP (calculated by dividing FS by Qes) is often used to determine if a speaker is best suited for a sealed or ported enclosure. An EBP close to 100 usually indicates a speaker is best suited for a ported enclosure. An EBP closer to 50 usually indicates a speaker is best suited for a sealed enclosure. A speaker with an EBP 50-100 might work well in both types of enclosures."

The 8" driver we built into a sealed enclosure has an EBP of… 156.

Well… fuck.

Guess we got some new enclosures to design… ¯\_(ツ)_/¯