How to build DIY transmission line speakers

Oof. Where to start with this one. What an anus of a project. It should have been an amazing build. Its should have been an absolute breeze, once I had it all figured out. It should have been a well planned, well executed joy of a thing. It wasn’t. Best laid plans and all that…

Right from the start of my speaker building odyssey I’d been fascinated by ‘transmission line’ or ‘t-line’ speakers. They seemed to be somewhat of a unicorn in the speaker design world. Too sensitive to room placement and tricky to tune the internal absorption and damping materials to make them a viable commercial proposition. But when done right, offering amazing performance – especially in the B.A.S.S.

The subs I built in my sound system build were rear loaded tapped horns – similar to a transmission line, but not the same. Horn speakers work on exactly the same principle as brass instruments, such as a trumpet, trombone or french horn. You have a specific ‘pipe’ length which resonates at a certain frequency – its pitch, or tuning. The tapped horn subs were tuned to 25hz. Very low B.A.S.S.

This gets very technical, very quickly. Go here and fist your mind with quarter wave theory. Fill your boots. The rabbit hole is deep. And full of science. To summarise: Sound waves – like any wave – have a wavelength. That length is measured in physical terms (cm, inches, feet, metres). The longer the wave, the lower the frequency. The shorter the wave, the higher the frequency. The greater the amplitude of the wave, the louder the sound. Crafting clever enclosures can enhance certain frequencies. Like B.A.S.S.

Stay with me… speaker drivers generate sound waves by turning electrical energy from an audio source in to physical motion. By rapidly oscillating the speaker cone, air molecules are moved in waves. Our ears register these pressure waves (relative changes in air density) as sound. All speaker drivers have a specific resonant frequency – a wavelength which the driver resonates at, which causes all sorts of problems (think opera singers shattering wine glasses with their voice). Transmission line speakers take the principle of matching a speaker driver to the correct amount of air pressure behind the cone (in this case the volumetric capacity of a shaped chamber or pipe), to help sort out resonance problems AND enhance certain frequencies. Phew. Enough of that. I made some plans…

Because my big system was too bloody loud to actually use, I figured I’d build some nice hifi speakers that I could actually listen to instead. I’d learnt from my builds to date that setting constraints was the way forward. So the mandate for this build was thus:

• Tall
• Thin
• Good looking
• Front ported
• Serviceable
• Full range

Taking those constraints – I searched for some appropriate drivers, and settled on these Pluvia 7 full range drivers.

Pretty little things. I thought if I’m going to do this right, I should properly embrace the nerd life and plan the enclosures using some nifty free software I found online. Unfortunately I cannot link to it as it is no longer available, as the author took it down for whatever reasons.

It basically helps you make the trade off between enclosure size and what frequencies you want to enhance. After much trial and error I ended up with the above frequency curve from a decently small, thin enclosure. I thought I had compensated enough to give decent bass response without needing a subwoofer – because t-lines are meant to produce phat, low bass. Turns out I hadn’t compensated anywhere near close enough. Its plain as day to me now looking at that graph… but I suppose that’s why learning curves are a thing.

Anyways, as I was embracing the nerd life, I thought I’d model the enclosures in some free 3D software (Sketchup) and really geek out. It was a great idea. If I hadn’t done this I would have messed up a crucial measurement that would have rendered the entire build completely hatstand (oh the irony..). Only problem was I had no idea how to use the software, so I had to learn it as I went. Hello learning curve…

Unfortunately I have a mostly hate/hate relationship with 3D software, so the process wasn’t much fun. But it was VERY satisfying when I finally got there.

Because I wanted this to be a super accurate, ideally replicable build I’d decided from the start I was going to get the wood CNC cut from a local supplier. There was no way I was going to get the design accurate enough with a jigsaw, a wing and a prayer.

The main reason this thing ended up so complicated and frustrating was that I was trying to be too clever. I knew that t-lines needed to be really solid to help with negating unwanted frequencies, so I’d designed everything to be double thickness. Because I thought I was smarter than I was, I made everything join together like a jigsaw puzzle to help gluing. Then I got wood (Gnurgle).

O frabjous day! callooh! callay! He chortled in his joy. What a wondrous sight it was to behold. I’d designed my very own millimetrically perfect speaker kit. And there it was, all ready to build myself. Marvel at its wonder! Bask in its glory! I’ll test out fitting it all together…

Clever me! You lucky sausage – being so smart. S.M.A.R.T. Well bloody done lad!

Hold on a minute… When I put them all together properly, everything seems ever so slightly… off. A bit… rattly. A bit… gappy. Wait a minute, there are tiny gaps, just less than a millimetre on all the joins. That’s not good. What gives?

It turns out that 12mm birch ply is not exactly 12mm birch ply. It’s 12.5mm. And someone hadn’t realised this. That someone was me. Everything was off by around 1mm. Because I’d been so ‘clever’ making all these super strong, super sturdy stepped joins it was all ever so slightly on the piss. All speakers need to be 100% sealed to prevent air leakage ruining the enclosure effects. This was 0% sealed. I’d royally banjaxed the whole thing. Kill me.

But I don’t give up easily. I knew it would be an absolute nightmare, and even with all the good intentions in the world I might not be able to save it, but I went ahead and got jiggy with my little dremel and some sanding bits. I had to shave 0.6mm off every single joining piece. What. An. Anus. HUGE one. Massive. But I puckered up and sorted it.

All those dreams of a perfectly finished, exquisite build – done for. But I still reckoned I could do it. So I ploughed on. Even if I couldn’t make it look super pretty, I could still make something that sounded great. Or so I thought. Initial tests were positive. They sounded crisp, clear and lovely… but very little B.A.S.S.

Its alright I thought. Once they’re all damped and sealed properly, they’ll come in to their own. Plough on Davey, lad, plough on…

So, 4 months after getting the wood eventually they were finished. Halle-bleedin-lujah

Now to be fair, its not all doom and gloom. They look fab – so much so my wife let me put them downstairs. Unheard of. They also sound amazing – apart from the fact there is very little low end. Which after everything I went through on this build was a massive let down. You can get bass out of them, but it overwhelms the little drivers at low to medium volumes, so its just not worth it. I ended up pairing them with a cheapy old active sub that I had kicking around and they sound peachy.

As they are downstairs, they also have to deal with two barely contained monkeys messing with them. So I had to build speaker covers to protect the drivers – which kind of kills the point of having pretty exposed drivers. But it doesn’t seem to be to the detriment of the sound

So, what have I learnt from this build?

Keep it super simple (K.I.S.S)

I can scarcely believe I’ve had to learn that lesson uh-gain… but there you have it. At least I’ve learnt a stack of things and ended up with some properly decent sounding speakers. It’s just about killed my desire to continue building speakers though, which is… well, it is what it is. That’s designing and building speakers for you ¯\_(ツ)_/¯

How to build a DIY dub reggae inspired sound system

Start at the start, Dave. Why did you do this thing?

Bass. Sub bass specifically. This is the story of how building a simple DIY sub blew out of all proportion. Because more bass is better bass, and the best bass is more.

B.A.S.S.

It also serves as an [im]practical guide how to hack together a fully working dub reggae inspired sound system in your attic. With the mere application of a few years, many hundreds of hours effort, and some £s.

To recap; The journey started here. I had almost no tools, knowledge or sense. But I had a shed, an attic and an internet. Which is all you need to build a sound system, it turns out. That, and a lifelong love of dub reggae and bass music. And whisky. Lotta whisky.

So, I had a sub as a starting point. Now I needed a vision. And that vision was B.A.S.S. …with the rest of a sound system attached to it. With scant regard to sanity, wisdom or personal freedom, I started reading everything I could about sound systems and speaker building. And made plans. Many, many plans. Like this:

Interestingly (to me) the system ended up looking and performing pretty much exactly as I planned it. Who knew. WAIT! mind blown… B.A.S.S = Build. A. Sound. System.

I digress…

I needed wood (fnurk). Turns out brand name DIY stores only stock really poor quality plywood. As I found out when building my first MVP sub. Why plywood Dave? Good question. Because MDF dust is carcinogenic. And plywood is prettier. But, as with just about everything in this project, it turned out to be much harder than you might first think (fnurk), to get good wood (gnurk). But I did. And it was glorious (gnargle).

One of the things about being an idiot, is that you learn how to cut unfathomably straight lines with fundamentally inappropriate tools. I built this entire thing using a cheapy jigsaw with some old blades that didn’t fit properly, with no jigs or guides – all freehand. I like to think of it as quintessential British pluck. Or idiocy – your shout.

B.A.S.S. – Yes, bass. I had a sub. It worked. It proved a principle, and it was ace. I knew how to build more subs. Problem was – drivers. I needed drivers. Drivers made from pure unobtainium. I mention this now, as I’ll come back to this story later. Spoiler alert – B.A.S.S.

A dub reggae sound system consists of subs (sub bass), bass (kick bins), mids (vocals) and tops (tweeters). All covering off specific parts of the frequency range.

I figured I’d work from the bottom up (Gnurgk). I wanted to design and build everything from scratch. Because being anything other than a complete masochist would be a cop out. I already had a sub, so I started with bass bins (kick bins). That’s when I realised I had bit off more than I could chew. So I figured I’d add some constraints.

My MVP sub used a little 6.5″ driver that made a BIG sound because of the clever chappies that designed the enclosure. Sealed boxes were simpler to build and more fault tolerant in their design. Perfect for numpties with ideas above their station, just like me. So I searched around for 6.5″drivers that might fit the bill. Using a couple of android apps that matched drivers to box volumes, I found Visaton ws-17e drivers. They were (crucially) cheap as chips, and even more crucially, available from a stockist less than a mile down the road from where I live… sweet serendipity.

Wait – android apps, box volume calculators… the actual f*ck?! What I hadn’t realised (before it was too late) was that to build speakers, you need a basic understanding of carpentry, joinery, maths, physics, sound engineering, acoustics, electronics, amplification and Thiele Small (TS) parameters (don’t @me, even now I couldn’t explain). The beauty of the internet is that you don’t need to know any of this stuff. Just find the right calculator[s] online, mash in the numbers with your pudgy meat sack fingers et voila – instant genius.

I’m not going to dive in to the technical details of the size and shape of these things. Keep it light and breezy, that’s the way (Leave a comment if you want to explore the nerd life). Suffice to say I built 4 kick bins – 2 bigger boxes and 2 smaller boxes, using the same drivers – to see what the differences were like. It was all a massive experiment.

Trivia – speakers are generally stuffed with wadding to stop unwanted frequencies reverberating around the inside of the enclosure and escaping through the driver – muddying the sound. The boxes you see above are all stuffed with polyester wadding. These are very simple, reinforced sealed boxes with a driver at one end, wired to a terminal cup on the other end (where you stick in your speaker wire from an amp).

Issue now was, how the hell do I funnel the correct frequency ranges to these things? I had to start buying hardware. And learn how to use it. And make somewhere to put it. So I stopped building speakers for a bit, and built an amp rack. To put my new amps and crossovers in.

Trivia – A passive crossover is a simple network of capacitors and coils, that allows certain frequencies to pass through a circuit, but not others. An active crossover is a piece of hardware (or software) that allows you to dynamically choose what frequencies are assigned to individual outputs. A passive crossover requires diligent planning, design and a strong knowledge of electronics. An active crossover costs £55 from Amazon.

At this point I had acquired three amps – one for sub, one for bass and one for everything else. I also had two active crossovers, because one went bang and I got a replacement. (you get what you pay for…). Proper sound systems have separate amps for each part of the stack, so I was keeping it real. At least that’s what I kept telling my wallet.

Then I started thinking about mids and tops. The tweeters turned out to be mercifully simple. You don’t even need to put them in a box as the dome is sealed. But I built some funky boxes anyway. Then threw them away and left them open. I used Monacor DT-300s with WG300 wave guides.

Because I had active crossovers and multiple amps, everything was essentially modular, so I could grow and test the system organically. For instance, instead of having the tweeters separate and everything else (vocals and bass) coming out of the kick bins (and sounding really muddy), I could use the smaller two kick bins as dedicated mids instead. With the vocals and mid-bass separated out, it sounded loads better. Separating out the sound so each different section does one thing, and one thing well was a win. Those particular Visaton drivers had a particularly wide, usable frequency response which allowed me loads of options.

Then it happened. Two Exodus Anarchy 6.5″ woofers came in to my possession. The drivers the original MVP sub design used, and pure unobtainium in the UK. Their story on its own is mental. Involving airline pilots, more air miles than Tyler Durden, layovers in Utah, San Francisco, New York, London, Kent and finally Bristol. 9 months I think it took in total to get them after I cheekily asked an American friend of my wife to buy some for me.

By that point I had run out of the juices (hrurk) required to build those bonkers tapped horn sub boxes (gneek). So I figured I’d use the last of my good wood (grurk) to build two more Mid boxes for vocals, and slap the two anarchy woofers in a plank. But hooked up to the amps so they could be broken in a bit. Which I did.

Everything was all getting a bit techno by this point and I was questioning what the f*ck I was doing with my life.

To the point where I damn near sold the lot and jacked it all in. Spoiler alert: I didn’t.

But I did have a long break from building stuff and did something more interesting instead. Though I can’t remember what.

Then it was time. I had come full circle. I had put together a fully functional (albeit rudimentary) sound system, but I was missing the final piece of the puzzle.

B.A.S.S

So I built two more subs. This was one of the most challenging things I’ve ever done. It took months. Blood, sweat, tears, the lot. What a journey. But boy was it worth it. I learnt so much. From building your own tooling and guides, through to sanding and finishing with amazing beeswax. All done with zero screws, all glued – for proper geek points. They are beautiful things, and provided I’m not a dick and blow the drivers, will last a life time.

So that was it, mission accomplished.

Or so I thought.

Turns out that with so many different elements, tuning it is a nightmare. Also, as soon as anything goes wrong, tracking down the issue is bloody hard. And don’t talk to me about wires. Never mention the wires. So. Many. Wires.

And then there’s my attic. Which is acoustically, a twat.

But I did it.

I. bloody. well. did. it.

There’s a couple of minor issues. One – I can’t actually listen to it. I have neighbours, and small children. It’s fecking loud. And one of the things about bass, is that it travels. Like REALLY travels. You know whales… gentle undersea leviathans? They talk to each other over hundreds of miles using sub-sonic low frequencies. Two – I can’t get it out of my attic. It’s too heavy, and too complicated to move. So I’m never going to really hear it at its best. Did I mention the acoustics in my attic are wack?

It IS very pretty to look at though.

And the kids dig an attic rave.

Additional 15th Jan 2020:

A DIY sound system is never ‘finished’. I ended up building a 4th tapped horn sub for a nice round number and putting a bunch of extra effort in to adding extra driver covers and making it properly nice to look at.

Which is nice. Because I rarely get to turn it on. 

There’s always the thought “Maybe I should re-build those bass cabs to improve the [excuse to tinker more]…” 

Update: Not sure if I mentioned this but I stripped and rebuilt the first MVP sub and built another sub (both with the 8 Ohm Tang Band drivers) so I have 4 x ‘Insubnia’ subs in this rig spread around the attic. It makes sick wubs, bro.