The making of: The Two Towers (a 25 driver Full Range line array)
After riding along on a few different line array threads I figured this project deserved it's own thread.
I wanted to get new speakers for my living room for a while but could not quite find something I liked.
The speakers I have right now are just too big to use in a proper setup. In a domestic setting with a girlfriend and a 7 year old son there's just not much room to place anything. After surfing the net in search for an answer I stumbled over several line array's.
Now that was something I thought had potential! Way lower floor space needed than my current speakers with 15" woofers.
So the idea was born to build line array's using 25 full range drivers in each array, long enough to somewhat be floor to ceiling.
Next problem, what should it look like? And what materials to use? I remember seeing a DIY thread with a translam construction. That idea was very appealing to me. You can make it any shape you want on the outside and the inner walls can be used to benefit the design.
I started up my favorite 3D program and started sketching. Pretty soon I had some ideas about the outer and inner shape. Here's a much later version to give an idea:
I wanted a round outer shape, round corners to help reduce diffraction. On the inside I choose a wavy shape to hopefully aid in scattering/diffusing the back wave and making the walls uneven in thickness. That last feature should help reduce resonances of the enclosure.
Also obvious are the braces, making it a potentially very stiff enclosure.
The total array design on the left and the final outcome of this project on the right:
(not too far off I presume)
13th December 2014, First sound: A memorable moment!
14th January 2015, Start of first measurements: Measuring my way to better sound quality
16th July 2015, Break trough in processing: Getting time coherency to work
(creating a time coherent correction in my listening room)
12th January 2016, Proof of time coherency at last! Tested with APL_TDA software
21st January 2016, First official review: Jan Fekkes reviews the Towers
The driver I choose for this project is the Vifa TC9FD-18-08, also known as Vifa 9 BN 119/8 in Europe.
From the specs this seemed like a very good driver for the price and after looking at reviews and projects with this driver I became more and more convinced this could work.
As 25 drivers in a line array without any EQ would not work I searched the web again for a solution and ended up with a Behringer DEQ 2496.
Imagine my surprise when I found someone on this forum who had used exactly that combination!
Check out: stupid-cheap-line-array page 4, post2648779
Time for some questions obviously :D. It felt good though, to find someone with similar choices and even better when that someone is that enthusiastic about what he created!
After first getting 2 Vifa drivers to get my own opinion on them I ordered another 50 somewhere in 2011. I also ordered the Behringer and expected to be able to start the next summer. But that didn't happen. I never found the time to start this project. I tried to find an economical way to get my layers of wood cut. CNC would be ideal but difficult to find in my area and comes I was worried about the price.
I had read water yet cutting could be used to cut wood, even though that felt like the last thing to do: getting water into the wood would seem like a nightmare to me :scratch1:.
At first I was thinking about MDF as build material for the stack. But to stack that much MDF and worry about expansion due to changing temperature/moisture I switched to Baltic Birch Ply. That should expand less in thickness than MDF and I can't say working with MDF grew on me the last projects I used that.
But a local firm claimed hardly any water would be soaked up by the wood due to the fine spray used. My only left concern was price again. Each array consists of about 125 stacked layers, that meant a lot of cutting!
To make a long story short, I didn't get any work on these array's done in 2012.
But that did give me some time to further develop my plans for these array's. Meanwhile the interest in line arrays on the forum continued and another member showed up with a marvelous array based on the same Vifa speakers: stupid-cheap-line-array page 21, post2890230
(a lot more info and discussion went on in that thread, just linking the result)
Member koldby's work peaked my interest for an aluminum baffle for my project. The back mounted baffle looks gorgeous to me so I started playing with that idea. But I wanted to make sure it wouldn't have a negative influence on the output. Again Google search to the rescue I stumbled on some measurements on a German forum. This shows the effect of a baffle of 9mm with fillet used in front of the Vifa TC9: http://www.diy-hifi-forum.eu/forum/s...ead.php?t=2157
I didn't want to go to an all aluminum enclosure but figured a baffle made from aluminum could have it's plusses. I would use one plate before the drivers with the fillet wave guide like shape and use another plate behind the drivers to mount them.
Something like this:
The open spaces behind the back plate and in between the two aluminum plates could be filled with mass loaded vinyl. A heavy acoustic rubber, in my mind serving to dampen the aluminum baffle while making it more sound proof.
Fast forward to this year. Due to the bad economy I got laid off at work after working for 16 years for that same firm. I was in charge of IT and by boss decided to outsource that part of the business to save some money.
That sped up my plans for this project big time. The economy is still in very bad shape around here so I had to keep in mind I could be out of work for quite some time. I figured it's now or never if I want to actually build this thing! So in between hunting for a new job I started getting everything ready to start.
I bought the needed tools for the job, a Router (never worked with one before) and a drill stand.
As the design work was finished I figured out how to do all this work by hand. I figured I could cut the Birch Ply with a jig saw, a bit oversized and use a template to shape it with a router on a table.
To be able to use the template more than once I had them cut from 8 mm aluminum. (water yet cut) At the same time I had them cut the speaker feet from 2 cm thick aluminum.
A Router table was easy enough to construct so off we go:
I started with a cheap € 80,- Router and some good router bit's. From what I had read the bit's were the important part to cut a lot of wood.
Well, that lasted a week with my production. The bearings on the Router were completely gone after that daily abuse. So that didn't go too well. After opening up my wallet a bit more I got a professional Router and what a difference that was! The only thing I had to watch out for is to keep the wood moving or it would burn!
Here's the first stack of a few chambers, also showing the templates used for the layers:
(you can also see an oversized layer cut with the jig saw on the right below the template)
So this could work! Aside from taking up huge amounts of time that is :D.
After my girlfriend tipped over a stack of finished layers I decided to stack them with some temporary threaded rods (M6 in a 8 mm hole so I could see how big it would become.
Here\'s the first stack taking shape:
This is awesome! - hang in there and you will soon have both a line array and a great job!
Thanks guys, yes it works, if one is crazy enough to put in the time :D.
A close-up of the chamber:
The layers used for the chamber are identical, just stacked in opposite order.
After days and days of jig saw and router work I had this:
Still another box to cut. At this time I was happy to be going for 2 channel stereo (lol).
Several weeks later I had everything cut and it was time to work on the braces which will hold the baffle in place. To be able to do it with some consistency I decided to make a simple tool to drill the holes.
This is why I got a drill stand and not a drill press:
Making use of my workmate to clamp the brace and use the tool to hold everything in place I could now easily drill the holes for the baffle mounts.
The nuts I used are a square piece of ply with a T-nut pressed in. Here you see the tool being fastened to one of the braces:
What about building a classic parallelepiped (with internal braces for stiffening and standing waves) and then apply rounded panel on lateral faces and the back?
Too easy? :D
Working your *** off making all the needed parts gives you a lot of time to think and rethink parts of the design. That isn't always positive though.
As is reading a lot on this forum. One always gets new ideas and insights but I tried to lock into my plans and try to avoid side tracking.
One of the things that had me wonder is if I should use threaded rods in the glue stage or just use wooden dowels for guidance of the separate layers.
I decided upon the first idea, and have the threaded rod fastened with rubber rings on the bottom and top of the stack to be able to let the wood expand/contract somewhat. In between the layers I have open spaces where I countersunk the wood to attach the template for routing. That space is filled with a rubbery glue that stays elastic.
Here's the setup for the glue stage:
The aluminum foot is glued to the floor while keeping everything level and the baffle is fixed to the roof of my garage.
A couple of straps would hold the braces firmly to the baffle. I used some spacers to have the baffle a couple of mm outside the line to be able to strap it down.
Another time consuming job, the glue stage. Here's what I did,
Glue 2 layers together and make them fit the baffle:
(here you see the countersunk hole, the layers are glued together at the non-countersunk side)
(the thread cutting tool is used from time to time to rid the bolts from residue glue)
After preparing 2 of these I glue them to the stack:
Glue the bottom one first, slide down the middle one, again glue and clamp:
(check level while fastening)
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