It all started after we moved into our new home.
I have some experience with building speakers, in the past I have build a horn, an active subwoofer and satellite speakers. There was also an unfinished project where I used Polyester mixed with sand and poured into a mold with an inside mold of polystyrene. It was on a summer day in the backyard of my parents house, there was no wind, the neighbors complained about the horrible styrene smell and finally finding out that I was using the wrong initiator that resulted in very high temperatures and in the end a cracked housing…!! Disaster!! They ended up as bird houses in a deserted area of the garden.
Back to now. Recently we moved to a new home and my actual speakers started to annoy me a bit; the high was a bit too “tsssss” and low was basically not really there. It was time for a new project! A big one.
Every project starts with an “investigation phase”, what do I want and what can I do?
The few requirements I had, were :
- Total costs lower than 3000 euro.
- Building it should not be ‘messy’, at least not in my home.
- This project should avenge my disaster with the polyester/sand.
- It has to be a poured Monolith. No wood work.
- High end. Unique shape. Professional look. Has to blend in. High quality sound.
Find help for the areas where I do not have the right competence and workshop/tools.
Soon I found out about the www.LoudSpeakerBuilding.com (www.lautsprecherbau.de) and the hype around Duetta. Surprisingly enough, there was even an Intertechnik studio at only 2.3km from my house. With some initial ideas, I made the step to visit them and found a very nice man called Udo, who enthusiastically welcomed me and even let me borrow the Duetta's so that I had the opportunity to listen to them in my home environment. Perfect! The speakers revealed never heard before sounds and it was a great experience! Not so great was to find out that a lot of my digital music is actually of low quality.
After several days, the executive decision was made to go for a 'Duetta-Einteilig' based design.
With the Duetta I mind I started with the design, with the following considerations in mind:
Standard Duetta design sticks out too far in the room, rotate it and you will even loose more space. Having a cylinder based design will solve this.
- If I want to pour the housing, the power on the molds will be big, however on a circle based design the shape will not deform.
- Eton speakers sound good, but are not that pretty. The yellow/green/gray color is not very attractive and do not match with the rest of the design. Solution, spray paint the drivers.
- The Eton chassis do look different for the 3 drivers. The ER4 is square and does not really match with the rest. And I also do not like speaker designs where you can actually see the screws. This will be solved by placing tailor made black alloyed aluminum rings over the chassis and it should harmonize the general look of the front.
- When the loudspeaker connectors “stick out”, they can easily be destroyed by the immense weight during transport or just moving them around. So I will hide them in the BR opening. Consequence is that the BR opening has to be moved to the back. Good thing is that it is totally hidden and will avoid the speakers becoming a parking place for toys.
In the mean time I did several researches after concrete pouring and mixtures and started to like the idea of a Terrazzo Epoxy mixture more and more. After a visit to an Estrich company specialized in Terrazzo (firma Aman from Beelen), I found myself a good partner for pouring the molds and polishing the speakers. After a discussion with my wife, we decided to go for a white shiny glossy surface with small Terrazzo stones.
It was time for some designing in Sketchup. This program was new to me, but after this project I dare to say that I can draw pretty much everything now in Sketchup.
Initially I started with a diameter of around 50cm, but soon came to the conclusion that the box looked to ‘clunky’ and needed to be thinner and taller. The target volumes for the upper chamber was set to 13l and the lower to 90l.
After a lot of puzzling, the result was a 120cm high speaker with a diameter of around 45cm, cylinder form, but the front cut off to hold the loudspeaker units (depth only 38 cm’s).
This by was my initial paper sketch, soon after followed several versions in Sketchup.
The final design was version10. The ER4 high toner was moved to the middle position so that it is at couch-sitting-ear height, the bass reflex pipe moved to the back and decoration rings added.
The bass reflex pipe will also be poured in and to make the housing even more stiff, I added 2 stiffening rings as can be seen in the detailed 'X-Ray' drawings.
I found out the hard way that Sketchup is not always very accurate with circles, at least not with the default settings. So in parallel I kept an excel sheet to check the calculations for volumes. I made a lot of use of the following formula. Hint, to draw more accurate circles in Sketchup, set the number of 'sides' to 96 for a circle. This can be typed in directly after selecting the circle tool.
Below an overview of volumes, I need around 63 liter of Terrazzo for one speaker.
And here is the plan that I used during the build (the red numbers correspond with the numbers in the upper table).
The outside diameter is calculated with 444,4 mm, (450 mm – 2 * 0,8 mm Steel thickness – 2 * 2 mm Grinding off) In SketchUp I made use of the feature to draw on' layers'. This helps to quickly show/hide specific details.
The skp files that I have created for this project can be found on my profile here on Lautsprecherbau.de. I have modeled the 3 used ETON drivers in the Duetta (ER4, 7_360_37Hex & 11_581_50Hex) for everybody’s convenience. Just import them into your own Sketchup model and you will get a good impression of how your final design will look.
For the molds, I used hard foam (styrodur) that is normally used as insulation under poured concrete floors. This material is very easy to shape, is more fine than the regular polystyrene, can be cut by using a hot wire technique and will be easy to release after the Terrazzo has been hardened. They normally come in plates of 1250x600mm. I got the 30mm and 39mm thick ones (purple and yellow).
The diameter for the outside mold had to be 45 cm and it became clear that this is not a regular size of pvc and after some internet research, I found an alternative in an iron pipe used for air ventilation. The one I got has a thickness only 0,8 mm, height 150cm and has a rim on one side. The pipe is relatively light weighted and requires an additional frame around it to support all the forces during the pouring. The rim will be used to clamp it.
The final total thickness of theloudspeaker walls will be 3 cm. However when the speakers come out of the mold, they will be polished and it is expected that around 2mm will be grinded off to get a super shiny surface. In the Sketchup model this has been taken into account as well, meaning that the inside and outside mold will be 32mm away from each other.
To build up the inside mold I have used a lot of steel. 4 big iron rods to hold all the styrodur plates together; at approx every 30 cm some extra rings and bolts. Since I do not want to drill into the concrete later on, I had to plan all holes in advance. I solved this by using small Aluminum pipes around the steel threads bolted together. Some bigger rods were used to bolt the inside to the outside mold-front plate. This made it relatively easy, I could just stick the 22mm brown plate with the inside mold mounted on it, into the outside mold and fasten it very tight onto the outside. The result was an already very stiff construction. I knew from my past project that the power would be enormous and that the little wooden frame on top of the mold has to avoid the floating.
The opening for the drivers were being made by using a 'Drehscheibe' and guiding it through the hotwire. To cut out the deeper segment I used a drill in a standard with a router head; ground with grinding paper to get the exact deepness.
Due to the enormous weight (130kg each) this little topic could not be forgotten. After pouring it already turned out that it was extremely difficult to just rotate the speakers a bit during the polishing process. It always took 2 people. In the terrazzo workshop we had the luxury of a fork lifter. This is also how we slid it into my Volvo XC60. When it dropped off the last few centimeters of the pallet, the car was directly equipped with a sport package (lowered). On the way back to home, my friend and I had to create an idea of how to get the speaker (we had to drive twice) out of the car at home without damaging it, but also without damaging ourselves (our backs or our pride).
We decided to build a ramp that we could use to slide it out in a controlled way, supporting the speaker on both sides. Once on the ground, we pushed it up and the journey upstairs (floor 3) started on a wheel barrow. Luckily we have an elevator! Once built up, I put some pieces of felt under it and moving it from its place is no problem at all on the smooth parquet.
The filling of the Terrazzo in the mold was done on a huge ‘vibration’ plate so that the air was shaken out. With respect to the mixture I can only tell that it is based on cement and that special additives have been added to make it flow better. To make sure that also the little holes were properly filled, we used small Terrazzo stones; this also leads to less grinding.
On the vibration table, we carefully filled the mold bucket by bucket.
The floating power of the styrodur core was immense and on the photo it can be seen that the inside mold has been lifted some millimeters; this despite all the efforts to make the mold as strong and stiff as possible.
The weakest link turned out to be the wood on the top of the mold. Next time I will use more steel! (will there be a next time? Oh yes, I am already working on a LP-Terrazzo :-)
Already after some days the big moment was there. We cut open the molds with an angle grinder and revealed the result. The mold has leaked a bit, since I forgot to close it with silicon, so we had to cut away some terrazzo to make it completely free. It looked a bit raw but … No detectable cracks! Yes!
This turned out to be a big job. First off all the immense mass is not so easy to move and polishing a round surface is definitely 3 times more the effort of a flat one. We also found the first small flaws, the mold had expanded itself somehow in the middle and the front was not straight. This had to be corrected by polishing off more from the middle.
In total 12 polishing/filling steps were required to get a smooth shiny surface. The result is perfect!
Building it up
Before building it up, I needed to take all the styrodur out. This turned out to be another massive task. For this I made use of an old drilling machine and a Dremel with extension and a router drill.
The result after it was empty (and cleaned):
To build up the filters I made use of an old cutting board from a famous Swedish company.
All the connections are soldered on the back side, also the wires are threaded through the board so that the soldered connections cannot be harmed during installation. On top of that I used a lot of hot glue to be absolutely sure that the components do not move, rattle or shake. I also labeled all the cables, to avoid making mistakes when I build the filters in. Here is the result of the 'Cutting Edge' technology! To mount the filters I used M4 iron thread rods that I have pushed in the styrodur mold before.
For the inside interior I used 5mm felt instead of 5.5mm "soft fiber boards". Felt is more expensive, but was in my case much easier, since the "soft fiber boards" are normally installed just before closing the housing and they do also not bend inside the round housing.
And to fill up the box I used of course the usual polyfill. One role in the mid compartment, 3 others loosely rolled up and divided in the 3 sections of the bass compartment.
The filter for Mid/High is installed against the BR pipe and the filter for the Low installed on the inside front side.
The connectors were installed. For this I slid away all the plastic and heated up the connector with an additional soldering gun (15W). And used another soldering gun (45W) to solder the 2 wires. At one connector I made the mistake to use too much soldering... the result was that one of the threads got full with soldering and it took me an hour with a lot of swearing make it clean again so that the bolt would run over it!
The cables to the mid and high speaker are threaded through the holes where the mold rods had been before. All these holes were later closed by using hot glue. The wires were just soldered on the speakers, to protect the speakers I used aluminum foil.
The ER4 is equipped with a wire with connectors and I got advised not to cut off these connectors since the wires are very thin and difficult to strip off and connect. So I used the single pieces of a connector strip to connect the ER4 to wires that go to the filter. For mounting the drivers to the housing I used M4 and M5 bolts which were screwed into T-nuts in the inside.
Since it was hard to predict how much there would be grinded of during the polishing process, I could only start with the design for the decoration rings after I had mounted the drivers.
On the internet I found a small specialized company called GreatStar who makes all kinds of rings for products for photography and telescopes. I sent my drawing and after several weeks I got 6 great black alloyed aluminum rings back by post. It was done very professionally.
I simply glued the rings on the terrazzo with a transparent glue with no dissolver.
So was it worth the effort? Absolutely! I have now a pair of great looking and fantastic sounding pair of speakers in my livingroom!
This project has cost me a lot of time. Every little step took thinking work because correcting afterwards is not really possible. But it is all been part of the fun of building loudspeakers yourself. Making small steps and learning as you go! That is what this hobby is about!
And did I meet my requirements?
- Budget wise, not. I went over with approximately 600 Euro.
- I kept most of the 'messiness' out of the house, emptying the mold was mostly done in the terrazzo workshop. Cutting styrodur requires a very good ventilation! I guess the damps are toxic, I had the opportunity to do this outside or sitting in a full opened door opening. What could not be avoided is that I needed some grinding and also using the router on the styrodur caused some fine dust.
I avenged myself! Yes! :-)
High End Design & Sound
The speakers nicely blend in with the rest of the interior, do not dominate at all, they look impressive though. The speakers are not directly noticed by visitors. I love the design, the dimensions are well proportioned. The round thick rings fit very well with the shape and do finish it off. I stepped away from black spraying the drivers. The ETON's I got, did look different (membrane color) to the ones that see in the listening studio. I guess these newer versions all use the same material, the greenish color is actually making it better looking :-) What I could do better are the rings over the ER4. To my opinion they are too 'deep' now. I have not heard a difference though after I mounted them. Do they work now as little ER4 horns? It took some time before the drivers were played in well and I am not even going to try to describe the sound. I don't have that much of comparison. What I can say is that the speakers sound unforgiving and precise. If you put bad quality in it, the speakers will directly tell you. This is in contradiction to 'lower end' other speakers where the sound will be muffled into a standard sound. Improving the rest of the chain can become a bit addictive, but can be seen as hobby of course. I am thinking of building a nice tube amp with a matching terrazzo housing :-)
Do they sound better compared to the wooden ones I borrowed? Difficult. I think you need the 2 versions side by side to make a good judgment on this. What is noticeable though is that the speaker housing does simply not resonate at all! I have played them at extreme loud levels, have put my hand on several locations but could not detect vibrations. This tells me that the mid and low drivers must work with minimal loss. I do sometimes get the feeling that the sound is very pure and clinical, but I absolutely love it!
One could discuss that the BR opening now ends in the area where the connectors are placed and that this is not a fully free opening. The area of the connector opening is double the size of the BR opening and I have rounded the ends of the BR by making use of silicon on the mold. This makes the pipe slightly shorter and should compensate for the not 100% free opening, well, that is at least my theory.
On the photos can be seen that the speakers are placed too close to the wall, the current living room setup does not allow a better setup.. (WAF:-). When I pull them forwards, the sound quality improves a lot. Luckily for me, we move house soon and the living room will be much bigger! The moving company will love me..
I am driving the speakers with a Pioneer VSX-LX70. This AVR has a feature called MCACC that does a EQ room calibration. After some experimenting, I learned that running the system in the 'pure' mode (with no room compensation) does not sound that good at all and when I listen to my FLAC music I run them now in 2.1 Stereo. I also allow a Klipsch SW115 (couch shaker) to rumble along a bit. On the photos can also be seen that I have been creative with patching my own cables. These are 4 pairs of 1.5mm2. They mainly look good with the speakers.
I think I also managed well to combine my own capabilities with experienced partners. The specialized work to mix, fill and finish the terrazzo was done by a company that has done this for decades, the same counts for the very nice black alloyed aluminum rings!
Special thanks to Sebastian, Steffen and of course to the team from Intertechnik providing this loudspeaker magazine and community.