By Harald Werner
07 Mar 2001
Printed from SpeakerBuilding.com, 04 Feb 2012 08:51
URL: http:///content/diy/1106/
The unique appearance, the precise dynamic performance, that is due to the hardness of the material used and the special form of this TML as well, and the focused, lifelike, spatial stereo imaging of voices and intruments caused by the "waistline" of the LS are the main features of "ammonit"; the appropriate name for the snails with an explosive sound, I believe.
The drivers used are a 170mm low-midrange driver and a 25 mm dome driver.The efficiency of these drivers is almost at its limit. The frequency response of my LS is balanced and around 90,5 dB. The curve dwindles at 70 Hz - that relieves the low-midrange driver from sub-bass. Therefore, a subwoofer is required. The dome driver is modified: A drilling hole in the magnet relieves the diaphragm from pole-core reflections.
The size of the LS depends on the drivers. The length of the TML should be around 6 feet. The weight of one snail is 21 kg. To this, the weight of the pedestal has to be added. So, the LS weighs around 40 kg. The costs on material for one LS are at around DM 300. It took three month to build the speakers.
If you have no experience with the work described, please read first all instructions before you begin working. Try to imagine how I have done it.
If you have some experience, it is not necessary to adhere strictly to the following instructions.
ALWAYS OBSERVE THE MANUFACTURERS´ INSTRUCTIONS WHILE USING ANY MATERIAL.
I wish you an enjoyable and creative loudspeaker assembly. Fig. 1. The Ammonite
In well-equipped DIY shops you can buy wire-netting fence (It is also used to keep rabbits away from young plants), which is available in different varieties: the plastic-covered is probably best for this project.
The mounting measurements of the low-midrange driver has to be observed when cutting the wire-netting. I cut the wire-netting to a 50 cm by 185 cm piece. This is so to bend, that it forms a 185 cm long tube. At the front end of this tube, tie the ends of the wire together on a length of 15 cm. Now, increasingly large strips of the remaining wire have to be cut away at each side where the wire meets forming the tube: beginning at the already tied-together front side you cut along the middle line, first only few millimeters, than more and more to the end of the tube (15 cm at each side at the end)
Now, the damping material can be brought in. I took the strongest rubber coated carpet, that was available, and cut a 170 cm long and 15 cm broad piece for each tube. There should be no carpet at the first 15 cm of the tube. You could use other materials as well: thick felt, strong synthetic material, etc. Then roll up the tube to form the snail. Using gloves is recommended. Beginning from the end, you bend the sides of the wire so that this builds the sidewalls of the snail´s basket. When the snail is rolled up to its final form, you should fix everything. This can be done with ordinary or plastic-coated wire. The damping material has to be fixed too. I did this with guitar strings.
The front opening must be controlled if the low-midrange driver fits in (Caution).There should be enough room, because the inner side of the basket will receive a layer of polyester later.
Then a piece of wire-netting, 20 cm broad and long enough to surround the front end in a distance of 1 cm can be fixed around the drivers mounting base, so that a double wire-net can be tied together at the front opening.
To reinforce the snail´s basket I took a very strong plastic-covered wire and wound it 4 or 5 times round the front end to strengthen the mounting place of the low-midrange driver. This wire can also be tied in the sidewalls of the winding alley.
The basket for the tweeter is U-shaped wire-netting turned upside down, that is fixed on top of the snail. This can be fixed in a place so that the magnets of the drivers are vertically in one line. Here, the cutout diameter of the tweeter will indicate the size (a little bit bigger) .
At the bottom side, two of the strong wires (ca. 50 cm long) should be tied-in crosswise so that the ends are long enough to be fixed around a reinforcement of the snail´s pedestal.
The fixing of the snail to the reinforcement of the base is better made after surfacing.
Do not forget to install the 2.5 mm copper cable from the drivers to the crossover.
Make sure that your constuction is strong enough to carry the heavy weight! Fig. 2. The Ammonite 2
Materials: polyester filler (car putty), polyester netting, gloves, spattles, acrylic glass, orbital jigsaw
Before starting the surfacing work, read carefully the "instructions for use" of polyester filler. You should work in an empty, well-ventilated room.
In car-assessory shops various polyester fillers are available. Even large supermarkets in Germany offer bargains. Regular filler without glassfibre will do.
Building-trade shops carrying different variety of polyester netting (this is normally used for plastering works at houses). Best for our intentions is the narrow-meshed; and two square meters will do nicely. Before mixing the filler with the hardener, you should cut the polyester netting into pieces of around 5 on 10 cm. When using the filler I recommend wearing gloves. You should work swiftly when you mix the polyester with the hardener. This applies also to the surfacing work. Do not mix too much filler at the first time, because it hardens in 4 or 5 minutes. Put some of the cutted polyester netting on the snail´s skeleton; perhaps you´d better begin at the bottom. Just apply the filler with enough pressure that it squeezes through the polyester-mash and the wire netting. Then press some more of the polyester-mash pieces into the filler: some of this pieces should enter only partly into the polyester filler, so that you get a better connection when you apply the next mixture. But just give the filler time to harden.
First of all, fix the mounting bases for the drivers. I made these from acrylic glass, which I cut with a jigsaw: the base for the low-midrange driver is a ring-disk,that was made out of a 1 cm thick acrylic pane (available in sanitary shops). Consider the mounting measurements of the driver to get the inner diameter, and add 4 cm to that to get the outer diameter. So, the ring-disk is 2 cm broad (but this can vary to the driver you intend to use). The base for the tweeter is made from the same material, but the shape should be more of an inverted "U", 1 cm bigger than the cutout diameter of the tweeter, and with a hole to let the magnet and the connetion terminal through. Here, I recommend drilling several little holes under the magnet hole (but not within the cutout diameter). This is to squeeze polyester filler through them to get a better connection.
The ultimate connection for the base of the low-midrange driver is made later, when you carefully drill the holes for the dowels, which hold the screws for the driver.
By fitting in this base apply the filler as described, press it through the double front part of the wire skeleton, apply quickly some polyester-mash pieces from the inside of the tube, apply here some more filler and smooth it with a spattle. Similar you procede with the base for the tweeter. Ensure that you keep the bases always clean.
Now you can give the final design to your snail: The walls of the snail should be at least 2 cm thick. No polyester netting is used anymore, but you can use the polyester filler with glass fibres. Nevertheless, the standard filler is easier to form.
The design depends on your taste, probably a rough outside like a fossil does look very nice as well. If you would like to have a smooth surface, you should fill all indentations and level all bulges. First you can use a rasp, than a coarse-grained sanding sheet. At the end you use more and more higher grained sanding paper.
Observe the safety instructions for the use of polyester filler!
For the design of the surrounding of the tweeter, I used the disassembled front plate.
The size of the base should be a little bit broader than the snail and long enough to carry the crossover (if you intend to buy stands from any manufacturer or blacksmith, build your base to match the size of the stand´s upper plate).
The cast for the base can be built with small wooden slabs and agular fastenings. Now the snail can be fastened to the reinforcement, which is placed at the center of the cast. The reinforcement should be made of very strong wire. Bent the ends down by 90°, so that it stand by itself. The frequency crossover can be placed in a small box under the reinforcement. The drivers´cables can pass into the box through a small hole. The 4 strong wires which leave the bottom of the snail should be wound around the reinforcement several times. The snail should stand by itself now.
Now you can cast concrete to make the base. Make sure that the reinforcement is about 3 cm away from the cast on every side. Cut more of the polyester netting into pieces of 5 x 10 cm.
Mix the concrete: dry sand and the cement are mixed in the ratio 3 : 1, then, under stirring, water is added until the concrete has a viscous consistence. A bucket of 20 l will be enough for one base. Pour a layer of 1 cm into the cast and stick some of the polyester netting pieces in it. Then pour another layer and add more of the polyester pieces (they should stick in the concrete in all directions, this will reinforce the concrete even better). The final top layer should be done without polyester. Stir the concrete carefully with a small stick to clear it of air bubbles. Fill the cast up again and smooth the surface of the concrete with a trowel. Keep the concrete moist for 24 hours. After 2 days carefully remove the cast, which can be used again.
The full hardening process of the concrete takes one month. Meanwhile, preparations for the paintwork can be done: small indents can be filled with polyester filler and bulges can be levelled. To obtain a particularly smooth surface, you can use a filler aerosol (available in car assessory shops).
After one month, 4 holes can be drilled from every corner of the frequency crossover box into the polyester hull of the snail (utmost care! Make sure that you drill in the right direction). With dowels and screws you can strengthen the snail to make it "bomb-proof".
In case you have used the filler aerosol on both the base and the snail, the varity of colours available is unlimited. In car assessory shops, super- and hypermarkets you can find the full palette of paints and varnishes in spray cans.
You could even take your snails to a professional varnisher. This is more expensive, but you can be sure the work will be perfect.
I did it on my own, but it was not easy: the aerosol paint in cans is very thin, which is why it should be applied in very thin layers and therefore more often. But give the paint time enough to dry.
The shades I used were "nacre" for the snails and "granit-grey" for the base. The paint for the base is a new type (manufactured by duplicolor), coarsely grained and giving an impression of real stone.
High pass: MKT Foil Capacitor 6.8 mF Air-Core coil 0.3 mH Efficiency adaption R1 2.7 W and R2 15 W Low pass : MKT Foil Capacitor 10.0 mF Air-Core coil 2.6 mH Impedance: 8 W
Fig. 1. The Ammonite
Fig. 2. The Ammonite 2
