The Ammonit

By Harald Werner
07 Mar 2001

The Ammonit
Preface
A certain similarity to a LS from the well-known British manufacturer B&W is the result of inspiration from seeing pictures in a journal. But even before that I was thinking about how to keep reflections away from the mebrane. Resonance tubes and Transmission-Lines (TML) get their dynamic range mainly from this fact, I believe. As an innovation, I have built my LS mirror-image-like, with a bass reflex tube at each end of the TMLs. However, the frequency-and impedance response shows typical signs of a TML.

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

The legend for self-assembly

Basket-work
Material: wire-netting (1m x 2 m), tongs & nippers, damping material, strong wires, copper cable (2.5 mm to connect the drivers with the frequency crossover), gloves.

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

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