Shortform building procedure

First of all, please be aware that this is a translation and a rewording of the orignal danish building instruction, it has been carefully reviewed, but the construction has not actually been built for 20-some years, so errors may have gone unnoticed. Any ambiguity shall be resolved by comparison with the danish text, supplied below. The construction is characterized by being a wooden, concrete reinforced structure. A special concrete mix is to be used in the casting of all non-flat surfaces to minimize weight and maximize strength. Consequently this is not a project that is recommended for the beginners first DIY project, it is for the advanced and technically skilled builder willing to devote the required time, care and precision. All measurements are metric and in millimetres, and precision is paramount, so work metric, do not convert to imperial, it would only be a possible source of error. Proceed with great care through the construction phases, there is NO undo once a stage is done. Deciding a loudspeaker cabling route though the cabinet fairly early is highly recommended. It is also recommended to let the cable run though the horn at least as far as to the end of the passage of panel H on the route of the sound, and only there to let it go to a connector in panel A, you should not fit a connector panel nor make a hole for the cable in the early, high pressure, part of the horn, unless you opt for having the cable connector on the front panel where it is easy to get it airtight. This is the recommended route so as to avoid any possibility that the cable can cause turbulence, a marginal point perhaps, but this construction is about perfection. Cut out the chip-board (MDF recommended, same thickness of plywood usable) in accordance with the material specification for the relevant horn model that you wish to build. Precision is required, the all joints must be airtight for the contruction to function as intended. Cut out in item E to make space for the loudspeaker magnets rear protrusion so that you can actually fit the loudspeaker to the cabinet. A tight fit to the loudspeaker rear contour is not required but don't take too much material out as rigididty of construction in this region is a paramount concern. Assemble items A, B, C, D and E - the joints involving the side panels, items B and the top panel, item C, should not be glued together now, This because removing the sidepanels and the top panel will be required later in the construction, but they must be screwed in place for precision assembly and ease of building, the rest of the joints should be screwed - no more than 100 millimetres between the screws - and glued. The reference points must now be transferred. This is easiest done by making a "mask" in masonite fitting the points to transfer to items E, I and G; the mask for item E may only go as far up as to the underside of item I. The actual transfer of precision drawn (!) reference points can be done via 1 mm holes in the "mask" by the use of nails. For the reference points for the concrete casting, you must remember to include the thickness of the form wall, and reference points for any curved structure may not be more than 30 millimetres apart. Reference points for the wooden items to fit to the cabinet shall be transferred to items E and H, the additional reference points for the concrete cast items shall be transferred to item E. Reference points shall now be transferred to items I, remember the mirror imaging, and fit itemss J, K, L and M to item I with screws no more than 100 millimetres apart and glue the joints. Make the required cutouts in item I and place the assembly in the cabinet, screwed and glued to E and A. Reference points shall now be transferred to item G, and F shall be cut to fit as per figure 3. Remember that the actual measurements on figure 3 are for the big version, the measurements for the small version are on drawing 4. F and G shall now be screwed and glued together and fitted to the cabinet and shall be glued to item E. Precision is required throughout. Item H shall now be fitted in place and glued to item E, and item N shall be fitted in place and glued to items F and K. You must now wait until all gluing has set properly, while you so do, you should inspect all joints for airtightness and smoothness. 48 hours is a reasonable period to wait and do something else in. The special concrete mix is made of 1 part gypsum, 1 part cement and 1 part sand for a good compromise between acoustic properties, strength and weight. Rigidity of construction is what makes a good horn work. After adding water the mix should have a viscosity somewhat akin to a thin sauce bernaise. This mix is very rapidly setting, so you should only make just what you need for each pour and discard the remains. The first concrete pour is the one on items G and F, the one that is required for getting item G to accurately produce the required horn expansion. The wooded surface should be covered with freshly applied white wood glue on water basis (PVA glue) and big headed nails or screws with say no more than 50 millimetres between each, preferably less, must be added to the surfaces in question so that they heads will be inside the concrete, so as to hold it in place. Allow the concrete pour to set properly, a minimum of 6 to 12 hours come to mind as a reasonable time. Don't rush things with this construction, rushing and precision don't mix very well. You shall now glue and screw item D to items F, E and on to the set concrete cast you just made using liberal amounts of glue. You can now remove the side panels, items B, and make the concrete pours on one side of item E at a time. Allow them to set reasonably, you can rush a little bit because the next stage will not put mechanical strain on those casts, but still: do not be too hasty. You will also have to make pours against the top panel, item C, onto panel N, but it is urgently required that you put a thin sheet of plastic between the cast and the top panel, Item C, because you can not progress with the construction without removing that panel. Allow the concrete pour to set properly, a minimum of 6 to 12 hours come to mind as a reasonable time. Don't rush things with this construction, rushing and precision don't mix very well. Next you clean up all edges and joints, and ensure - by abrasive methods or by patching with pure gypsum that all is smooth, neat and airtight. Then and only then can you permanently screw and glue the sidepanels, items B, in place. Now you should remove the screws that held Item C, the top panel, in place. Even with the plastic in between it is likely to appear to stick to the concrete pour on N. Deliberate, but not extreme force, is the answer, tap the rear of it gently with a hammer, and it should come unstuck, it is only the surface unevenness that should hold it in place. It is now time for the stage that requires the ultimate precision, making the concrete pours in the top section. Remember: the earlier in the horn, the more precise it has to be, and the more vital that all surfaces are smooth. And then, and only when the pours have set fully, can you fit the top panel with screws and glue. It is the zone of the construction that has the highest internal pressures, and thus also the zone where rigidity and avoidance of any leak is paramount. Airtightness and liberal amounts of glue, even if they cause "running" inside the horn, is a better choice than a loose fit with too little glue and too few screws. Make the hole for the loudspeaker unit in Item D, the front panel, and you are basically done, now you "only" have to fit the loudspeaker unit and to get it to sound right. If you forgot to include cabling for the loudspeaker, the only option you now have is to let it go through the front panel below the unit.

Kortfattet byggebeskrivelse for Egoist-hornet

Efter at træstykkerne er tilskåret, jævnfør oversigten, udskæres der for højtalerens bagside på E. Stykkerne A, B, C, D og E samles, således at bund, bagplade og midterstykke limes og skrues sammen, medens resten KUN skrues sammen. Målepunkter skal nu overføres, og det er en stor lettelse at lave en skabelon i masonit til stykkerne E, I og G; E-skabelonen skal kun gå til I's underkant. Overførsel af målepunkter til træstykkerne foregår gennem 1 mm huller i skabelonen ved hjælp af søm. Ved målepunkterne for støbningen skal man huske at medregne tykkelsen af det materiale, der skal støbes efter (bruges som støbeform), og målepunkterne anbringes med en afstand på højest 3 cm. Målepunkter for de træstykker, der skal isættes kabinettet overføres på E og H, medens yderligere målepunkter for støbningen overføres på E. Målepunkter overføres nu på stykkerne I (husk spejlvending) og stykkerne J, K, L og M limes og skrues på I. Tilskæring af I foretages, og det hele anbringes i kabinettet, således at det limes til E og A. Målepunkter på G overføres og F tilskæres; se figur 3. De to stykker limes og skrues sammen og anbringes i kabinettet sammen med stykkerne H og N, idet de fastlimes til E, og N fastlimes til F og K. Kabinettet er nu, når limningen er tør, klar til støbning. Støbemassen kan blandes af 1 del gips, 1 del cement og 1 del sand. Efter tilsætning af vand skal blandingens konsistens være som en mellemting mellem ymer og vand. Blandingen stivner ret hurtigt, så det kan ikke anbefales at lave mere end der umiddelbart skal bruges ad gangen. Første støbning, der skal foretages, er den på G og F. Træfladerne der skal støbes på indsmøres i kunstharpikslim, og der kan (bør) yderligere anbringes storhovede søm for at fastholde støbemassen. Når støbningen er tør fastlimes D på F, E og på støbemassen under brug af megen lim. Sidestykkerne kan nu tages af, og støbningerne i E-skabelonens område gennemføres. Der skal endvidere støbes på stykket N, men inden denne støbning skal der anbringes et tyndt stykke plastik mellem støbning og topstykke, idet dette SKAL kunne tages af. Når støbningerne er tørre og afrettede fastlimes sidestykkerne. Husk at topstykket SKAL kunne tages af. Når limningen og støbningerne er tørre tages toppen af ved at den bankes ud mod kabinettets forside for at løsne den fra støbningen på N. Støbninerne i toppen gennemføres, hvorefter toppen NU limes og skrues fast igen. NB! - toppen skal sidde urokkeligt fast. Der udskæres for højtaleren, og kabinettet er færdigt.

get me back to the horn menu page please!

get me back to the main index please!

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