Rerurn to Romy the Cat's Site
In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.
Post Subject: Materials for Mass Loading Wooden StructuresPosted by Paul S on: 7/23/2010
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Romy, I often work with materials like this, for specialized restoration and reinforcement projects, and I have used it for my own speakers, as well. You mention ~ 1/2" thickness, and indeed thickness is an important consideration in selecting most of these materials. I have used "medium set" acrylic-modified marble and stone mortar mixed with various proprietary cement products with good results. Custom makes good, reasonably priced modified marble and stone mortar, and Rapid Set makes two similar products I admix with the "medium-set" morter, depending on the end use thickness I want: I use Rapid Set's Mortar Mix (contains medium-fine sand) for 1/2" thickness and above, and I use Rapid Set CementAll for thicknesses significantly under 1/2"; the CementAll (if there is sand, it is very fine) will basically feather down to "zero". All these products can be successfully intermixed to specific advantage by someone who understands their properties.
Althought these combinations are very stable, it never hurts to staple expanded metal mesh down prior to application. I have also tried a few times a new thin-set and medium-set mortar called Versa Bond that is formulated to work without mesh to span cracks in concrete slabs without letting cracks "read through" tile set directly over these cracks. You MIGHT be able to use this stuff without mesh; but because of the way you will be building the horn, I think it will move around too much for any mortar without mesh; not to mention the fact that the Versa Bond is $30/sack...
Most all of the "flexible" mortars you'd want are slow drying. Most of the stable "cement" products are fast drying, especially in hot weather, although they do sell crystals to mix in with the water that extend working time. Mixed, the two "mortars" give reasonable working time for a pro, given realistic batch sizes, TBD.
If you build the first part (throat) of your horn from wood, you might use this sort of admixed material to "parge" the inside of the throat to make it any shape you want, and you could also use it to transition and tie smoothly into to the main, 4-sided part of the horn. Applied with care, this stuff sticks to wood, most metals, and many other materials very tenaciously, particularly if surfaces to be covered are prepped with a coating of concrete "glue" prior to mesh and parging.
This stuff is heavy, like cement; it IS cement... You might want to pre-calc final weight before you put on too much...
Best regards,
Paul SRerurn to Romy the Cat's Site