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Originally Posted by GAWD
So you suggest leaving my riser open rather than closed filled with fiberglass?
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Yes, the risers I'm using are designed for a front sound stage or a riser for seating. There are better design options for raising a sub.
As I mentioned in a post on the last page, there was research done with materials that have slightly more effective <125hz absorption coefficients. Lower pcf fiber glass is much more effective in the LF range. Foam in this instance would be a bad idea. The concept seems to be letting the air easily pass between the fibers, which is different from conventional mass based dampening. If you look at the
coefficients page you can see that lower density fibers seem to be more effective at 125 (and below according to Terry Montlick, PhD in acoustics). If you build a cube, with only the top and bottom enclosed, you'll want to get a nice, light fiberglass to fill the void with and some acoustically transparent cloth to wrap it in. You do want to use gloves and a dust mask, tho I found that home made masks from old t-shirts worked so much better then the average dust mask for dealing with fiberglass. After you fill the void with the insulation just wrap the 4 uncovered sides of the cube with the cloth and staple it on.
As long as it's stapled well you shouldn't have to worry about fibers from the insulation. Fiberglass is commonly used for dampening panels and the only thing protecting you from those is the same layer of acoustically transparent cloth. I've been in labs where it's left uncovered. The cloth you can get from any place that sells a variety of fabrics, you just have to select one that you can blow through when you place your face over it. As long as air can easily pass through it'll work fine. This will setup will help absorb excess bass energy from the vertical node. In theory it will decrease the dip or peak created by the standing wave at that frequency. If you want to provide better isolation, just by a set of rubber feet for the riser. Remember, raising a sub by that height might require repositioning to find the sweet spot again. I also question the 25% rule, as it's based on a simulation using 4 subs, one in each corner. I'm not convinced that in most scenarios (less then 4 subs) it would provide the best position. I would suggest doing the sub crawl, with your head at the new height for the sub to find the sweet spot. You can always test the 25% position during the sub crawl process.
Edit: I remember recently reading a comment, I hunted it down. This was from the artical written by Ethan Winer concerning Acoustic Treatment and Design for Recording Studios and Listening Rooms:
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Although 703 and 705 fiberglass panels are more effective than foam of the same thickness, they are usually covered with fabric for appearance, and to prevent the glass fibers from escaping into the air. This adds to the expense and difficulty of building and installing them. (In practice, fiberglass particles are not likely to escape into the air unless the material is disturbed.)
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