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Gold Member Username: ExerciseguyBrooklyn, NY United States Post Number: 2758 Registered: Oct-04 | http://www.skiingninja.com/Diffraction-Be-Gone-p/dbg.htm |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 13713 Registered: May-04 | . Felt has been used for several decades (since the AR-9's in the late '70's) as an absorptive material to minimize diffraction effects in the high (and sometimes lower) frequencies. Spica made extensive use of felt mats on their front baffle to control the directivity of their drivers. There was a bit more to it than this simple tweak can affect when Bau used the felt across the entire front baffle of a TC50 or Angelus but the idea is mostly the same. Do keep in mind you are working with a wide dispersion driver in most cases - a dome type tweeter - that would normally radiate to the sides of the speakers and therefore into the room. These off axis wavefronts can have substantial additions to the in room power response of the speaker and by using the felt rings you are now minimizing these additions by minimizing the dispersion pattern. This will to some extent change the perceived frequency balance of your speakers since your ear hears all of the information provided to it and those early reflections do provide a gentle boost to the high frequencies in most rooms. Or not so gentle in some rooms that tend toward overbearing high frequency content. The off axis response can also smear time elements that provide accurate spatial clues if the room is not set up to work with the dispersion patterns of the drivers. So give a little and take a little here with this tweak. Some designers also include what is known as "baffle step compenstaion" to account for out-in-the-room placement of their speakers. The felt rings are likely to not work well with this sort of design since frequency balance compensation has already been designed into the speaker. By using the rings you will slightly minimize or alter the need for and placement of room treatments at the early (first) reflection points. You will also alter the frequency balance you hear in the room and by narrowing the dispersion pattern of the tweeter you will also narrow the sweet spot for good imaging. If you value being able to move your head and not have the image shift radically to one side, then these rings probably won't work in your system. It's a trade off you'll have to try in order to determine its value. An absorptive panel or tube trap placed to the side of the speakers might be the better solution for such a system. For that simply go down to the fabric store and buy a few yards of thick poly-batting (used to stuff pillows or comforters) and roll it into a tube to place alongside your speakers. You might ask if the shop has any spare cardboard tubes about 2" in diameter to place at the center of your roll to provide a bit more stiffness and ability to stand upright. You could also find a one to two inch thick foam panel at the fabric store (normally used for cushions) which would work very much like the felt at all but the lowest frequencies and this could be a start on your experimentation. This is easy to work with and you could experiment with various shapes of center cut out (a shape roughly similar to a boat hull has been a favorite among the DIY'ers). Various sorts of rings have been sold in the after market over the years and a simple circular center hole has been the most common though various shapes provide various results. You might also experiment first with a few adhesive backed felt pads you can pick up at the hardware store or craft store. Buy the thickest pad you can find in a 4" X 4" piece and cut your own center hole. Try two stacked together if you think the first has some benefits. If you find this a suitable tweak for your system, you can usually buy bulk felt from any shop that cuts gaskets or build up your own from the felt you find at the fabric store. Or pop for this guy's products. . |