![]() ![]() Don't even consider using anything that is purely or even largely synthetic. It is more reflective than it is absorptive. The acoustic quality of these compositions varies, primarily as a function of the percentage of real wool in the felt and its density. It has many uses that I won't go into, but it is used in combination with various synthetic materials to produce the numerous types available. This is, of course, the naturally derived felt taken from sheep. The best that I've found-and I believe that there is consensus on this-is real wool felt. Quantifying its effectiveness has not been so well documented, and there is a wide range of felt compositions. ![]() ![]() Wool has been used for years for diffraction control. Obstructions on the baffle (as in a stepped baffle).Adjacent driver size and diaphragm shape.Baffle edge geometry (square, roundover, chamfer, and so on).The impact of diffraction is highly dependent on several factors: The directivity of the larger drivers also minimizes the influence of diffraction. The diffraction that affects midranges and woofers is - for the most part – not controllable due to the frequencies concerned. Why do I say tweeter? Because diffraction is primarily a tweeter concern. I prefer to use an absorptive material (felt) placed on the baffle after offsetting the tweeter. In combination, offsets and roundovers are useful. The roundover must also have a rather large radius to be most effective. Although effective, this adds construction complexity. You can mount drivers with an offset from the centerline (useful on its own), but this only changes the distribution in the time and frequency domains it doesn't actually reduce the amount of energy re-radiated.Īnother way is to round over the baffle edge. More than one way exists to deal with diffraction. You would somehow like to stop the diffraction from any obstructions, but how? The diffraction can't be controlled by any kind of box placement or room treatment. Box placement and room treatment are used to control that to a degree. You're familiar with this latter aspect of reflections. It arrives at the listener position, altering the perception of the sound, since its arrival is close enough in time that you perceive it as being part of the main sound wave.ĭelays that are longer (such as reflections from walls) are perceived differently and are not confused with direct sound. This interference is delayed in time from the main sound wave and is a function of the distance to the diffracting obstruction (such as the baffle edge). This causes interference with the main sound wave that is traveling outward toward the listener. The results of attempts at diffraction control were a bit surprising.Ī sound wave will diffract when it encounters one of the obstructions mentioned. These latter have been of more interest to me recently as I now prefer a baffle that offsets the drivers (a "stepped" baffle) to attain a better phase relationship between drivers in order to improve the crossover design. Obstructions are primarily other drivers (midranges or woofers) and baffle edges and protrusions. This article shows examples of diffraction and a commonly used, yet inexpensive, method to control it.Ĭabinet edge diffraction, which is unavoidable, is the result of any obstruction or cabinet boundary (edge) that changes how the sound wave moves across the surface of the baffle. Past articles in Speaker Builder and audioXpress have dealt with the issue. Judicious use of the right kind of felt is all that is necessary. There are many differing positions on what to do about it - if anything at all - but diffraction can be largely controlled. You'll probably find a thread on it anytime you go to one of the major boards. 36, Number 6, June 2005Ĭabinet edge diffraction is a hot topic on Internet message boards. Originally published in audioXpress, Vol. This article shows an easy way to control baffle diffraction using a stepped baffle example.ĭiffraction Doesn't Have to be a Problem by David L.
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