For those of you who don't know, diffraction is the reflection of waveforms shorter in length than the width of your speaker cabinets or those produced by your tweeters. This is not something owners of Gallo speakers, for example, or any baffleless speaker to include planars, need be concerned with. It is for the owners of box speakers with right or near right angles. Price is per pair.
Those green and red circles in the illustration by Al Ludwig are not a part of any recording that you own and are additive in your frequency and time domains. They are late arriving, out of time and phase. Some speaker manufacturers, not very many, compensate for a rise in the frequency domain caused by diffracted waveforms summing in by reducing the tweeters output just above of the crossover, but the time and phase anomaly persists to the detriment of the clarity and dimensionality inherent in your finest recordings.
I use natural wool felt and individually fit to the dimensions of most any speaker baffle and offer with a 30 day trial period. You should give it a try. You just might find that it is the best value audio investment you've ever made.
Robt E Greene, Technical Editor of TAS, honored my product with a Golden Ear Award in '08. His comments and those of others can be seen on the back page at my website above (live link).
Thank you and see you in the forums.
