Posted by Jose [ 41.213.63.246 ] on March 02, 2009 at 15:24:02:

I have been experimenting with reducing diffraction in my line arrays based on some enthusiasm on the web for this with commercially available felt surrounds for tweeters. I have used strips of felt with two thickness, 9.5mm (3/8") and 3.2mm. I used various combinations of long 40mm wide strips on either side of the Fountek ribbons and along the outer aspect of the woofers. I have a two way array with 10 Eton 5.5" woofers and 9 Fountek CDM 2.0 ribbons tweeters.
I then did measurements using my Tact 2.2XP of the frequency response. I also looked at the impulse responses over time but these did not show major differences.
The major effect of reducing absorption by using felt is to induce a dip in the frequency response between 2-4 KHz of between 1.5 and 4 dB depending on the thickness and number of strips. The strip along the outside of the woofers did nothing audibly or wrt the measurements. The main effect seems to be on the tweeters.
My freq response at the listening position is pretty flat at the 2.45 KHz crossover thus the effect of the thick felt on either side of the ribbons was to remove some life and sparkle from the music. The thinner felt did not sound much better but the dip was was less pronounced. I have settled on a single strip of the 3/8" felt between the woofer row and tweeters. This causes a shallow dip of about 1.4dB between 2 and 4 kHz which is quite pleasant. The sound does seem a bit more focussed with more precise imaging.
Based on my experiments however I would avoid excessive use of felt around tweeters unless the speakers and crossovers have a rise in the frequency response in this range.

I would be interested to know if any of you have tried to reduce diffraction in your arrays and your findings.

Regards

Jose

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