Back chamber effect (Oris Horns)

by Don Reid, Rural Northwest Georgia, USA, Saturday, March 02, 2013, 05:58 (1752 days ago) @ Rudy81

Gentlemen, I really enjoyed your exchange regarding the back chamber covers on Oris 150s. I too have Oris 150s which I drive with an AER MD3 drivers. I have also used the Lowther PM4s with AER diaphragms. My experience might not be relevant to you because my application is different from either of yours in that I use digital crossovers with very steep rolloffs of 96dB/octave for both high pass and low pass with nominal 160Hz and 7kHz crossover points in a triamplified set-up with bullet tweeters and corner horn bass cabinets. Maximum bass extension wasn't a big concern to me with this arrangment.

What prompted me write is to mention that instead of leaving the back chamber covers on or off I settled on a third alternative which I have now been using for years. When I listened to the Oris with back covers on and then with them off I heard characteristics I liked and others I disliked with both arrangments. Just as an experiment I made two new back covers from high density wool felt 19 mm thick. I cut a circular hole in each felt cover. The holes were arbitrarily cut the same diameter as the ports in the back chamber covers which came with the horns. I really liked what I heard with the felt covers. The sound had a smoothness, control and very pleasing realistic quality that I hadn't heard before.

I assumed at that time that I would keep experimenting with other sorts of back covers, but I have been pleased enough with the sound that eight years later the same felt covers still cover the back chambers.

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