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http://www.geocities.com/kreskovs/John1.html
http://www.audiocircle.com/index.php?page=2
http://www.acoustic-reality.com/ar-sxo.htm
http://soteria.com/brown/docs/speaker.htm
http://www.metrum-acoustics.nl/eng.metrum-acoustics.nl/index.html

http://www.speakerbuilder.net/web_files/Articles/perkinsxo.htm
http://madisound.com/cgi-bin/discuss.cgi
http://216.239.39.104/translate_c?hl=en&u=http://www.es-audio.de/
http://esl.hifi.nl/index.htm
http://www.goodwinshighend.com/roomdesi.htm
http://www.fortunecity.com/marina/pontoon/3/audio/elliptic/elliptic.html
http://www.studio107.nl/
http://www.ambiophonics.org/
http://www.amplimo.nl/
http://www.audiogrid.com/arsl.html

http://www.audiocostruzioni.com/i_e/links/links-mondiale-diy/links-mondiale-diy.htm