Thank you for the manual. For the D4 version, they work perfectly at 34.15Hz. So, tuning less than 45 is definitely a must! A 3" round port is not enough for these drivers. if you were to utilize round ports, (2) 6" round ports are best. You need more to optimize efficiency. Having that 3" port is so they can keep the box small for you, because consumers love compact stuff, and it keep the tuning low. The port should not control tuning any more than the compression area and when it is used jsut for tuning, it is being used wrong. it needs to be used for coupling the driver to the atmosphere, not constrain it for lower tuning......just a heads up for those interested in designing. That is my basic take on what you have going so far. Hope it helps. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif