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I\u2019ve started the construction of the Concentric Three \u2013 M5<\/span> loudspeaker design. The main feature in this design is the KEF SP1632 co-axial driver unit.<\/p>\n The KEF SP1632 is an aluminium\/magnesium 5\u201d mid-range driver paired with a 1\u201d aluminium dome tweeter mounted in a wave-guide like setup. There are a lot of co-axial PA drivers available to DIY:ers, but there aren\u2019t many so called HiFi drivers available to choose from. SEAS has a couple of drivers, but in my opinion none of them come close to the features and performance of this new KEF driver.<\/p>\n Since the driver is a pure mid-range and cannot play bass, it has to be paired with a woofer or mid-woofer in a three-way design. In this first setup I chose to pair the KEF SP1632 with two SB Acoustics 5\u201d mid-woofers in a D\u00e1ppolito configuration mounted in a Dayton 28 liter M-T-M enclosure.<\/p>\n The KEF driver is mounted in a closed box with a net volume of about 2.5 liters. In the Dayton enclosure this leaves about 12 liters each for the two mid-woofers and is about optimal for these drivers. A port tuning between 38-40Hz seems feasible and will be tested.<\/p>\n This loudspeaker could be built as a stand-mount monitor like I do or as a floor-stander, perhaps paired with an active sub-woofer in the excess volume of the floor-stander.<\/p>\n One could say that this design very much look like the KEF R500, but let me point out that I don’t<\/span> intend to build any sort of clone of the KEF \u201cR\u201d loudspeaker series. I don\u2019t have a clue how the filter design used in this loudspeaker series look like besides the official specification about cross-over frequencies etc. In fact it\u2019s not interesting at all, since all I want to do is to find a truly nice co-axial driver for my loudspeaker design and in this case the KEF SP1632 was the best driver I could find for my design needs.<\/p>\n I will base my design on the measurements I\u2019ve done on the SP1632 and that alone together with my own preferences will decide the cross-over topology cross-over frequencies and so on. As a DIY:er I have the advantage not having to consider making design choices based on reducing cost for e.g. the filter design. Consequently I will use the quality and the amount of cross-over components needed for the intended design.<\/p>\n I don\u2019t know if KEF has done such design choices with its R series designs, but for a commercial loudspeaker manufacturer like KEF they always have to weigh in production cost and often in this price range at the expense of a non-optimal performance.<\/p>\n The details of the driver unit measurements can be found here:<\/p>\n