This will be my first personal project in a long time. I was planning to get started this summer and then my son was born 5 weeks early and kind of threw things off. I’m calling this project BILC, which stands for Because It Looks Cool. This design uses four, 4” bass drivers (Dayton Audio ND105-4) per side, one 4” midrange (Peerless 830870 HDS PPB), and one 1” tweeter (Tang Band 25-1744S) so it is going to be a tower of drivers! And who doesn’t think that looks cool?
Why is it named BILC? Looking at this design rationally, There are a lot of things that tell you not to build this. While the ND105-4 can play down to 40 Hz, it still needs a decent size box (about 0.3 cu ft) to do so, which means for 4 of them we need about 1.2 cu ft. And while the four 4” drivers have almost the surface area of about a standard 8” woofer, the 8” woofer would work in about the same size box. Also, these aren’t necessarily cheap 4” woofers at a $23.29 ($93.16 per side) so looking at something like the Peerless by Tymphany 830869 8" Nomex Cone HDS Woofer at Parts Express, I could basically get the same size box, cheaper price, and most likely better distortion performance. So why did I choose to do this? BILC… and the one benefit a front firing 8” woofer can’t give you – a slim tower.
While the pictures of the drivers show the tweeter at the top, I’ve changed my mind since taking the picture and starting to plan the cabinets. I’m now going with the mid on top in the layout so it will be a MTWWWW. The cabinet external dimensions will be 44” H x 6.5” W x 14” D. This gives me about 1.53 cu ft of total internal volume available to work with before bracing, drivers, and ports. I will be taking up around 0.2 cu ft for the midrange chamber leaving about 1.3 cu ft for the bass drivers after accounting for all the bracing, port and drivers.
The bass enclosure will be tuned to 49 Hz, which produces and EBS alignment with an f3 of 42 Hz. I’ll be using a 3” PVC port to achieve this and keep port velocities under control up to about 50 watts of input power. One of the unique things about the ND105-4 is that while the xmax is pretty standard at 4 mm, the xmech 10 mm so there is still lots of excursion past the xmax limits. While driving something past xmax isn’t a goal, these will be used for bass only, and bass distortion is less audible than midrange distortion. This means there will likely be some useable output beyond xmax before they really start to become objectionable and also means you can really crank them without fear of damage. The woofers will be wired in a series parallel configuration so if the specs are accurate, even with full baffle step I should end up at a realistic 87 db @ 2.83 V. This is one additional benefit over going with something like the Peerless 8” I mentioned earlier. That driver after full baffle step would put me around 83 dB @ 2.83 V. Likewise, the Dayton RS225-4 would put me around 85 dB @ 2.83 V.