SB23MFCL45 Stereo sub project

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Hi all,

I’ve decided to post a thread of my current project in case anyone is curious about this driver and, well, to hold myself to finishing what I started. The inspiration was to offload the low end so my full range towers (Alpair 10p pensils) can do their best on midrange. I have a ported sub from when I was younger that provided a proof of concept but really didn’t have the vibe I was looking for. I wanted to keep things small with deep extension so I opted for sealed with a small driver and a healthy amount of excursion. Since I thought I may end up crossing higher than normal sub duty, and to help make up for the smaller cone area, I decided to build a pair.

After a busy weekend I finished fabrication on the first of the pair today and got a listen in. No measurements yet but the sound is good enough that I’m excited to get the second up and running. One was probably enough for the spls I need (modest) but crossed at 110 Hz I do get a sense of localization in the bass so I think a stereo pair will be nice.

I went a bit bigger than Bessel alignment to soften the q and leave some headroom on excursion. The box is 12x15x15” of 18mm Baltic birch. It should be about 1 ft3 internally. It’s currently stuffed with some polyester fluff I had in the supply closet.

Pictures in a subsequent post.
A couple pictures in the living room. The pads are some packing foam I found to keep from scratching the floor until rubber feet are added.


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Somehow I managed to give myself more trouble building the second box but by the power of the orbital sander they both look kinda nice. No clue how to properly finish them though. If the towers are any indication this project might be done :D

Doubling the cone area definitely adds authority to the low end.


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So my laptop is crashing when I open REW due to a graphics problem so I don't have access to proper measurements. Despite this I did some "pen and paper" adjustments last night:

  • Padded the sub signal down 8db to account for the differences in amp/speaker sensitivities
  • Made a -2db shelf above 400 hz for a rough baffle step compensation based on a calculator I found on the web
  • Added some gentle low frequency boosting based on simulated roll off with consideration to typical room gain (assuming a 2db per octave rise below 200hz)

I also added some gain back in above 10khz to boost the "air" a little after the BSC. It sounds nice, no clue how it measures but overall it was worh the time and $$.

I just realized today that I never followed up with a sweep. Attached is one sub driven pretty close to clipping. The mic is a bit farther than a meter because it's currently set at tweeter height for another project. It's funny, the response goes so high that I thought I'd forgotten to mute the mid/tweeter that I had been measuring. It's on the floor now, tucked about 6" from a rear wall and 3 feet from a side wall. I've got a very subtle 4bd boost at 3Hz (Q of .5). Pretty satisfying for such a small driver but I'm glad I have two ;)
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