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My nearly-4-year 4-way speaker project has reached a plateau. A little Tassie GTG today made me reflect that it's all been worth (some of) the struggle. The design and build thread is: The most recent photo: But this is a hobby, and this is SNA. Things must proceed. The words "so, it's basically the same as last time" really touched a nerve today (just kidding, you-know-who 😉). This must never happen again! I've played a few low tones and walked around the space - 10 x 6 m, with 3.2 m concrete ceiling, and noticed nulls, halfway along room, at the sides. Not huge, but a bit of a sag around 50-55 Hz. It's a passive system. No DSP. The design aimed to maximize bass extension by doing what few seem to do: use a large vented box. These are 240 litres, with twin 102mm diameter vents. So the new intention is to build 2 subs (stereo of course) to augment the bass, and place them in the "null" areas. This can hopefully coincide with the same distance from the listening position, so there are no time-delay issues. The best option would seem to be in the joint of wall/ceiling, behind the listening position, a bit more than half-way back into the room. How to get them there was an unresolved discussion today. They will be around 320 litres internally, and likely approach 100 kg each; securing them is the easy part, getting them there is another thing. A "sub-crawl" would necessitate a reversal of gravity. I initially thought the best driver would be the same as my 15" SBA woofers, but I was recently tempted by some gorgeous Acoustic Elegance TD15H drivers, so decided to model them in WinISD. It was all settled for a couple of days, then I simmed the SBA's more recent "long-throw" version of my woofer. It's a bit confusing, as the TS parameters are very similar, including X-max. The 3 drivers in this graph are: SB42FHC75-6 black (mine) SB42FHCL75-6 red (new long-throw) Acoustic Elegance TD15H blue These all have LP (hi-cut) filters applied. The black one is the same as my 4-way woofer, cutting off at 100 Hz, as with its present passive 4th-order filter. The blue trace, the AE driver, was very appealing, but both are completely blitzed by the (red) FHCL, so I've ordered 2 of these. Also, the 3" voice coil and greater power handling* (*Edit: wrong - see later posts) appealed. The red and blue traces have a 60 Hz 2nd order filter applied. Of course, this can be adjusted in real life to match the 4-ways and the room. The box sizes are 300 to 320 litres, all vented. So I can't be saved from the spend, but maybe your comments can help me with the next stage - designing the boxes for the wall-ceiling corners? As a cube, internally they could be around 700mm each way, but I anticipate angled baffles, from 45 degrees to whatever into the room. Looks like they'll need to be about 1.6m "wide".