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Need some help with my B&C 18SW100 design
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<blockquote data-quote="Max Warasila" data-source="post: 211705" data-attributes="member: 3845"><p>Hi! Here's some comments/feedback as someone who's built a double 18" subwoofer long these lines.</p><ol> <li data-xf-list-type="ol"><strong>Overall Box Tuning:</strong> Your "target" volume and tuning for the 18SW100 should probably be ~33Hz and ~200L (7 cu.ft.). These are B&C's numbers and they simulate well. I'd tune a little higher myself.<ol> <li data-xf-list-type="ol">You are indeed correct to model it as each chamber individually.</li> <li data-xf-list-type="ol">22.5" x 45" is a perfectly acceptable dimension to restrict yourself to, but you're going to need to make it <em>at least </em>30" deep, probably more like 32" or more.</li> <li data-xf-list-type="ol">Interestingly, you have created a cabinet in BBP6 that is the correct internal volume before the port is calculated and drivers are added. This is a weakness of BBP6, as the port in simulation is nearly always significantly longer than you need. If you can put in a correction factor, K, then you should put in about 1.7. Somewhere on this forum is the figure I'm using for this, but I can't ever find it, so I'm referencing my printout. I wish WinISD did this, without glitching and refusing the input, but it's free so oh well. The reduced internal volume in the sim is causing most of the garbage you're seeing in your freq. response.</li> </ol></li> <li data-xf-list-type="ol"><strong>Port Tuning: </strong>Your port should be even bigger than this.<ol> <li data-xf-list-type="ol">Given a port a little bigger than this, several of us have arrived at about 10" or so for our port depth. Personally, I do mine a little bit longer, but it's all personal preference and prototyping.</li> <li data-xf-list-type="ol">Again, port length in simulation is never equivalent to the real world. It's always wayyyy longer than it should be, especially in BT218 like designs where boundaries play into the port as much as they do.</li> <li data-xf-list-type="ol">Triangular ports are kinda garbage. Just saying.</li> </ol></li> <li data-xf-list-type="ol"><strong>Cone Excursion:</strong> Anything besides a K20 or bridged PL9.0PFC can't break the large format B&C subwoofer drivers.<ol> <li data-xf-list-type="ol">Your cone excursion is representative of the real life scenario. I assume that you are simulating this with the quoted Xmax on the B&C spec sheet. Forget it. Use Xvar, and remember that you have 28.5mm of excursion before damage. That should calm your fears.</li> </ol></li> </ol><p>Alright, I don't think I've given too many secrets away that you couldn't have figured out by spending an excess of money on plywood for a prototype and then kicking yourself.</p></blockquote><p></p>
[QUOTE="Max Warasila, post: 211705, member: 3845"] Hi! Here's some comments/feedback as someone who's built a double 18" subwoofer long these lines. [LIST=1] [*][B]Overall Box Tuning:[/B] Your "target" volume and tuning for the 18SW100 should probably be ~33Hz and ~200L (7 cu.ft.). These are B&C's numbers and they simulate well. I'd tune a little higher myself. [LIST=1] [*]You are indeed correct to model it as each chamber individually. [*]22.5" x 45" is a perfectly acceptable dimension to restrict yourself to, but you're going to need to make it [I]at least [/I]30" deep, probably more like 32" or more. [*]Interestingly, you have created a cabinet in BBP6 that is the correct internal volume before the port is calculated and drivers are added. This is a weakness of BBP6, as the port in simulation is nearly always significantly longer than you need. If you can put in a correction factor, K, then you should put in about 1.7. Somewhere on this forum is the figure I'm using for this, but I can't ever find it, so I'm referencing my printout. I wish WinISD did this, without glitching and refusing the input, but it's free so oh well. The reduced internal volume in the sim is causing most of the garbage you're seeing in your freq. response. [/LIST] [*][B]Port Tuning: [/B]Your port should be even bigger than this. [LIST=1] [*]Given a port a little bigger than this, several of us have arrived at about 10" or so for our port depth. Personally, I do mine a little bit longer, but it's all personal preference and prototyping. [*]Again, port length in simulation is never equivalent to the real world. It's always wayyyy longer than it should be, especially in BT218 like designs where boundaries play into the port as much as they do. [*]Triangular ports are kinda garbage. Just saying. [/LIST] [*][B]Cone Excursion:[/B] Anything besides a K20 or bridged PL9.0PFC can't break the large format B&C subwoofer drivers. [LIST=1] [*]Your cone excursion is representative of the real life scenario. I assume that you are simulating this with the quoted Xmax on the B&C spec sheet. Forget it. Use Xvar, and remember that you have 28.5mm of excursion before damage. That should calm your fears. [/LIST] [/LIST] Alright, I don't think I've given too many secrets away that you couldn't have figured out by spending an excess of money on plywood for a prototype and then kicking yourself. [/QUOTE]
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