First sub design - Help?

So, I'm starting to look at building a subwoofer to place behind the couch for WAF reasons. I have a nice little area behind there and am thinking of building a 3.5-4cf box (24X36*8)ish.

Now I have been reading a lot and am curious if this WinISD model looks ok...
Tried a couple woofers and landed on the Dayton DCS385 - 15".

- group delay seems in check (hz*ms is always under 400)
- cone excursion stays under xmax
- it's behind the couch so I used 0.5m distance and this keeps the SPL higher than I would probably ever need

Couple questions
- I "voluntarily" crippled the extension a bit (f3 is about the max output) is this okay? puts the -3 SPL at 23hz this way, but less loud. I live in a duplex, well insulated I never hear the neighbors but I don't want to exagerate lol.

- How exactly does the system input power work? I kept it low (64W) and max amplifier apparant load power is at 90 VA?? what does this equate to?

Thanks for any help


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FWIW, normally in an attached housing or similar app, 'we' want a fairly low tuning with a high F3 [slow roll off], ideally at around 0.5 - 0.577 Qt. This gives a 'taste' of low bass without being obnoxious with F3 around where most of your music's strong mid-bass is rolling off [normally 50-60 Hz] and if a bit lower F3 can be tolerated, then just boost it since it's so close there's sufficient dynamic headroom assuming the amp is rated high enough.

Haven't used WinISD since shortly after the 0.7 program came out, so long gone from memory beyond it was a bunch more accurate in some ways with lots of useful new features, some WRT power handling. Anyway, most of us use Hornresp nowadays, which is much better overall.

90 VA @ 1.0 power factor = 90 W, so with no PF, no way to know what it actually is: How to convert volt-amps (VA) to watts (W)

Thanks for the response!

- What do you mean by attached housing? you mean for nearfield use? I thought people generally aim for .707? although I have often read that lower is often smoother and more likeable.

- When aiming for a specific Q... is is the rolloff we are after mainly? If I have a Q of .7 but play around with PEQ to have the rolloff more gradual than 0.7, would I gain the advantages of a lower Q ? any tradeoffs?

- Is it okay to cripple the 40-80hz response to allow for a smoother roll-off (and thus simulating a lower Q ?


Either way I think a 15inch for my application is too big, looking at the RSS315HF-4 which models better in a 3.5 cf enclosure, thanks!