In order to verify your numbers. I will need the T/S parameter for your driver.
Please note that variances in size must be significant to make a measurable impact on performance. Make sure in a sealed speaker design that you account for adequate bracing and acoustic dampening. If your interested in constructing the best enclosure possible. Of course a speaker can be perfectly acceptable with little bracing or dampening, but the more you have the closer to reference level you get. So go as extreme as you can.
Scan Speak 18W/8531
Fs 28.50 Hz
Re 5.80 Ohm
Sd 150.0 cm2
Vas 59.0 l
Xmax peak 6.50 mm
(Le) 0.35 mH
(Le2) 0.00 mH
(Re2) 0.00 Ohm
Nominal Power 70.0 W
I definitely plan to add damping material to the walls as well as some internal bracing. I'll be using a PE 1.0 cu ft (about 28l) cabinet, and filling the base with sand to meet the Unibox numbers. I want to use the ideal Qts of 0.707 as unibox suggests, if that number is indeed ideal for a sealed design.
I've modeled this an there is no need to add sand. Bracing and dampening will more than take care of the differences(which are negligible). You'll want to dampen the sides of the box with the following if you can.
1/4" thick peel-n-seal apply with a heat gun.(constraint layer)
4" Thick rock wool or fiberglass on the rear wall. 2" thick on the other walls. (dampening layer)
Get some 1"x 2" oak and put in braces every 4" or so on each axis if you can.(bracing)
Make sure to use some gasket sealer tape in between your mid-range driver and the cabinet unless you want to hear screws with your music.
The above image is a comparison between your P-E box and the unibox recommendation. It clear there is no audible difference between the two there for sand isn't necessary. An audible difference is where a value of 1db or greater occurs. Since you will be adding some dampening and bracing your volume will approach the unibox model anyway further making sand unnecessary.
Thanks so much! I figured the bracing would absorb quite a bit of space, good point. I planned to use the asphalt damping mats from PE, along with various forms of OC703 in the cab. I've never seen or used peel n seal, I have to check that out!
Hopefully the parts will all be here next week, and I can route the baffles, and connect everything for a nice holiday gift to myself!