Hi All, This will be my first sub build. I am doing the age old trick of trying to build something for next to nothing and so far have the following items. Gemini GXA 750 power amp. I bought this second hand for £50.00. It claims to do 750W RMS into 4 ohms in bridged mode. Earthquake Tremor X 154. I got this for £75.00 new on ebay, they normally go for quite a lot more. I chose this as it seemed good value for money and the Americans seem to love them. I am having trouble trying to work out what size box would be best. The sub spec is as follows - 15" Single 4 ohm Tremor-X Series Subwoofer Power Handling: Peak: 1500 watts, 750 watts RMS Impedance: Single 4 ohm Sensitivity: 86.3 dB Mounting depth: 6-3/8" Free Air Resonance (Fo): 28.815 Hz Electrical "Q" (Qes): 0.890 Mechanical "Q" (Qms): 2.657 Total Speaker "Q" (Qts): 0.667 Effective Piston Area (Sd): 105.774 sq. in. REVC: 3.700 ohm BL: 15.910 TM VAS: 4.90 cubic feet One way linear excursion 30.48mm The manual states that a sealed box should be H 17 x W 17 x D 15 (Dimensions shown are external Dimensions using 3/4" MDF) I make this 1.877ft3 / 53.151 Unibox gives me 0.608 ft3 / 17.2l (90db 20Hz at 750w) WinISD gives me 35.02l (93.5db 20Hz) for a sealed box. Out of curiosity I wanted to see how big a ported box would be in WinISD. The results are 22.61l tuned to 18.21Hz. This confuses me further as I thought that a ported box was always bigger than a sealed (and this is making me doubt my accuracy)? Would someone with a bit more experience than me mind looking this over. I think I am doing everything correct although I am still getting to grips with the Thiele/Small parameters so could be putting a decimal point in the wrong place. I would really appreciate your help. The only space I have in my lounge is in the back of the room so originally I considered a down firing sub but from what I've read this doesn't seem like a good idea especially being such a cheap model. I am now considering a triangular box in the corner. Size isn't a massive issue but I would like to keep it as small as possible. Thanks for your help. I have a young family so I will be squeezing this in when I can. Pictures to follow.