Hello all! My 1st 18" PA sub simple build

Hi folks!
I've zero building experience nor tools, so will use a local speakerbox shop to cut/assemble this for me. They have a CNC router.

Target is to improve on the JBL SRX/STX subs in a budget. 
Driver im hoping to use the the P.Audio GM18-1800N, which i believe to be a budget clone of the B&C 18SW115. 

Front slot for ease and convenience. I have available to me a full DSP suite to fine tune, including FIR and IIR. Amplification can be 1200-1300watt Class D or Class H heavy. Eventually i would aim to build 3 pairs so I can do cardioid setups. 

I will use winisd for sim, then speakerbox.pro for box construction and built in Fusion360, all new to me and learning as I go. I have accounted for, hopefully correctly, 10.5L for driver displacement and another 2 for bracing, handle recesses etc. 

Please assist me on this build. Many thanks and gratitude.
I will post my work next.

Best,

Edited by Sidhu - 08 March 2026 at 1:43pm

Subbox pro. 
Woofer displacement set to 10.5L (ill see what braces addup to in Fusion and possibly adjust)

Panel list is:

Box External Dimensions Width × Height × Depth	620 × 550 × 667.2 mm
Material Thickness	18 mm
Net Internal Volume	165 L
Tuning Frequency	38 Hz
Port Area	440 cm2
Port Inlet Width × Height	85.6 × 514 mm
Port Length	298.6 mm

Edited by Sidhu - 06 March 2026 at 7:44pm

Much thanks Larry! I am not too sure what it all means in the real world, or how these sims translate. Once I build and measure ill have a better understanding of the correlation im hoping. 

My attempt was to keep port velocity and excursion in check and an SPL above 120,  This was the only permutation combination resembling common box dimensions that fit that i could figure.

Complete driver details:



Edited by Sidhu - 09 March 2026 at 4:31pm

Looking at the modelled frequency response, with - 3db points around 38hz and 68hz, it looks like you could improve the alignment to increase overall efficiency and useable bandwidth quite a bit. I'll have a play with the driver and see what I come up with.

The limited bandwidth is more likely due to the use of HPF 4th LR @30 // LPF 4LR@80 than the cabinet tuning.

You might want to see how this looks on your sims. I came up with a different alignment, with larger cab, and lower tuning. Yours appears to be tuned at ~40hz, which sacrifices a bit of low end extension, and has a knee around tuning frequency, before rolling off quickly. 

Thanks Larry,