2023 SBA GSub Alternative

Design Goals

A less costly (the SBA driver is more available and about $200 AUD less each than PD186 in AUS/NZ far as I can tell), a tad better performing alternative 2x18” enclosure to the GSub design on this site. 

Also, as CNC and CAD is more accessible today in 2023 than in 2001 (GSUB) - this design will include full 360 CAD model available to download in all standard 3D file types, in addition to 2D CNC layout nesting for your local CNC shop. 

Suitable for entry level sound systems looking for a cheap but high quality 2x18” design with stacks of low end that doesn’t require large amounts of amplifier power and when truck pack sizing is not an issue.

Should anyone wish to build I'd be happy to provide some build advice along the way and come and perform some calibrated measurements of frequency response, maximum real world SPL, waterfall and other time domain measurements, and impedance via REW + DATS.

Rough Cost Guide: 

3 x 18mm B/BB Birch Plywood $550 AUD

2 x SBaudience ROSSO-18SW650 = $700 AUD

1 x Neutrik ST-NL4MPRXX = $7 AUD

1 x Titebond Ultimate 3 Wood Glue 1L = $36 AUD

16 x M6 threaded inserts/furniture nuts = $17.60 AUD

16 x M6 40mm bolts = $12.80 AUD

1 x Bag of R2.5 polyfil = $100 AUD

CNC machining time = Depends on your shop but I'd guess this would be between $600 - 1200 AUD

1 x paint, varnish, oil, etc. to builders choice = ..........

Total Cost Guide = $2023.4 AUD

I'd say you could absolutely do it for less if you were frugally minded - also good to keep in mind going with four 'adequate driver' 2x18's for a system is more displacement/output at maybe similar cost than going for half as many, very expensive big BL/XMAX neo jobbies.

As these are 'relatively low wattage' per box before XMAX limit you may well get away with running two enclosures per side off one of your select fav Chinese 1RU Class D amps at a 2ohm load per side and still have some headroom to spare. for those sweet sweet transients, keeping your amp rack costs low and allowing you to live the dream whilst still making rent.

Fusion model URL: https://a360.co/3PeIrfL

Construction should be easy peasy - all butt joints ready for screw/glue or glue/clamp action. I would recommend Titebond Ultimate 3 for any outdoor use as it's waterproof, not to mention easy to work with.

Drivers should be bolted into the 36mm double thickness baffle using long M6 threaded inserts/furniture nuts screwed into the rear of the baffle before full assembly and glue-up.

If you have a router handy, and either a large radius chamfer or round-over bit (10-12mm for example) it might be worth running it over the long edges (540mm) of the inside and outside of the main port walls, unlikely to give much of an audible difference but it will look quite nice. I would also recommend using a large radius round over bit for all external enclosure edges to assist with ply peel/delaminate over time - especially if you will not be painting the enclosure.

Grilles should be made of 2-4mm powdered coated stainless steel and fixed to the baffle grille strip via builders choice.

SpeakOn connector plug rebate size is for a Neutrik ST-NL4MPRXX

Drivers: 2 x SBAudience ROSSO-18SW650

http://www.sbaudience.com/index.php/products/subwoofers/rosso-18sw650/

Material - 18mm Birch Plywood

Limiting factor in design: Linear driver XMAX (Same as GSub tbf just with more output before XMAX)

Other notes: My personal experience with using GSubs is that when driven hard both port chuffing and power compression is an issue. Power compression is harder to get around without cooling systems, but the chuffing caused by air velocity in the vent is reduced in this design compared with the GSub by using a slightly larger port volume/dimensions so when EQ’ing at port tuning frequency to get that extra extension and output we are not exacerbating the chuffing on musical peaks, therefore reducing the levels of acoustic distortion and increasing cleaner output.

Comparison to GSub via WINISD:

Max SPL at XMAX for both - Purple is the SBA ROSSO, dark green is PD.186. 

Filters: 24db Butterworth HP at 29hz

Simulated response (with no EQ at port tuning frequency) = 32hz to 200hz usable frequency range (-6db) 

Simulated response with PEQ at tuning = -3db at 33hz

XMAX limit no PEQ at tuning:


XMAX with PEQ at tuning:


Simulated output with PEQ at tuning:


Vent velocity at maximum output with PEQ at tuning (keeping in mind WinISD seems to exaggerate this parameter):

Enclosure Gross volume = 436.10400 litres

Minus Drivers = 16.16 L

Minus Bracing = 4.66 L +2.65 L + .8 L = 8.11 L

Minus Handles = 13.65 L

(Port/vent volume already excluded)

Total = 37.92 L

Enclosure Net volume = 398.19 L




18mm Chamfer on Port Edge Suggestion (top down view)

Some drawings:

CNC Nesting Layout (2D DXF) here:  

https://drive.google.com/file/d/1_3KpMoZJq6rU8mL6Cme55Hp-BBpJs1Ci/view?usp=sharing

Looks like there may even be an extra 1/2 remaining on the last sheet you could use to make a set of dolly boards to lug your amps/subbies around with 

All pieces are nested with 15mm between pieces and 15mm from sheet edge on 2400mm x 1200mm.

And above all else, remember to have some fun, make some saw dust, and play it loud!