| Designer | Type | Build | Size |
|---|---|---|---|
| SB Acoustics | 3-way, 12" woofer, bass reflex (front slot port), sealed midrange chamber | Easy with SB's walnut cabinet and assembled crossover; advanced if you build the cabinet | 720 mm tall |
Short answer: the Gema is SB Acoustics' big, retro-styled 3-way: a 12" woofer, a 4" paper-cone midrange in its own sealed chamber and a 1" soft-dome tweeter, in a 720 mm tall birch-ply cabinet with a slot port across the front. It's meant to sit on a low stand or plinth rather than the floor. With SB's ready-made walnut-veneer cabinet and an assembled crossover, it's a screwdriver job, just a heavy one. Building the cabinet yourself is a serious woodworking project.
A quick note before we start: we haven't built or listened to the Gema. This is an overview of what's in the kit and what's involved, not a review. Everything about how it's designed and how it performs on paper comes from SB Acoustics' own page, manual and drawings.
What SB says about it
SB calls the Gema an homage to the big-cabinet, big-woofer speakers of the 1970s. The design notes SB highlights:
- A 12" SB34NRXL75-8 woofer in a large, well-braced cabinet, with a big slot port opening at the front, tuned to 28 Hz.
- A dedicated 4" midrange, the paper-cone SB12MNRX2-25-4, covering 680 Hz to 3 kHz in its own sealed enclosure. SB picked it for good efficiency, low moving mass and linearity.
- A 1" SB26STAC soft-dome tweeter with a die-cast aluminium faceplate, an optimised rear chamber and a full copper cap.
- 18 mm plywood: SB "highly recommends" building it from high-quality 18 mm ply.
SB's placement starting point: 2.5 to 3 m between the speakers, generous clearance from side and rear walls, raised about 25 cm on a stand or plinth, tilted back about 6° with a slight toe-in. The pair is mirror-imaged, with the tweeter and midrange intended to sit on the outside.
SB's published specs
| Gema | |
|---|---|
| Tweeter | 1" SB26STAC-C000-4 soft dome |
| Midrange | 4" SB12MNRX2-25-4 paper cone, sealed 12 L chamber |
| Woofer | 12" SB34NRXL75-8 |
| Crossover frequencies | 680 Hz and 3,000 Hz |
| Frequency range | 36 Hz to 24 kHz |
| Sensitivity (2.83 V/1 m) | 87 dB |
| Nominal impedance | 6 Ω |
| Max SPL | 108 dB |
| Recommended amplifier | 50 to 200 W |
| Enclosure | Bass reflex, 61 L for the woofer, front slot port tuned to 28 Hz |
| Cabinet | 18 mm birch plywood, 720 x 430 x 360 mm (H x W x D) |
| Weight | 36.2 kg (see note) |
All figures are SB Acoustics' own. Two don't line up: the manual prints the port tuning as "8 Hz", which looks like a typo for the website's 28 Hz. And the manual calls 36.2 kg the pair weight, which seems light next to the smaller Rima's 21.8 kg per speaker. Plan for a heavy box either way.
Gema or Rima?
The Rima is a newer, smaller sibling with the same layout and tweeter: a 10" woofer in a 610 x 363 x 305 mm cabinet, rated at 84 dB and 8 Ω (SB recommends 100 to 200 W). The Gema is the bigger, more sensitive of the two and wants a bigger room.
The parts
Each speaker uses one of each driver. Each link shows today's price:
| Part | For a pair |
|---|---|
| SB34NRXL75-8 12" woofer | 2 |
| SB12MNRX2-25-4 4" midrange | 2 |
| SB26STAC-C000-4 1" tweeter | 2 |
Then add:
- Crossovers: an assembled pair with wiring, Gema assembled crossover pair
- Cabinets: SB's ready-made walnut-veneer pair in 18 mm birch ply, Gema cabinet pair. Or build your own from SB's drawings.
Or get the full kit, with every part for a pair in one go: SB Acoustics Gema speaker kit.
What's involved
With SB's ready-made cabinets and crossovers
The Gema manual has no step-by-step section: you work from its exploded view, parts list, damping pattern and schematic.
- Damping: SB's cutting pattern gives 19 pieces of 20 mm Dacron per speaker. Most of them line the midrange chamber, with a few on the rear and floor of the bass section.
- Crossover: screw it into the cabinet (nine 4 x 16 mm wood screws) and wire it to the stainless terminal panel and the drivers.
- Drivers: they fit with hex socket screws into threaded inserts, M5 for the woofer and M4 for the midrange and tweeter.
- Left and right: the cabinets are mirror images, so check which is which before you start.
Get a second pair of hands for lifting and for setting the woofers in.
Building the cabinet yourself
SB's nine-page cabinet drawing covers every board. This is a big job:
- A double-thickness baffle around the woofer, with every driver recessed flush.
- A separate sealed midrange chamber with its own divider, plus internal braces in the bass section.
- Mitred outer edges, a full-width front slot port and mirrored left and right baffles.
You'll want a router, plenty of clamps and room to work, then a veneer or other finish. Keep the internal volumes (61 L and 12 L) and the port exactly as drawn. Building the cabinet covers the techniques.
Building the crossover yourself
Per SB's schematic, the Gema crossover is 17 parts: three resistors, seven capacitors and seven inductors, including a 20 mH inductor and a 470 µF capacitor in the woofer section. It's a real step up from a 2-way board. Passive crossovers explained covers layout and parts.
Who it suits
- Good fit: a large room and someone who wants a big, classic-looking 3-way with a 12" woofer. 87 dB and a 6-ohm load, with SB recommending 50 to 200 W, puts it within reach of plenty of decent amps.
- Think about: size and weight. Each cabinet is 720 x 430 x 360 mm before the stand, and SB's placement advice needs space around them. If that's too much, look at the Rima. Building the cabinet yourself is advanced woodwork.
SB's documents
- Gema user manual (specs, drawing, exploded view and parts list, damping pattern, crossover schematic)
- Gema cabinet drawing
- SB's Gema page