Gema — Classic 3-Way Loudspeaker
A large three-way in the spirit of the 1970s: a 12-inch Norex woofer, a sealed dedicated midrange, a soft dome tweeter, and a crossover by Danesian Audio.
A three-way in the 1970s idiom. Per cabinet: a 12″ Norex paper woofer, a 4″ Norex midrange in its own sealed chamber and a 25.4 mm textile dome, over a front slot port tuned to 28 Hz.
About the Gema
The Gema is Danesian Audio’s three-way tribute to the big floorstanders of the 1970s, when a generous enclosure and a large bass driver were what a serious speaker looked like — classic proportions, current drivers. The enclosure is that size for one reason: it gives a 12″ woofer the volume it needs to go deep and stay controlled.
Per cabinet: a 12″ SB34NRXL75-8 woofer, a 4″ SB12MNRX2-25-4 midrange and a 25.4 mm SB26STAC-C000-4 textile dome. Cabinets are walnut veneer matt, supplied without grilles — the Gema was drawn to be looked at.
The baffle is laid out asymmetrically, the three drivers offset to one side, and the cabinet is finished in walnut veneer matt. It is a period shape drawn to sit in a modern room, which is more or less what the cabinets it is quoting were doing in 1975.
Key features
- One 12 inch SB34NRXL75-8 Norex paper woofer per cabinet, on a 75.6 mm voice coil
- One dedicated 4 inch SB12MNRX2-25-4 Norex midrange, in its own sealed chamber
- One 25.4 mm SB26STAC-C000-4 textile dome with a die-cast aluminium faceplate and a full copper cap
- Front-facing slot port, tuned to 28 Hz
- Crossover designed by Danesian Audio and supplied as a set alongside the cabinets
- Walnut veneer matt cabinets, supplied as a pair without grilles
- SB Acoustics recommends 18 mm plywood for anyone building the cabinet themselves
Technical specifications
- Frequency range
- 36 – 24000 Hz
- Sensitivity (2.83V / 1m)
- 87 dB
- Nominal impedance
- 6 Ω
- Max SPL
- 108 dB
- Recommended amplifier
- 50 – 200 W
- Crossover frequency
- 680 / 3000 Hz
- Enclosure type
- Bass reflex (woofer), sealed (midrange)
- Port tuning frequency
- 28 Hz
- Drive units
- SB26STAC-C000-4, 4 inch SB12MNRX2-25-4 and 12 inch SB34NRXL75-8
The cabinet
The cabinet is well braced, and the exploded drawing shows what is inside it: internal bracing and partitions, three driver cut-outs and a slot port across the front baffle. The volume is there for the 12″ woofer. The midrange does not share it — it is closed off in a sealed chamber of its own.
- The front-facing slot port is tuned to 28 Hz.
- The midrange sits in a sealed chamber of its own, separate from the woofer’s volume.
- SB Acoustics recommends 18 mm plywood if you are having the cabinet built.
The crossover
The crossover is Danesian Audio’s work — the Danish design house that draws SB Acoustics’ kits, which Sinar Baja Electric then manufactures in Surabaya. It comes as a set alongside the cabinets, and the schematic on this page gives every component value in it.
Placement
A cabinet this size is unforgiving about where it stands. Three things to settle before anything else:
- Space them 2.5–3 m apart, and clear of the side and rear walls.
- Raise them about 25 cm on a stand or plinth, and tilt them back 6 degrees.
- The tweeter and midrange are drawn to fire straight out; toe-in is a matter of taste and of the room.
Tweeter — One SB26STAC-C000-4 per cabinet
A 25.4 mm textile dome on a ferrite motor with an aluminium faceplate. A soft dome suits the Gema: the cabinet and the big paper woofer are voiced warm, and a textile dome finishes that thought.
| Parameter | Value | Parameter | Value |
|---|---|---|---|
| Nominal impedance | 4 Ω | Force factor, Bl | 1.6 Tm |
| Free air resonance, Fs | 750 Hz | Voice coil diameter | 25.4 mm |
| Sensitivity (2.83 V / 1 m) | 91.5 dB | Voice coil height | 1.3 mm |
| Total Q-factor, Qts | 1.12 | Air gap height | 2.5 mm |
| Mechanical Q-factor, Qms | 3.0 | Linear coil travel (p-p) | 1.2 mm |
| Electrical Q-factor, Qes | 1.78 | Magnetic flux density | 1.15 T |
| Effective piston area, Sd | 6.2 cm² | Magnet weight | 0.22 kg |
| DC resistance, Re | 3.2 | Rated power handling | 120 W |
| Voice coil inductance, Le | 0.04 mH | Net weight | 0.53 kg |
| Moving mass incl. air, Mms | 0.3 g |
91.5 dB with a free air resonance of 750 Hz and 120 W rated power handling.
The manufacturer’s own description of the construction: a die-cast aluminium faceplate, a vented rear chamber and a full copper cap in the gap. SB Acoustics publishes its page for the SB26STAC-C000-4, and the full parameter set for this and every other model we carry is in the SB Acoustics core-range catalogue.
Midrange — One 4″ SB12MNRX2-25-4 per cabinet
A 4-inch Norex paper midrange on a 25.4 mm coil, ferrite motor, cast aluminium chassis — a dedicated midrange rather than a small woofer, in its own chamber.
| Parameter | Value | Parameter | Value |
|---|---|---|---|
| Nominal impedance | 4 Ω | Force factor, Bl | 3.9 Tm |
| Free air resonance, Fs | 63.5 Hz | Compliance, Cms | 1.5 mm/N |
| Sensitivity (2.83 V / 1 m) | 90.5 dB | Mechanical resistance, Rms | 0.4 kg/s |
| Total Q-factor, Qts | 0.32 | Voice coil diameter | 25.4 mm |
| Mechanical Q-factor, Qms | 4.19 | Voice coil height | 9.4 mm |
| Electrical Q-factor, Qes | 0.35 | Air gap height | 5 mm |
| Equivalent volume, Vas | 5.3 L | Linear coil travel (p-p) | 4.4 mm |
| Effective piston area, Sd | 50 cm² | Magnetic flux density | 1.03 T |
| DC resistance, Re | 3.2 Ω | Magnet weight | 0.4 kg |
| Voice coil inductance, Le | 0.15 mH | Rated power handling | 50 W |
| Moving mass incl. air, Mms | 4.2 g | Net weight | 0.92 kg |
90.5 dB and an Fs of 63.5 Hz on a 4.2 g moving mass, which is what lets it keep up with a 12-inch woofer on one side and a dome on the other.
A Norex paper cone on a low-damping rubber surround, drawn for the midband rather than being a small woofer pressed into the job. In the Gema it works the band between the crossover points, 680 to 3000 Hz. SB Acoustics publishes its page for the SB12MNRX2-25-4, and the full parameter set for this and every other model we carry is in the SB Acoustics core-range catalogue.
Woofer — One 12″ SB34NRXL75-8 per cabinet
A 12-inch Norex paper cone on a 75.6 mm voice coil, a rubber surround, a large ferrite motor and a cast aluminium chassis. This is the part that makes the Gema look like a 1970s floorstander, because it is the part that made 1970s floorstanders sound the way they did.
| Parameter | Value | Parameter | Value |
|---|---|---|---|
| Nominal impedance | 8 Ω | DC resistance, Re | 6.2 Ω |
| Free air resonance, Fs | 22 Hz | Voice coil inductance, Le | 1.20 mH |
| Sensitivity (2.83 V / 1 m) | 91.0 dB | Moving mass incl. air, Mms | 93.00 g |
| Total Q-factor, Qts | 0.28 | Force factor, Bl | 16.60 Tm |
| Mechanical Q-factor, Qms | 5.50 | Net weight | 8.90 kg |
| Electrical Q-factor, Qes | 0.29 | Recommended port tuning | 22 Hz |
| Equivalent volume, Vas | 205.00 L | Suggested ported volume | 67.89 L |
| Effective piston area, Sd | 508.00 cm² | Suggested sealed volume | 37.77 L |
Fs 22 Hz, 91 dB, a Bl of 16.6 Tm and 508 cm² of piston area. Sensitivity like that is what you get for moving air with cone area instead of excursion.
SB Acoustics’ own suggested reflex tuning for this driver is 22 Hz. The Gema’s box is tuned to 28 Hz, which is Danesian Audio’s alignment for this cabinet rather than the driver’s default. SB Acoustics publishes its page for the SB34NRXL75-8, and the full parameter set for this and every other model we carry is in the SB Acoustics core-range catalogue.
The cabinets arrive finished
Every cabinet in the photographs on this page is what turns up on the pallet. They are cut, assembled and finished at the same works that makes the drivers, on the same machines, to the same tolerances — so the job in front of you is the acoustics: mount the drivers, wire the crossover, fit the damping.
One finish, chosen to suit the design: walnut veneer, matt, on a set of two cabinets. The Gema is drawn to show its drivers, and the set is supplied without grilles.
Tell us which finish you want when you enquire and we will confirm it against the current factory list before anything is ordered.
Who the Gema suits
- A room that can take 2.5–3 m between the cabinets and still keep them off the walls.
- An amplifier inside the 50–200 W band SB Acoustics recommends, driving 87 dB at 6 Ω.
- Anyone who would rather have a 12 inch cone and a 28 Hz port than a small box and a subwoofer.
Artisan Acoustics is the appointed distributor for SB Acoustics in Singapore and in East and West Malaysia. Ask us about placement, amplifier matching or exactly what the kit contains.
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