Sofia AMT 31   Shelf speaker as in K+T 6/2024

Technical data
  • impedance: 6 Ohm
  • sensivity (2,83V/1m): 82 dB
  • size (HxWxD): 340 x 170 x 270 mm
  • frequency range (-8dB): 40 - 33000 Hz
  • crossover frequency(s): 5000 Hz
  • speaker type: bass reflex
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Sofia AMT 31 is a two way compact speaker.

Sofia AMT 31 is a bass-reflex cabinet loudspeaker with drivers of Mundorf and Wavecor.

The kit is delivered with the following drivers:
- a Mundorf AMTU60W1.1-C air motion transformer (ribbon-tweeter)
- a Wavecor WF120BD12 woofer

The loudspeaker has been developed by Dennis Frank and Daniel Gattig.

The crossover consists of:
- a 3rd order high-pass filter (18 dB per octave slope) for the tweeter.
- a 2nd order low-pass filter (12 dB per octave slope) for the woofer.

The frequency response of this speaker is perfectly linear.

The decay spectrum is nearly perfect.

At low volume, i.e. 85 dB at 1 m, the nonlinear distortions are below 0,5% above 300 Hz and doesn't exceed 0,6% at 95 dB at 1 m between 300 and 15000 Hz.

An excerpt from the Klang+Ton review (Translation of the author into English)

Conclusion of the magazine Klang+Ton:

Our kit consists of

  • Wavecor Mid/Woofer WF120BD12, 8 Ohm, die cast, kevlar/carbon cone
  • Mundorf AMTU60W1.1-C
  • 2x Bass reflex tube HP50, 50x143mm, black
  • Damping fleece MT Bondum 800 (30 x 50 x 2 cm)
  • 0,5x PE sealing tape, 5x2 mm, 7.5 m
  • 0,5x Damping Sonofil 100 x 35 cm for 20 litres
  • Binding Post PK28 I, gold plated (one pair, red and black)
  • 1,5m Speaker cable 2x1.5 mm2, transparent
  • 0,5x Pan screws 3.5x17 black, torx, 8 pieces
  • Visaton Countersunk screws 3.5x25, 8 pcs
  • Plan for DIY kit

the crossover components (right),
to be mounted on a small wooden board.

  • ClarityCap PX capacitor 1.2 μF / 250 Vdc
  • ClarityCap PX capacitor 4.7 μF / 250 Vdc
  • Jantzen Cross Cap MKP capacitor 4.7 μF / 400V
  • Audaphon MKT CAP 22 μF / 160 Vdc
  • 1.4 mm air core coil, 1.0 mH/0.29 Ohm
  • 0.7 mm air core coil, 0.39 mH/0.49 Ohm
  • 0.7 mm air core coil, 2.7 mH/1.53 Ohm
  • Metal-oxide resistor, 10W 2.2 Ohm (red-red-gold)
  • Metal-oxide resistor, 10W 8.2 Ohm (grey-red-gold)
  • Metal-oxide resistor, 10W 12 Ohm (brown-red-black)

Kit without cabinet, price per speaker   EUR 510,00 excl. VAT: € 428.57 / $ 471.43

Kit with high-end crossover

The high-end kit is delivered with baked varnish air core coils on important parts of the crossover for minimizing microphonic effects. - The current flow through the coil creates a magnetic field which sets the reel of wire in motion. This motion induces a voltage in the coil which adds itself to the signal. The stiffer the reel of wire is, the less the signal will be altered. The capacitors for the Mundorf AMTU60W1.1-C are of type polypropylen (MKP) Clarity-Cap ESA 250 V.

  • ClarityCap PX capacitor 4.7 μF / 250 Vdc
  • ClarityCap ESA capacitor 1.2 μF / 250 Vdc
  • Jantzen Cross Cap MKP capacitor 4.7 μF / 400V
  • Audaphon MKT CAP 22 μF / 160 Vdc
  • Mundorf baked varnish air core coil BL71, 0.39 mH/0.51 Ohm
  • Mundorf baked varnish air core coil BL71, 2.7 mH/1.53 Ohm
  • Mundorf baked varnish air core coil BL140, 1.0 mH/0.30 Ohm
  • Mresist Classic 2,2 Ohm / 10 Watt
  • Mresist Classic 12 Ohm / 10 Watt
  • Metal-oxide resistor, 10W 8.2 Ohm (grey-red-gold)

Kit with high-end-crossover without cabinet, price per speaker   EUR 542,00 excl. VAT: € 455.46 / $ 501.01

Impedance correction

If you want to use a valve amplifier with this speaker an impedance correction should be employed. In this case the component quality is less important; therefore, we offer only one kit (upon request higher quality components are available).

  • Audaphon MKT CAP 22 μF / 160 Vdc
  • 0.7 mm air core coil, 0.05 mH
  • ceramic resistor 6.8 Ohm/20 Watt

Price per impedance correction for one speaker, to be mounted on a small wooden board.     EUR 12,20 excl. VAT: € 10.25 / $ 11.28

universal PCB

If you prefer to mount the crossover components on a universal PCB instead on wood
PCB 150x115 mm, tin plated, price per unit:   EUR 4,70 excl. VAT: € 3.95 / $ 4.34
We recommend one board per kit (2 boards per speaker pair)


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