Co-Bold   Floorstanding as in K+T 2/2022

Technical data
  • impedance: 12 Ohm
  • sensivity (2,83V/1m): 83 dB
  • size (HxWxD): 900 x 210 x 225 mm
  • frequency range (-8dB): 35 - 29000 Hz
  • crossover frequency(s): 3000 Hz
  • speaker type: bass reflex

Co-Bold is a two way floorstanding speaker.

Co-Bold is a bass-reflex cabinet loudspeaker with drivers of Bold North Audio .

The kit is delivered with the following drivers:
- a Bold North Audio BDT-2901 tweeter
- a Bold North Audio BWX-6501 woofer

The loudspeaker has been developed by Thomas Schmidt and Thorsten Fischer.

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

The frequency response of this speaker is nearly linear.

The decay spectrum is nearly perfect.

At low volume, i.e. 85 dB at 1 m, the nonlinear distortions are below 0,4% above 500 Hz and doesn't exceed 1,1% at 95 dB at 1 m between 300 and 15000 Hz.

Our kit consists of

  • Bold North Audio BDT-2901
  • Bold North Audio BWX-6501
  • Bass reflex tube HP70, 70x220m, black
  • 0,5x PE sealing tape, 5x2 mm, 7.5 m
  • Damping Sonofil 100 x 35 cm for 20 litres
  • 0,25x Foam N25, 97,5x49x4 cm, black
  • Bi-wiring Terminal T122 Au with brass, gold plated
  • 2m Speaker cable 2x1.5 mm2, transparent
  • 0,5x Pan screws 3.5x17 black, torx, 8 pieces
  • 1,5x Pan screws 4x20 black, torx, 8 pieces
  • Plan for DIY kit

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

  • Audaphon MKP CAP Superior 2.7 μF / 400 Vdc
  • 2x Audaphon MKP CAP Superior 4.7 μF / 400 Vdc
  • Audaphon MKP CAP Superior 6.8 μF / 400 Vdc
  • Mundorf air core coil L140, 0.56 mH/0.20 Ohm
  • 1.4 mm air core coil 1.8 mH/0.41 Ohm
  • 0.7 mm air core coil, 0.10 mH/0.27 Ohm
  • 0.7 mm air core coil, 0.15 mH/0.28 Ohm
  • Metal-oxide resistor, 10W 8.2 Ohm (grey-red-gold)

Kit without cabinet, price per speaker   EUR 384,00 excl. VAT: € 322.69 / $ 342.05

Kit with high-end crossover

The high-end kit is delivered with baked varnish air core coils 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 Bold North Audio BDT-2901 are of type polypropylen (MKP) Clarity-Cap ESA 630 V.

  • ClarityCap ESA capacitor 4.7 μF / 630 Vdc
  • ClarityCap ESA capacitor 6.8 μF / 630 Vdc
  • Audaphon MKP CAP Superior 2.7 μF / 400 Vdc
  • Audaphon MKP CAP Superior 4.7 μF / 400 Vdc
  • Mundorf baked varnish air core coil BL71, 0.10 mH/0.23 Ohm
  • Mundorf baked varnish air core coil BL71, 0.15 mH/0.28 Ohm
  • Mundorf baked varnish air core coil BL140, 0.56 mH/0.20 Ohm
  • Mundorf baked varnish air core coil BL140, 1.8 mH/0.43 Ohm
  • Metal-oxide resistor, 10W 8.2 Ohm (grey-red-gold)

Kit with high-end-crossover without cabinet, price per speaker   EUR 452,00 excl. VAT: € 379.83 / $ 402.62

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, 0.68 mH/0.70 Ohm
  • ceramic resistor 18 Ohm/20 Watt

Price per impedance correction for one speaker, to be mounted on a small wooden board.     EUR 13,30 excl. VAT: € 11.18 / $ 11.85

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 / $ 4.19
We recommend one board per kit (2 boards per speaker pair)


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