CT 309   Shelf speaker as in K+T 3/2020

Technical data
  • impedance: 6 Ohm
  • sensivity (2,83V/1m): 84 dB
  • size (HxWxD): 302 x 124 x 241 mm
  • frequency range (-8dB): 65 - 21000 Hz
  • crossover frequency(s): Hz
  • speaker type: Horn reflex

CT 309 is a compact loudspeaker with a full range driver.

CT 309 is a loudspeaker with drivers of Mark Audio .

The kit is delivered with a Mark Audio CHN 50 full range driver

The loudspeaker has been developed by Thomas Schmidt.

The crossover consists of:
- a blocking circuit in series with the full range driver.

The frequency response of this speaker is nearly linear.

The decay spectrum (waterfall spectrum) shows a decelerated swing-out behaviour in the mid-range.

At low volume, i.e. 85 dB at 1 m, the nonlinear distortions are below 0,7% above 500 Hz and doesn't exceed 1,3% at 95 dB at 1 m between 300 and 15000 Hz.

Our kit consists of

  • 0,5x Mark Audio CHN 50 Generation 1, one pair
  • 0,25x Damping Sonofil 100 x 35 cm for 20 litres
  • 0,5x Foam N25-30, 100 x 50 cm, black
  • Binding Post PK31, gold plated (one pair, red and black)
  • 1m Speaker cable 2x1.5 mm2, transparent
  • Plan for DIY kit

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

  • Audaphon MKP CAP Superior 15 μF; / 400 Vdc
  • 1.0 mm air core coil, 0.68 mH/0.39 Ohm
  • Metal-oxide resistor, 10W 3.9 Ohm (orange-white-gold)

Kit without cabinet, price per speaker   EUR 50,69 excl. VAT: € 43.70 / $ 51.13

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 Mark Audio CHN 50 are of type polypropylen (MKP) Clarity-Cap ESA 250 V.

  • ClarityCap ESA capacitor 15 μF; / 250 Vdc
  • Mundorf baked varnish air core coil BL100, 0.68 mH/0.39 Ohm
  • Metal-oxide resistor, 10W 3.9 Ohm (orange-white-gold)

Kit with high-end-crossover without cabinet, price per speaker   EUR 64,63 excl. VAT: € 55.72 / $ 65.19

Kit with LowCost crossover

The LowCost kit is delivered with:

  • JB, electrolytic capacitor, bipolar advanced, 15μF / 50 Vdc
  • 0.7 mm air core coil, 0.68 mH/0.70 Ohm
  • Metal-oxide resistor, 10W 3.9 Ohm (orange-white-gold)

Kit with LowCost-crossover without cabinet, price per speaker   EUR 43,87 excl. VAT: € 37.82 / $ 44.25

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).

  • JB, electrolytic capacitor, bipolar advanced, 33μF / 50 Vdc
  • 0.7 mm air core coil, 0.22 mH/0.39 Ohm
  • Metal-oxide resistor, 10W 12 Ohm (brown-red-black)

Price per impedance correction for one speaker, to be mounted on a small wooden board.     EUR 8,70 excl. VAT: € 7.50 / $ 8.78

universal PCB

If you prefer to mount the crossover components on a 140 x 102 mm universal PCB instead on wood:
Universal PCB RA140, order no.. I-2765, price per unit:   EUR 3,61 excl. VAT: € 3.11 / $ 3.64
We recommend one board per kit (two boards for a speaker pair)


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