The B 200 - 6 Ohm was fitted in a narrow column speaker with a net volume of around 100 litres. Due to the high Q-factor, one would normally have a relatively strong increase in reverberation response at around 60 Hz in a normal enclosed chamber or bass reflex cabinet. To prevent this, and indeed to take full advantage of the bass reflex principle, we thought up this little arrangement which, to our knowledge, has not been done before.
The chamber is split into two equal parts by a separator. On the rear wall, we built a vertical tunnel as a Helmholtz resonator which was tuned exactly to the frequency of the increase. This tunnel was then loosely filled with a packing of wool. In its undamped state, this resonator absorbs just the amount of the increase and even causes a slight dip in this range. You can vary the amount of packing used to achieve the required frequency response. In this way, we managed to ensure that the bass reflex did not produce overpowering bass despite the bass reflex tuning.
In keeping with the frequency response so typical of wide-range speakers with increasing medium- and top-range frequencies, this speaker, too, has an unacceptably high-pitched sound. So we applied a passive correction circuit (five simple components) to smooth off the frequency response in a very simple but effective manner for a full-range loudspeaker. Depending on the acoustics in the room and personal preference, the 15 ohm series resistance can be changed. Reducing it to 10 ohms will result in an increase in the high-frequency range, while increasing it to 22 ohms will dampen the treble more effectively.