Solo 100

Art. No. 5984

Characteristics - Sound Properties

The B 200 6 Ohm was fitted tin 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.

Frequency response

Construction

The ring around the driver is a purely design-orientated enhancement and has no acoustic function. Since wide-range drivers tend to bundle the sound quite noticeably in the medium range, you will not have to worry about the baffle step or indeed any other impairments from the baffle.

This cabinet will require a certain amount of carpentry skill and experience. You will need to be good at handling a surface milling cutter. If you are not so sure of your abilities, you can make a much easier cabinet. In that case, do without the ring, built a simple cube and add a narrow chamfer along the edges. An alternative, but a more difficult one, would be to make the chamfer wider above and below the driver and have it taper off as it gets near to the driver. Due to the relatively strict beaming of the wide-range speakers, this will have virtually no effect on the acoustic properties.

Inner damping

The inner damping of the two chambers at the top and bottom is a simple matter (see illustration). You will have to ensure, however, that the lower chamber is damped before you glue the speaker cabinet together. Afterwards, it will not be possible unless you screw the rear wall into place instead if gluing it. The damping of the vertical tunnel, on the other hand, will affect the bass frequency response. Cut one mat (1/2 a bag) along one side in such a way that it is the same width as the inside of the cabinet. Then we pushed the mat into the tunnel from above and about halfway down. This is easily done through the cut-out in the baffle. If you push it down further than halfway, you will get less low-frequency bass (and vice versa). This enables you to fine tune the system to meet the acoustic requirements of the room.

Crossover

Inner Damping