MB 115-B

Art. No. 5932

Characteristics - Sound Properties

The MB 115/B building suggestion is a bass speaker for professional musicians. If fullrange musicians' speakers need boosting the bass department, you need bass speakers with a comparatively high level of efficiency. Bass reflex speakers have the advantage of a low limiting frequency, but this also means they need a large cone area with the large cabinet that this entails, in order to produce sufficient sound pressure. A completely uncompromising bass speaker should really be enormous. However, the MB 115/B makes use of a cleverly designed flare geometry, perfectly matched to the BGS 40 8 Ohm driver, to produce a relatively compact horn. A limiting frequency of 50 Hz is a perfectly respectable level for a musician coupled with an output level of 96 dB above 60 Hz under open-field conditions (no walls, no floor) at just 1 watt is an excellent starting point for extreme bass pressure. It must be taken into account that, positioned on the floor away from walls, this figure increases by 3 dB and near a corner by as much as 9 dB. We measured peak output levels of as much as 125 dB (above 60 Hz) under favourable conditions. And all that with the typical horn-like, bone-dry sound characteristics an experience for aficionados of solid-level, dynamic sound!

The horn sound develops in a vortex beginning in front of the diaphragm and moving outwards towards the opening. At the rear, the woofer acts on a small, enclosed compartment. This prevents the stroke in the low bass and subsonic ranges from becoming too extreme which prevents mechanical damage to the driver. The impedance curve retains a pleasingly high level throughout. This means that the booster is not overloaded and the voice coil does not overheat. Crucial points in the tough daily life of professional musicians.

Active separation is recommended. This allows the optimal position between separating frequency and slope rate to be found. As a cost-saving alternative, we have also developed a passive crossover. This system separates at 150 Hz and goes well with the top-of-the-range MB 208/H, if the recommended high-pass section is used ( refer to MB 208/H ).

MB 115/B is part of the combinations:
PA Combination A
PA Combination B
PA Combination C
PA Combination D

Frequency response

Construction

The boards will need bevelling first to ensure a good fit, using a hand-held circular saw, for example. Next, cut out the port for the woofer in the baffle (part 12) and pre-drill the fixing holes. To fix the driver in place, it is also possible to use drive-in nuts and matching bolts. After this, screw and glue the strengthening strut (part 9) to the baffle. Place parts 8, 11, 12 and 13 together "dry" to form a chamber, just to check that they form a good fit. Next, make the cut-out for the loudspeaker in the frame (11). The chamber can now be glued and screwed together. Ensure the glued joints are absolutely airtight. Then position the chamber on the outer side of a side wall and mark around it with a pencil. Align the chamber with the base. Repeat these steps with the other chamber on the other outer wall. Later, when you screw the cabinet walls together, ensure the pencil marks are visible on the outsides of the side walls. This will facilitate the correct positions of the screws.

Now glue and screw the base, rear wall and top to the side wall and the reflectors (1 and 7). The strengthening strut (9) and reflectors must be solidly fixed to the appropriate wall. Before attaching the other side wall, the cables and connections have to be carefully arranged. Any holes drilled through the wall of the chamber for cables must be carefully sealed afterwards, e.g. with mastic.

Fitting the loudspeaker in the rather tight confines of the chamber is a tricky piece of work. However, it is possible with a fair amount of patience, and you will be glad you took your time over it. Finally, close off the chamber with the cover (part 10). Use plenty of sealant and insert at least 10 screws evenly spaced all around the edge.

Transporting the speakers is much simplified if you fit carrying handles, available in good DIY shops.

Crossover (optional)

Enclosure