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What is CBT?

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A traditional line array speaker suffers from lobing and comb-filtering issues, thus leading to a chaotic and non-constant directivity. The CBT avoids these problems and yields a uniform directivity with almost no side lobes.

The dispersion pattern of the CBT depends on how it’s implemented which can be done in numerous ways. A CBT can be designed as free standing (PA applications), as a ground plane array or attached to a ceiling (PA or surround).

As a ground plane array the CBT avoids completely floor reflections and minimizes greatly ceiling reflections. The floor is actually used a mirror of the speaker, doubling the speaker in size and power. With ceiling mounting, it’s the opposite. It uses the ceiling as mirror and avoids ceiling reflections while greatly reducing reflection from the floor. In both cases the CBT minimizes the need for any acoustical treatment in the vertical plane.

The measurement below shows a comparison between a traditional straight line array and a CBT. We can see that the line array has large deviations in the vertical plane, while the CBT measures extremely constant.

Great sound everywhere

Due to the lack of lobing and comb-filtering and extremely uniform direcitivity , the CBT speaker provides great sound both in near-field and far-field as well in every direction as illustrated below.

One single CBT speaker can be sufficient in many PA applications

When a CBT is designed with a wide horizontal dispersion pattern, one single speaker will in many cases be enough for sound reinforcement where stereo isn’t required. The combination of a wide 180 degrees horizontal beamwidth with an extremely uniform directivity may render the need for an extra speaker, thus saving expenses and time to set up a system. The sound will be very consistent whether one is on-axis of the speaker or far off to the sides.

Less sound level variation from front to back

Another benefit of the CBT is that volume doesn’t change as much with distance as with other speakers. This makes the sound level more constant at various distances.

This is illustrated below where the green line represents a traditional point source speaker and the black line a CBT ground plane array.

Up till 30,4 m (100 feet), the CBT only drops 3 dB per per doubling of distance . This means the CBT is a great advantage in many sound reinforcement situations as the sound level will vary much less for the crowd compared to a point source. Below 30,4 m, the CBT will loose 6 dB per doubling of distance, similar to a point source.

This also implies that the CBT can function as a stage monitor for the musicians as well as a sound reinforcement speaker for the audience. It can do both tremendously well when the CBT is placed behind the musicians. © Keele & Omholt Technologies 2022
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