The BMA CT from ClearOne is a patented ceiling tile beamforming microphone designed to provide excellent pickup and intelligibility, whilst maintaining minimal visual impact on the aesthetics of modern meeting spaces.

With built in acoustic echo cancellation, noise cancellation and beam selection eliminate the need for per-beam AEC processing, lowering overall DSP resource requirements.

POLAR conducted informal pickup and intelligibility tests in a real boardroom to benchmark the performance of the BMA CT.

Pickup Diameter:

As a rule of thumb, the below distances can used a guideline when specifying microphone quantities and designing a given space for best performance and overall speech intelligibility. It is of paramount importance to understand that the acoustics of a space will have a significant impact on usable distances in real world applications. A common metric used to determine the reverberation tail length of a given space is the RT60.

BMA CT: ~ 4m Radius (Assumed RT60 ~500msec or below.)

Real-World Intelligibility Tests:

POLAR installed a ClearOne BMA CT into a functioning boardroom space to obtain intelligibiltiy metrics from a referenced acoustic source, passing through Converge Pro 2 DSP via the analogue output into the RCA input of a calibrated XL2 meter, where the measurement was taken.

For our calibrated acoustic source, we used a NTi Talkbox STIPA test signal, referenced at 60dB(A) @ 1M.

We used an ambient noise correction file to deduct from the overall measured STI measurement which was collected from a 30 second interval of ambient room noise.

We tested the measured intelligibility via the BMA CT and the Converge Pro 2 analogue outputs at 1.5, 3, & 4 metres.

STI Qualification Bands:


CategoryNominal STI valueExamples of typical uses (for natural or reproduced voice)
A+>0.76Recording studios
A0.74Theatres, speech auditoria, parliaments, courts, Assistive Hearing Systems (AHS)
B0.7Theatres, speech auditoria, parliaments, courts, Assistive Hearing Systems (AHS)
C0.66Theatres, speech auditoria, teleconferencing, parliaments, courts
D0.62Lecture theatres, classrooms, concert halls
E0.58Concert halls, modern churches
F0.54PA systems in shopping malls, public buildings offices, VA systems, cathedrals
G0.5Shopping malls, public buildings offices, VA systems
H0.46VA and PA systems in difficult acoustic environments
I0.42VA and PA systems in very difficult spaces
J0.38Not suitable for PA systems
U<0.36Not suitable for PA systems

1.5 Metres:

3 Metres:

4 Metres:

The Room:

The room used was an untreated 8.2 x 6.3m x 2.4m boardroom with a layout and microphone position as shown below: