Selecting a Multi-Channel DAQ System for Acoustic and Vibration Measurement

Selecting a data acquisition system for acoustic and vibration measurement requires understanding several interacting technical requirements: sample rate and the resulting upper frequency limit; ADC resolution and the achievable dynamic range; the number of simultaneous channels and whether phase coherence between channels matters; IEPE power supply specifications for condenser microphones and piezoelectric accelerometers; and the software integration options for the analysis you need to perform.

The most common mistake in DAQ selection for acoustic measurement is prioritising sample rate while neglecting anti-aliasing filter design. A 102.4 kHz sample rate with a first-order anti-aliasing filter does not provide useful measurement bandwidth to 51 kHz. Verify that the DAQ system specifies -3 dB bandwidth and anti-aliasing filter performance for the sample rate you will use.

Key DAQ Specifications for Acoustic Measurement

• ADC resolution: 24-bit provides approximately 144 dB theoretical dynamic range — adequate for all acoustic measurement applications
• Sample rate: 102.4 kHz provides usable bandwidth to approximately 40 kHz; 196 kHz to 80 kHz — verify the anti-aliasing filter specification
• Simultaneous sampling: all channels must be sampled simultaneously; sequential sampling introduces inter-channel phase errors that invalidate multi-channel analysis
• IEPE current supply: 4 mA constant current at 18–28 V compliance voltage — verify compatibility with your microphone preamplifier requirements
• Input voltage range: ±10 V peak is standard; verify that the full-scale range is appropriate for your signal levels
• Noise floor: verify the instrument self-noise in μV (not just ADC bits) — 1 μV input noise floor corresponds to -120 dB re 1 V/Pa with a -26 dB sensitivity microphone

Channel Count and Application Requirements

• 4-channel: field survey measurements, impedance tube measurements, small array work
• 8-channel: ISO 16283 building acoustics (simultaneous 5 receiver positions), moderate array work
• 16-channel: ISO 3744 sound power (10-point hemisphere simultaneous), large array, pass-by with multiple positions

PLACID PQ401 (4-ch), PQ801 (8-ch), and PQ1601 (16-ch) DAQ systems all use the same chassis design with 24-bit simultaneous sampling, selectable IEPE current supply, and open SDK for software integration.

Scalability and Future-Proofing

When selecting a DAQ system, consider channel count scalability. A system that can be expanded from 4 to 8 to 16 channels by adding units, with all units synchronised to a single clock reference, provides significant long-term flexibility. The PLACID PQ range uses a common clock synchronisation interface across the PQ401, PQ801, and PQ1601, allowing a 4-channel system purchased today to be expanded to 16 simultaneous channels without changing the software or calibration methodology.