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SM50 Sound Level Meter & STIPA Tester

The Bedrock SM50 Sound level Meter Class 2  from Bedrock is provides both Sound pressure level measurements (SPL) and is STIPA meter to measure Sound Transmission Index as STIPA- which is the industry standard. This Class 2 Data-Logging meter with certificate of conformity is an industry leading instrument in STI measurement for public announcement – which is mandated to be tested in rail, metro, airports, large conference rooms or any location with public announcement system to check the speech intelligibility of sound i.e., the ability for any person to clearly hear & understand announcements made on the PA or speaker system. 

SM50 STIPA meter is equipped with the following advanced modules:

  • Class 2 Sound Level Meter (SLM)


  • Real Time Analyzer (RTA)


  • Fast Fourier Transform (FFT) Analyzer

  • RTA Logging


  • RT60 Measuring (Reverberation Time)


  • Level (L%)


  • Noise Curve Analysis


  • Sound Pressure Level (SPL)


  • Total Harmonic Distortion plus Noise (THD+N)


  • LAeq logging


  • Statistical Acoustics and Building Acoustics SRI/STC


Equipped with a Class 2 electret microphone & preamp (1/4”), 30 mV/Pa sensitivity and a dynamic range of 21- 132 dB, this instrument gives accurate and reliable results in less time. With an easy plug-and-play method of operation and tripod mounted long term data logging, this class 2 stipa sound meter is perfect for longer duration of sound measurement. This data can be stored in the 4 GB internal storage or send to PC as .csv files for data viewing in spreadsheets; audio recordings also saved in .csv files.


SM50 is a STIPA sound meter that is accurate, reliable, and easy to use for even first-time users of STI measurement. Equipped with Quick STIPA (~18s per reading) as well as STIPA Pro (~25s per reading), even seasoned STI users will find all the features they were looking for- in a much simpler format in this speech intelligibility meter.



STI averaging available in SM50 Sound level & STIPA meter does multiple STIPA measurements consecutively and take a (moving) average across up to five measured STI values.

STIPA pro module has five screens:

1. STI and spectrum: display measured STI, octave spectrum and dBA level 2.


2. Measurement details: display all measurement details including the MTF

3. Settings: configure the STIPA pro module.

4. Additive noise: enter and enable/disable a noise spectrum to add to data

5. Browse measurements: review saved measurements


These measurement details will enable more experienced operators to determine not only the speech intelligibility of the tested channel, but also the causes of intelligibility reduction induced by the channel.


Full STI

Although fast and robust, STIPA has its limitations: only 2 modulation frequencies are measured per octave band, whereas the complete Speech Transmission Index measurement scheme calls for 14 modulations per octave band. This means that STIPA is under sampled in the modulation domain. For many systems, the measured STI is not (or hardly) affected. However, some cases call for “Full STI” measurements:

  • Whenever echoes are present (delayed loudspeakers, large halls and cathedrals)
  • When tested systems or channels feature complex combinations of distortion factors.

The Full STI module implements a novel measurement algorithm, that leverages the advanced signal processing capabilities of the SM50.

  • A novel test signal is used, which repeats 7 different patterns (segments) in a circular fashion.
  • Each pattern roughly follows the approach of STIPA: each octave band is simultaneously modulated with 2 modulation frequencies.
  • Each pattern takes approx. 9 seconds to complete. The whole measurement is completed in 65 seconds.
  • The patterns are set up in such a way that all modulation frequencies (out of the set of 14) have been used in each octave band once the full 65 second        cycle is completed. Hence, all 14 modulation frequencies are tested in all 7 octave bands.
  • The first phase of a new measurement is a synchronization phase, during which the analysis algorithm determines when to expect transitions between patterns. 



Bedrock SM50 advanced sound level meters with their versatile interface & tripod mounted setup can be are used for a variety of measurement applications including environmental noise, noise pollution, vehicular noise equipment & automotive design noise measurements, R&D, building acoustics, sound insulation, acoustic equipment testing, audio professionals amongst other applications. 

Conforms to major international standards like:

  • IEC-60268-16 rev. 4 & rev. 5
  • IEC-61672 Class 2 / ANSI S1.4 Type 2
  • IEC-61260 Class 0
  • ISO-717-1 / ISO-16283 / ISO-140
  • ASTM E336 / ASTM E413 ISO-3382-2
  • ANSI S12.2 / ISO-1996 AES17

Each SM50 speech intelligibility meter comes with an individual declaration of conformity and calibration certificate to differentiate the instrument from market variants. They also come with more functionality which will be added through free future firmware upgrades.


The SM50 is a versatile multi-point STIPA meter perfect for sound analysis and STI measurement – either tripod mount or handheld.


Kit Contains:

  • SM50 Instrument with class 2 mic
  • International charger adaptor
  • USB cable
  • Windscreen
  • Carrying cord
  • User manual
  • Calibration certificate
  • Ruggedized Case

The SM50 when combined with BTB65 Talkbox (available as Speech Intelligibility Kit) can be used to effectively measure STIPA- wherein the Talkbox acts as the source of STIPA signals and the SM50 measures/ analyses the signals seamlessly enabling multiple point testing in a short time with highest level of accuracy.

Optional BAC2 Calibrator is available to verify and calibrate the SM50. Provided with individual calibration certificate.




Product Specification
Function Guideline / Application SM50
Modules / Functions
Sound Pressure Level Meter (SPL / SLM) IEC-61672-1 : 2014, ANSI S1.4,    Class 2 / Type 2
Frequency Weighting Choose frequency method A ,C, Z (A : weighted, C : weighted , Z : Unweighted)
Time Weighting Choose based on time frames FAST , Slow, Impulse
Equivalent continuous (EQ)   Computes the time-integrated level over the
measurement interval
Sound Exposure level (SEL)   Time-integrated value normalized to 1 sec
Peak Value   Highest instantaneous value within an interval
Max Hold Lock on highest values measured Maximum level during the measurement
interval; Used with Fast, Slow or Impulse time weighting
Measurement Time  Set duration of measurement Set Measurement Time or Continuous (for infinite)
LEQ Long-term  logging/monitoring (LAEQ) Monitoring of continuous environmental noise / logging of sound levels, e.g. LAeq15min Track equivalent continuous sound pressure level  (LEQ) develop over time with simultaneous logging of A/C/Z
Real Time Analyzer (RTA)  Frequency Analysis for separate frequency bands Frequency analysis in range 20 Hz to 20 KHz for frequency bands 1/1, 1/3, 1/6 or 1/2 octaves. Two spectral views present- frequency weighting or time weighting
Fast Fourier  Transform Analyzer (FFT) Perform spectral analysis with higher frequency resolution  Up to 32768 data points, with Zoom In/Out feature, Spectral analysis for identifying exact frequency and level of signal components and study of harmonic structure of sound
L%, Statistical acoustics  Acoustic statistics based on threshold expressed as percentile, e.g. L10 to L95 can be measured Simultaneous measurement and display of six different settings
RTA Logging Long term monitoring of special characteristics of sounds  Spectrograms, with averaging window between 1 to 999 seconds of spectrum in 1/1, 1/2, 1/6 or 1/12 octave as well as A, C , Z weighted equivalent continuous levels
Electro-Acoustics & Electric Analysis        
Digital Storage Oscilloscope  Inspect acoustic signals, in particular periodic signals, in time domain Yes, up to 20kHz
Polarity  Check polarity of loudspeakers Yes,  Use test signals provided or use with BTB65 Talkbox
AC Volt Meter for Line Level Signals Assess Output level Yes, Measure Vrms, dBU, dBV
Total Harmonic Distortion & Noise (THD+N ) Quantify distortion levels in electro-acoustic equipment.   Value THD+N is expressed as a percentage (%) or a signal-to-noise ratio (dB)
Fundamental Frequency Estimation   Yes, Measurement in Hz with pitch & offset
Building / Structural Acoustics        
Sound Insulation: Evaluate airborne sound transmission loss 4 different frequency dependent measures :  D, Dn, DnT, R
Sound Reduction Index; Sound Transm. Class (SRI / STC ) For specifying and measuring sound insulation   4 metrics R'w ;  Dn,w ; DnT,w ; STC
Room Acoustics        
Reverberation Time (RT60) Measure sound energy decay Full Octave and 1/3rd octave measurements are supported. As per ISO-3382, Suggested to be used with BTB65 Talkbox
Noise Curves  Choose method based on standard. NR, NC, PNC, NCB, RC, RCII
Speech Intelligibility Test (STI) Measurement
Basic Intelligibility Measurements (Quick STIPA) For Public address systems, quick measurement in 18 secs Yes
Advanced Intelligibility Measurements (STIPA Pro) For Public address systems, measure in 25 secs Yes, with capability to enable/disable additive noise 
Full STI (IEC-60268-16) Most reliable complete STI measurement in 65 secs Yes, 14 Modulation frequencies tested in 7 Octaves
Speech Level Meter   Yes, (CF. 602168-16)
Qualification Band Shown   A (Excellent) to U(Bad)
Acoustic Specifications
Linear Range, Electric Input (dBuV)   21 ~132dB
Measurement Range (dB) , Linear Range with Supplied Microphone, dBA SPL   30 ~122dB
Frequency Range (Hz) Covers entire range  heard by human ear 20 ~20.000
Accuracy (dB)   0.5
Resolution (dB)   0.1
Octave Filter   Class 1 1/1, 1/3, 1/6 and 1/12 octave filters
  31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz, 8 kHz, 16 kHz
Analysis Rate   93.5 times/sec
Sampling Frequency (kHz)   48
Add Text Annotations to Measurements Yes 
Capability to Record Audio of all Measurements Yes, in .wav format
Automatic Level Calibration Procedure   Yes
Calibrated Recording of Audio on Internal Memory   Yes
Real-time Calibrated USB Audio Device Mode   Yes
Declaration of Conformity   Declaration of conformity provided with individual Calibration certificate 
External Calibrator   Optionally available
Display   Full-color 3.2” resistive LCD touchscreen display
Microphone Connector   XLR 48V
Microphone Provided with Instrument   Class 2 electret microphone & preamp (1/4”), 30 mV/Pa sensitivity
Data Storage for measurement data and audio (GB)   4
Remote Control from PC via USB (either through Serial Commands or Cloning of the Display)   Yes
Data Output   To PC, files can be saved as .csv for data viewing in spreadsheets ; audio recordings also saved in .csv files
Battery   Rechargeable Internal Battery, 2500 mAh
Capability to Connect to External Power Supply For long duration continuous measurement Yes, instrument can connect via USB port to power banks or charger
Internal Real-time Clock and Calendar   Yes
Size/Weight   210 x 85 x 55 mm( excl. microphone); 530 g ( including microphone)
Temperature/ Relative Humidity    -10 to +55 ⁰C; 0-95%
Colors   Grey and black
Supply will include   Microphone (Class1 for SM90 / Class2 for SM50 AND SM30), USB charger, Intl. Charger adapters, measuring instrument, cables, windscreen, manual, carrying cord, USB flash drive with test signals & software tools in a ruggedized waterproof carrying case
  • Fast Fourier Transform (FFT) frequency analysis
  • Real Time Analyzer (RTA) 1/12, 1/6, 1/3 and 1/1 octave, IEC-61260-1:2014 class 2
  • Reverberation Time (RT60), ISO-3382
  • Noise Curves (NR, NC, etc)
  • Long-term Leq logging/monitoring (e.g. LAeq15min)
  • Spectral logging (RTA logging & spectrograms)
  • Statistical acoustics (percentiles, e.g. L10 and L95)
  • Digital storage oscilloscope (<=20 Khz)
  • THD+N with firmware 2.6
  • STIPA measurement
  • Fundamental frequency estimation
  • AC Volt meter for line level signals
  • Loudspeaker Polarity measurements
  • Automatic level calibration procedure
  • Calibrated recording of audio on internal memory
  • Real-time calibrated USB audio device mode
  • Sound insulation: D, Dn, DnT, R’
  • SRI / STC (sound reduction index; sound transm. class)
  • Remote control from PC via USB (either through serial commands or cloning of the display
  • Low start up period of 20sec after power up
  • Class 2 electret microphone & preamp (1/4”), 30 mV/Pa sensitivity
  • 4 GB Internal Memory
  • Full-colour 3.2” resistive LCD touch display


Frequently Asked Questions (6 answered questions)
The difference lies in the accuracy. Class1 are accurate to 0.1dB whereas Class2 are accurate to 0.5dB.

Person name: Asian

STIPA denotes speech intelligbility, i.e measurement of intelligibility of sound as heard by the user. The SM50 incorporates a scale which provides a measurement from A to E, classified as Excellent to Bad.

Person name: Asian

FullSTI takes about 1 minute to test , STIPA (more aimed at public address system takes 20 sec). Quick STIPA has an 18s test time.

Person name: Asian

Yes, it can perform Reverberation Time Meter (RT60), electro Acoustics (built in oscilloscope) & Sound Insulation-frequency dependent airborne sound insulation between rooms according to ISO- 16283-1:2014 (Dn, DnT and R') and ASTM E336.

Person name: Asian

A variety of statistical applications are built in the instrument , user selectable, such as LAEQ module for long term monitoring and logging , FFT, L Level for statistical distribution of sound levels during the measurement period.

Person name: Asian

SM50 is a class 2 meter. for Class 1, refer SM90.

Person name: Asian

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