The Optimus+ Yellow is a range of basic sound level meters built to international standards (IEC 61672) and available as either Class 1 or Class 2 sound level meters. The range is the entry-point for Cirrus Research's well-renowned Optimus+ range. The Optimus+ Yellow noise level meter is capable of measuring the maximum noise level during a session, and provides simple and easy-to-understand data, including frequency weightings and time history.

The Optimus+ Yellow is a state-of-the-art noise level meter that has been designed by the engineers at Cirrus Research to meet the very latest international standards in sound measuring and monitoring.

Most suited for applications where only basic noise level data is required, the Optimus+ Yellow can record the sound pressure level (SPL), maximum sound level (LMax) in decibels, which refers to the loudest recorded noise level during a period of data capturing, and on specific variants, allows for data logging of the sound levels measured over a user-defined period of time. This data will give you a basic understanding of the noise levels where you are measuring, and will allow you to identify any particular noise hotspots.

It has a bright and easy-to-read colur display allowing you to see the noise level in decibels (dB) in real-time on-screen, providing you with a clear and instant indication of the sound levels measured.

The perfect entry-level sound meter for basic noise measurements

Optimus® is a Registered Trademark of Cirrus Research plc

We want to make your job easier, so we designed to Optimus+ Yellow to offer the highest level of performance without the complicated setup.

  • Every parameter is measured simultaneously, so you can't choose the wrong function or miss any data
  • All it takes is 3 button pushes to get the Optimus Yellow to start measuring. Switch On. Calibrate. Start. It's that simple
  • With it's large display, you can easily view your measurements on-screen

If you choose the data logging version of the Optimus+ Yellow, we'll include our NoiseTools noise analysis software so you can keep a record of your measurements. View the full specifications on the product table below.

You can upgrade this instrument to an Optimus+ Red or Optimus+ Green at any time, future-proofing your investment. Contact our Noise Experts today to find out more.

  • Measures everything you need simultaneously
  • Just switch on, calibrate and start measuring!
  • Large screen so your data is easy to read
  • Lightweight ergonomic design so it’s easy to use
  • Available with either a Class 1 or Class 2 microphone
  • Backed by our 15-year “no quibble” warranty
  • Long battery life
  • 4GB internal memory with the option for up to 32GB
  • Bluetooth connectivity, allowing you to use your device with a compatible smartphone
  • Factory personnel
  • Alarm installers
  • Fire alarm noise level testing
  • Community noise assessments
  • Machinery servicing and maintenance
  • Noise ordinance servicing

Applicable Standards

IEC 61672-1:2013 Class 1 or Class 2

IEC 61672-1:2002 Class 1 or Class 2 Group X

IEC 60651:2001 Type 1 I or Type 2 I

ANSI S1.4 -1983 (R2006), ANSI S1.43 - 1997 (R2007)

ANSI S1.25:1991


Class 1 MK:224 pre-polarized, Class 2 MK:216 pre-polarized

Microphone Preamplifier

MV:200 Removable Preamplifier (All versions)

Total Measurement Range:

20dB to 140dB RMS Single Range

Noise Floor: <18dB(A) Class 1, <21dB(A) Class 2

Frequency Weightings

RMS: A, C, & Z Measured Simultaneously

Time Weightings

Fast, Slow & Impulse Measured Simultaneously


High resolution display. Ambient light sensor & illuminated keypad


4GB (B Version), 32GB factory fit option


Measurement verification data stored in secure memory

Time History Data Rates (Global settings)

10ms, 62.5ms, 125ms, 250ms, 1/2 sec, 1 sec, 2 sec (User selectable)

VoiceTag Audio Recording (B Version)

Up to 30 seconds of audio notes with each measurement

Measurement control

Pause & Back Erase with user selectable duration


Size: 283mm x 65mm x 30mm

Weight: 300gms/10oz


4 x AA Alkaline

Battery life

Typically 12 hours with Alkaline AA

Typically 20 hours with Lithium AA Non-Rechargeable

Battery life is dependent upon the battery type, quality & screen brightness


USB Type B to PC

AC & DC Output via ZL:174 (2 x Phono, 1m)

Multi-pin IO for external power via ZL:171 cable (2.1mm socket)

External Power: 5v-15v via MultiIO socket via ZL:171 cable (2.1mm socket)

Tripod Mount

1/4" Whitworth socket


Material: High Impact ABS-PC with soft touch back & keypad


Temperature: Operating -10°C to +50°C, Storage -20°C to +60°C

Humidity: Up to 95% RH Non Condensing

Electromagnetic performance

IEC 61672-1:2002 & IEC 61672-2:2003

Except where modified by EN 61000-6-1:2007 & EN 61000-6-1:2007

Language options

English, French, German, Spanish. Other language options may be available

Software Support

NoiseTools Download, Configuration & Analysis software supplied as standard. Compatible with Microsoft Windows XP, Vista, 7 & 8 (32bit & 64bit)

Measurement Functions

CR:152A & CR:151A

Displayed Functions


Measurement Run Time

CR:152B & CR:151B

Displayed Functions


Measurement Run Time

Stored Functions

LXYMax & Time History of LXYMax

Time & Date of Measurement Start

where x=A ,C ,Z; y= F, S, I

Other functions may calculated by the NoiseTools software and displayed on download.

What our customers say..

It is a first class instrument and should be the prime tool of all environmental and occupational health officers...

Dr Philip Dickinson, Professor, Massey University, New Zealand

Product Datasheets

Get More Infomation

Which Optimus+ Yellow is right for you?

There are four versions of the Optimus+ Yellow sound level meter, 2 with Class 2 performance and 2 with Class 1 performance.

The table below shows the different versions and options available with each instrument.

You can also use our interactive Optimus Product Selector to find the best instrument for you.

Instrument Class 1 Class 2 Sound Level Data Logging VoiceTag Software Support Measurement Kit
CR:152A Yes Yes CK:152A
CR:151A Yes Yes CK:151A
CR:152B Yes Yes Yes Yes Yes CK:152B
CR:151B Yes Yes Yes Yes Yes CK:151B

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