The Octave Filter Set Type 1613 is a compact, portable unit which contains eleven passive band-pass filters for octave analysis. It is primarily designed for use in conjunction with the Precision Sound Level Meter Type 2203 or the Impulse Precision Sound Level Meter Type 2209. Four screws are used to join the 1613 and the Sound Level Meter together, making a portable noise and vibration analyzer. Filter centre frequencies are 31.5 Hz to 31.5 kHz arranged according to the preferred frequencies of ISO Recommendation R266 (i.e. related to multiples and sub-multiples of 1000 Hz). Each filter satisfies the requirements of ANSI S 1.11 — 1966 for octave band filters of class II and IEC Recommendation 225. The filter should be fed from a signal source of impedance less than 25 O and the load impedance should be 1 46 kQ in parallel with 40 — 60 pF. This means that the 1 61 3 is not recommended for use with the Vibration Meter Type 2510 (filter output impedance 100 0) or for driving the Power Amplifier Type 2706 (input impedance 15kO) without suitable buffer stages.