MLSSA Acoustical Measurement System

1 MLSSA Acoustical Measurement System Industry Standard Pink-MLS and White-MLS Outputs Adjustable Bandwidth: 1 kHz to 40 kHz loudspeaker Measurements Integrated QC PASS/FAIL Functions Thiele-Small Parameters with SPO Option Speech Intelligibility per IEC 60268-16 Room Acoustics per ISO 3382 Room EQ Using the Adaptive Window Industry Standard Since its introduction in 1987, MLSSA (pronounced "Melissa") has become the loudspeaker industry's standard measuring System as recognized by the world's leading loudspeaker designers and manufacturers. MLSSA is also the System chosen by automakers, academicians, acousticians, recording studios and government agencies for many other applications including room equalization, room acoustics measurements and speech intelligibility measurements. MLSSA , an acronym of Maximum-Length Sequence System Analyzer, pioneered the MLS (Maximum-Length Sequence) Measurement method, which offers an unsurpassed combination of speed, noise immunity and time-bandwidth product.

2 The user-friendly MLSSA software offers a rich set of post-processing functions to satisfy the needs of a wide range of audio professionals including loudspeaker designers, sound engineers and Acoustical consultants. Room and loudspeaker Equalization The advent of surround sound and digital equalizers has created an urgent need for fast accurate in-room frequency response measurements. MLSSA provides a solution through its innovative Adaptive Window Measurement method which is psycho-acoustically more accurate than conventional real-time analyzer (RTA) measurements. If desired, RTA-type room frequency response measurements can also be performed by MLSSA . In either case, spatial averaging of room measurements taken at different microphone locations is directly supported and functions are provided to perform surround-sound EQ as well as surround-sound level adjustments.

3 Sampling at exactly 96 kHz is supported to facilitate the use of fast convolution processors to perform room and loudspeaker equalization. loudspeaker Designers and Manufacturers loudspeaker designers find MLSSA indispensable for producing competitive designs especially for the high-end audio market. MLSSA 's 40 kHz Measurement bandwidth is essential for characterizing tweeter resonances and, its integrated 3-D waterfall display of loudspeaker sound decay (see figure) is much valued by loudspeaker designers and reviewers alike. When interfaced to a motorized turntable MLSSA performs automated polar measurements to completely characterize loudspeaker dispersion and directivity. MLSSA also performs loudspeaker impedance measurements. Other measurements are provided to assess loudspeaker time-coherence. Integrated QC PASS/FAIL functions are included for production testing of loudspeakers or drivers.

4 Acoustical Consultants MLSSA provides an array of measurements required by Acoustical consultants. Measure room and performance hall acoustics, noise levels as well as speech intelligibility. MLSSA measures room acoustics according to ISO 3382 in 1/1, 1/2 or 1/3-octave bands. You can also measure noise levels in 1/1, 1/2, 1/3 or 1/6-octave bands as well as the noise criterion (NC) rating. STI and RASTI measurements properly account for the effects of reverberation, echoes, loudspeaker distortion and the background noise. Portable DAT recorders can be used to perform STI and Acoustical measurements in large spaces and/or at remote locations without moving MLSSA to the site. DRA Laboratories Sarasota, FL, USA Web site: loudspeaker Measurements Anechoic Frequency Response A primary application of MLSSA is measuring the anechoic frequency response of loudspeakers without an anechoic chamber.

5 To measure the anechoic frequency response of a loudspeaker MLSSA uses cursors to select only the initial portion of the measured impulse response before the arrival of any room reflections (see figure below). MLSSA then applies an FFT to the selected segment to yield the anechoic frequency response of the loudspeaker (see figure right). Because MLSSA measures directly in the time domain, it is a simple matter to discover any room reflections that might contaminate the Measurement and then window them out of the results. Methods that measure directly in the frequency domain, such as TDS, gated-sinewave or dual-channel FFT, require more complicated procedures for insuring that room reflections are excluded. Moreover, unlike gated-sinewave analyzers, MLSSA also correctly measures true loudspeaker phase response. Near-field Bass Response Unfortunately, in typical rooms, such windowed anechoic measurements are valid only down to about 200 Hz using any method.

6 To obtain the anechoic frequency response in the bass region MLSSA uses a near-field Measurement method and then splices this result to the anechoic free-field high-frequency Measurement to cover the full audio range. MLSSA therefore allows you to determine the full-range anechoic frequency response and anechoic phase response of even the most complex loudspeaker systems having any number of drivers, ports or passive radiators, all without an anechoic chamber. Cumulative Spectral Decay Plots A cumulative spectral decay (CSD) plot is a 3-dimensional display that reflects a loudspeaker 's frequency response as well as its phase response. A CSD plot resembles a waterfall and shows how a loudspeaker 's acoustic output decays, at each frequency, in response to a steady-state sinewave input that is suddenly turned off. CSD plots reveal otherwise hidden enclosure or other resonances and are used to assess loudspeaker transient response.

7 A CSD waterfall is illustrated on the front cover of this brochure. Time Coherence and Acoustic Center MLSSA includes special measurements to assess loudspeaker time coherence. In the time domain the step response is provided. More comprehensive frequency domain measures of loudspeaker time coherence are the excess phase and excess group delay. Excess phase is the difference between the loudspeaker 's actual measured phase and its theoretically minimum phase as calculated from its frequency response. Similarly, excess group delay is the difference between the loudspeaker 's actual group delay and its theoretically minimum group delay. MLSSA also calculates the Acoustical centers of drivers based on the measured excess phase. Impedance Measurements MLSSA performs fast accurate impedance measurements of speaker drivers and loudspeaker systems. Both impedance magnitude and phase are measured.

8 The MLSSA Speaker Parameter Option (SPO) makes full use of MLSSA s accurate impedance measurements to determine the Thiele-Small parameters of dynamic Laboratories Sarasota, FL, USA Web site: loudspeaker Measurements (continued) loudspeaker Polar Response MLSSA conveniently measures free-field loudspeaker polar response either manually or using a motorized turntable. Polar frequency response curves are normally plotted using a special waterfall display. You can optionally equalize all the off-axis measurements to the on-axis response thus showing only the change in the loudspeaker 's frequency response for the off-axis angles (see figure below). The waterfall data can easily be imported into MS Excel to generate circular polar plots at selected frequencies (see figure right). Optional smoothing of the polar response data from to octave is provided. MLSSA also calculates loudspeaker sound power response, directivity index and directivity Q from measurements of vertical and horizontal polar frequency response.

9 Distortion Measurements MLSSA calculates even, odd and total harmonic distortion from power-spectrum measurements taken in the near field or in an anechoic chamber, using an external sinewave generator. Harmonic distortion results can be exported to a text file for display and further analysis by other programs. MLSSA also determines multi-tone intermodulation (IM) distortion vs. frequency from MLS measurements taken in the near field or in an anechoic chamber. Because an MLS contains many thousands of pure tones, much like music, MLS IM distortion measurements are more representative of loudspeaker distortion than either harmonic distortion or conventional two-tone IM distortion measurements. QC PASS/FAIL Functions In the frequency domain, MLSSA provides for comprehensive automated QC PASS/FAIL testing. An unlimited number of arbitrary upper and lower QC limits curves can be pre-defined and stored on disk.

10 Both fixed and floating limit curves are supported. A third optional limit curve provides for distortion and/or buzz testing. You can also optionally store a reference Measurement of a "sweet" loudspeaker or driver. Thereafter, MLSSA will display the decibel difference between the reference unit and the unit under test and then the QC PASS/FAIL functions will operate on this difference curve instead of on the measured curve. MLSSA will also automatically check for correct loudspeaker and/or driver polarity. Post-processing Functions MLSSA offers a comprehensive set of post-processing functions for testing loudspeakers. In the time domain, MLSSA will compute loudspeaker energy-time curves from the measured impulse response. In the frequency domain, you can display phase, unwrapped phase, minimum phase, excess phase, group delay and excess group delay. You can also smooth any frequency response curve from to octave.