Smaart White Paper

White Paper Measuring and Optimizing Sound Systems: An introduction to JBL Smaart™ by Sam Berkow & Alexander Yuill-Thornton II JBL Smaart is a general purpose not intended as an inflexible procedure, acoustic measurement and sound system rather as the starting point for you to optimization software tool, designed for modify as you like and assist you in use by audio professionals. Running on a understanding and optimizing sound Windows® computer and utilizing system performance. almost any standard Windows compatible (MCI compliant) sound card, 1) What am I trying to measure and JBL Smaart offers an accurate, easy-to- why? use and affordable solution to many of the measurement problems encountered Before making measurements of a sound by sound system contractors, acoustical system it is critical to ask yourself, “What consultants and other audio am I trying to measure and why?” professionals. The performance of a sound system, JBL Smaart was designed by a team whether it is a permanently installed consisting of acoustical consultants, system, touring sound system, or some sound system designers, mixers, and hybrid of the two, is determined a installers. The goal of the project was to number of ways, both qualitatively and create a tool which would provide easy quantitatively. The following is a list of access to information which will help some of the most important questions to systems sound better, by identifying ask when determining the level of potential problems and quantifying performance of a given system. system performance. To meet this goal both a real-time module and disk-based • Frequency Response: Does the analysis module were developed. Perhaps system have the ability to deliver sound most importantly, the features within over the intended frequency range, within JBL Smaart suggest a methodology for the expected deviations? optimizing sound systems. This methodology is developed and explained in this paper. The method described is • Power Handling: Can the system and whether it is an existing system, a handle the desired amount of power touring system, or a new system to be without excessive distortion or failure? optimized. • Coverage: Does the system provide However, there are several steps we feel sufficient coverage of required areas at are necessary to any successful exercise all frequencies? in sound system measurement and optimization. The order in which they • Subjective Quality: This is always the would be followed might differ according most important criteria. Does the system to the tuner’s personal preference and the meet the task at hand. The procedure outlined audience/owners/performers/operators here is based on our own experience and expectations for perceived sound quality? assumes a system that is already in place. • Stability: Does the system feed back The Transfer Function & System with microphone(s) open and the gain set Configuration to a useful level? (This is obviously not important if the system is playback only.) At the heart of JBL Smaart’s Real-Time Module is the transfer function • Noise: Is the system noisy? Are hums, calculation. The transfer function (stated buzzes and other unwanted noise present simply) is a comparison between the in the system? input and output of a system. The transfer function of a system can be • Configuration: Do you understand displayed in either the time or frequency the system configuration? Some sound domain. To make the results of this systems have groups of speakers driven calculation easy to understand, JBL from a single source. Others are divided Smaart displays the result in the into several sections, each controlled by a frequency domain. To accomplish this different set of control circuitry (such as calculation JBL Smaart compares two equalizers, delays, crossovers etc.). signals, each of which are input to your computer’s sound card. • Operation: Are all components of the system working? No piece of hardware or software (even JBL Smaart) can accurately answer all of these questions by itself. Tuning a sound system requires an understanding Fig. 1 of the hardware, a discerning ear, accurate measurements, and a disciplined Figure #1 displays a typical setup for and systematic approach. We doubt that using JBL Smaart to make transfer any two system tuners approach the function calculations. The use of two problem exactly the same way. Also, the signals, measured at the input and output process necessarily differs, depending on of a system, allows JBL Smaart to the complexity of the system in question display a comparison of the input and output as a function of frequency. This configuration allows the test signal to be A Step-by-Step Approach noise, music or almost any broadband signal. The Coherence function feature of STEP 1: Evaluation Listening JBL Smaart is used to check the validity Before you begin measuring a sound of the data, thus helping users to system, we strongly recommend listening understand whether that data is reliable. to it! You should attempt to qualitatively For the transfer function calculation to be answer the questions listed on the valid the two input signals must be previous page. This will require you to aligned in time. This can be accomplished move around and listen to each section using the Delay Locator and Internal or subsection of the system. Explore the Signal Delay features edges of the coverage pattern to see included within JBL Smaart. where the various elements are covering and where they are not. It may also be After making a measurement in the helpful to turn off parts of the system in configuration displayed in Figure #1, the order to make a more detailed evaluation results may be stored and the system of various subsystems and components. reconfigured as shown in Figure #2: Practical Note: Unless you designed the system, take some time to try and understand what the system designer had in mind and how the various elements relate to each other. Fig. 2 STEP 2: Identify Potential Problems Examining the list of questions above, Measuring the transfer function of the are there any obvious problems that need equalizer (Figure #2) is particularly to be addressed? For example, unwanted useful when the resulting transfer noise, such as hums and buzzes function is inverted and overlaid on top associated with ground loops and “dirty” of the previously stored loudspeaker power, can degrade system performance measurement. The need to switch and should be addressed before JBL between measurement points within a Smaart testing is begun. Loose and system suggests that the use of an intermittent connections should be fixed. external mixer, as configured in Figure A gain structure that leaves the system #3, may prove extremely useful in the hissing should be explored and corrected. field: Practical Note: The system must be stable before trying to make measurements. Systems that seem to be changing gain or have noises that come and go are not good candidates for critical measurement. Spend some time sorting things out first. Fig. 3 STEP 3: Select Measurement Points & Positions Practical Note: Acoustical reflections of This is one of the most important steps in sound energy from large (and some not the process. You need to select so large) surfaces may generate “comb measurement points that will show you filters” in the measured signal. The what you need to see. There are two result is a system of dips in the kinds of measurement points: electrical frequency response that are evenly and acoustic. spaced in frequency. They are easiest to see when the frequency axis is set to Electrical measurement points are used linear, as they appear to be a set of to sample the input or output of a valleys evenly spaced across the plot. particular piece of equipment. If you want to measure a piece of equipment, or STEP 4: Compare Positions the result of a string of series-connected In making acoustic measurements of any pieces of equipment, make the system, it is important to make a number connections at the input and the output. of measurements to make sure that you are not being fooled by something Acoustic measurements are made with a affecting the measurement (such as microphone. When making transfer reflections). Move the microphone function measurements, a reference around and look at what happens to the signal is also required. The connection measured frequency response. Also, you for the reference signal should be made may wish to put sound absorbing at the input of the speaker system, the materials on the floor between the source input of the processor if it is a processed and microphone to reduce the effect of system, or at the input of the system’s the reflected sound energy from the floor equalizer(s). (this is another good place to think “mirror”)... Microphone selection and placement are very critical. The microphone must be a STEP 5: Set Equalizers and Delay known quantity. A measurement Settings microphone should be of high-quality Setting equalizers and delays can be very construction, having the flattest time consuming. There seem to be two frequency response characteristics that distinct stages to the process: coarse you can reasonably afford. When adjustment and fine tuning. In the first selecting the microphone position, ask stage, large adjustments to EQ and delay yourself two questions: “Is this a useful settings are used to make a system place to make a measurement?”, and roughly correct. Sometimes, the sheer “What other things will the microphone size of these adjustments may seem a pick up in this location that might affect little daunting, but if things are sounding the measurement?” Reflections into the right, you are probably OK. The next side or back of a measurement stage takes place when the system is microphone can seriously reduce the getting close to right.

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