MEASURING SPEAKERS Demian Martin Product Design Service Burning Amp Workshop 2019
AMPS AND SPEAKERS CANNOT EXIST WITHOUT EACH OTHER • The traditional crossover is a dinosaur • Commercial speaker systems are self contained with electronic crossovers and multiple amps all matched to varying degrees. • Most are designed in Asia by teams with little sensitivity to the finer points in audio. Demian Martin Product Design Service Burning Amp Workshop 2019
WHY ARE YOU TESTING YOUR SPEAKERS? • Identify a problem • Confirm performance per design • T esting components before the design phase Demian Martin Product Design Service Burning Amp Workshop 2019
SPEAKER PROBLEMS • Frequency response • Distortion • Driver compression • Rub and Buzz Demian Martin Product Design Service Burning Amp Workshop 2019
DRIVER PROBLEM AREAS Voice coil alignment • • Voice coil centering • Lead out flex hitting the cone • Polarity Reversed • Surround not stiff enough or too stiff Cone issues • Loose stuff under the dome • • Spider breakdown Demian Martin Product Design Service Burning Amp Workshop 2019
WHAT TO TEST FOR • Response • Distortion • Noises • Polarity • Sensitivity Demian Martin Product Design Service Burning Amp Workshop 2019
TOO MANY OPTIONS • Frequency response At what SPL? • • Compression? • Which angle? • Distortion 2nd and 3 rd harmonics • • IM? • Distortion vs. level? • Delayed resonances Or stored energy? • • Impedance vs frequency Demian Martin Product Design Service Burning Amp Workshop 2019
ACOUSTIC TEST ENVIRONMENT • Anechoic Even if you have the room its too small! • Ground Plane The most practical and easiest to implement if you have space • Near field high frequency windowed Only good to 500 Hz if you are lucky. Demian Martin Product Design Service Burning Amp Workshop 2019
ANECHOIC CONSTRUCTION Concrete walls Suspected and isolated from the building and ground Fiberglass wedges that are 3’ long on all surfaces Expensive and special purpose. Not for listening. Not really needed for speakers anymore.; Demian Martin Product Design Service Burning Amp Workshop 2019
GROUND PLANE MEASUREMENT Typically 6 feet (2M) Floor must be hard and preferably rigid (concrete, hardwood, tile). 6 feet corrects for the acoustic gain from the reflecting surface Demian Martin Product Design Service Burning Amp Workshop 2019
GROUND PLANE MEASUREMENT -2 Reflections determine the low frequency limit for accuracy. The relationship to work with: Sound travels around 1 foot per mS. 1 mS is the reciprocal of 1 KHz. So a 10 mS first reflection will limit you to 100Hz. Demian Martin Product Design Service Burning Amp Workshop 2019
GROUND PLANE MEASUREMENT -3 Hard surfaces are better for this since determining the reflection is easy. Soft surfaces blur the reflections by absorbing the high frequencies so the waves become harder to see. Demian Martin Product Design Service Burning Amp Workshop 2019
WHAT WE ARE OFTEN REDUCED TO Set up microphone and speaker around 1 meter apart in a room and hope for the best. Reflections will degrade the measurement. You can still sort out a number of aspects. Measure at different lengths so separate room, driver and cabinet diffreaction Demian Martin Product Design Service Burning Amp Workshop 2019
EQUIPMENT Demian Martin Product Design Service Burning Amp Workshop 2019
DEDICATED SYSTEM • Pro level • Listen • AP Complete solutions needing only a PC with dedicated Etc. • hardware for measuring speaker systems. • Clio More focus on manufacturing than R&D. • Clio Pocket • Praxis • Omnimic • Quantasylum Demian Martin Product Design Service Burning Amp Workshop 2019
PC + MIKE SYSTEMS • ARTA • REW Software that works with soundcards and more • Others standardized microphones • Minidsp Umike • UMM6 • Similar microphones Demian Martin Product Design Service Burning Amp Workshop 2019
DIY SUITABLE TEST EQUIPMENT • Packaged: Easy to setup and get useful info somewhat limited in measurement capability Omnimic • • Clio Pocket • Umike + REW • “Assembled” need you to buy a microphone Used by hobbyists and some professionals Cost effective • Software • ARTA • REW • Hardware • Focusrite • Behringer • Dayton Demian Martin Product Design Service Burning Amp Workshop 2019
MEASUREMENT MICROPHONES • What is different • Directional performance of an omni measurement microphone • How to use and not use Demian Martin Product Design Service Burning Amp Workshop 2019
3 MEASUREMENT MICROPHONES How the marketing department wants them to look B&K 4135 ¼” free field microphone $$$$$ Nady CM100 Measurement microphone $ Girardin microphone $? Demian Martin Product Design Service Burning Amp Workshop 2019
ACTUAL MEASURED PERFORMANCE Real measurements in Bruel & Kjaer 4135 “compromised” conditions of three microphones using a Girardin Pioneer ribbon tweeter. The B&K is very expensive. The Girardin is an ECM Nady microphone capsule ($1) on the end of a 12” brass tube. The Nady is a used mike from 1 dB per division and 2KHz to 50 KHz. eBay. Within limits they can all The Nady can be “calibrated” to maybe 30 KHz work if you know what to with a correction file. Without you will probably expect. boost the top end if you attempt to correct that far. Demian Martin Product Design Service Burning Amp Workshop 2019
ON AXIS VS OFF AXIS RESPONSE Even the best microphones cannot defy mother nature. On axis they will have a rising response compared to off axis starting at some frequency depending on dimensions. For a 1” mike the differences start at 1 KHz. ½” 2 KHz and ¼” 4 KHz. Know how your mike is calibrated. Demian Martin Product Design Service Burning Amp Workshop 2019
WHY THE HIGH FREQUENCIES ARE BOOSTED ON A FREE FIELD MICROPHONE There is a pressure buildup on the surface of a plane normal the the acoustic wave. It peaks at 6 dB when the wavelength matches the diameter. Demian Martin Product Design Service Burning Amp Workshop 2019
ON AXIS AND GRAZING (90°) RESPONSE NADY MICROPHONE On Axis Grazing 2.5 dB Note the difference with the grazing incidence dropping at an increasing rate. Demian Martin Product Design Service Burning Amp Workshop 2019
MEASUREMENT SYSTEMS i. They can all lie ii. Interpreting the output. 1. If it doesn’t look right its probably wrong and usually cockpit error 2. Have a known reference around, ALWAYS! Demian Martin Product Design Service Burning Amp Workshop 2019
ELECTRICAL TEST • Impedance • Principles • Voltage across driver • Current through driver • Ohms law (for AC) • Follow software vendors instructions • Use a known resistor to verify • Drivers change with level T est at low level for Thiele/Small parameters Demian Martin Product Design Service Burning Amp Workshop 2019
ACOUSTIC TESTS • Response • Distortion • Waterfall • ETC or Analytic Demian Martin Product Design Service Burning Amp Workshop 2019
CRUDE TEST Demian Martin Product Design Service Burning Amp Workshop 2019
IMPULSE RESPONSE Direct Reflections Demian Martin Product Design Service Burning Amp Workshop 2019
UNWINDOWED Demian Martin Product Design Service Burning Amp Workshop 2019
WINDOWED: CORRECTED FOR WOOFER DELAY Phase transition Demian Martin Product Design Service Burning Amp Workshop 2019
WINDOWED: CORRECTED FOR TWEETER DELAY Phase transition Demian Martin Product Design Service Burning Amp Workshop 2019
ETC OR ENERGY VS TIME Initial Peak First reflection More junk Demian Martin Product Design Service Burning Amp Workshop 2019
CUMULATIVE SPECTRAL DECAY OR WATERFALL Initial response Decay Demian Martin Product Design Service Burning Amp Workshop 2019
ARTA RECORD SCREEN Demian Martin Product Design Service Burning Amp Workshop 2019
ARTA IMPULSE Demian Martin Product Design Service Burning Amp Workshop 2019
ARTA RESPONSE Demian Martin Product Design Service Burning Amp Workshop 2019
ARTA ENERGY TIME CURVE Demian Martin Product Design Service Burning Amp Workshop 2019
ARTA WATERFALL Demian Martin Product Design Service Burning Amp Workshop 2019
ARTA BURST DECAY Demian Martin Product Design Service Burning Amp Workshop 2019
REW Demian Martin Product Design Service Burning Amp Workshop 2019
REW MEASUREMENT SCREEN Demian Martin Product Design Service Burning Amp Workshop 2019
REW LEVEL AND PHASE Demian Martin Product Design Service Burning Amp Workshop 2019
NOW THAT YOU HAVE THIS WHAT TO MAKE OF IT? • Things to fix • Driver balance • Broad peaks and dips • Crossover stuff • Cabinet diffraction • Driver spacing • Things to not fix • Deep sharp notches you won’t hear them. The fix is worse than the problem • Noises: driver response problems. Replace the driver. Demian Martin Product Design Service Burning Amp Workshop 2019
HANDS ON TESTING ELECTRONICS • Electronics • Quantasylum • Suite of measurements Demian Martin Product Design Service Burning Amp Workshop 2019
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