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PPST
Phased PointSource Technology™ (PPST) was initially designed to solve a major problem with large-scale sound reinforcement. More transducers can generate the desired sound output but fewer transducers create better sound. Introduced as a core technology in the KF900 Series to specifically address this large-scale complexity, PPST is an ultra-sophisticated process of measuring, modeling, and optimizing arrays. PPST involves generating high-resolution measurement data for each separate element of a loudspeaker array and using this to model performance at a variety of listening locations. For this purpose complex data, with both frequency and phase information, is used. The goal is to manipulate the signal path of each array element for maximum integration and minimal interference. PPST is then capable of specifying DSP configurations for each transducer/horn element. These DSP-controlled elements are used to create arrays custom configured to venues ranging from moderately sized music sheds to the largest stadiums. In the case of larger venues, consistent SPL can be maintained over the entire audience area - from just 25 feet below the array to over 700 feet away from the system.
The PPST Process
The PPST meausrement/modeling/optimization process creates specific DSP settings for each cell in the array. In the case of the array illustrated above, 14 different DSP channels are required to drive each column.
The process begins with a round of precision measurements of each cell of the loudspeaker array in the exact position the modules would occupy in an array. Measurements are accurate to 1/10th of an inch or 10 kHz.
Using microphones set at fixed positions around our test facility, phase and frequency measurements are taken on-axis as well as at 15, 30, 45, and 60 degrees below the horizontal axis.
After the data are normalized to 1/6th octave resolution and "windowed" to isolate first arrivals, the results of the entire measurement round are fed into a proprietary goal seeking computer program called F-Chart. F-Chart sums the measurements of each cell to create a composite frequency response plot for the entire array and then manipulates delay and amplitude parameters for each cell to align response at each of the five measurement angles.
EAW engineers monitor F-Chart's progress -- usually over the course of a few days -- until they feel certain that total system response has been optimized and then fine tune the DSP settings for use in a specific venue. Using the venue's actual geometry and intended array location, the vertical beam profile is custom tailored.
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KF900 Series array shown with each module in a different color. Complex pre-configured DSP integrates the modules into a single acoustical entity.
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These illustrations show predicted average dB SPL at a variety of locations along the central axis of the array (upper left) at Olympic Stadium. Each white arced line represents a 6 dB difference ranging from 97 dB SPL (far right) to 127 dB SPL in front of the array.
The black lines indicate the measurement angles of 0, 15, 30, 45 and 60 degrees below the horizontal axis. Distances were calculated to provide accurate representation of high frequency losses due to air absorption.
At both 500 Hz and 6.3 kHz, all listening positions receive sound at a level somewhere between 96 and 105 dB or ±4.5 dB. On-site adjustment at installation brought actual response to within ±2 dB.
PPST accepts the well-documented but poorly understood effect known as air absorption as an important parameter to address when designing long throw arrays. Using a technique we call high frequency pre-emphasis PPST arrays project HF information more than 700 feet. Even level and frequency response at distant listening positions results from uneven response at 1m. Note how much "hotter" it is right in front of the array at 6.3 kHz as opposed to 500 Hz.
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To read more about PPST, please read the PPSTwhitepaper in .PDF format.
Products that utilize this technology:
KF900 Series
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