Why was Focusing Technology developed?
Even in well-designed professional loudspeakers, inherent sonic flaws such as phase plug reflections, horn resonances and cone resonances can cause undesirable audible artifacts. Implemented through advanced digital signal processing, EAW Focusing™ generates complex filters that correct these imperfections and improve the impulse response of a loudspeaker. This is accomplished by isolating linear, time invariant and spatially consistent anomalies in a loudspeaker’s response and eliminating them through advanced processing. The result is a high output, controlled loudspeaker that provides a pristine transient response equal to that of a direct radiating studio monitor.
The EAW Focusing process compares the output of the loudspeaker system to its input. The resulting digital signal processing implemented with EAW focusing corrects for any differences. This means the sound you put into the loudspeaker system is the same sound you get out, providing predictable performance and clarity in the listening area.
Focusing & the EAW Greybox
This technology is FIR filters with hundreds of values, painstakingly created in our pit lab to improve phase anomalies as sound exits horn loaded products. This becomes especially important for products that deploy a large horn. You may have heard our speaker presets referred to as greyboxes. This is our proprietary term for our speaker tuning, and a large part of the greybox is Focusing.
EAW creates custom grey box settings in our engineering lab for every product we make. These grey box settings come preloaded in EAW software and electronics. When you are unable to use EAW electronics, we offer support for popular third-party processing and amplifier platforms. These options can be found on our website.
They are named grey boxes because they are comprised of the IIR, FIR, and dynamics settings created by EAW engineering to achieve consistent voicing, perfect impulse response and loudspeaker protection. These settings function like a “black box” and are not user adjustable. On the other side, there is a healthy complement of processing objects available to the user to adjust as the design requires. These settings function as a “white box.”
When combined an EAW “grey box” is created.
Horn Honk
Horn honk, better defined as horn resonance, is when a wavefront encounters a discontinuity along a horn’s expanding walls. This produces a sound reflection. All horns have such a discontinuity at their mouths. Likewise, diffraction slots, used to achieve wide HF patterns in constant directivity horns, present a severe discontinuity at their exits. These discontinuities cause a portion of the sound energy to be reflected to the compression driver where it is both partially absorbed and partially re-emitted, often several milliseconds late. For a transient signal, this repetitious process results in a resonance that produces a decaying sequence of impulses at the listener rather than a well-defined impulse. Because low frequencies tend to be reflected more strongly than high frequencies, the most problematic reflections are in the lowest octaves of the horn’s usable range. The excess energy from these reflections builds up and results in distinct colorations at frequencies related to the path length of the reflections.
Splashiness
Splashiness is produced by compression driver phase plugs. Phase plug openings are arranged so that the path from any point on the driver’s diaphragm to an opening is relatively short. The intent is that all of the driver’s sound power leaves via the “nearest exit” in the phase plug. However, some fraction of the sound arriving at any phase plug opening will continue past and arrive at a second opening where this sound is divided again.
Thus, rather than a single acoustical impulse, transient energy leaves the phase plug and reaches the listener as a decaying sequence of impulses. The decaying impulses from one signal invariably overlap and mask details in subsequent HF signals. The result is the masking of transient attacks and the lack of high frequency detail and subtleties normally, cleanly reproduced by direct radiating, but low output, HF drivers.
Full Range Loudspeaker Concerns
In a compact, 2-way loudspeaker, physical limitations result in an HF horn size that virtually dictates the crossover frequency be set above the LF driver’s optimum upper frequency limit. This problem is especially troublesome with larger LF drivers. The LF driver must reproduce frequencies where its transient response is sloppy, and its sonic character is muddy. The crispness of the horn-loaded HF system only accentuates this character.
A major source of the LF driver problems is the vibrations that travel from the voice coil through the cone material to the edge surround. Here they are only partially absorbed, meaning a portion of their energy is reflected through the cone to the voice coil. Some of this energy is then reflected up through the cone. This repetitious process results in resonances. Unlike a horn, these reflections tend to be strongest at the upper end of the woofer’s usable range.
Digital Signal Processing & Loudspeaker Correction
The primary tool available for dealing with loudspeaker anomalies is DSP (digital signal processing). The usual method for employing DSP begins with the measurement of a loudspeaker’s frequency response. This response is then inverted to generate a complementary “preconditioning” set of filters.
These filters should correct the performance anomalies in question. The problem is that the measured response includes two kinds of anomalous behaviors. The first are linear, time invariant, and spatially consistent anomalies, meaning behaviors that don’t vary with the loudspeaker’s operating conditions or the ambient environment. These are correctable behaviors. The second are nonlinear, time variant, and spatially variant anomalies, meaning behaviors that vary with the loudspeaker’s operating conditions or the ambient environment. These are uncorrectable behaviors.
Because both types of behaviors are lumped together in the measured response, the preconditioning filters end up including filtering for the uncorrectable anomalies. This condition makes the response worse in some directions and at output levels that differ from the original measured response. To further complicate matters, certain behaviors can permanently change with use. This means such filtering would not only cease to be helpful over time, but likely detrimental to reproduction accuracy. As a result, DSP has not provided the illusive cures for very specific and obvious anomalies that include honk, splashiness, and cone resonances.
Spectrograph Acoustical Analysis
The solution begins with EAW’s proprietary, software-based, spectrograph for acoustical analysis. This spectrograph, along with other analysis tools, is used to investigate the unprocessed responses of the loudspeakers’ HF and LF subsystems in various directions and at various levels. This analysis allowed various performance anomalies to be isolated from each other. In this way, those anomalies that were linear, time invariant, spatially consistent, and therefore correctable, could be distinguished from anomalies without those characteristics, and which were therefore not correctable.
Next is to apply appropriate DSP to correct those anomalies. EAW utilizes custom DSP algorithms specifically engineered to provide the required filters for correcting loudspeaker anomalies. The resulting filters had to possess the required precision and accuracy in both the frequency and time domain. At the same time, any uncorrectable anomalies would have to be ignored by the filters.
This advanced processing is Focusing. The anomalies and resonance problems corrected are specific to each loudspeaker design. The internal physical details must be known, the anomalies must be carefully analyzed, and appropriate filters must be custom designed.
With Focusing technology applied to the inherent HF and LF anomalies, EAW loudspeakers provide a pristine, transient response and lack of coloration equal to that of world-class, direct radiating studio monitors.
EAW products are continually improved. All specifications are therefore subject to change without notice.
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