U.S. Patent No. 6,219,426 issued April 17, 2001


New Acoustasonic SFX II
acoustic guitar amp

Groove Tubes SFX product:

Fender SFX
The Next Generation Comes to Instrument Amplifiers
by George Petersen - Mix Magazine

July 10, 1998, at the Summer NAMM show in Nashville, Fender will unveil SFX™ (Stereo Field eXpansion), arguably the most important breakthrough in instrument speaker technology since the introduction of the Leslie speaker. A bold statement, perhaps, but the SFX effect simply has to be heard to be believed. The system is also affordable, adaptable to existing amp rigs and based on acoustical principles so simple that once the word gets out, 100,000 audio engineers around the planet are going to kick themselves, wondering, "Why didn't I think of that first?"

Unfortunately, there's no way to create a usable stereo field from a standard combo guitar amp, whether the speakers are side by side or stacked atop each other. Move two cabinets to either side of the stage for maximum separation and the audience along the center aisle hears the spread, while listeners on either side hear mostly one side or the other. Essentially, SFX is a system for creating/playing back huge stereo effects from two speakers that are placed near each other, or within the same cabinet.

Licensed by Fender, the SFX system was developed and patented under the name CPS (Center Point Stereo) by Groove Tubes founder Aspen Pittman and Drew Daniels, who has served as AES Chairman in Los Angeles and is an electro-acoustic engineer who has worked for JBL, Tascam, Fender and Walt Disney Imagineering.

So how does it work? According to co-inventor Daniels, the process is extraordinarily simple: "The basic principle is like M-S [mid-side] miking in reverse." A stereo signal from a guitar preamp or effects loop feeds two speakers: One channel is routed through a sealed enclosure with its cone facing forward, representing the "mid" part of the signal. And like the "side" part of the M-S miking equation, the bottom speaker is mounted on a baffle (perpendicular to the top speaker) within an open-sided enclosure to generate a figure-8 dispersion, where one side is out of phase with the other.

"The SFX electronics process stereo signals into sum and difference signals," explains Daniels. The signals that started out as "left" signals are made into signals that add acoustically in the air around the cabinet, causing the SFX speaker array to steer the combined acoustical output of the two speaker elements toward the left side of the cabinet. Signals originally from the "right" are made into signals that subtract acoustically, causing the SFX speaker array to steer the acoustical output toward the right side of the cabinet.

By simply adjusting the balance between the two speakers and feeding a stereo source (such as the onboard DSP effects built into the new Fender amps), a massive ambient field is formed that can envelope a medium-sized room. "Hearing SFX is like hearing surround TV for the first time," beams co- inventor Pittman. "It makes the amp sound huge and not just left/right, but deeper." Pittman does add a warning about using the system for the amplification of recorded playback material: "Compared to ordinary stereo, SFX is not as accurate. However, its surreal reproduction enhances stereo effect."

At NAMM, Fender will show three SFX amps: The $999 SFX Keyboard 200 has two stereo and one mono input for keyboards; the $899 Acoustasonic SFX is designed for acoustic instruments; and for players who want SFX but already have a favorite amp, the $749 SFX Satellite is an add-on single-12 cabinet with onboard amp and DSP.

While SFX technology is currently only offered in instrument amps, other applications come to mind, although large-scale concert P.A. probably won't be among them, due to the feedback con-siderations of very wide dispersion systems. How-ever, SFX could be ideal in special venue or theme park installations, or possibly as a replacement for cinema surround speakers. It will be interesting to see where SFX goes next.

Fender, 7975 N. Hayden Road, Scottsdale, AZ 85258; 602/596-9690; fax 602/596-1384.
Web site:  www.fender.com.

These materials copyright ©1998 by Intertec Publishing