Heard about the new killer on the loose? Don’t worry, it’s only killing subwoofers.
I’m talking about the soundtrack to Edge of Tomorrow. In the film’s first few seconds, high-level tones at 29, 24, and 19Hz in the LFE channel are causing the drivers in some subwoofers to bottom out -- a potentially damaging situation in which the woofer’s voice coil is hurled so far back that it slams against the back plate. Not only have I read Internet reports about this, I experienced it with a subwoofer I was testing. This scary situation reminded me of the old audiophile shibboleth “Simpler is better.”
I first encountered these deep tones while testing a different subwoofer. Although much smaller than the sub that had the problem, this one didn’t emit so much as a single audible chuff of port noise, yet it still gave me the awesome thrill ride that the engineers who mixed Edge of Tomorrow intended. What was the difference? The smaller subwoofer had a fairly steep subsonic high-pass filter at about 20Hz, to attenuate any potentially damaging subsonic tones. It apparently also had a fairly conservative limiter setting that throttled back the sub’s amplifier before it could damage the driver.
Some audio enthusiasts might applaud, in theory, the simpler approach of using a shallower high-pass filter and a less aggressive limiter setting. Some might even say that it’s preferable to have no high-pass filter and no limiter. But I don’t see what’s “musical” or “accurate” about a subwoofer bottoming out.
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