Report The Low Frequency Content Thread (films, games, music, etc) in Bass Content Posted December 17, 2014 All enclosures fall prey to their native responses in 2pi space. I would at least build one sealed enclosure and see how it measures in room (to see room gain profile, as it will cut down on those harmonics seen in 2pi). Now that REW can do distortion calculations with a regular sweep, it should be quite easy to see if you could do sealed, or if a quasi-IB or LLT will allow you the SPL/distortion needed and still hit the <10Hz goal. You are absolutely correct about harmonics when playing back ULF. They can easily be detected, and the fact that you are taking it into account in the planning phases is quite good. JSS Although I'm sure there are a few effects that are comprised of a single sine at 'x' Hz < 20 Hz, they are rare and I haven't experienced any to date. The important things to remember in anticipating the audibility of harmonic distortion in-room are 1) the effect of room gain on harmonic distortion as a percentage and 2) the masking of harmonic distortion by the sound design result. A good example is the recent EOT opening scene effect. The 10 Hz fundamental is simultaneous with a 3HD tone at 30 Hz @ -10dB, or 31.6% harmonic distortion, a 5HD tone at 50 Hz @ -20dB, or 10% harmonic distortion, etc. If, as an example, your sub generates 20% 2HD harmonic distortion at 10 Hz and you have typical +15dB room gain at 10 Hz and +5dB at 20 Hz the harmonic distortion drops as a percentage to around 5% with odd order harmonics being completely masked by the design of the effect. I submit that it is impossible to audibly detect that. Adam recently posted his speclab cap of that scene mic'd at the seats and it looks like he's around 10% 2HD at 20 Hz from the 10 Hz fundamental, but that's running the subs at 5-10dB above reference level and I will still question whether anyone could audibly detect that amount of distortion. At reference level, the distortion level would be <5% and absolutely inaudible. Back in the day it was the Irene scene from BHD and when comparing the mic'd at the seats version to the looped version it was easy to see the distortion drop to <5% with room gain and with odd order harmonics being completely masked by the fundamental structure of the effect. Yes, playing a single sine makes it simpler to detect audible harmonic distortion but there are no pure single frequency sine waves in nature nor in sound effects. In fact, as a general rule, ULF sound effects contain an incredibly wide array of frequencies. Neither is it possible to know exactly what the original version of a star ship going to warp should sound like vs the final version presented to the seats by your system. The bottom line is that, based on many years of listening and measuring tests, filtering out the bottom half of soundtrack effects because of the possible audibility of added harmonics based on projections derived from ground plane test results of a single driver version of a subwoofer would be a tragic mistake without very specific tests done in-room with actual program source.