Stephen:
I primarily work as a theatre sound designer, but I find the
conversations here both very interesting and connected to theatre
sound, so I enjoy lurking here.

In talking with another theatre sound designer, he explained he used a
lot of low frequency (sub 80 Hz) that could be felt by our muscles as
a way of emotional impact. His theory was that film sound designers
are doing this so much, audiences will expect it in the theatre too.

So my question is... do these low frequencies exist in your films
(intentionally or inherit to the medium), and what is their purpose or
affect?

Randy Thom:
Sounds in the range of 30 to 80 hertz are used fairly often in films
these days. Some would say too often. It can be a good way to make a
moment powerful without making it seem too loud. We tend to associate
very low frequencies with dramatically powerful events... like
earthquakes... and earthquakes are rarely loud. These very low
frequency sounds are often derived from sounds already in the mix.
There are hardware and software "sub harmonic generators" that will
into which you can feed an explosion, or anything that already has
some significant low frequency content, and the sub generator will
produce lower harmonics of that sound. And sometimes the 30 to 80
hertz sounds are produced on their own. For those who might not be
aware of it, the ".1" in a "5.1" sound system is for these extremely
low frequencies. Of course, many theaters won't reproduce those low
frequencies accurately, and some won't reproduce them at all, so it
isn't wise to depend TOO much on them.

It's generally considered a bad idea to have continuous sub material
in a long sequence. Much better to use it sparingly. That way it has
more impact when you do use it.

Paul Grajek:
Using low frequency information is especially useful in film as great way to
enhance perceived loudness, yet not raise the decibel level too high. The
more broadband your soundtrack is at any given time, the louder it will be
experienced, allowing you to save the truly loud parts (with more high
frequency content) for meaningful moments. Explosions in "The Incredibles"
are a great example. They are deceptively soft compared to average Hollywood
explosions because they contain largely low freq content to allow the music
to be heard at the same time without too much masking. I'm sure these film
techniques could translate nicely to theater.

Ryan L. DeLap:
Stephen, I'm also a theater sound designer; I've used low frequency sound in multiple
shows as means of impact, and quite effectively. For instance, our theater
did a rock opera featuring the music of David Bowie, and the opening song
was "Space Oddity," with the shuttle launch. When the band got to the part
of the song when the shuttle launches, we used a sound effect of a rocket
launch and cranked up the lows through the subwoofer, which created more of
a felt effect than heard effect (which went great with the light designer's
effects!). This let the band come through clearer without masking or
distortion. We've also used it for explosions for battle scenes. Quite a
useful technique if done properly and in moderation!

Excerpt from thread "Building in Low Freq" started Jul 14, 2007 at Sound Article List

Film Sound Question & Answers