Most racing sims do not have untapped bass. This is the downshifting spectrum from the Panoz in PC2, one of my favorite cockpit sounds with a low V8 exhaust note, and you'll see that it's dead below 40 Hz. At 20 Hz, it is -20 dB from the sound peak, a full 100x quieter than the sound peak. AC, AMS, and rF2 do no better. I haven't checked Raceroom's spectrum, but my ear says it does no better.
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ACC is a bit of an exception. This is the BMW's cockpit spectrum, both upshifting and downshifting. You can see it is alive below 20 Hz. Unfortunately, the sound energy comes from annoying cabin harmonics (possibly artificially boosted since you can see a straight slope in the graph) rather than anything motorheads find enjoyable. While there is sound below 40 Hz, most of us would probably rather not hear it in this case!
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By the way, anybody can easily make these graphs using the free Audacity program.
From general experience with tests mainly only involving AC and ACC. What I can say is that lots of cars idle sensation will have low bass rumble and their own character from engine or transmission sounds. Some car sound mods are really good too.
A "gearshift" may not be the best example for low bass usage from sim-game audio. Also better perhaps to see the output at 0dB, to then see what Hz are +/- with realtime changes being made.
As said (if you boost the bass) for the lowest frequencies,
it can make a big difference with some cars.
Unlike just using the soundcards EQ, with additional PEQ software/hardware we can boost or cut exact frequencies and use a preferred slope for any desired crossover.
Now, of course with game audio, we cant apply such to only single sound elements (eg: gear change) but it is possible to monitor the frequencies some sound effects use. Then with tactile transducers, potentially used in a role to boost (specific frequencies) the preferred/desired audio effects may use.
I come mainly from the tactile perspective here more than subwoofer usage but any bass sounds, be it from speakers or headphones, having nice felt bass (via tactile) used with good audible bass, makes it all more enjoyable and entertaining. For me personally both compliment each other fantastically in extending the immersion but I do prefer or feel more immersed with good headphones and being 1-1 with the audio than speakers.
What can be done, well It really depends how far into this a user wants to go.
These days with an iPad and a USB multichannel interface with free or affordable software is quite amazing.
Using EQ software like ProQ3 and Signal Scope X for monitoring the audio (or many other options available) is very impressive but certainly not hardware most sim users will consider. If routing audio into such hardware, it can give full DAW control via loads of professional plugins, even "subharmonic synthesizer" if desired.
This will generate
lower harmonics to what the "original audio contains". Typically 1 or 2 octaves below the original fundamental frequency.
I have a couple of these laying around that I bought a few years ago, might be fun to play around with or find more modern digital plugins to use. (video gives an example in subharmonics)
I don't expect many people will go to such lengths, not at all..... On my own build, the "audio soundstage", as well as the "tactile immersion" with control of it for improved immersion, is a major focus but its also kinda a hobby in its own too.
I look forward to digging deeper into some sim titles audio in the future.