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Just how important are  subharmonics and undertones in audio, and how they affect tone? 

I played around for a while with the Townshend supertweeters,  this is a ribbon tweeter that you can barely listen to:  you plug it in and put it next to your ear and can barely listen to a hishsishisi (they claim 20khz-100khz).  Once you place it on top of a speaker with limited high frequency response,  say 18 khz,  a big change can be heard on the sound mainly on midbass!! Of course this is an effect caused by subharmonics and overtones going higher than what we are able to hear! (Good luck time aligning these things at 20 khz!!!)

To have a tweeter that goes up to at least 40 khz is a big thing and really helps a lot to the "tone" or perception of audio, we all have listened to this effect.
A bunch of modern tweeters go up to 50 khz.  I just use the example above because it does nothing under say 18khz and it is funny how it is hard to see if they are even working! 

I like to think of ULF on these same terms, it is a frequency we can barely hear (depending on xover steepness) but which brings those undertones and subharmonics that "complete" the sound of a musical wave with all its companions...

BR cabinets and other bass solutions need to have a high pass installed, to avoid excessive cone movement,  thus limiting the frequencies they are playing to a certain point,  ussualy 20- 25 hz,  even if they never really get down there,  it is mainly a mechanical solution.  A sealed enclosure can have what is called an open bottom,  meaning no high pass at 20 hz.  This allows for the driver to bring out a certian level of undertones even if they come at a lower amplitude,  say minus 6-9 db they are still present and one can notice them.  

Now I play a lot with a bass solution that inlcudes a LF and ULF with different drivers in different cabinets:  Pro drivers down to 45 hz and a big 15" servo subwoofer from around 40 hz down to supposedly 16 hz (no way to really measure down there).  Both have sealed cabinets; the bass is very good. But it is a PITA to put in phase.  When not in phase both drivers can fight each other to the point where lowering the level on the LF or ULF can add bass to the room!  The thing is we are using a 140 hz UBH and we needed a LF solution that would go up to 150 hz with stamina!  I could not find anything that could go up to say 200 hz and down to 20 hz with the dynamics and character needed to match up to a horn system!  And we really wanted it to go under 30 hz!!!

So eventually the ULF channel should work in the same way a "supertweeter" UHF works,  adding all these harmonics to the fundamental note.


Now someone is about to jump out with a new product  made out of cow dung from the hymalayas and silver covered Berylium that resonates in such a way that you cannot listen to it "ever" but adds these subharmonics and undertones that make your system sound sooo much better,  and it can even be aplied over the phone!!

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