The Virtual Subwoofer effect is surprisingly effective and clean sounding. Not as muddy as other virtual sub effects I've tried.
It sounds like a mix of the
phantom fundamental effect along with some magic thump enhancement. Surprisingly effective with headphones like my Sennheiser HD600 and Grado SR60/SR325is. Maybe one reason it works so well with those headphones is that those headphones may have been used to tune and develop the effect.
Tricks with pseudo fundamentals are also used in
some pipe organ stops to give the effect of a 32-foot stop using 16-foot pipes. I've heard some organs live that use that effect for a 32-foot stop. For example the
Glenn Memorial Organ at Emory University. Works well. Not as strong as what a true 32-foot pipe would be, but does the trick effectively.
Some songs need a little bass help with the HD600 or Grados. Usually if I enable the Virtual Sub it is at the 6" setting. Sometimes 8". Occasionally at 10" if the song or music requires that much boost.
For example R.E.M.'s Eponymous sounds thin on the Senns and Grados. The 6" virtual sub fixes that nicely. Rescues the album better than trying to do a bass boost with EQ.
Another example is Iron Maiden. It needs bass drum thump enhancement and some boost to get the bass driving the music. Especially with songs like The Trooper (the galloping bass makes that song). Unfortunately the Grados and Senn HD600 don't bring out that aspect of the bass. Virtual Sub to the rescue. Iron Maiden is one where I do 8" or sometimes 10" with the Senns or Grados.
Another example is Nirvana's Nevermind. That album is a bass disaster on the Senn HD600 and Grados without the virtual sub. 8" or 10" sub to the rescue.
My Denon D2000 headphones do low sub bass very well and plenty strong. I've never needed to use the virtual sub effect with the Denons.
Anyways, I love that virtual sub effect. Really saves the day when it's needed. Especially with some headphones that are limited in bass extension and punch. Sometimes though I do wish for a 9" sub for when the 10" is too much and the 8" not quite enough (like with some songs on Nirvana Nevermind on the HD600).