C to C

Acoustic vibes go F to F because of the sound quality of the aluminum alloy. There are low C instruments, but the notes below F can sound thin and weak. I've heard a few low C instruments that sound decent. Additionally, the cost of the extra half octave significantly drives up the price, and transporting them can be challenging.

OK... so we all crave low notes. A guitar goes down a minor ninth below us. Piano goes all the way to the basement.

Yes, it's a natural aspect of music to place the harmony below the melody and, if you pick any three octave range and try to do both within that, that limits both elements to two octaves or less. If your vibes concept is that it is a keyboard instrument played with mallets, you will have a problem and not one that is easily solved because, as was mentioned above, the vast majority of bars lower than the low F (even sometimes the low F and F# on standard range instruments) have a LOT of bell tones and sound icky other than in a melodic usage.

so... My vote is: don't do that. Think of your instrument as though it is a vibraphone with its own unique abilities, strengths, and limitations and play that way. Yes, our voicing are similar to guitar, so a lot of the time, those will work. Piano voicing tend to sound less pleasing and many require greater than three octaves to execute. But, vibes voicings always work. Playing with a linear concept instead of a harmonic one as a primary focus nearly always helps (the ear will fill in the rest... even Bach didn't insist on playing every note of a chord as a vertical structure). A bassist who knows how to play with a vibist is a huge factor. Understanding the physics of the instrument is a good place to start.

If you want to hear this in action, there is an older recording that is wonderful in this way. The leader was Eric Dolphy and the vibist was Bobby Hutcherson. It's called "Out To Lunch". On this recording, Bobby finds the perfect way to both accompany and solo. It works perfectly with the bassist (Richard Davis) and drummer (Tony Williams) to create a full sound throughout and NEVER sounds like he's trying to be a piano or guitar.

That said, every time I have heard Mike Manieri play on his beautiful 4-octave Yamaha, I've thought, "wow, that's beautiful, I wish I had those notes on my axe". But, here's the thing about Mike. He sounds just as good on a three octave instrument. I have NEVER heard him play in a setting where my reaction was, "that's great, but it would have been really good if he had another octave". Same goes for Gary Burton, Adrian Rollini, Dave Friedman, Dave Samuels, or any of the other wonderful players we associate with 4 mallet technique.

If you really want those low notes, my advice is to stick with your midi controllers. The MalletKAT is not a set of vibes, but it is a wonderful instrument in its own right. Anyone who tries to shame you by telling you it's not "real" or "authentic" should probably be ignored anyway. :)