I agree with Gary .... sorta. YAMAHA harmonizers should be behind the lead voice (because they can't compete with the original signal), and only one above with proper compression to smooth it out. It's not the worst sound, but I could never endorse it.
On the bright side - with TC harmonizers, you can actually feature the extra voices, in equal levels as the lead (when called for). An Everly Bros tune needs both voices to be the same volume. No one is singing "backup" in that duo. Many of you know that I use the harmonizer as a "signature" sound to my shows, and I like to think I don't over use it. I DO however, use it A LOT. I feature Carpenter-like treatments, and Mills Bros bounces all night long.
There is an art to singing like you're in a vocal group, and it's not a s simple as hitting the "on" button. Vocal groups, like the Lettermen had very plain, non distinguishable voices, and sang with no vibrato, or flash. The simpler, the better when blending 3 or 4 voices together.
The biggest mistake I hear in novice attempts is to just turn it on, and leave it on ... even in a chorus that features harmony, sometimes the backups drop out on certain words ... like "a' and "the" ... little words. I'd be happy to discuss the techniques that I've found to work best with anyone who'd like to call. I just hate typing these diatribes. 215-284-1328
Ciao!