I've met Tom Fellenbaum several times over the years, and I know that he build excellent instruments. I bought one of his bowed psalteries years ago, and it was wonderful in craftsmanship and in sound. I don't know what he's up to now.
If my information is correct Fellenbaum is a builder in Black Mountain NC. He has slowed down on building dulcimers to keep in stock, but does build to order. His dulcimers are well crafted and typically have a bit wider and deeper body. There is no standard for dulcimer dimensions and builders have their own preferences. Like Ken said, tone is influenced by volume of the sound box.
The woods the instrument are made from won't make any discernable difference in the pitch of the sound. The overall body dimensions (internal cubic inches) do. How big is the body compared to your other "low tone" instruments?
I haven't heard of Fellenbaum dulcimers ina quite some time. My memory of them is that he builds a fairly deep/wide dulcimer for a 26-27" VSL.
updated by @ken-hulme: 12/01/21 07:01:45AM