The Humminbird Side Imaging units don't have a dedicated Down Imaging crystal, BUT an experienced owner can get very good images.
What Humminbird units have a dedicated Down Imaging crystal? (if any)
None of the HB's have a dedicated crystal to create DI. They all (HB) uses the SI crystal to create the DI.
Lowrance has a crystal for both DI & SI.
Obviously you know nothing about Humminbird products and little about Lowrance products.
Every Humminbird model that has DI in the model name uses a transducer that has a DI crystal and a 2D crystal. There are about a dozen of them.
The Humminibird units with SI in the model name use a transducer that has two Side Imaging crystals and a 2D crystal.
Those units generate a DI image via computer programming.
Lowrance units that have DSI in their model name use a transducer that ONLY has a Down Scan crystal--NO 2D crystal.
The new model Lowrance Elite-7x HDI unit uses a transducer that has a Down Scan crystal and a 2D crystal. That is the first model that company has produced that does Down Scan and 2D sonar.
The HDS units with Structure Scan use two transducers, one has the 2D crystal and the other has two Structure Scan crystals and a Down Scan crystal.