Not sure it "improves" the sound, that's subjective. But many who have treated the interiors on vintage MIJ kits say it adds a degree of projection...but overall, doesn't really change the sound. At least, not in an overt way.

It's not a bad idea to treat Luan though. I've used Danish oil, works nicely. Luan get's SO dried out. Plus it can enhance the look. I've known some that have painted the interiors white, like old Ludwig's...no sound difference, just aesthetics. Looks nice though.

Try it out.

I have used a couple coats of satin polyurethane on double headed toms and also several coats of white enamel on single headed toms- no difference really on the poly except maybe 'deeper' sounding- (fuller) and the enamel did enhance projection.The BETTER thing I did was freshen bearing edges = making them clean and consistent- really improved clarity and tone / helped with tuning. (and seals those dry plies!)

I've done it before on a few kits, mostly just to seal them and make them stronger.

When it comes to drum's sound, 95% of it (IMHO), is tuning and head selection. Also remember how Luan is naturally. Very porus and stringy. You can't argue with science, and science says that the harder and smoother the surface, the more reflective the sound waves will be. Conversely, the softer and rougher the surface, the more absorbed the sound waves will be.

By sealing/laquering the interiors, it certainly makes them smoother and harder, thereby making the sound waves more reflective. On mine, I did notice a small difference in projection and resonance, but not nearly the difference in changing from say a Coated Ambassador top and bottom to a clear Pinstripe top and bottom would have made.

Thanks to all for this advice and for providing a better understanding of the Luan wood surface. I appreciate it.

Not sure about the sound difference, but I treated the wood on my snare with Danish oil. It soaked it up and will harden and preserve the wood. Couldn't hurt. I plan to do it to the rest of my set. 1966 Stewart.