We all know that granite is hard. Hardness is "resistance to abrasion", and has little I can think of to do with audio.
Rigidity, which granite also is, will affect cabinet flex and the ability of the cabinet to ring only parts. It does not prevent the entire cabinet from moving. Every object has a resonance, and Newton demands a reaction for the actions of the cones. Unless you hooked up a velocimeter: you don't know what the cabinet is doing.
I have developed and manufactured a product before; but thanks for assuming.
I didn't factor labor of building the speaker into the materials cost. That's why it's called a "materials cost" as opposed to a "labor cost".
Of course, even if I did you could then say I had not covered the costs for a facility, and costs for tools, and you get taxed differently (assuming you've setup an LLC, which to do properly costs a few thousand to have the lawyer review your paperwork). Then there's a whole bunch of new taxes to deal with... and all this assumes you don't have any employees. Once I got my first one of those, it got really nasty.
Of course: Every manufacturer has to deal with these things as well: so we should see similarity in materials-to-cost ratios that are similar for all "appropriately priced" speakers.
First, depending on the quality of Granite, it can range from $40 to 200 per SQ ft.
You can get it considerably cheaper than that. I had already not simply looked up the least expensive; and I had also not looked up volume sales. If he's saying $40 is as low as it goes: he's lying. I cannot comment as to what he might actually consider buying. It's possible that $35/ft^2 granite "isn't good enough"; but it most certainly does exist.
Your description of "walks into a factory" doesn't seem well thought out at all. To properly do business in China (my ex is Chinese and runs a business which includes importing from China) requires a great deal of the right bribes in the right places. Even then: without careful monitoring / control, quality is poor. It's not that China cannot make good quality stuff, it's that it's difficult to get them to do so.
Dennis Murphey can likely discuss what buying cabinets from China was like.
The $15K price of the speakers includes matching stands which requires over 30 square feet of stone. Also, they are offering these speaker in custom finish options, so that means the price the stone can vary substantially. The speakers that were sent to me for review were a grade 4 stone (1 being the lowest and 5 being the highest). Again far more costly than $40 SQ ft, not even factoring in labor costs.
All right. Let's go for $200/ft^2. That's 5x $40, so it turns $800 into $2000. Add another $1500 for $400/ft^2 stands and our material costs for $15k speakers are now $4,560... without labor. Did the granite he used actually cost him $400/ft^2
Did he tell you that costs per ft^2 vary based on the size of the slab you need to cut from? Most of the numbers are built around counter-top assumptions. If you used smaller pieces... say the size of bookshelf speaker walls, it would be less .
Better still: Why don't you just tell us what he is paying for the cabinets?