I have two Bill F Tuba HT subs. They’re each 3 feet x 3 feet x 2 feet and weigh 150 pounds. Absolutely nothing that I’ve ever owned or listened to compares to them for music or movies.
The only thing I can see it doing is making the dispersion coming from the horns narrower than if the horns were front mounted. How audible it actually is is beyond me.
That topic has been discussed before. There’s no doubt that what you’re describing will alter the sound from the horns, how much though is the question.
You want to know what the horns and woofers are made of? The horns are a type of plastic, the woofers are a fiber composite.
The motorboard is either MDF or plywood.