Experience with stacked subwoofers?

If you have decent speakers you only need one subwoofer maybe two.

It’s a gimmick from a marketing standpoint. Not sure how meaningful the changes and I’m not hearing much on what it does up above and there seems to be limited enthusiasm.

Why not Stack tweeters and mid range drivers.

I stack my dishes and silverware and that really works good.

A Ripole Subwoofer might be the one to investigate. 

Everyone hears differently and has different values regarding audio purchases. I've heard several systems with REL 6-packs. I didn't like the sound of any of the systems I've listened to with 6-packs. I actually own dual REL subs, so I'm not being a REL hater.

Thanks for all these responses. I have two Rel t7s in stereo in my current set up, which were one of the greatest improvements made. In my own personal experience, I have found subwoofer replacement and even toe-in to make a significant impact on the quality of the base that I hear from the listening position. Not just the amount of bass, but the ability to hear distinct differences in the notes from one to the next. Having experienced a dramatic difference with that, I’m imagining that adding a height dimension would also be significant. So I’m intrigued with the idea of stacking three subwoofers, each tuned to accomplish something slightly different. 

A good friend of mine has a pair of GR Research, Double Trouble open baffle subs. 

One stack per channel.

Probably the best sounding subs I’ve heard.