In the studio several years ago I used a 15" stage monitor as a kick mic along with an ATM25. I ran it to a DI and had to attenuate it 40 dB to not overload my mic pres. It had strong low freq output and sounded very muffled on the top end. When time aligned with the ATM25 it sounded surprisingly tight, but a LOT of 50-60 Hz. I think I low passed it at 200-300 Hz, gated & compressed, then blended it around 30% for extra gut punch. For me it was more hassle than was worth so I haven't done it since - but the band sure liked the idea!