A Dobro or a National (both trade names) have a metal pan inside the guitar which vibrate from a "spider" which emulates off the bridge. They are not all meant for slide playing, but the cheaply made necks, on regular "Spanish" guitars (in the twenties and thirties) warped and almost created this technique! What a twist! Square neck models are to be played on your lap. Bottleneck is played on a "Spanish" necked model, if the action is high enough.