We present a stereohaptic accessory mounted on the back of a head mounted display (HMD) to enable spatial haptic interactions in spatial computing applications. The accessory consists of two broadband haptic actuators placed symmetric to the sagittal plane of the back of the head, and digitally connects to the HMD via the USB port. We provide design guidelines to achieve engineering performance and human-factor requirements, and build a prototype module. We utilize Android’s audio support to independently control dual haptic channels. To accommodate haptic content design, we utilize audio based authoring tools and custom algorithms to auto generate haptic content directly from the audio media. We use these development tools to build haptic experience for watching videos, bare hand interactions, and mitigating cybersickness. Our evaluation shows that the accessory increases immersion, engagement, user efficiency and reduces VR sickness in dynamic spatial environments.