Once you are satisfied with your impulse response, the final step is to generate an .sdir file, and a plug-in setting. When done, your newly created impulse response can be used in Space Designer.
Click the Create Space Designer Setting button.
Choose File > Create Space Designer Setting.
Impulse Response Utility will generate an .sdir file of your impulse response and save it in the following directory: ~/Library/Application Support/Logic/Impulse Responses.
A plug-in setting file for your impulse response is also generated and saved in the following directory: ~/Library/Application Support/Logic/Plug-In Settings/Space Designer.
The next time you open Logic Pro, your newly created impulse response will be available to Space Designer.