It seems reasonable that the sound level would be close if all the speakers are about the same distance from the SPL meter and they generally are the same. I took a brief look at the 970 manual, and like the 990 manual, it fails to say to turn up the main volume control when calibrating the speakers. I usually set the volume at 0db and then shoot for 80db on the SPL meter. Others in the Saloon calibrate with the main volune at -10db and 75db on the meter. I imagine the higher volume takes care of ambient noise that could influence the settings. Let us know if increasing the main volume yields a different result. Enjoy!