I will see if I can clarify these two measurements. The Listening Window and the Sound Power, or Total Radiated Sound Power, are the two main curves in what has been coined the “Spinorama”. Both these curves are averages of a "family-of-curves”, or amplitude response graphs, measured in an anechoic chamber. The Listening Window will always be an average of a group of curves centred around the on-axis curve. The Sound Power will always be an average of curves taken in all directions around the loudspeaker in an anechoic chamber. Exactly which curves are used, at which degrees of steps, and using which weighting will vary a bit depending on who is doing the measuring and when. This type of research began in earnest in the 1970’s when Dr Floyd Toole began comparing various anechoic measurements to strictly controlled listening tests at the National Research Centre (NRC) in Ottawa, Canada. I was fortunate enough to have been involved in this research at the NRC for eleven years. Over the years we were able to refine the importance of the various measurements taken based on the results from the double-blind listen tests. The magnitude of this research is daunting as you need to verify consistency in the double-blind listen test results across many people and environments. A handful of companies have continued the research since the NRC days, Axiom being one of them. API being another one, which is where Andrew was before Axiom. API, because of the Mirage line, did a lot of research into the nuances of omnidirectional loudspeakers on this research. When Andrew first arrived at Axiom it was really interesting to chat about our various findings since the NRC years. Following this time Version 4 was born.
For a conventional front-firing loudspeaker the Listening Window should be linear across the frequency band and the Sound Power should have a consistent tilt downwards from 0 dB in the low frequency to around -10 dB at 10 kHz when compared to the Listening Window. For an omnidirectional speaker the way to read it is a bit different as now you have the ability in the design phase to bring the Listening Window and Sound Power closer together. In order to maintain a proper spectral balance, you cannot just bring the Sound Power curve up to match the Listening Window, instead both need to move towards each other. By creating the LFR1100 Active we had an incredible amount of control over the five driver sets which allowed us to experiment with making the Listening Window and the Sound Power the same. I think you will love the result!
