In the previous post I mentioned the 'Spinorama' which is a standardised collection of loudspeaker measurements, there are 6,
The first is the simple axial frequency response, which also happens to be the most important when evaluating a loudspeaker. Ideally this should be as flat ( as few peaks and troughs) as possible.
Black line above is the on axis FR.
The next measurement is the 'Listening window' ( the green dashed line above) this shows us what a person sitting generally in front of the loudspeaker will hear.
The closer it matches the on axis response the better.
The next measurement is the off axis response ( early reflections curve), this is the energy that leaves the speaker at extreme off axis angles. A lot of the sound we hear in our rooms has been reflected from the room's boundaries.
The long dash blue line above is the early reflections curve, in a well designed loudspeaker the early reflections curve will match the listening window and both will match the on axis curve. The early reflections curve is the average of of eight measurements taken at +/- 40, 60 and 80 degrees, in the horizontal plane and 50 degrees in the vertical.
Next 'Sound Power', which is a weighted average of all seventy measurements and captures an accurate representation of all the sound emitted by the loudspeaker.
The sound power curve should not have broad undulations and should largely parallel the others, it may however have a slightly more down tilted slope.
The final two plots are Directivity Index ( on axis response minus the sound power) and the Early reflection directivity index, ( early reflections minus the sound power) what we are looking for in these two curves are smooth plots with a slightly upwards trajectory.
Spinorama data of the Dutch@Dutch 8C courtesy of the excellent Erin's Audio Corner.
In the next issue we will look at some loudspeaker measurements and try to correlate
the measurements to how the loudspeaker might actually sound.