This does not address nearly enough the sine qua non thing to measure: horizontal radiation pattern, that is, frequency response by angle. (As B&) know as well as anyone.) What we hear when we listen to a speaker in an enclosed space IS its radiation pattern (MDavis 1970s). That was not a new thought many decades ago (Jensen 1944, followed by Olson, Beranek, Villchur, Hegeman, Janszen, others, later Allison), and now the fact has been well-quantified for preferability the last 30y or more (Toole, Olive).
But the high end and even a few testing experts had to go chase a dozen other, largely hearing-irrelevant factors. Atkinson’s talk is an exhaustive example.
My understanding is that this lecture is not intended to be a comprehensive list of all types of loudspeaker measurements. It’s an explanation of the measurements that John typically performs when he’s reviewing a loudspeaker for Stereophile magazine. Since directivity measurements would be difficult, if not impossible, to perform for most speakers that they review, it’s not in the list. On the other hand, there are many good nuggets of information in there….
k, if you feel so. I do not see many nuggets, so should reread.
Assessing hor radpat is not all that hard, in my extensive experience, but it does take labor. Since 1989 I have schlepped maybe 50 loudspeakers outside (it has to be quiet, of course) and measured their hor RP all the way round and published the reviews in a range of second-tier magazines. Plus room responses at various locations. I employ a temporally averaging RTA, another sine qua non, of which dbx pro designed and manufactured the first. Noise-based.
Temporal averaging (which permits any spatial averaging desired) has recently become a feature on all competent RTA-type devices, including the better smartphone audio measurement apps, even though it was an ANSI supplement (and THX) spec ~25y ago.
The first 10-20 measurements I did appeared long ago in this windy ramble:
With temporal averaging there is a way to get reliable hor RP data in a room, but it takes a smidgen of savvy, and then normalization afterward.
You can extend what David said about radiation pattern to the effect of radiation pattern on the surfaces near the speakers – the walls & furnishings that reflect the speaker’s output. If you can imagine the reflections as additional sources on the other side of the walls and draw a plan view of that, you have what is called the image model of the entire situation. THAT is what we are hearing in all cases. Now imagine the size of this model due to the speaker positioning and amount of reflected sound emitted, and you can directly relate the depth of the model to imaging depth of soundstage, and the width of the image model relates to the impression of spaciousness. If all of those reflections are absorbed or inhibited in a mistaken idea that all we want to hear is the direct output of the two speakers, then the whole soundstage collapses down to the speakers and a thin line between them. If you mis-position a multidirectional speaker you will get a distorted soundstage with uneven imaging all across it, such as placing speakers too close to the corners or the side walls, you will get a clustering of acoustic images that will cause a hole in the middle and stretched soloists. If you place the speakers 1/4 of the room width in from the side walls and out from the front wall you will get an image model with perfectly even image sources all across it.
These are the most important, most audible effects of radiation pattern. We all know about frequency response and distortion, which are pretty well under control nowadays, but the above described imaging effects of radiation pattern, room positioning, and acoustical qualities of the reflecting surfaces have not been understood or studied as imaging effects and I hope to illustrate that at the AES level.