Originally Posted by Jon AA
I'm not sure how you're making that circle. Much of the information you are saying is important is contained in the spinorama, or at least can be surmised from it. So there's your correlation.
I don't agree with that--but maybe my definition of "excellent" is different than yours. How are you defining "excellent?"
For example most would agree the Spins of the M2 are brag-worthy, and they are a very well controlled directivity speaker over much of the frequency range. Yes, they have a wider coverage than many other CD speakers, but are more narrow than some (Grimani, etc). Compared with many non-CD cone/dome designs, they're much more narrow over some portion of the frequency range.
Let's assume for a second the criteria you gave above are correct. If one wants precise, accurate imaging, you would look for well controlled directivity--flat or only slightly declining early reflection and sound power curves, but you'd want those curves to fall well below the listening window curve, indicating less energy is being directed outside the listening window. If you want more spaciousness, envelopment, you'd look for the early reflections and sound power curves to be much closer to the listening window curve, indicating the speaker is producing more energy outside the listening window than the first speaker.
Seems plausible to me. If you could show through testing that this (or a similar) correlation held up, a Spinorama would tell you much of what you needed to know if you knew what to look for.
Let me try again...
Imaging doesn't actually exist as a physical phenomenon in space and time. Imaging only exists in your brain. It is totally and completely a psycho-acoustic phenomenon. In order for the brain to determine the point of origin of a sound, it must determine its location in 3-dimensional space. Sound localization and directionality are determined by the listener using arrival times and intensities. In order for the brain to determine where a sound is originating in space, there needs to be two ears to hear the sound and a brain to calculate the similarities and differences between what one ear is hearing and what the other ear is hearing.
The sound source exists in 3-dimensional space. However, the imaging of that sound relative to the listener in terms of 3-dimensional space only exists in the listener's brain. The ears hear a slightly different sound at the right ear than the left ear, and the brain calculates the sound origin in 3D space. This is known as the Head Related Transfer Function or HRTF. It is a mechanism that evolved to help mammals to determine the source of threats. Have you ever seen a dog tilt it's head? This is so the dog can change the effect of the HRTF ad more easily locate a sound source:
A "phantom" image is calculated by the brain when the two ears receive signals from two different sound sources.
A "central" phantom image, as depicted above, is a construct in the brain where the ears hear the exact same sound, ("exact" in terms of arrival times and intensities) and the brain calculates that the sound originated at a point in between the two sound sources. However, there is no "real" sound source at the point the brain calculates to be the sound source. It's a "phantom."
Equally importantly, these phantom images only exist in the brain when the listener is listening from the exact position that allows them to be created. If the listener is seated off-axis of the two speakers, the central phantom image created in the brain disappears and the sonic image collapses to the side of the closer speaker.
Phantom images can also be located in other imaging locations by using the Precedence or Haas Effect. This is also known as "The Law of the First Wavefront."
The precedence effect
or law of the first wavefront
is a binaural psychoacoustical
effect. When a sound is followed by another sound separated by a sufficiently short time delay (below the listener's echo threshold), listeners perceive a single auditory event; its perceived
spatial location is dominated by the location of the first-arriving sound (the first wave front
). The lagging sound also affects the perceived location. However, its effect is suppressed by the first-arriving sound.
While the ear/brain uses both arrival times and intensity differences to determine the point of origin of a sound, the arrival times
are the predominant factor. In fact the intensity differential of the sounds arriving at one ear vs the other needs to be on the order of 10 to 15 dB to become dominant. This why the law is called the Law if the FIRST Wavefront, not the Law of the LOUDEST Wavefront. (You can verify this in your own system very easily. Setup the system for ideal central imaging, using a recording that has a strong central image, (female voice recordings are good for this.) Listen to the voice and ensure it is phantom imaged from directly in front of you. Then change the distance setting of one speaker vs. the other. The central image will move side to side based on whichever speaker has an earlier arrival time.)
Now look at the Spinorama. I don't see ANY information about arrival times contained in the FR measurements. Frequency Response measurements, (also known as Magnitude Response measurements), only describe intensity differences of speakers at different frequencies. There is no time response information in the measurements. More importantly, there is definitely no time differential response information between the arrival times of TWO or MORE
speakers... in the FR measurements of a single speaker.
There may well be a way to measure a speaker PAIR's ability to portray a binaural acoustic event. However, I suspect it will need to be a measurement of multiple speakers with multiple mics... in the time domain, not the frequency domain. There must be a way to describe the differing abilities of speakers to portray sonic images. However, as I said previously, the Spinorama ain't it.