What kind of active speakers?

Check out NHT also.

Musicnoise,

I listen to everything. I don't think active speakers have a preferred genre. Active speakers are almost all SS design (for obvious reasons), which would be a limiting factor for some users.

Bob, I actually have presumed - from reading some articles, somewhere - that near field monitors were designed specifically for a "close monitoring" setup, exclusively

That is true - some are definitely designed and voiced this way. They will not work at farfield distances.

Basically, the only speaker that will work at all and any distance (with no worries about toe-in etc.) is one with a wide even 80% dispersion across most of the frequency range (say up to roughly 10 Khz). Any speaker that has a narrow dispersion will only work at a specific suitable distance or at a range of distances that can be achieved by adjusting tilt, toe-in and listening spot for a particular room.

This is simply due to physics, here is an analogy:

1) A narrow dispersion design is like a flashlight with a narrow beam. Stand too close and point it straight at the eyes and it may be too bright. And slight changes of a few inches will almost always completely change the light reaching you and what surfaces in the room are "lit up" (the reflected light in the room). Listener position with respect to the flashlight matters a lot in terms of what is seen. Point the flashlight at a book and you have a great reading light and can see very clearly just the book.

2) A wide dispersion design is like an ordinary incandescent light bulb with no focus. It just lights up the whole room evenly. It is much less sensistive to placement or distance. Given a sufficently powered bulb the whole room can be lit fairly evenly...but it needs a lot more power to do its job and while the room is lit evenly it may not be as bright as one might like in a particular spot.

What we hear (like what we see) is a combination of direct and reflected energy (and this ratio changes as you go further from the source). Only a speaker with an even power response (wide even dispersion) will sound the same over a broad range of locations in a room.

Since the work by Dr Floyd Toole in the late 70's and early 80's, many modern nearfields have moved towards wide even dispersion and are extremely flexible. However, even among "wide dispersion" designs there is a significant degree of variability (as there is with consumer designs too).

Bob,

Dr. Floyd Toole is an executive at Harmon (JBL) - I believe your speakers are designed using Toole's approach - wide even dispersion with useable signal up to 80 degrees. Most all nearfields are designed this way - and many have a waveguide so that tweeter matches the woofer in dispersion at the crossover. I'd bet your speakers are probably peerfectly flat up to at least 30 degress off axis.

So is the waveguide's effect solely around the crossover region?

As you go lower in frequency the driver radiates widely - by adding a waveguide it will narrow the radiation pattern and reduce off axis energy. The waveguide will increase the loading on the driver slightly and therefore you can cross it over slightly lower or you can get slightly more SPL out of it before compression. It won't affect the tweeter response much at high frequencies.

The advantage is to get slightly a lower crossover from a tweeter and then to match the dispersion to a 6 inch driver that is already starting to beam. This produces a smooth seamless transition in the off axis response. If it is done well you have absolutely no way to identify that there is a tweeter and separate woofer (from a reasonable listening distance). Also, one can achieve an even power response - this means the speaker has a flat frequency response at all angles - so it excites the room evenly at all frequencies with no imbalances from reflections. This is an example of what you get without a waveguide and a tweeter crossed over quite high. This is an example with a lower crossover ( a smoother off axis response). This is what you get with an even lower crossover at 2.4 Khz and a waveguide - absolutely beautiful!

See also Aeronet and Elliot Sound and Genelec Waveguides

It won't affect the tweeter response much at high frequencies.

But it may help to flatten the off axis response at higher frequencies (at the expense of narrowing dispersion slightly.

The idea of sound field integration (if that's the correct term) based on distance to the listener is confusing to me. I don't have a visual image in my head as to what's going on.

Try to imagine how as a listener you are hearing the direct signal and the reflected signals. Depending on where you sit or where you place the speakers you will hear primary reflections at a different angle. If the speaker off axis curve looks just like the on axis curve ( nice and smooth and matching well if only all around lower in SPL) then the reflected energy will contribute evenly at each frequency to the overall speaker response. This means you get an even power response or you hear the same sound energy and flat frequency regardless of where you sit or where you place the speaker. Move close to one wall and you will hear more reflected energy from that particular angle - but as long as what is reflected is the same frequency response curve that is directly reaching your ears then you hear the combination which is the same sound.

If you have a speaker that beams in a narrow fashion like a flashlight at some frequencies and then widens to a broad floodlight at other frequencies (like the first example I gave) then you will be much more challenged to find a good listening position with an even response - move to one side and you may miss the side wall reflection from the narrow flashlight upper midrange but you will still get the "broad floodlight" tweeter response full in your ear - oops - all of a sudden it sounds different!

This may explain many observations where slight tweaks are adamantly claimed to produce different sounds. The mere movement of the listener a few inches (for example leaning forward) may be enough to audibly change what is heard ( a decibel or so over an octave or two is enough) and this becomes attributed to the tweak rather than being blamed on the speaker.

Musicnoise,

I have this book. It is excellent although a bit long winded for a useful reference. (Not enough math for my tastes but plenty of psychoacoustic discussions)

A smooth off-axis response I understood to be important to obtaining a larger listening region, but I had not given any thought to its impact on reflections. That makes sense.

Especially important when you realize that we hear the energy from the room up to the first 40 msec after the first arrival - this is called Haas effect - so the intensity of reflections really do matter and the speaker placement and listener sweetspot will be much more versatile if the speaker has flat frequency response on as well as off axis (it can be of lower amplitude off axis but it should be flat and with no "midrange scoop" or other broad peaks or troughs).