A horn is a type of waveguide. And yes, they do help sensitivity. It directs all the acoustic energy into a narrower beam of sound. By squeezing more energy into a smaller area, you get a more powerful soundfield in exchange for broader coverage. It is also more efficient in that it loads the tweeter with a higher acoustic impedance.
Sensitivity is simply the amount of energy a speaker can produce for a given amount of energy, usually some SPL quantity for 1 watt or 2.83v at 8 ohms at 1 meter in an anechoic setting. Speakers with higher sensitivities usually have a greater dynamic range than those that have low sensitivities, but that is not a hard rule. There are speakers with low sensitivities that are able to handle a lot of power and have a very wide dynamic range, and there are high sensitivity speakers that can't handle much power and thus have low dynamic range.
Controlled directivity is a broad and overused term. It means that the dispersion pattern is narrow or controlled in some fashion so sound isn't just spraying out over a broad area. I wouldn't pay attention to the term unless you know the user knows exactly what they are talking about. It should probably be ignored outside of research papers.
Movies and music mostly have the same demands as far as loudspeaker performance. Movies can dig a bit deeper than most music, if you like action and science fiction movies. Generally speaking, a good home theater system is also a good music system, and vice versa.
Unless you regularly listen to music at 95-105dB, movies are a bit more demanding.
I would define controlled, constant, uniform, or whatever you want to call it, directivity as an off axis response that doesn’t vary in amplitude with frequency. No speaker in the real world is capable of doing this perfectly across the entire frequency range, but speakers can be designed to come close, especially in the range above 1000khz, where timbre and imaging distortions from reflections can become a problem.
I seem to remember reading somewhere that the JBL 230 was based on technology from the JBL M2 which is know is very highly regarded.
w.r.t driver and horn design, I don't know anything and am learning from this discussion.
Is there any consensus answer to these questions -
1. horn loaded CD driver (or from what I read here, in waveguide) result in higher sensitivity
2. higher sensitivity = ability to play louder without distortion, aka dynamics (is this the right definition?)
3. controlled directivity is better or worse?
4. do 1-3 apply to movies/HT or also to music?
1. Yes, loading any driver into a horn increases its sensitivity due to better impedance matching to air, it also reduces distortion by significantly limiting excursion.
2. Generally speaking, but there are exceptions. Plenty of inefficient speakers can put out ridiculous sound pressure levels with very low distortion, like subwoofers for instance. To make a driver have a very low extension while being small in comparison to the wavelength (sub bass frequencies are huge in comparison to the diameter of a sub, 30hz, for example, has a wavelength of 37 feet, while a subwoofer may only be 1 foot in diameter) you generally trade efficiency. With a stiff diaphragm, high power handling, and a lot of xmax (the amount of distance a speaker can travel back and forth), a small, inefficient driver can reproduce very high volumes with low distortion given ample power.
3. I’m of the opinion that it’s almost as important as a flat on axis frequency response, because it A. Ensures that the reflected sound is similar to the direct sound AND depending on how wide the pattern is, it reduces the amplitude of those reflections compared to the direct sound, for example, a horn that had a 90x90 pattern, such as the Klipsch, radiates sound -6dB horizontally at 45 degrees, and -6dB vertically at 45 degrees off axis. Each 15 degree off axis increase translates to about 2dB less output compared to the direct sound. A speaker that doesn’t exhibit controlled/constant directivity may be -3dB at 1khz 45 degrees off axis, but -12 dB at 10khz.
When a speakers amplitude varies with directivity off axis, you have two problems, the first problem, anybody sitting off axis (to the left or right of where the speakers are aimed), they hear something different than those on axis. Best case scenario, they hear rolled off treble response, worst case, they hear a “notched” treble response because of lobing. The second problem, is that in regular small rooms, the sound we hear is a mixture of the direct sound from the speakers and the reflections off the walls/floor/ceiling. Reflections that arrive at our ears within a 50-80ms window are perceived as the same sound, so our brain simply combines the two sounds into one. If a speakers direct sound is accurate, but the reflected sound is not, then the
perceived sound will be inaccurate. A speaker that exhibits controlled/constant directivity doesn’t have this problem (or the problem is significantly less, as perfect directivity control just doesn’t exist) because the direct and reflected sound is more or less the same across the frequency range.
Floyd Toole has done a lot of research on this, and in blind tests, listeners prefer speakers with uniform off axis response. See:
http://www.cieri.net/Documenti/Altri marchi/Harman Group - Maximizing Loudspeaker Performance in Rooms (Floyd E. Toole).pdf
4. A good speaker sounds good with everything, but unfortunately, all designs involve compromises. By far, the biggest compromise in home audio is size. You can make an excellent sounding speaker flat to 20hz that’s very efficient, has high power handling, and a flat frequency response, but it’s probably gonna be bigger than your refrigerator.
Lots of smaller inefficient speakers sound excellent with music at 80-85dB, they probably sound great with movies too, but if you put them in a big room and try to play movies at reference volume, they’ll sound awful due to overwhelming amounts of distortion, and you might even let the magic smoke out.
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