What these waveguides do is solve the age-old problem that all conventional high frequency drive units have with the beaming high frequency content in an ever increasingly narrow coverage angle. This means that you can only hear full frequency content if you are directly in front of the speaker (or nearly so). It’s important to realize that ALL loudspeakers exhibit this behavior to some degree –Acoustic Lenses or a Conic Section Array™ GREATLY mitigate the problem.
Why is this “beaming” of high frequencies phenomenon a problem? Well, it’s in the high frequencies (above approximately 3kHz) that the attack of a drum, the pluck of a string, the sibilance of the voice, the brassiness of trumpets and the “air” in music lives. It’s the high frequencies that bring life to recordings; too little and everything sounds “soft” and un-engaging; too much and things get “hard” and “edgy” sounding — which is very fatiguing to the ear. This problem is particularly acute in loudspeakers for cinema use.
In cinema sound we need to provide as consistent an experience as possible to all seats. In larger rooms especially, many of those seats can be significantly off-axis to one or more speakers. People in those seats miss out on some of the high frequency content. But it gets worse.
So far, we’ve only talked about the sound that goes directly from the speaker to the listener’s ear. Speakers radiate sound in all directions. What about the sound energy that goes from the speakers and bounces off the walls, floor and ceiling before getting to the listener?
Turns out those reflections are really important to the human auditory system. Without getting too technical, they make recordings sound more “real.” When those reflections, which create the ambient tone of a room, are deprived of high frequency content, whether by the speaker or improper room acoustics, the experience of the listener is significantly compromised. All too often, BOTH of these problems exist, and yeah, it gets worse…
In cinema sound, we have requirements for higher sound pressure levels (SPL) than in most normal music listening environments. Movie sound tracks can have extreme dynamic range. Higher SPL can help us “get into” the movie. In rooms that are larger or where the client has a desire for particularly high SPL, loudspeakers can get put under extreme stress. To cope with this, speakers designed for cinema use are designed to be more robust.
At higher frequencies, horns are used to increase efficiency. They accomplish high SPL in part by–you guessed it–beaming energy even more narrowly! This is what you have to do if you have to play loudly. No matter how expensive or what it’s made of, the 1” dome tweeter found in most hi-fi speakers simply cannot push enough air to achieve the sound pressure levels we require. It gets even worse, though.
At lower frequencies, to meet the requirement for high SPL, special drivers are used for the woofer and midrange. “Special driver” translates to woofers and midranges that are more efficient and handle more power – virtually always at the expense of distortion and smoothness of overall frequency response. Also, midrange drivers for cinema are frequently over sized for robustness. This brings the beaming problem down even lower in frequency – to the vocal range.
In case you’ve ever wondered, these are the major reasons why PA speakers don’t sound like hi-fi speakers, and why people say things like, “Speakers for movies are not as good for music.” But, there is a solution…
The Conic Section Array waveguide delivers constant horizontal directivity over a 160-degree coverage angle. Even at extreme off axis angles of 70 or 80 degrees, there is no roll-off of high frequencies. As you move off axis, the behavior of a speaker with a CSA is that the overall level is somewhat attenuated, (about 6dB at 80 degrees) yet the shape of the frequency response curve remains quite flat. Outfitted with a high quality compression driver, we are able to bring a level of performance that even well designed audiophile loudspeakers cannot attain, but at sound pressure levels no audiophile speaker could ever achieve.