Originally posted by phookat
No, it doesn't fail. It isn't perfect either, but it helps. Direct beaming is a luxury that you don't have, if you want more than one person to be listening to the sound (or if you don't want to convert your living room into a foam-padded sound chamber).
It doesn't fail? Let's examine the basics of sound dispersion, early reflections and directivity in a typical room.
A typical loudspeaker radiates 360 degrees on lower spectrum with gradually raising directivity towards higher frequencies. The directivity is dictated by the physical size of the frontplate of the speaker as well as the size of the actual elements. The larger the element the lower frequency 'beaming' will occur. This means that a 1" tweeter has highly directional properties above 5-8 khz with steadily growing radiation field under that.
A typical two-way loudspeaker has a mid-bass of 6.5". A midbass of that size on the other hand is highly directional in the top range of the crossover frequency. This mismatch is one of the toughest problems in the simple two-way loudspeaker design. The mismatch not only affects off-axis sound quality but also creates bumps&gaps to the total power spectrum of the speaker (meaning the overall amount of sound per frequency). This mismatch is sometimes dealt with by using a smaller midrange cone or by increasing the lower spectrum directivity by a directional horn. An extreme example would be Amphion which extends the vocal range of its 2" tweeter all the way down to 800hz by using a huge 8" directional horn together with a Seas magnesium alloy 8" mid-bass.
A typical non-directional speakers sound is completely dominated by the power spectrum with only minimal amount of direct radiation involved. This means that when a speaker radiates sound, not only the direct and pure sound is broadcasted to the listener but also the first, second etc. radiations from walls, floor and the ceiling are bouncing about in the room and catching also the listening position. To make matters worse, the time delay between the direct sound and the reflected sound causes interference which human ear picks up like a comb filter. The result is an extremely distorted high frequency pickup in listening position.
When you look at an EQ and what it does (alter the direct sound output) you quickly see that an EQ is completely powerless in its presumed task of correcting room alterations. At most it can work in the bass regions where standing waves produce bumps and lows every octet in conjunction with the size of the room. A room width, height or lenght will cause bass interference with each matching quarter of frequency. 20hz sounds have a wavelenght of 17 meters so a room with 4,25 meters dimensions will cause that frequency to cancel out in the middle of the room and double in the corners of the room.
Even with this the EQ can't do much else except increase or decrease the overall amount of sound produced - the actual reasons and effects of the cancellation are not effected at all. The reason why EQ:s are used in studios is that they are used to shape the overall tone of the recording and microphone response alignment. They do not and can not fix anything outside the direct recorded sound i.e. reproduced sound from a speaker.
Planar speakers then again work around this problem by having a huge radiating surface (remember the surface/directivity equation) combined to a dipole operating method. A dipole speaker has no box so the front and back radiation can travel freely around the speaker. Since front and back radiations are at opposite phases, full cancellation on the side of the speaker happens even at bass frequencies. The result is a radiation field roughly the shape of figure 8 meaning the speaker will radiate sound mostly to back and front of the speaker.
This means that a planar speaker will have considerably less effects from all first radiations, the difference is especially big on floor radiation which typically creates most of the problems. And that my friend, is the key to having high quality sound reproduction in a room without 100" paddings on the walls.
