A Question About Time Alignment

To those suggesting that phase coherence doesn‘t matter: listen to a recording in- and out of polarity (i.e. reverting phase) and pay attention particularly to the leading edge of instuments. If you can‘t hear the difference either buy a better system or have your ears checked.

Regarding time allignment: the wider the diaphragms are appart, the harder it is to achieve since 1st and subsequent reflections will be affected by the distance between diaphragms. This particularly affects higher frequencies with their more bundled dispersion characteristics.

Hello Paul6001.  All the sound waves move at the same speed. The wavelengths vary with frequency, but not the speed of their travel. We are trying to reproduce music that arrived sometime in the past on the diaphragm of a microphone. We do not want to add any more time "smear" when we listen to that recrded music. The microphone(s) "hear" what you would hear sitting in the same place as the microphone(s). We want to produce the same sonic patterns in our room that the microphones picked up. So we don't want parts of that recorded sound to reach our ears earlier or later than other parts. Don't mess up the puzzle! If it gets messed up, we won't be able to reassemble in our brains the sound pattern that hit the sensitive parts of the "mikes." If we distort that pattern, we will not be able to successfully reconstruct the performance captured on the recording. The feeling of "being there" depends on an accurate reconstruction of the sound patterns in the recording. Woofers are generally larger than tweeters. If we mount them on the same panel, the voice coils that vibrate to reproduce sound are at different distances from the panel (this is why flat panel speakers have an advantage in accurate sound reproduction - all the sound leaves from the same place). So the sound from the woofer arrives a bit later than the sound from the tweeter. That's the problem some speaker builders try to solve by either moving the tweeters backwards or moving the woofers forward. That leads to some odd loking boxes, but, if perfect reproduction is the goal, it's worth it. Ideally, all the sound producing parts of the speaker system are at equal distance from your ears. Happy listening.

@boomerbillone +10

Mike

Two other things I can add to the discussion:

1- An interesting situation exists in the case of line-source loudspeakers, a good example being the Magnepan MG3.7i. This speaker has a long, vertically-orientated ribbon tweeter (a real good one), with magnetic-planar drivers for midrange and bass frequencies running along side the tweeter. In the instruction manual for the 3.7i, it is advised that the speaker be positioned so that the tweeter is slightly further away from the listener’s ears than is the midrange driver. The reason for that is that the speaker’s crossover creates a slight time lag in the midrange driver. With the tweeter and midrange driver equidistant from the listeners ears, the two drivers are not quite time/phase aligned. 3.7i owners need to experiment with varying degrees of toe-in, until the highs and mids sound coherent. With a dynamic loudspeaker (cone & dome drivers in a box)---with the drivers aligned vertically, as most are these days---tilting the enclosure forward or backward can sometimes be used the same way. Raising or lowering the enclosure instead achieves the same result, of course.

2- In a number of his YouTube videos, Danny Richie explains why tweeter and midrange drivers should be mounted as close together as possible. And why the higher the x/o frequency between them, the closer they should be to each other. That is because at the high frequencies tweeters are producing sound, the wavelengths are very short. Danny explains it all far better than can I, so if interested do a search on YouTube for GR Research. A free primer in loudspeaker design basics!