Horizontal vs. Vertical Alignment
I was wondering about horizontal vs. vertical alignment of drivers in a speaker. The vast majority of speakers have their drivers in a vertical line. There are some exceptions, notably MTM center channel speakers. And there are others of course, but the majority are vertically aligned.
Why? Is it just easier? Or is it because stereo is a horizontal difference medium? Does horizontal driver alignment wreak havoc with stereo imaging?
It seems that any polar response problems that would occur in the horizontal direction would also occur in the vertical - just rotated 90 degs. But maybe they don't matter as much in the vertical.
I would think that if the drivers were time aligned at the listening position, then it shouldn't matter. But that could change quite a lot if you move around the room.
Seems like a silly question, but is there any personal experience or any reference texts out there that might shed light on the matter? Looking at some designs on paper- the horizontal placement just looked wrong. "That won't work!" Or will it?
I'd say it is because the ears, the sofa and the horizon is... horzontally aligned... :) We tend to move mostly in the horizontal direction.
Any errors in the horizontal direction will be much more audible than in the vertical direction. For example, if there is a horizontal difference in the frequency response in the directions of the two ears, the brain will have access to this difference simultaneously. To hear that is a task that is much easier for the brain than listening to the signals at two different occasions standing and sitting in the sofa. It is also easier than comparing the direct sound with that reflected from the ceiling; the reflection itself will have an effect in the frequency response.
That does not mean that the vertical directivity is non-important, it is just less important.
In fact, I am a bit sceptical to most center speakers having a horizontal MTM layout, and I suppose that the main reason is that it should fit nicely under or on top of a TV set. The center speaker in movie theaters are typically vertical, just like the left and right speakers. It is often spoken of that the center in a home theater setting should have a similar response as the L/R speakers, but having the horizontal MTM is in conflict with that, at least a bit to the side in the sofa.
But then again I might be wrong...
The horizontal MTM is also vertically alligned. Sound from the two midrange drivers would merge. It's more like a concentric than horizontal allignment.
Because our ears are on a horizontal plane (most of us anyway) the phase difference allows us to determine the apparent direction of the sound. That holds true down to about 180Hz. Below that, the ears are too close in terms of wavelength to determine the direction.
If an instrument goes up and down over a crossover region on unalligned drivers, it will sound as though it is moving.
You are spot on with the stereo being a horizontal medium. The original technique for recording stereo was with two mics, spaced about 8", with the axis at 60 - 90 deg. Commonly called "crossed mics"
These days with multi channel recording, it is up to the mixing engineer to "pan" the mics, ie adjust how much signal from a channel, is fed to the left and right output channels.
We used to use a Shefield Labs recording of Lincoln Mayorga for testing. That LP was mastered live. Stereo Mic to cutting lathe, and the finals were pressed onto high quality vinyl, no recycled vinyl in the mix(that's what happenned to unsold records, label and all)
Many systems in those days (circa 1978) had poorly alligned drivers. Can you picture a grand piano moving 5 inches because the player went up an octave?
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