Hello Acgman,
Axiom speakers are designed to produce the widest possible lateral dispersion, because NRC research has shown that the more consistent the sound is at increasing lateral angles from the speaker (off-axis), the more spacious and open the speakers will be judged in blind listening tests. At least half the sound that reaches your ears is comprised of secondary reflections from walls and objects to the sides of your speakers, so making the response off-axis as similar as possible to the on-axis (in front of the speaker) response is one of the main design goals.
Now, sit and listen to your M3ti's with them in a normal vertical position. Play music with wide frequency content and lots of treble and high frequencies. Listen carefully as you slowly stand up--the tonal balance will change to a greater or lesser degree.
This is caused by cancellation and lobing effects between the woofer, the tweeter, your particular room, and the tweeter's vertical dispersion characteristics. If you then lay the speakers on their sides with the tweeters in, the dispersion of the tweeter in lateral directions will be uneven and the aforementioned cancellation effects will be imposed on the speaker's lateral radiation. So it will sound different if you move to one side or the other, just as it did as you slowly reached a standing position.
Placing the M3ti's with the tweeters out will introduce a similar set of interference and cancellation effects which may or may not sound all that different than with the tweeters in.
You can conduct these tests in mono with one M3ti vertical and one horizontal in each position, ideally on stands out from any walls. Switch between them as you play the same musical content. They will sound different, I assure you. You may accept the changes to the spectral balance and find them inconsequential. It depends on the particular speaker and your listening room, and where the speakers are positioned. Placing the speakers on shelves in a horizontal position introduces even more effects from adjacent surfaces. Reflections from these surfaces cause cancellatios and emphasis at different frequencies, causing the tonal balance to change and almost always worsen.
This happens when you place any speaker on the floor as well. Typically you will get a 3 dB increase in bass and upper bass emphasis. Male vocals may sound "full", fat or chesty. If you tip the speakers back, these effects may lessen somewhat.
I have done blind listening tests in the past to some very expensive floorstanding speakers ($7,000/pair in the '80s) that had a large woofer very close to the bottom of the speaker's front panel. The speaker sounded very boomy and fat. When we raised the speaker off the floor by 18 inches, it sounded far better, and got much higher scores in the listening tests.
When you change the orientation of any speaker to something other than the designer intended, you are basically undoing all the careful engineering that went into adjusting the speaker's dispersion to yield the smoothest tonal balance and consistency over a broad horizontal angle to the front of the speakers.
Regards,
