someone please explain this "toe-in" affect

[tboooe]

Hi, tonight while listening to some music I noticed that it seemed that more sound was coming from the right speaker. The center phamtom image was also skewed to the right side a bit. At first I checked my balance settings, then my cables...everything was as they should be. I started to worry that maybe my left speaker was blown or something. Then I noticed that my left speaker was "toed" in a bit. Straightening this out fixed everything. I got a nice, smooth LR spread of music with a good center phantom image.

So I was wondering if someone could explain to me why toeing in the left speaker resulted in the right speaker seeming louder? I tried to research the BW website and this was all I could find..
"To offset this a little, you can use the fact that a speaker’s response decreases in level off axis. Toeing the speakers in, so they point at or just in front of the central listener can help to reduce the central image movement. If you move nearer to, say, the right speaker, the increase in its loudness is offset by your being more off axis. Conversely, you move more on axis to the left speaker, which offsets the fact that you are further away."

What does "off axis" mean? Is the above paragraph related to what I experienced?

Just curious about the scientific rationale....

[misterdoggy]

I think you've figured it out on your own. ou might want to use a spl meter to actually measure the decibels from the "sweet" listening point to make sure your speakers are putting out the same amount. Radio Shack sells a good meter.

[bigburner]

tboooe, I occasionally have to adjust the toe-in to correct what sounds like a volume imbalance between the left and right. In fact I have removed the spikes on my fronts to make them easier to move around. I find that toe-in has much more impact on my sound than the distance between the speakers or the distance between the speakers and their environment.

[tboooe]

Thanks guys...does anyone know what the scientific reason is for what I described?

[akhter]

By rotating the speakers you are effective changing the distance between the tweeter and ur ears. When the distance is equal between the sound coming out of the left and right speakers, the sound will appear 'balanced'. If the sound from one speaker comes to you quicker, the system will sound biased towards that speakers. Keep in mind that it is a little tricker that that based on the room/walls/furniture as a lot of the sound is reflected and because of that just rotating will change the distance travelled significantly.

[tboooe]

thanks akhter...but what i dont understand is this..when my left speaker was toed in, my right speaker sounded louder..it would seem that by toeing in the left speaker that decreased the distance to my left ear so the left speaker should sound louder. In my mind, I am imaging a right triangle and the theory that the hypotenus distance is shorter than the sum of the two other sides..in other words, the left sound was traveling along the hypotenus and the right sound would have to travel first straight then make a right turn to get to me right ear. This is probably totally wrong but it is how I imagine the sound traveling.

[RobP]

sound travels in waves, imagine dropping a pebble into water, the ripples created are much like sound waves. If you dropped that pebble directly in front of you then the front of the curved ripple would reach you first, but if you dropped that pebble a little off center (or off axis) either way the front of the curve would pass you and you would receive the "weaker" portion of the ripple. Most speakers are direct radiating with the peak of their energy output on axis, so if you have one pointed directly at you the sound waves from that speaker will reach you slightly before your off axis speaker, much like those ripples in the water. Of course this is in an open field scenerio, when you factor in walls and furniture then things get a little more complicated. but thats another story.

[JetFlyGuy]

Soundgravy hit the nail on the head, and that is what they mean by "off axis" specifically they are pointing out the drop in dB as you move off of an imaginary stright line predicated on a right angle being drawn from the face of the speaker. The loudest theorical point at any given distance from the speaker is if you are standing on the line.

[Aussie Geoff]

Hi,

Another benefit of getting toe in consistent is that sound takes a finite time to travel. If the two speakers are aimed so that the front faces are each at right angles to a central listening position (i.e. Toed in) then the sound from each will arrive at the same time and in phase. This helps a lot with stereo imaging as the ear will hear the sounds from each speaker arrive at the same time, especially with some speakers that have quite directional treble.

Now, personally I like to not toe in so much (when I can with the speakers) so as to create a broader "sweet spot" for the audience. Many good speakers will radiate phase coherent sound over a wider than normal angle (some can be as little as 10 degrees for treble). If you have a speaker with a reasonable dispersion, toeing in less strongly to create a broader area where the two speakers are reasonably pointing at the listener can mean that several people can enjoy a great stereo image...

Geoff

[tboooe]

Thanks Geoff. I found that with my 805S, I dont need to toe them in at all. They are about 5" apart and I set 15" away. With the speakers pointing straight forward, I get a very nice spread of sound and central image that is to too focused. Its more like the sound is coming from the entire width of the speaker separation. I also have some dm601s3 in my bedroom and I found that I have to toe them in a bit to get good imaging.