You had to ask didn't you?
There is no way whatsoever to remove or prevent it! Beaming occurs because your cabinet is made up of multiple sound sources all sending out their own version of the signal. In the case of a multiple driver cabinet it is easiest to consider each speaker as a signal source to grasp the principle. That is an oversimplification for the moment but it serves to demonstrate what causes beaming.
When you are "on the beam" positioned at equal distances from these points, all of the signals arrive at your ears at the same time. You are getting the full range of frequencies more or less as they are leaving your drivers. When you move off the beam the path distances from each speaker begin to differ. That then means that the signals from the points further away take longer to arrive at your ear and are therefore out of phase with the closer signals when they do. This means the multitude of signals begin to cancel each other when your ear adds them which lowers the level. This cancellation effect is frequency dependent because the wavelength of the signals gets smaller as their frequency rises. So it produces a "comb" type filter with the effect most noticeable at the highest frequencies and virtually no cancellation for frequencies where the wavelength is much longer than the difference in path length. Hence you get a drop off of frequency bands at the top end at some points off the beam. If this gets extreme it is even possible that at some frequencies the signals come back into phase a whole wavelength later and they add together again which is the cause of the comb effect.
As I said, the problem is simplest to understand if you consider a multiple driver cabinet with a number of speakers set apart on a flat baffle as they would have to be. It is however also the case even in a single driver cabinet as any speaker driver acts as a set of multiple points on its cone each one acting as an omni-directional point source. The idea that cones send most of their high frequency from the centre aimed straight forwards is a MYTH! It is absolutely the wrong thing to assume to start your argument for anything in this field. People believe it to be so simply because of this beaming cancellation effect which means that maximum high frequency is naturally heard on the centre line. That is due to cancellation of the real multiple signal paths not because the speaker is sending out more from its centre. Every point on the cone acts as a full frequency point source vibrating across the whole frequency spectrum. That is why tweeters are tiny! There are less point sources on their cone/dome and a lot less spacing between those points in relation to the signal wavelength.
The spacing of the drivers in a 2x10", 4x10", 2x12" or 4x12" or in fact any multiple driver setup makes this effect absolutely unavoidable in at least one plane. It doesn't matter how you try to "scatter" the signals (as in the useless Beamblockers which even introduce other bad effects like signal bouncing back into the speaker and then forward again off the cone to be even more out of phase than ever), or how you angle them (as in specialist cabinets with split baffles angled inwards or outwards). That delay due to different path lengths cannot be removed, hence beaming can never be totally removed. I should say that those other systems may sound better to your own ears, that is a subjective thing. But it is due to the other random factors that they change and the fact that your setup may have other problems which they may reduce. They can do absolutely nothing to circumvent the Physics of beaming and it is immoral to claim that they can when all of this is incredibly simple to demonstrate in a laboratory and has been done with the results being made public!
The only system I have ever seen that actually works is Jay Mitchell's "Mitchell rings" and this only works for single drivers. Just as Mitchell predicted and openly stated would happen, these produce other effects like a slight drop in high frequency level overall but that can be balanced with tone controls. They are set up as the opposite to the commercial Beamblockers. It is a setup where a flat open cell foam "doughnut" across the entire front of the driver is used to remove the high frequency content from the outer area and only allow it to escape through the centre hole. Low and middle frequencies which have longer wavelengths and do not show the same degree of beaming pass straight through the foam. They are very easy to make and fit but the correct material in the correct thickness with the correct sized centre hole is essential.
Jay Mitchell seems to have come up with this idea as he was disgusted with the way some commercial people were cashing in on people's ignorance. He is not a popular character in some areas of the audio world, he takes no prisoners in any argument about the Physics of sound, but he is a very highly respected audio engineering expert who has published academic papers on aspects of audio reproduction. He made nothing out of the idea, he runs a very successful audio design consultancy with profits elsewhere, and happily gave the explanation and plans to the public along with his high tech anechoic chamber measurements of the rings and competing systems to prove his point. Very few people even bother to look into it even when it is pointed out to them, (like this
, as their "Guitar Gurus", many of whom have no real engineering background, simply poohpooh him and insist that the myths are still true. They just prefer to swallow the bullshit the sellers of other systems feed them and blank the evidence which proves that those other systems do not live up to their claims!
And Stevie Ray Vaughan knew nothing about the physics of this when he draped his towel over his cabinet. It doesn't prevent beaming, it simply drops the level of the frequencies he didn't like in his signal. Path length is the key. The speed of sound is constant for all of the signals coming from your cabinet into the same environment. You can't change that.
Home
I have posted before on how ridiculous they are in the light of the Physics and results of high level engineering tests and you don't want another diatribe from me on a mathematical technical matter.) I have been tempted for a while to try it with a G12M loaded 2x12" cab to see what difference if any that makes but I don't have the right cab to hand.
,so when you plug in you will almost certainly disagree,just adding to the conversation.