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Aiming and beaming
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<blockquote data-quote="ciaonzo" data-source="post: 8573089" data-attributes="member: 607015"><p>I think the best place to start would be to mention that time alignment will not correct for off axis concerns. These are two different things and saying this up front will make the discussion a bit easier so we aren't confusing the two issues.</p><p></p><p>Let's talk about off axis response (also referred to in this context as beaming or lobing or directivity or dispersion or radiation or power/polar response) and your physical install abilities. When a wavelength is small in relation to the size of the driver that is producing it, you will experience beaming. The effect sets in gradually as frequency gets higher, it's not all at once. If you can manage to put every driver on axis, or mostly on axis to you and the passenger, this is the best starting point. Not everyone can do that, though, and that's why we start getting into off axis discussions relative to driver diameter. Those who cannot manage any type of special install will be locked into the difference between being very off axis to the driver's side speakers and being mostly on axis with the passenger's side speakers. Probably safe to say that most are sitting about 60-80 degrees off-axis from the driver's side speakers and so this will be your single biggest concern when deciding how to cross at a point where you won't suffer because you're that much off-axis.</p><p></p><p>If you take a driver and hold it in your hand while feeding it a full range signal (lots of treble and higher midrange content) and begin turning it away from you, you can begin to appreciate how well that driver will perform off axis. Naturally, as you get off axis the high frequency content falls off because of the beaming/directivity behavior. Next try this with the same content but while applying the low pass filter and slowly adjusting it downward to remove the treble, and then the upper midrange, and keep repeating this turning experiment until you can no longer appreciate a difference in the high frequency performance when you are well off axis. This would be the highest frequency you will be able to use this driver without any directivity concerns. You are effectively ensuring that the power response of this driver is the same no matter what angle anyone is to it. This way when you hand off to the tweeter, it will closely match the off axis performance of that driver as it begins it's area of responsibility for the musical signal. This is of much less concern between an 8" and 5.25" driver because of the frequencies you are likely to choose to cross between those drivers. Slope might be the only reason you may still consider the off axis performance in that region. That's pretty advanced, though, and gets us into lobing territory. This discussion assumes steeper 18 or 24 dB slopes.</p><p></p><p>So, now that you have a nice even polar response from all your drivers, you will want to introduce your time alignment. This is intuitive as it sounds. You simply want to get the arrival time of all those separate wavefronts to land upon your ears with as little discrepancy as possible. Basically holding back the wave launch from the drivers closest to you, or giving the drivers furthest from you a head-start so that everyone can get to your head at the same time.</p></blockquote><p></p>
[QUOTE="ciaonzo, post: 8573089, member: 607015"] I think the best place to start would be to mention that time alignment will not correct for off axis concerns. These are two different things and saying this up front will make the discussion a bit easier so we aren't confusing the two issues. Let's talk about off axis response (also referred to in this context as beaming or lobing or directivity or dispersion or radiation or power/polar response) and your physical install abilities. When a wavelength is small in relation to the size of the driver that is producing it, you will experience beaming. The effect sets in gradually as frequency gets higher, it's not all at once. If you can manage to put every driver on axis, or mostly on axis to you and the passenger, this is the best starting point. Not everyone can do that, though, and that's why we start getting into off axis discussions relative to driver diameter. Those who cannot manage any type of special install will be locked into the difference between being very off axis to the driver's side speakers and being mostly on axis with the passenger's side speakers. Probably safe to say that most are sitting about 60-80 degrees off-axis from the driver's side speakers and so this will be your single biggest concern when deciding how to cross at a point where you won't suffer because you're that much off-axis. If you take a driver and hold it in your hand while feeding it a full range signal (lots of treble and higher midrange content) and begin turning it away from you, you can begin to appreciate how well that driver will perform off axis. Naturally, as you get off axis the high frequency content falls off because of the beaming/directivity behavior. Next try this with the same content but while applying the low pass filter and slowly adjusting it downward to remove the treble, and then the upper midrange, and keep repeating this turning experiment until you can no longer appreciate a difference in the high frequency performance when you are well off axis. This would be the highest frequency you will be able to use this driver without any directivity concerns. You are effectively ensuring that the power response of this driver is the same no matter what angle anyone is to it. This way when you hand off to the tweeter, it will closely match the off axis performance of that driver as it begins it's area of responsibility for the musical signal. This is of much less concern between an 8" and 5.25" driver because of the frequencies you are likely to choose to cross between those drivers. Slope might be the only reason you may still consider the off axis performance in that region. That's pretty advanced, though, and gets us into lobing territory. This discussion assumes steeper 18 or 24 dB slopes. So, now that you have a nice even polar response from all your drivers, you will want to introduce your time alignment. This is intuitive as it sounds. You simply want to get the arrival time of all those separate wavefronts to land upon your ears with as little discrepancy as possible. Basically holding back the wave launch from the drivers closest to you, or giving the drivers furthest from you a head-start so that everyone can get to your head at the same time. [/QUOTE]
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