Aiming and beaming

[Sguirrelfeather]

Did a lot of reading on this yesterday, and have come to the conclusion that as long as your crossovers are set properly for the size of your speakers, you can, for the most part, almost eliminate beaming. As such, many feel that makes aiming not quite as critical as it could be. So...on to my question.

I'm upgrading my setup to a three way in the front. I have 3/4 domes in the A-pillars which will probably remain where they are. I have 5 1/4" mids in the doors, and I have 8s I still need to install. I'm going to take a shot at making door pods for the 8s and 5 1/4s. Since I'll have the opportunity to aim them in a direction other than what the factory door would allow, I'm wondering what you guys would do. I've read about people aiming each side toward that side's seat headrest, others aim them for the driver's side headrest, and some align them so they meet in the middle of the car. I do have a HU I will be installing which can be networked, has time delay, and 13 band EQ. I'm sure eventually I'll probably just wind up playing around a bit until I like how it sounds, but am looking for input. Thanks!

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[ciaonzo 5,000+ posts]

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.

 

[trumpet 5,000+ posts]

Did a lot of reading on this yesterday, and have come to the conclusion that as long as your crossovers are set properly for the size of your speakers, you can, for the most part, almost eliminate beaming. As such, many feel that makes aiming not quite as critical as it could be. So...on to my question.
I'm upgrading my setup to a three way in the front. I have 3/4 domes in the A-pillars which will probably remain where they are. I have 5 1/4" mids in the doors, and I have 8s I still need to install. I'm going to take a shot at making door pods for the 8s and 5 1/4s. Since I'll have the opportunity to aim them in a direction other than what the factory door would allow, I'm wondering what you guys would do. I've read about people aiming each side toward that side's seat headrest, others aim them for the driver's side headrest, and some align them so they meet in the middle of the car. I do have a HU I will be installing which can be networked, has time delay, and 13 band EQ. I'm sure eventually I'll probably just wind up playing around a bit until I like how it sounds, but am looking for input. Thanks!

If we reference the chart, pay attention to the columns with the colors shaded from green to yellow to red. Above that are polar response diagrams. Basically we want to stick to the columns associated with a polar response diagram in which the blue line is more circular. Those are the green squares.

Practical Application of the Data

So we want to keep the speaker's response as wide as possible. You may or may not be able to match the numbers in the green squares. What you're looking to do is select a Low Pass Filter crossover frequency.

For your 5 1/4" mids, start at "5". We're matching up with 3/4" dome tweeters, and that means the 5 1/4" mids should play up through the low end of the tweeters. For this example let's say the 3/4" tweeters should be crossed at 4.5 kHz in order to prevent damage at high volume. This puts the 5 1/4" mids well into the range of narrowed response(aka beaming).

What Does This Mean for Me?

I'm keeping this as short as possible, but hopefully you've gotten the idea of what to do with aiming the 8s and tweeters. The only speakers that need to be aimed on axis are the 5 1/4" mids.

 

[Sguirrelfeather]

Both answers VERY helpful! Now I just need to figure out a rig to aim my speakers and hold them in position so I can find the best compromise between practicality and SQ.