# Please define/explain "beaming"



## Ge0 (Jul 23, 2007)

I've read a few instances where DIY'ers were warned about drivers BEAMING under certain circumstances. 

What is beaming?

How does this add ill side affects?

Under what circumstances does beaming occur?

Can Spider man kick Batmans ass?

Ge0


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## tcguy85 (Oct 29, 2007)

i wanna know as well.


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## ErinH (Feb 14, 2007)

tcguy85 said:


> i wanna know as well.


x3.

And while we're at it how about these:

Colorful
Colored (is it the same as the one above?)
bright
airy

I can never define the way a speaker sounds. All I have in my arsenal of adjectives is "good", "bad", "alright" and their synonyms.


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## Whiterabbit (May 26, 2006)

this is the dual slit experiment.

http://homepage.univie.ac.at/Franz.Embacher/KinderUni2005/waves.gif

Note how the pattern of the beams on the wall form a series of dots.










note how the series of dots decrease in intensity RAPIDLY from the center.

Now, imagine a speaker cone not as two slits, but thousands of points of sound, all interfering with each other. what a complex system to model!

But the pattern ends up much the same. With one very intense point of sound in the center, and radiating in all directions is the interference patten here. This is beaming.

Now, beaming is frequency dependent as well. when your wavelength is 12 inches long (1000 Hz I believe?), you dont have many point sources on a 6 inch cone! But when your wavelength is 1 inch, youve got many on a 6 inch cone!

Now look at your typical tweeter or midrange frequency response plot. Note how on axis it rolls off at a particular frequency? Now see how off axis it rolls off sooner? This is the interference pattern reducing the top end due to beaming.


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## Whiterabbit (May 26, 2006)

and why do we care about beaming? Because when you run your 8" or 10" midbass up to horn territory, your speakers might beam. And when you align your speakers oh so carefully so that they sound GREAT in the drivers seat, the early rolloff drastically changes in the passenger seat. Screwing any chance you will ever have a 2 seat car.

Now here is a neat concept to think about. Let's say you are using midranges installed in the kickpanels, crossfiring (WAY off axis). But lets say the cone is small such that the crossover points do not allow the driver to play up into the range the speaker starts to beam. Thus, the highly offaxis FR plot looks the same as directly onaxis.

....Does the speaker aiming direction REALLY matter? 

and lets take the reverse while we are at it. If you install a driver and use it well into the beaming range, would you be OK crossfiring the driver in the kickpanel versus tilting more onaxis?


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## Thumper26 (Sep 23, 2005)

nice.

bikinpunk, i think of bright as right before harsh, i.e. you got the treble boost on. i think of airy as having a sound where even if the image isn't good on your dash, it's still hard to point to the tweeter with your eyes closed.


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## FoxPro5 (Feb 14, 2006)

As described by werewolf from another forum post:



werewolf said:


> The off-axis dispersion of any driver will "narrow" as frequency increases.
> 
> At low frequencies, any driver will display a wide dispersion pattern ... meaning that you will measure similar SPL on-axis, 30 degrees off-axis, or 60 degrees off-axis. As freqeuncy increases, the off-axis response will drop ... this is equivalent to stating that the dispersion pattern is "narrowing", like a "beam" of light.
> 
> ...


If anyone else has something to add, by all means (ahhhem Moley  )


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## ErinH (Feb 14, 2007)

Rabbit,
When I saw the question asked I honestly wasn't expecting an answer like that. I figured it would be alot of 'opinions'. I didn't realized that "beaming" is actually a technical term. Learn something new everyday. 





Thumper26 said:


> nice.
> 
> bikinpunk, i think of bright as right before harsh, i.e. you got the treble boost on. i think of airy as having a sound where even if the image isn't good on your dash, it's still hard to point to the tweeter with your eyes closed.


Makes sense. I'm not poet by a long shot.


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## Abmolech (Nov 2, 2006)

Too slow.

I have no idea on the important stuff like batman versus spiderman. 
Usually "beaming" is used in a negative light.
It refers to off axis response, but more particularly to minimum frequency, at which the off axis response becomes considerably poorer.

For example 
An 8 " cone radiating driver, starts to beam around, 1717 Hz. Speed of sound = approx 1145 feet per minute at sea level. 1145 *12 = the speed of sound in inches, divide by the diameter (8") = approx 1717 Hz.

Why at 8"?
Because a cone can be thought of a series of radiating points, the larger the cone diameter, the more points.
At some frequency, the points will start to interfere (nulls) with each other. Logically this will start with the points that are the greatest distance apart. In this case, the furtherest points apart are 8", as the frequency continues to rise, more points will be involved in causing nulls.

IE at 2051 Hz (6.7") 1/3 of the cone will be involved in causing nulls. This changes the dispersion pattern from a sphere (if unhindered) to 1/3 PI steradians, IE it narrows to become like the beam of a lighthouse.

If you are not sitting in this beam, you lose this frequencies of sound.

Not all beaming is poor, infact if we wish to keep our sound away from reflective surfaces it can be a very useful feature.

See wave guides and arrays.


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## Thumper26 (Sep 23, 2005)

abmolech, i totally understood what you just said, whereas with whiterabbit's explanation, i understood the pictures, but things weren't exactly clicking in my head.

thanks!


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## durwood (Mar 7, 2007)

A little more info:

http://www.diymobileaudio.com/forum/showthread.php?t=18255


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## Abmolech (Nov 2, 2006)

Glad I could help.
I am huge fan of wave guides, arrays and horns in a car.
Not only do the maximise SPL (Load air), they can allow to focus the sound away from some nasty refections (IE floor to roof etc).

Did I mention they also take advantage of early reflections when the sound velocity is low, rather than fighting them?

They also control the dispersion allowing for much better nearfield listening.

The only disadvantage of them is ignorance.


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## thehatedguy (May 4, 2007)

And before we start all of the "what can I do to stop beaming of speakers in my car threads," you have to realize that there will always be a speaker beaming in the car- your tweeters will always beam if you are using anything larger than 1/2" domes.

But I don't worry much about beaming...especially running midbasses to horns in a 2 way setup.


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## ErinH (Feb 14, 2007)

So, in a nutshell, the larger the driver and the higher the frequency it plays, the more chance of "beaming" there is?

And the opposite is true? 

This being based on low frequencies being more 'non-directional'?


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## ECLIPSEsqfan (Sep 2, 2007)

Abmolech: Could you maybe post something about using beaming to your advantage in an automotive setting? Please feel free to use any hypothetical driver sizes and freqency response numbers car type etc... I can't supply any off the top 

Looking forward to an answer


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## Whiterabbit (May 26, 2006)

no, the non directionality of a given frequency is based on ear spacing, not on cone size. read my first post, good visuals there.

the larger a driver is, the lower the frequency is that will have multiple point sources on a single cone (based on the wavelength and cone diameter relationship). And multiple point sources on a single driver leads to beaming.


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## ErinH (Feb 14, 2007)

Whiterabbit said:


> no, the non directionality of a given frequency is based on ear spacing, not on cone size. read my first post, good visuals there.
> 
> the larger a driver is, the lower the frequency is that will have multiple point sources on a single cone (based on the wavelength and cone diameter relationship). And multiple point sources on a single driver leads to beaming.


I'm a hands-on learner, you'll have to forgive me.


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## Abmolech (Nov 2, 2006)

beaming to your advantage?

Possibly the most recognisable would be the ribbon tweeter.
(It even has a built in wave guide )

Let us assume the ribbon is 3/4 wide, and therefore it would start to beam (Vertical, like a book opening out), at about 18320 Hz, however, it is 6 " long and therefore it would start to beam horizontally about 2290 Hz.

To calculate this 1145 *12 / the distance across the driver.

This might be useful is we were mounting in the "A" pillar to reduce the dash and roof reflections. 

We could get clever and use the dash and a pillar area as a wave guide, or the kicks, to increase SPL and direct the wave away from medium reflections.

Take a step up, and use an array, to gain even more directivity, especially in a wave guide. Of cause you can get carried away and use a car computer, and use time delay on each radiating driver in an array to create even more directivity. 

As long as your in the nearfield, and the reflection is in the far field (behind you) your listening experience in a car should be unrivalled. (Except by monophonic, which stereo will never beat )


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## Ge0 (Jul 23, 2007)

Thank all of you for helping me better understand this topic. I knew that off axis response starts to attenuate prior to on axis response for some time now. That is evident in a drivers FR plot. I just did not know why.

Although I couldn't begin to design a system that utilizes this effect to my advantage at this point, I at least have a basic comprehension of what is going on so I can follow along with such conversations. 

I also understand that I might want to consider lowering the crossover point of my door mounted 6.5" mids from 3.2KHz down to roughly 2KHz. This could be causing some WEIRD effects seeing how the drivers side speaker is extremely off axis whereas the passengers side is not. This could account for some differences in frequency response from left to right side.

Ge0


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