# Explain On Axis and Off Axis



## Elektra (Feb 4, 2013)

Hi Guys

It's a silly question but I need clarity as to what is considered On Axis and what is considered Off Axis.

My interpretation is - On Axis the center of the driver is pointing to your ear - both sides - so left side of the car is pointing to the drivers left ear and right hand side pointing to the drivers right ear...

Am I correct? 

Or is On Axis considered to be this - left side of the car playing parallel to the passenger or drivers ear (depends the country) and the right side of the car firing parallel to the drivers ear - so essentially the mids and tweeters are perpendicular to the dash... 

See pic below...











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## Lanson (Jan 9, 2007)

Off axis (not a switch) generally refers to the speaker cone being angled away from the ear by a significant degree. I think the "official" number is 30 degrees but to me, off-axis is closer to 50-60 degree, due to the way beaming works.

Use this to help with on-off axis beaming points










As you can see, off and on-axis, the severity of beaming really is what we're talking about as even a small tweeter beams eventually. But 30 degrees is about where that becomes noticeable.


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## Jscoyne2 (Oct 29, 2014)

fourthmeal said:


> Off axis (not a switch) generally refers to the speaker cone being angled away from the ear by a significant degree. I think the "official" number is 30 degrees but to me, off-axis is closer to 50-60 degree, due to the way beaming works.
> 
> Use this to help with on-off axis beaming points
> 
> ...


I never did get how to read that thing

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## Elektra (Feb 4, 2013)

Jscoyne2 said:


> I never did get how to read that thing
> 
> Sent from my SGH-T999 using Tapatalk




Makes 2 of us... Lol!


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## Jscoyne2 (Oct 29, 2014)

Elektra said:


> Makes 2 of us... Lol!
> 
> 
> Sent from my iPhone using Tapatalk












That will answer your question. 

However you have to take into effect beaming and reflections and diffraction when aiming a speaker. 



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## Elektra (Feb 4, 2013)

What does a beaming speaker sound like? Is it obvious? 


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## gijoe (Mar 25, 2008)

Elektra said:


> What does a beaming speaker sound like? Is it obvious?
> 
> 
> Sent from my iPhone using Tapatalk


Beaming sounds quieter, look at the FR chart above. When a speaker beams the sound is literally focused into a smaller beam. Outside of that beam, those frequencies aren't as audible. The FR shows all of that, but ask questions if that's not clear.


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## Elektra (Feb 4, 2013)

gijoe said:


> Beaming sounds quieter, look at the FR chart above. When a speaker beams the sound is literally focused into a smaller beam. Outside of that beam, those frequencies aren't as audible. The FR shows all of that, but ask questions if that's not clear.




So theoretically you hear more information if you place your speakers inside the beaming range... 

This is theoretically the most ideal situation? 


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## rton20s (Feb 14, 2011)

On axis is more like your second drawing than your first. If you picture








firing straight out of the center of the speaker, that would be the axis for 0 degrees. (Straight up on the half circles in fourthmeal's graph.) 

The angle of off-axis would be measured as if you had another laser that shot from the center of the speaker to your ear. The difference in angle between the on axis laser and the ear laser (no matter what the plane) would be your off axis angle measurement. 

From the two examples posted above we can see that, as a general rule, the farther off axis you get the more the top end will be attenuated. "Roll off." Now, every driver is different and they really do have to be looked at on a case by case basis (including how the driver will be used) to determine exactly how important on-axis vs off-axis is. For instance, if you are playing a midrange within a passband that low passes the top end before beaming, it doesn't really matter. On a tweeter, and even more importantly, running tweeterless with a "full range" driver, on/off-axis alignment can be critical.


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## gijoe (Mar 25, 2008)

Elektra said:


> So theoretically you hear more information if you place your speakers inside the beaming range...
> 
> This is theoretically the most ideal situation?
> 
> ...


The idea is that you don't want to play a speaker above it's beaming point, unless it is perfectly on axis. Even if it is on axis, however, if you move your head a couple of inches, those frequencies will drop like a rock. To avoid this, we try to place our filters before a speaker beams, so the sound remains omnidirectional. This a big reason why people don't recommend playing a 6.5" above 2-2.5k. Getting a 6.5" on axis is nearly impossible, in a car, without drastic modification, so we just low pass before beaming.


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## Elektra (Feb 4, 2013)

gijoe said:


> The idea is that you don't want to play a speaker above it's beaming point, unless it is perfectly on axis. Even if it is on axis, however, if you move your head a couple of inches, those frequencies will drop like a rock. To avoid this, we try to place our filters before a speaker beams, so the sound remains omnidirectional. This a big reason why people don't recommend playing a 6.5" above 2-2.5k. Getting a 6.5" on axis is nearly impossible, in a car, without drastic modification, so we just low pass before beaming.




This is probably why a 3 way is better than a 2 way - as you can cross each driver before beaming takes place and worry only about the tweeter placement or angle - correct?

If a speaker beams at say 2000hz does that mean you cross it at 2000hz or before 2000hz considering the slope so say 12db the speaker actually plays higher (4000hz I think) does that mean all the frequencies above the 2000hz will beam? So to avoid this do we cross the driver rather at 1000hz so that the 12db slope frequencies are still within the beaming range? 


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## rton20s (Feb 14, 2011)

And while we have focused on top end roll off, there is more that can happen on the top end besides off axis attenuation. Below is a graph of an arguably pretty nice driver. However, look at the frequency response variations on the top end! I would not want to try to use this driver full range in a car. You might be able to tune it to be pleasing for the driver in a specific position, but outside of the sweet spot things will be all over the map. 

Now, take that same driver and low pass it at 4kHz or lower and it will probably be very nice.


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## sqnut (Dec 24, 2009)

Elektra said:


> What does a beaming speaker sound like? Is it obvious?
> 
> 
> Sent from my iPhone using Tapatalk


Beaming creates an imbalance between L/R response so frequencies above say 2.3khz (for a typical 6" mid) will be louder from the the far side speaker which is more on axis. It will pull the image to hotter side, it's not tonal difference thing.


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## Elektra (Feb 4, 2013)

sqnut said:


> Beaming creates an imbalance between L/R response so frequencies above say 2.3khz (for a typical 6" mid) will be louder from the the far side speaker which is more on axis. It will pull the image to hotter side, it's not tonal difference thing.




I see... So if the driver is below the beaming frequencies the balance between left and right is more balanced and the image is more focused?


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## gijoe (Mar 25, 2008)

One thing you need to know in order to fully understand beaming, is that speakers are omnidirectional below that point. 

Imaging a speaker hanging in the air, the sound from this speaker will be the same in all directions. It will be the same in front of the speaker, in back, above, below, everywhere. The sound can be visualized as a sphere emanating from the speaker in all directions.

Once you start to play frequencies that are too high (the speed of sound, divided by the diameter of the radiating surface) that sphere begins to become more focused, think of a football, the higher you play that speaker, the sharper the points become, and the more narrow that beam is. Inside that beam, the sound is the same, outside of it, it is significantly attenuated (see graph in rton20s' post). This happens to the both the front, and back of the speaker (with the exception of the influence the basket and magnet play on the backwave), but we disregard the back since we are using an enclosure, or baffle that makes the back wave irrelevant in most cases.


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## sqnut (Dec 24, 2009)

Elektra said:


> I see... So if the driver is below the beaming frequencies the balance between left and right is more balanced and the image is more focused?
> 
> 
> Sent from my iPhone using Tapatalk


Correct. Although thanks to the cars environment and reflections, even below beaming point some frequencies will be hotter from the left and others from the right. Above the beaming point they will be progressively louder from the more on axis side.


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## Elektra (Feb 4, 2013)

gijoe said:


> One thing you need to know in order to fully understand beaming, is that speakers are omnidirectional below that point.
> 
> Imaging a speaker hanging in the air, the sound from this speaker will be the same in all directions. It will be the same in front of the speaker, in back, above, below, everywhere. The sound can be visualized as a sphere emanating from the speaker in all directions.
> 
> Once you start to play frequencies that are too high (the speed of sound, divided by the diameter of the radiating surface) that sphere begins to become more focused, think of a football, the higher you play that speaker, the sharper the points become, and the more narrow that beam is. Inside that beam, the sound is the same, outside of it, it is significantly attenuated (see graph in rton20s' post). This happens to the both the front, and back of the speaker (with the exception of the influence the basket and magnet play on the backwave), but we disregard the back since we are using an enclosure, or baffle that makes the back wave irrelevant in most cases.




Thanks great explanation... 


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## Lanson (Jan 9, 2007)

Jscoyne2 said:


> I never did get how to read that thing
> 
> Sent from my SGH-T999 using Tapatalk



So first, think of the top graphs in terms of axis. Straight up is 100% on-axis. 90 degrees to each side if of course, fully off-axis. So in simple terms, you can seel that for a given speaker size at a given axis, the response will be more and more direct (beaming ahead instead of being omni-directional) the further up the frequency chart we go. All speakers beam, but the size of the speaker changes the beaming frequency.

Point is, you can see that, just like those graphic charts showing on and off-axis results, the effect is not an on-off switch, it is more gradual instead. 

The chart here just gives you a way to see it for a given speaker size, for a given amount off axis. The math of that (the wavelength calculation) is just the math, but the impression here is to know that a 1" tweeter will become more and more directional the higher the frequency. Aka another way to think of a response graph.


In practical terms, I've had great success in using this chart (and mathematical extensions of it) in making 3-way setups in vehicles. I used this in the Vette, and my own Flex most recently. Doing so let me pick good crossover points to keep the response right off-axis.


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## danssoslow (Nov 28, 2006)

On and off axis is easy to understand (and consequently, that graph) when you understand what the axis is. Imagine sticking a laser pointer into the pole vent, removing the duustcap, and turning the laser on. That red laser beam is the axis.


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## Elektra (Feb 4, 2013)

Ok so here is the next question - if my understanding is correct...

Position of drivers is to some extent irrelevant so long as you cross your drivers below the beaming point - more importantly is to deal with reflections as best as possible like maybe aim the drivers more towards the roof of the car so that you minimize the reflections - the only driver that appears to be more important is the tweeter as we can't cross the beaming point out so we need to aim this driver to minimize the effects of beaming... 

So taking all this into account - is there anything wrong in aiming the tweeters say 0-10deg off axis for BOTH ears - this might mean the tweeter pods are not uniform in terms of angles - essentially a more single seater car? 

Is this correct? I know for the sake of aesthetics the pods are the same angle - but a certain compromise is been had? 

See pic below.. 16deg off axis seems to be uniform - BUT does it not depend on the size of the dash? Bigger the dash the harder to get that angle? 











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## MB2008LTZ (Oct 13, 2012)

Elektra said:


> Ok so here is the next question - if my understanding is correct...
> 
> Position of drivers is to some extent irrelevant so long as you cross your drivers below the beaming point - more importantly is to deal with reflections as best as possible like maybe aim the drivers more towards the roof of the car so that you minimize the reflections - the only driver that appears to be more important is the tweeter as we can't cross the beaming point out so we need to aim this driver to minimize the effects of beaming...
> 
> ...


So if you can't place the speakers at said angles, wouldn't time alignment compensate for that?


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## seafish (Aug 1, 2012)

MB2008LTZ said:


> So if you can't place the speakers at said angles, wouldn't time alignment compensate for that?


TA compensates for differences in distance, not differences in off axis repsonse.


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## sqnut (Dec 24, 2009)

If you're playing a driver in its non beaming pass band, you don't have to worry about angles, eq is way more important.


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## Lanson (Jan 9, 2007)

All the above is true, and remember our ears are less sensitive to time alignment "issues" with tweeter frequencies, and more sensitive to spl. Of course, doing proper time alignment if you can is cool, but if you for some reason can't, it isn't the worst thing to happen.


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## g35man (Jun 24, 2016)

Subd


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## Babs (Jul 6, 2007)

Right. If you are low-passing below the point of divergence (if that's a proper way to put it), the angle will be more critical for considerations of reflections than of freq response from driver directly. Reflections in car playing a huge part of overall response and other related nasties such as comb filtering etc. So you have to take the placement, position, crossover points all into account. And there's no better tool than simply testing in locations and angles. 


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