# on axis vs. off axis



## spmpdr (Nov 5, 2009)

This might belong in the dumb question forum , Im not quite sure I understand on axis and off axis theory. Ive been doing some research on the subject and have gotten lost i think. Could some please define when speakers are on axis and off axis? Also I would like to know when its best to run off axis or on axis? Is this based on the speaker specifications or the mounting position or both?Ive read so much on this subject my brain is literally hurting now!!!!Please explain in lamens terms if possible.


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## zblee (May 18, 2010)

spmpdr said:


> This might belong in the dumb question forum , Im not quite sure I understand on axis and off axis theory. Ive been doing some research on the subject and have gotten lost i think. Could some please define when speakers are on axis and off axis? Also I would like to know when its best to run off axis or on axis? Is this based on the speaker specifications or the mounting position or both?Ive read so much on this subject my brain is literally hurting now!!!!Please explain in lamens terms if possible.


on-axis means that the speaker is basically pointing straight at you, off-axis means the speakers are facing each other ( in most applications ) so people will sometimes put the tweeters in the A-pillars, if they have them "on-axis" with the driver seat, when sitting in the driver seat you would be looking straight on with the tweeters for both sides. if they are in the a-pillars "off-axis" then the tweeters would be literally pointing directly across the dash and at each other.. 

as for what do you, it is personal preference, try both see what sounds better... and i believe some speakers do better off than on, and vice versa...so do some research with speakers being used and see what majority of other people have been happy with , "on" or "off"

hope this helps and makes sense


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## 94VG30DE (Nov 28, 2007)

I would think on-axis vs off-axis depends on your intended crossover frequency. B/c as far as I'm concerned, on-axis assumes the entire bandwidth of what you are expecting to hear from the driver is coming in a straight (non-reflected) line from the driver to you. This takes into account that different drivers beam at different frequencies. 

For example, I would consider my sub "on-axis" even though it's turned 90 deg from my head, b/c at the frequency it's reporducing orientation doesn't matter. A mid is slightly less-flexible, depending on the pass-band you are looking at. And since a tweeter (small cone diameter) will beam earlier than the sub, on-axis would be "whatever direction it needs to point so that the frequencies above where it starts to beam are on-axis." Basically you only have to tune for the highest frequency the driver will produce. 

When it's "best" to run on-axis depends on the driver, the install, and your ear. Honestly it is what sounds best. Some people deliberately run bright tweeters off-axis to attenuate the top-end. Some run off axis to direct the beam a certain way, so that they are hearing a certain reflexction rather than no reflection. Ideally you can set it up in different positions and see what's best for your vehicle and equipment combination.


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## spmpdr (Nov 5, 2009)

zblee said:


> on-axis means that the speaker is basically pointing straight at you, off-axis means the speakers are facing each other ( in most applications ) so people will sometimes put the tweeters in the A-pillars, if they have them "on-axis" with the driver seat, when sitting in the driver seat you would be looking straight on with the tweeters for both sides. if they are in the a-pillars "off-axis" then the tweeters would be literally pointing directly across the dash and at each other..
> 
> as for what do you, it is personal preference, try both see what sounds better... and i believe some speakers do better off than on, and vice versa...so do some research with speakers being used and see what majority of other people have been happy with , "on" or "off"
> 
> hope this helps and makes sense


Thanks man the does help alot So my idea is this: Im adding a set of tweeters to my set up and want to place them in the corners of my front windshield facing the opposite seat. ( driver side tweeter aimed at passenger side head rest, passenger side tweeter aimed a drivers seat head rest) would this be considered cross firing?


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## derickveliz (May 15, 2009)

Great thread, specially for new fans like me, what about where to aim or what to aim at?

in other words, installation would be symmetrical or not?

Thanks.


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## spmpdr (Nov 5, 2009)

94VG30DE said:


> I would think on-axis vs off-axis depends on your intended crossover frequency. B/c as far as I'm concerned, on-axis assumes the entire bandwidth of what you are expecting to hear from the driver is coming in a straight (non-reflected) line from the driver to you. This takes into account that different drivers beam at different frequencies.
> 
> For example, I would consider my sub "on-axis" even though it's turned 90 deg from my head, b/c at the frequency it's reporducing orientation doesn't matter. A mid is slightly less-flexible, depending on the pass-band you are looking at. And since a tweeter (small cone diameter) will beam earlier than the sub, on-axis would be "whatever direction it needs to point so that the frequencies above where it starts to beam are on-axis." Basically you only have to tune for the highest frequency the driver will produce.
> 
> When it's "best" to run on-axis depends on the driver, the install, and your ear. Honestly it is what sounds best. Some people deliberately run bright tweeters off-axis to attenuate the top-end. Some run off axis to direct the beam a certain way, so that they are hearing a certain reflexction rather than no reflection. Ideally you can set it up in different positions and see what's best for your vehicle and equipment combination.



Thats great info, thanks. So im planning on a second set of tweeters in my three way active set up . I plan on using these up high somewhere on my dash or in the a pillars. They will be used to bring up my sound stage and only play from 9000 hz up. Any recommendations on how to set this up to get the best results? I have to run them off the rear channel of my h/u to allow for adjustments.


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## pionkej (Feb 29, 2008)

94VG30DE said:


> I would think on-axis vs off-axis depends on your intended crossover frequency. B/c as far as I'm concerned, on-axis assumes the entire bandwidth of what you are expecting to hear from the driver is coming in a straight (non-reflected) line from the driver to you. This takes into account that different drivers beam at different frequencies.
> 
> For example, I would consider my sub "on-axis" even though it's turned 90 deg from my head, b/c at the frequency it's reporducing orientation doesn't matter. A mid is slightly less-flexible, depending on the pass-band you are looking at. And since a tweeter (small cone diameter) will beam earlier than the sub, on-axis would be "whatever direction it needs to point so that the frequencies above where it starts to beam are on-axis." Basically you only have to tune for the highest frequency the driver will produce.
> 
> When it's "best" to run on-axis depends on the driver, the install, and your ear. Honestly it is what sounds best. Some people deliberately run bright tweeters off-axis to attenuate the top-end. Some run off axis to direct the beam a certain way, so that they are hearing a certain reflexction rather than no reflection. Ideally you can set it up in different positions and see what's best for your vehicle and equipment combination.





spmpdr said:


> Thats great info, thanks. So im planning on a second set of tweeters in my three way active set up . I plan on using these up high somewhere on my dash or in the a pillars. They will be used to bring up my sound stage and only play from 9000 hz up. Any recommendations on how to set this up to get the best results? I have to run them off the rear channel of my h/u to allow for adjustments.


Some of the information going on here is getting different concepts mixed together, so I'm going to try and sort it out a bit. 

First, the original question. On-axis means that the speaker (any speaker) is facing/aimed at the intended listener. Off-axis means that the speaker (any speaker) is NOT facing/aimed at the intended listener. It doesn't matter if it is 90 degrees (like a door mounted speaker) or 30 degrees (like some kick panels), if it isn't aimed at you, it's off-axis.

Next, is beaming. Beaming occurs as a the dispersion pattern of sound narrows. This doesn't matter if the speaker is a sub or a tweeter, they all exibit beaming. However, as the driver gets smaller the beaming point goes up, not down. This means that a 1" tweeter should be able to play 3khz clearly off axis, a 5.25" mid can play it with some loss out output off-axis due to beaming, and a 12" sub will suffer considerably in output if you tried to play 3khz (not that you would) off-axis. Below is a chart and the link that I got it from:

Beaming of speakers:

Assuming 30C or 86 degrees F:

12" ~ 1,150Hz
10" ~ 1,380Hz
8" ~ 1,720Hz
7"~ 1,970Hz
6.5" ~ 2,120Hz
5.25" ~ 2,620Hz
4" ~ 3,440Hz
3" ~ 4,950Hz
2" ~ 6,880Hz
1" ~ 13,750Hz 

http://www.diymobileaudio.com/forum/diy-mobile-audio-sq-forum/29124-power-beaming.html

Now, a point that also must be considered is that as frequency goes up, wavelegths get shorter, and sounds become more directional. Since wavelengths are so long at low frequencies, it is difficult to pinpoint location as long as rattles aren't giving it away. This is why the sub can be in the trunk but sound like it is "up front" with the rest of the speakers when properly setup. Now, even though tweeters/mids aren't beaming at 3khz, the sound waves are shorter and have become more directional which means if they are aimed off-axis you should have a loss in output because the sound is "missing you". Think about it like a sub is a shotgun and a tweeter is a rifle. The shotgun spreads things around so aiming isn't so critical, but you aim a rifle off-axis (away) from the target and the bullet will miss.

All of that being said, on-axis does not mean good sound (neither does off-axis). In my build, I put both the driver and passenger seats in the same location, sat in each seat, and aimed the mids and tweeters about 4" in front of my face. What that does is leave the far side speakers around 15 degrees off-axis and the near side speakers around 30 degrees off-axis for each listener. This gives me and my passenger (if they are my height and don't move the seat) a natural attenuation on the near side speakers because they are more off-axis. This was done purposefully and gives me a good soundstage for both seats. I haven't started with eq or t/a but will optimize those for the driver seat. So while I will probably have better imaging, my passenger will experience nearly the same staging and balanced levels I enjoy. I know everyone (including me) wants a "aim your speakers like this and use these crossover points for the best sound" type answer, but it really does take some trial and error to get it set up like you like. This also goes for speaker locations. I was planning on putting my tweeters in the kicks and getting super-tweeters like the OP mentioned, but read on here to wait and see how it sounds. I ended up with the tweets in the a-pillars and no super-tweeters and I don't regret it one bit. It just took trial and error.

Hope this helps and I will be happy to answer any other questions I can or refer you to a thread to help if I don't know the answer for sure.


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## 94VG30DE (Nov 28, 2007)

pionkej said:


> Some of the information going on here is getting different concepts mixed together, so I'm going to try and sort it out a bit.
> ... et al.


Thanks for that. I knew what I was saying didn't feel quite right as I was typing it, but wasn't sure how to structure it to get the correct point across. Thanks for taking the time to straighten the point(s) out. 

As a side note, I believe there is a lot of good discussion on this issue in the "improve my soundstage for $2" thread, which is stickied. Should be worth a re-read...


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## Oliver (Jun 25, 2007)

http://www.diymobileaudio.com/forum/diyma-tutorials/5664-kickpanel-speaker-locations-pros-cons.html

good info from Rick in here


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## pionkej (Feb 29, 2008)

a$$hole said:


> http://www.diymobileaudio.com/forum/diyma-tutorials/5664-kickpanel-speaker-locations-pros-cons.html
> 
> good info from Rick in here


That was the basis of where I aimed my midranges. I started there and moved them till I was happy (not far).


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## spmpdr (Nov 5, 2009)

pionkej said:


> That was the basis of where I aimed my midranges. I started there and moved them till I was happy (not far).


I did the same. My passenger mid is on axis in my kick panel while the tweeter is off axis . MY driver side mid and tweet are both off axis. My mid bass mounted in my doors are both off axis. The tweeter's im planning to add to my system will be tested both on and off axis and in different positions on my dash and a -pillars.Thanks for the info everyone. I was making it way more complicated than it needed to be!!!


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## Oliver (Jun 25, 2007)

G'luck ! 

frequency charts that show the 3 different lines ... on axis , off axis at 15 degrees and off axis at 30 degrees can help in this quest.


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