on axis? off axis?

[lithium 358]

can someone please explain these concepts of on axis and off axis to me.

[ABXX49 20]

I, too, am interested.

[95Honda 486]

The axis is the angle of the listener/measurement referenced to exactly staight into the loudspeaker. For example, 0 degrees would be like your head staring into the dustcap of the speaker. 45 degrees off axis would be you with the speaker 4' in front of you and 4' to one side, NOT pointed at you. 0 degrees would be ideal, anything less than that is not. This is beause loudspeakers (for the most part) are not ideal pointsources and vary in response depending at the angle (referenced as "axis") you are to them. The biggest problem with a conventional driver is they beam, or become more directional, as frequency and cone diameter goes up. This is what phase plugs, diiferent cone geometries, etc try and overcome. In general, the larger the cone, the more it will beam and the more cruddy the off axis response is. If you look at the off axis response of say an 18" woofer vs. a 4" mid at say, 1 Khz, you will see a huge a difference say 45 degrees off-axis.

Why does this matter?

Think about the last time you listened to a car stereo and you were exactly on axis with the loudspeakers? (subs don't matter because the frequencies are too low) Hardly ever, right? So, you were mostly listening off axis... Therefore if you are in this situation (like most of use) it is really important to choose drivers that have as flat of an off axis response as possible at the angle we will be to them when they are installed.... And all drivers have different off axis reponse, so try and do your homework and look for the best response, after you have nade sure everything else about the driver will work, of course...

Hope this sums it up for you guys...

Edited October 15, 2008 by 95Honda

[ABXX49 20]

Thanks man, good read! Now if you are in the drivers seat and you have a tweeter in the a-pillar facing you. Is that considered 45degrees on axis?

[KU40 173]

anything at 45 degrees from you would be off axis. Only basically staring straight into the speaker is on axis. If you have the tweeter swiveled or mounted so that it's pointed at your head, it would be on axis, 0 degrees. If that tweeter (I assume you're talking about the driver's side) is pointing straight across to the passenger side's A-pillar, then you'd be approximately 45 degrees off axis when sitting in the driver's seat.

[///M5 2,833]

You may have seen me harp about mounting locations and such for different drivers. Everyone wants to know where to mount their tweeters for instance, without describing what they have for a car or for tweeters. I have never met two different tweeters that sounded their best in the same mounting location. Some like to be near on axis, some completely off, it all depends on what sound you like and more importantly the roll-offs of the individual driver. While I almost always prefer my mids on axis, I can't say that I have ever really heard a tweeter in a car that I prefer on axis. Obviously I haven't tried them all though.

[lithium 358]

thanks for the responses. i got some velcro and im trying my tweets in different spots. pg rsd comp set. started with them in the factory location and i had good stage height but they are way to bright for me on axis. especially when i play alot of rock music. i think its also got alittle to do with my pos hu. but anyways i had them there in the a pillar then i try reversing polartity cause it suppose to do something... idk what, but i did, and it did do something and i liked it alittle more... right now i moved them down pretty close to the woofer basicly afew inches above the mid and im playing around with the direction with the swivel. im just not sure on were to aim the passenger side. i also think the stage is alittle to low now. so my next option in up about 4-6 inches basiclly halfway between the current location and the factory a pillar location. im just playing with it till i can go active later this year. i think it was /m5 that recommended a 2" full range instead of a tweet? maybe that would be an option. im going to try to go with AA carbon mids aswell. i've got this pair of polk tweets hanging around that i might use temporarily if i dont have the money for some nice tweets right away.... and if i blow them do to bad settings i dont really care. lol

sorry kinda babbled. thanks agian guys

[///M5 2,833]

Everything is a compromise.

When playing with things, shut off the mids and only listen to the tweets. Then you only have one polarity switch you need to make, once you add the mids there are many more combinations of phase to deal with.

[lithium 358]

is that safe to do with a component set? i thought i heard that not having both hooked up it somehow messed up the crossover?

[manbeer 0]

i use gobs on fun-tack on the back of the tweeter to mess around with the mounting positions

[KU40 173]

is that safe to do with a component set? i thought i heard that not having both hooked up it somehow messed up the crossover?

It is safe. The mid and tweeter are on two completely different circuits once the signal gets past the input on the crossover.

[lithium 358]

i use gobs on fun-tack on the back of the tweeter to mess around with the mounting positions

ya that sounds like an good idea too. my dad just happen to find some velcro in walmart the other day. i put the hook side on the tweet and the other stuff on the door. they camp in like 1 or 1.5 inch circles. they stick enough to hold the tweet but i can take them off with out damaging the door. i had to clean the spot on the door because i use armoural whipes to clean them.

Edited October 15, 2008 by lithium

[95Honda 486]

Switching polarity will cause a huge change in response in the crossover region, as much as 6+ db. This can make a huge difference to your ears, especially since most 2-ways are crossed over where your ears are very sensitive (2-4KHz).... Sometimes the dip you may get from switching the polarity is just the ticket at taming a nasty peak... Or the peak you may get might help a nasty null you have in the response of the driver...

And there is no right or wrong with polarity in regaurds to a 2-way, especially with 12db slopes (which alot have)... The textbook answer is simply "whatever way sounds best"....

[lithium 358]

im goin to switch the polarity on the tweets tomorrow night. i did like it more when i had them switch and located up in the window sails but im liking them more off axis and closer to the mid like they are now.

[MikeS 0]

Couldn't he just pad the tweeters, and attenuate to taste?

[lithium 358]

ohya i heard some one say something about putting material infront of the tweeter. i think it was fleece.... idk

hows it work?

[Rybaudio 0]

Here's a picture showing what has been desribed above. If the disc in the picture is the speaker's cone, the O-looking letter (the greek letter theta) is the off-axis angle to the listener at point P.

Edited October 17, 2008 by Rybaudio

[95Honda 486]

If a tweeter sounds better off-axis, this is usually a problem with the crossover or attenuation level as Mike S suggested. When they design most drivers, they are usually designed primarily to be listened to on axis. The cheap, cruddy car audio passives usually cause alot of these problems...

Alot of people think metal domes sound harsh, and fabric doesn't... Etc, Etc, and while the final product (speaker, crossover, cabeling and amp) definetly sounds this way, it is rarely due to the tweeter itself, mostly the crossover. Car audio crossovers are cheap, even the best ones NEVER contain the best topology (I don't mean parts quality, I mean BSC, notches, traps, etc), and alot of times all these bad things we hear are a direct reflection of this...

I know saying this doesn't really help anyone, but I thought I'd throw it out...

[lithium 358]

that makes alot of sense thanks.

what about "padding the tweeter"? what's that all about?

[///M5 2,833]

An Lpad is a portion of the crossover that limits the output of one of the drivers. Typically used to lower the output of a tweeter to correspond to a mid as they are intrinsically more sensitive.

[lithium 358]

thanks for the info m5.

ill continue to play with the location and polarity for now.

Edited October 17, 2008 by lithium