24 replies to this topic

[CobbaDan]

I was reading an ancient post from muzzy last night talking about the focal krx3's and how the tweeter sounded great on axis and like poo off axis, and it got me thinking.


If the tweeter mounted on the drivers side is pointed towards the passengers head rest (on axis)

and vica versa

the tweeter mounted on the passenger side pointed at the drivers headrest (on axis)


Wouldnt that mean that the tweeter mounted on the drivers side would sound like poo to the driver because its off axis to the drivers position

and vica versa

the one mounted on the passenger side would sound like poo to the passenger..


hmmmm

[~thematt~]

The levels of understanding for on and off axis response by a lot of people on this forum is very basic indeed.

There is no difference between on axis, and off axis, response for a driver below its beaming point. Above its beaming point, the only difference is the degradation in amplitude, relative to frequency. Even then, almost the entire contributing factor is the size of the cone/dome, not the manufacturer.

The differences that you hear in your car, between an on-axis and off-axis speaker, are due to the environment (and the interaction with the driver). Not the speaker.

To achieve a good effect from the tweeters (really the only speaker you'll operate above the point of beaming), the best effect is achieved through the application of waveguides. That way, you'll increase/control your dispersion across all axis.

[Captn_Awesome]

*claps*

Man I love when people who have a clue respond to questions like this.

[SCorpion]

~thematt~, on Apr 20 2009, 10:17 AM, said:

The levels of understanding for on and off axis response by a lot of people on this forum is very basic indeed.

There is no difference between on axis, and off axis, response for a driver below its beaming point. Above its beaming point, the only difference is the degradation in amplitude, relative to frequency. Even then, almost the entire contributing factor is the size of the cone/dome, not the manufacturer.

The differences that you hear in your car, between an on-axis and off-axis speaker, are due to the environment (and the interaction with the driver). Not the speaker.

To achieve a good effect from the tweeters (really the only speaker you'll operate above the point of beaming), the best effect is achieved through the application of waveguides. That way, you'll increase/control your dispersion across all axis.

what about polar response?

[Pulse-R]

polar response is the same sort of thing as axial response.

just a different graph, with different information.

axis is about frequency response (FR) at a few angles, polar response is angular response (hence polar) at a few frequencies.

if you do a complete map of frequency/angle and intensity, you end up with a 3-D map of the speaker's output pattern for a given input level.

make it at varying levels and you have a 4-deminsional map.. yay!

but not very useful for the most part.

speakers should be mounted how they sound best - on-axis or off, to get the best possible result.
If that means you need waveguides, then so.

[br85]

~thematt~, on Apr 20 2009, 10:17 AM, said:

The levels of understanding for on and off axis response by a lot of people on this forum is very basic indeed.

There is no difference between on axis, and off axis, response for a driver below its beaming point. Above its beaming point, the only difference is the degradation in amplitude, relative to frequency. Even then, almost the entire contributing factor is the size of the cone/dome, not the manufacturer.

The differences that you hear in your car, between an on-axis and off-axis speaker, are due to the environment (and the interaction with the driver). Not the speaker.

To achieve a good effect from the tweeters (really the only speaker you'll operate above the point of beaming), the best effect is achieved through the application of waveguides. That way, you'll increase/control your dispersion across all axis.

Well answered indeed. You may find that some drivers have different off-axis respose below beaming point as well, but certainly not as erratic, and 1 octave below beaming point pretty much means there will be absolutely no difference. (you might feel air from a door midbass on your leg instead of air in your face from the same midbass right in front of your head.)

[muzzy66]

CobbaDan, on Apr 19 2009, 03:16 AM, said:

I was reading an ancient post from muzzy last night talking about the focal krx3's and how the tweeter sounded great on axis and like poo off axis, and it got me thinking.

If the tweeter mounted on the drivers side is pointed towards the passengers head rest (on axis)

and vica versa

the tweeter mounted on the passenger side pointed at the drivers headrest (on axis)


Wouldnt that mean that the tweeter mounted on the drivers side would sound like poo to the driver because its off axis to the drivers position

and vica versa

the one mounted on the passenger side would sound like poo to the passenger..

Yes, it means exactly that.

Tweeters typically begin to "beam" (i.e. get effected by off axis mouting) at somewhere around 8khz-10khz give or take (depends on the individual tweeter exactly what frequency it begins at, and to what degree).

In the case of the Focal TN52, data suggests it first begins to beam at roughly 7khz, but this low down the effect is minimal. Once you get to 10khz however, the tweeter will be 3dB down @ 45deg off axis (compared to on axis). By around 13khz, the difference has increased to about 5db.

So, in the sample layout you referred to, from the drivers seat, the passenger side tweeter would be at least 3dB louder then the driver side tweeter once from 10khz upwards. This does indeed create some 'evil' effects on the sound.

Contrary to what some would suggest, this does not only effect tweeters. It will effect your midrange drivers just as noticably - the only difference is that with mids, we can pretty much eliminate the effect by crossing the speaker over before the point of beaming (usually around 1khz - 1.6khz for a 6.5" woofer).

The difficulty here is that if you want to do this without having a nice big hole in your midrange, you need a tweeter that can play down to 1.2khz / 1.6khz comfortably - good luck. I can think of about two tweeters off the top of my head (AirCirc, XT25) that actually have a usable response down to 1.6khz, and I can think of about two tweeters (Peerless HDS and Seas 27TBFC/G) that have usable distortion down to 1.6khz. I can't think of a single tweeter that has both, and so I really can't think of a single tweeter i'd actually recomend crossing at 1.6khz (let alone 1khz).

So, if you want to achieve this you pretty much need to use a small 3" or 4" dedicated midrange - a these will typically begin to be effected by off axis response when they reach 1.6khz - 2khz. Tweeters that can handle 2khz comfortably are still few and far between, but a handful of them do exist.

So in theory, you can get aroud this problem with midwoofers. With tweeters though, you really can't because they have the task of playing everything from 2khz-4khz upwards.

The issue you bring up here, is the specific reason why I've chosen to angle the tweeters in my car (and my previous one) the way I have. It's essentially the one 'critical angle' as I like to call it - the one angle where the left and right tweeter are always practically identicle in angle, no matter where you sit in the car. When mounting the baffles I got the left one a wee bit off, so it hasn't worked out 100% precisely on the angle I wanted but it's pretty close.

My opinion from both of my installs is, it works.

Of course if you aren't fussed about a two seat stage, then it's not so difficult - you can simply mount both tweeters on axis to the driver and be done with it. I like the challenge of makign my car sound great from either seat, so I make my own life difficult

Either way, my Rainbow isntall (before the current one, and the one before it) has the tweeters angles precisely how you have described (passenger tweeter aimed to driver, driver tweeter aimed to passenger) and I've got no doubts that the sound suffered as a result. It's not just the direct effects (poor frequency response on one side) but the indirect effects that make it significant.

Imaging for example, can be heavilly affected heavilly by this.

Have you ever sat in your car, listened to the image, and then set the ballance on your head unit a couple of notches to the left - notice that when you do this, the overall image shifts to the left? This is because the left side speakers are producing greater output then the right side speakers, so the image is "pushed" into the direction of the dominant speakers. Same thing happens in the above scenario. Since the passenger side tweeter is 3dB+ louder then the driver side tweeter from 10khz upwards, every time a note higher then 10khz is played, the image moves to the left of the car. This is particularly noticable on female vocals, where a female singer will be firmly locked in the centre of the stage, and then as she hits a very high note her voice will suddenly shift about 10cm to the left, and then back again when she gets back down to the lower note. This was a characteristic that was present on every single system I had until I came up with the idea of putting both sides' tweeters on the same angle to normalise upper frequency response.

If you have 6.5" mids in your doors off axis, and you run a relatively high crossover (2.5khz+) to the tweeter, then you will most likely also hear it in your mids. This is because when your mids are in your doors, the driver side mid is typically nearly a full 90 degrees off axis, while the passenger one is only about 60degress off axis. The higher your crossover is on your component set, the more noticable this will be - the Focal K2P's for example, use a crossover point somewhere above 3khz (I forget exactly where) and so the effect would probably be significantly more noticable on a set like this, compared to something like Morel Elate's (which from memory cross over around 2.2khz or thereabouts).

It wasn't an issue in the previous install of mine, because my Revelators were angles like the tweeters ('critical angle' on both sides). In my current install though, even though I'm using 4" mids crossed over at 2khz, there is still a very slight audible difference between the left and right midrange (since both are off axis in the doors).

Edited by muzzy66, 22 April 2009 - 02:22 AM.

[~thematt~]

Try keeping your posts shorter, as it will also challenge you to say with less words, more accurate information. That ^ post, is full of misinformation and anomalies.

It is unfortunate that so many people, when 'trying' drivers inside a vehicle, almost always believe that the problems they hear are properties of the driver, when in actual fact, its the acoustic response of the entire package. This includes Xover points, slopes, boundary interaction, environmental interaction amongst other things. Just because you can hear something wrong, doesnt mean its the driver's fault. Rarely it ever is.

In fact, you'll find that most drivers that have differing off-axis measured responses will be due to either testing parameters (mic position, baffle properties, etc as is the case with comparing SEAS to SCANSPEAK) or whether or not the driver has a well designed waveguide built in (such as the T330D, or the TLR, or the Hiq's)

FYI, beaming is determined from an equation based on diameter. Here is an approximate from DIYMA

Quote

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

As can be seen, unless you're using a widebander or a 5.25"+ for midrange duties, you shouldnt be having any issues with beaming in the midrange, midbass or subbass. If you are, its not the driver, but the installer that needs work.

What this means is, if your speaker is playing below your beaming point, 'aiming' of a driver will have as much effect as 'aiming' the sun towards the earth. Its stupid and useless. The only concern you should have is how the driver interacts with its environment, and how THAT affects the sound.

If your speaker plays above the beaming point, as I mentioned before, use waveguides to allow greater dispersion along the axis that you want, and less dispersion in the axis that you dont want. This way, you can 'program' your speaker to give you the response curve for both drivers, or both speakers to give you the same response for the driver.

[muzzy66]

Matt, you can post your entire lifetime of theoretical formulas all you like, but until it actually works in the real world it's useless and irrelevant.

Take a look at physical measurements of an 8" driver, 6.5" driver, 10" driver, 4" driver.

Find me a single 4" cone midrange that has the same frequency response on axis as it does 90degrees off axis, at 3.5khz, and I'll give you a gold star.

Equations and forumla's are nice and useful - when they work. Sometimes they don't work, and often they are misinterpreted.

Take a pair of any 4" cone driver, put them in ANY realistic environment (even an anechoic chamber if you so wish) and measure the output (either with your ears or a microphone, or whatever the hell you want) at a point where one driver is completely on axis, and the other is 90 degrees off axis, and if the measurement is exactly the same up to 3.4khz I will kiss your shoes and wash your car.

Until you can do that, then your words and theories are irrelevant and pointless.

I don't care if the off axis response of a 6.5" driver at 2khz is different to it's on axis resposne because of the driver, the environment, the earths atmosphere, or gods own will - the fact remains that it is and that there WILL be different output from 1khz - 2khz from a 6.5" driver if it's on axis, compared to if it's off axis.

If you are going to deny what your ears tell you, what microphones tell you, and what every electronic measure device on the face of the earth tells you, based purely on your convienient little "approximate" mathematical formula then knock yourself out - but in the real world a 4" driver will get affected by off axis response FAR before it hits 3khz, a 6.5" will be affected significantly earlier then 2khz, and many 1" tweeters will be affected long before they reach 13khz.

If you want to belive otherwise, then you're only lying to yourself.

On this planet, real world measurements take precendence over theoretical formulas.

So, don't go calling me a liar unless you can prove me wrong - and in my world, mathematical theory is not proof.

Edited by muzzy66, 22 April 2009 - 02:26 PM.

[BMWTurbo]

~thematt~, on Apr 22 2009, 01:22 PM, said:

What this means is, if your speaker is playing below your beaming point, 'aiming' of a driver will have as much effect as 'aiming' the sun towards the earth. Its stupid and useless. The only concern you should have is how the driver interacts with its environment, and how THAT affects the sound.

I just wanted to quote the above thematt as your last statement there should is critical.

I might set up a rig tonight (if I get time) and do some on and off axis response curves for a 3inch TB driver. I'll keep the mic the same distance and will graph the response through the various range from on-off axis.

Edited by BMWTurbo, 22 April 2009 - 02:29 PM.

[~thematt~]

There are various levels of evolution that allow people to garner a level of understanding, and apply it with increasingly good results.

You have people who deal with the theoretical (scientists)
You have people who deal with the practical (the wrenchmonkeys)

Then you have the camp of people who investigate the theoretical, like Scorpion, Pulse-R, br85 etc, to understand it, and then apply it to the practical. (Engineers). Simon (Pulse-R) and Danny (Fury) are two people I know who have evolved their understanding to the point where they actually achieve results (on MEA anyway).

It is entirely your choice as to whether or not you wish to understand the basic principles. Just dont sit in a room and sling mud on those who do, because they'll always exceed your results anyway.

And BMWTurbo, go have a look at www.Zaphaudio.com. Wonderful reference for the same sort of tests, on varying types of drivers at varying sizes.

[BMWTurbo]

Thanks thematt... Saved me some more testing Such a good resource the Zaph site.



Seems the Hi-Vi BS3 3inch driver starts to vary around 3.5/4khz whcih is slightly under the estimate above, but that could be due to actual cone area.

*EDIT* My own results tonight, though not super accurate, only taken in my lounge room which has many reflections.
Driver mounted in vented enclosure sitting on a chair roughly 450mm above the polished wood floor.
Mic set up at driver level about 600mm from the driver, 0-15-30-45-60-90 degrees Off-axis. It's fairly obvious which response curve is which.

 TB_3_INCH_Axis_Response.JPG   74.83K   7 downloads

Again at 250mm from the driver same conditions as above, but 0-15-30-45-60-75-90 degrees.

 TB_3_INCH_Axis_Response_250mm.JPG   71.71K   7 downloads

Edited by BMWTurbo, 22 April 2009 - 08:28 PM.

[~thematt~]

BWMTurbo, did you test without a baffle?

[BMWTurbo]

thematt - the test driver is mounted in enclosures specifically designed for them. There were not mounted in a baffle board or the like, I don't really have enough room etc to set up a test to that degree.

[~thematt~]

The reason I ask is because there are two points on your output graphs that I can see, that can be simply responses from the baffle, not the speaker. The closer I look, the more I'm convinced that these responses are due to baffle stepping in the horizontal, and the vertical. As you get closer to the driver, the response changes, but the location is the same.

Keep in mind that as you move the microphone off-axis, the baffle-step response will change too. At a full 90deg off-axis, you'll catch the orginal sound, but you'll also catch the step response, AND the reflected response off the SIDE of the speaker box at its maximum. Obviously all the other off-axis responses will change too, but to lesser degrees.

Try mounting them open air (no baffle), and measuring that way. I've done this before, and the only anomalies I detected were a result of the mounting flange. I simply discarded frequencies that high anyway.