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Vertical dispersion on planars. How much?
Vertical dispersion on planars. How much?
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Old 21st August 2010, 08:37 PM   #21
Armand is offline Armand  Norway
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What can I say.. This is exactly the information I have been looking for. Thank you guys for taking your time to enlighten me. Especially a big thanks to bolserst for taking your time to do the measuments. Impressive!
Also nice to see that the measured frequency response fits the theoretical calculations.

I assume that when you measured the NEO8 you measured it one meter from the centre of the driver. When you turn the driver 5 degrees, it will be the same as moving the mic (sin5*1m) 8.7 cm which is just outside the "soundbeam" that streches 7.5 cm to the sides from the centre. Your measurements clearly shows that there is SOME dispersion it that axis also. Just a few dB drop on the top octave..

-3dB@13kHz when 5 degrees off centre is well within my requirements for a centre speaker. It means that I have a vertikal "window" at 4 meters distance of (sin5*4m*2) 70 cm. In other words: There is no need for two drivers unless I feel the need for standing up during the movie....

I am going to tilt the driver slightly so that I am in the middle of the soundbeam when seated.

If I get around to it I will post some pictures, measurements and impressions when it's all finished.

Armand
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Old 17th February 2012, 01:00 AM   #22
a.wayne is offline a.wayne  United States
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Years ago, we had received a few of these BG units, I'm not sure the BG model , but they where about 14 ins long if memory serves me right. After weeks of testing and voicing those drivers we had decided not to use them , as i thought they had a very noisy character and was not not very musical , very efficient and played as loud as you would wan them , but nothing to our reference ( Heil) and another planer protoype driver we were working with.
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Old 20th February 2012, 08:43 AM   #23
Remlab is offline Remlab  United States
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Bg models are 75", 50", 48", 40",10", 8", and 3". Never has been a 14" Model. The 10" x 5" has only been available to the public for a around 3 years in limited numbers. Before that, they only used it in their own speaker designs. Are you sure it was a BG model ?
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Old 9th June 2018, 11:51 PM   #24
WrineX is offline WrineX  Netherlands
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Quote:
Originally Posted by bolserst View Post
Me being me, just couldn't leave things hanging like that.
So I borrowed a BG8 from a friend and took a quick set of measurements to compare with the calculated theoretical off axis response.

Measurements were taken at 1m from the BG8 mounted in free air on a pole attached to rotating platform.
I estimate the width to be about 5 15/16" = 0.1508 m.
Theoretical response calculated using the sinc function mentioned in post#3, and the cos(theta) response for a dipole radiator.

Plot #1
The measured off axis response for the BG8 on the long axis.
Note that I didn't bother to notch out the cavity resonance.

Plot #2
Same data set, just normalized to the on axis response.

Plot #3
Normalized measurements compared to theory for 5, 10, & 15 degrees off axis.

Plot #4
Normalized measurements compared to theory for 30, 45, & 60 degrees off axis.

NOTE: Due to length of measurement window, ignore measured data below about 350Hz.
i know very old post. but i was still playing with my planars and noticed that the first measurement of these neo's look EXACTLY like mine and i was about to give up..... that cavity resonance......


plot 1 the cavity resonance is exaclty what i have and exactly same frequency to any ideas to get rid of that ? or just notching or crossing over before that? i tried for months, all kinds of different stuff mylars,wires,foils, tension etc etc, until for fun i coated the planar and used the whole thing as ESL at the same time (first as esl then , as planar magnetic and also both).... guess what exact same response , so cavity from the magnets and the metal creates this awesome peak that is rather hard to get rid off. when i think of it it becomes clear why single ended the peak is half as bad

stuffing in between the magnets would that solve anything ? might try that. although i have a bad feeling it wont solve it all



By the way does anyone has an idea what creates the resonance, is it the space between the magnets ? or between magnet and foil ? or steel to foil? i mean nothing corresponds to a wavelength of ~14Khz except for the width, but i see this is almost all panels of all sized in width

Last edited by WrineX; 9th June 2018 at 11:57 PM.
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Old 10th June 2018, 03:24 PM   #25
bolserst is offline bolserst  United States
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Quote:
Originally Posted by WrineX View Post
..... that cavity resonance......does anyone has an idea what creates the resonance?
It is a combination of 4 things that define fr(resonance frequency) and Q :
1) Mass of the diaphragm + conductors (heavier makes fr lower)
2) Gap distance between diaphragm and magnets (larger gap makes fr lower)
3) Thickness of the channels or slots between the magnets including the outer plate. There is also an end correction similar to port end correction for vented enclosures. (thicker makes fr lower)
4) Percent open area. (Q increases as % open area decreases)

As you noted, the same behavior exists for ESLs, but usually it is more troublesome for planar ribbons because of the higher mass of the diaphragm and conductors, the added thickness of the magnets, and the lower % open area. The Monsoon drivers have higher diaphragm mass, but the %open area is much greater than the Neo8. A comparison was posted as Attachment #2 here:
Monsoon - Surprisingly Good!

A simple way to think about the cavity resonance is in terms of a Helmholtz resonator like a vented enclosure where the compliance or springiness of the air in the enclosure resonates with the mass of the slug of air in the port tube. In this case, you have the compliance of the air trapped between the diaphragm and the magnets resonating with the mass of the diaphragm and the mass of the air in the slots between the magnets.
I had posted some further descriptions in another ribbon thread here:
DIY ribbon dipole tweeter, reductio ad minimum #196
DIY ribbon dipole tweeter, reductio ad minimum #202
DIY ribbon dipole tweeter, reductio ad minimum #347

JonasKarud also posted a measurement where he had removed the front side of a Neo-8 planar:
DIY ribbon dipole tweeter, reductio ad minimum #185

The recently published AES paper mentioned in another thread discusses this behavior in more detail and shows how to use LTSpice to model the reflections between the different components of a planar ribbon or ESL and determine the response including the main resonance peak(aka cavity resonance) as well as the HF roll-off and additional peak and dips.
Superb article on HF ESL phenomena (IMHO)
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Old 10th June 2018, 07:38 PM   #26
WrineX is offline WrineX  Netherlands
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Nice Bolserst as always ! i did kind of hinted most as the above but most definitely not in that amount of detail !!! thanks for the summation, i am gone read those articles and hope i could sim it. although not to handy with simulators haha. i will give it a try since with all these options that contribute there must be a way of counter the most troublesome i hope. for instance high Q outside pass band, is ok with me the splice sounds like it could save me some major rebuilding time every time i want to test something i will try to post me the findings if i got any would be great to solve this problem once and for all (for my construction that is )

Open area i maxed out with the metal i have, perfectly aligned magnets to the hole paterns, and aligned opposing metal plates to.

the first 2 i can do something with,

1- Mass, the thinnest foil i used right now was 6 Micron foil, but because it is only going to house the tweeter section i can easy use 3 micron, and maybe just maybe even 1 micron. but i am aware of course that the biggest mass comes from the wire/or trace whatever it is. in this case wire. since i dont see any benefits (for trace) when comparing the 2 weirdly enough so i stick to that.

I did see my fr shift on a panel where i had used 0.172mm wire and 0.132 wire from 12.5 to 14 Khz~ i am not sure what happens with undriven areas? for instance in this case i wired the panel half half, so i could see the difference on the exact same unit. but i dont know if the heavy side influence the lighter side (left part and right part of the foil)
i will look for even thinner wire, but i think this was it (aluminium wire by the way)

2- Distance, i can change the distance, i think i used 0.8mm in this case but since i am really only worried about using it as a tweeter maybe down to 500Hz max or so (yes rather low) i think i could get away with 0.5mm, they are gone be like 80 cm long so the low end gets bumped more then the high end when making longer and longer , so i hope to reach that 500 as wekll as getting as high as i possible can.

Last edited by WrineX; 10th June 2018 at 08:06 PM.
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Old 10th June 2018, 08:20 PM   #27
WrineX is offline WrineX  Netherlands
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3- might be a problem for me that means i either have to buy thiner and really small neo's , or skim of some of my rubber magnets from 3mm to 2 mm should make a nice improvement. i also lose output of course. but by making the distance smaller i gained a tiny amount. and lastly since it is a push pull tweeter that driven areas is like 29mm wide (rather big tweeter) i might get away by using only 0.5mm metal instead of the 1mm i used so far(might then take a look at open area to when im at it damned haha). since it is really sturdy. so in the end loads of stuff i could try haha............it never ends
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Old 11th June 2018, 05:52 PM   #28
WrineX is offline WrineX  Netherlands
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Soo some interesting stuff... not what i wanted to see parse.

Bolserst do you know what tension on the foil does with this whole thing ? since by the look of it, it plays a role.

So i shaved of 0.5mm from the magnets on one stator and as well from the spacer. i screwed up the measurement by measuring the light coil and the heavy coil at the same time (already thought wtf exactly the same ) but that should not mater much in terms of seeing what happens to the peak when i decrease the thickness of channels.. and nothing happend they where the same no shift of the peak.

Then i found out by mistake (and trew away these measurements.....)

Redit measuring 2 rows of light 0.135mm wire vs 4 rows of heavy wire 172mm.

yes it would be nicer to have 4 and 4 but the magnet structure was made for 6 wires. and if i use uneven the wires end up on the wrong side of the panel .

any how beside less output they look rather the same and i was mostly interested in the peak only. so here they are in

picture 1. 0.135mm wire vs 0.172mm

You can see the thinner wire has the peak a little higher, spl is not right, since one wire has 4 turns in the magnet gaps and the other only 2. i leveled them at resonance, but when i think of it i might have gained the thin wire to much since it uses less of the foil and is only near the edge of a spacer it probable cant even put out the same volume at res. so the height of the peak we cant compare. just the shift, i think.

Picture 2.

No i thought it is fun to see what happens to Push pull (BLUE) vs single ended , the single ended (BROWN) is measured with the metal plate facing the mic, to make it a bit more fair. also only one wire gauge is used throughout. also it is the same panel just added a backside

now what is funny, the resonance goes down as expected in push pull, and the cavity fr goes down to. But when i add the push pull from the first picture with the same wire (Purple) you can see that panel had higher resonance since the PP version is as high in res as the (brown) single ended version. now what is fun that the cavity resonance fr is also the same as the single ended version. even with an extra metal plate and magnets behind it. sooo, by the looks of it it is even more complicated ? foil resonance dictates something as well looks like it ? Bolserst any idea what is happening here?

Oh one last thing i just thought about, in pic one it might not even be the fact the wire is lighter that the peak shifted, but the fact it only played near the spacer where the resonance sort of looks higher ? i mean if i made single wires all over the foil and measured them from left to right one wire at the time (might be very interesting by the way), i bet i get different resonance and one main resonance ?
Attached Images
File Type: jpg pp wire 0.172 vs 0.135.jpg (94.9 KB, 70 views)
File Type: jpg pp vspp and single.jpg (104.7 KB, 69 views)

Last edited by WrineX; 11th June 2018 at 06:01 PM.
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Old 11th June 2018, 06:05 PM   #29
WrineX is offline WrineX  Netherlands
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i thought so many times about making a panel i could adjust resonance on the fly i might have to build one. so i can leave everything the same and see what resonance does EXACTLY with the peak.. and while im at it i might do the single wire test to to see what happens to a conductor when it is near a spacer or more in the middle of the foil where it is aloud to move more... so much to test if you suck at mathematics
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Old 11th June 2018, 06:21 PM   #30
zmyrna is offline zmyrna  United Kingdom
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this method seems to cure the resonance on Neo3
BG NEO 3 FR optimization
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