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Old 5th July 2007, 11:27 PM   #11
jnb is offline jnb  Australia
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Calvin, your posts are very informative and helpful.

I was wondering the same thing as MJ Dijkstra. What if the diaphragm was not made too tight so the roll-off wasn't too high, and add wings, or even put the panel in a box like a conventional speaker.
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Old 6th July 2007, 08:07 AM   #12
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Hi


My plan was to avoid notch filters and equalizing as much as possible.
The notch filter probably can be avoided by silicone dots on the membrane. I've used this technique with several esls (it is also used by audiostatic) and this kills the resonance very effectively. However, in case of curved esls, the dots cannot be (partially) hidden by the horizontal bars as the dots must be placed in the middle of the membrane. So you will see them. Not a big problem for me.
Hopefully the equalizer can be avoided by the wings, but we can only know after measurements.

martinjan
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Old 9th July 2007, 01:03 PM   #13
Calvin is offline Calvin  Germany
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Hi,

You can add wings to lower the frequency where Phase-Cancellation starts, but Youīd need unpractical wide wings. With a 10" wide panel P-C effects the range below ~800Hz, a 5" wide Panel will be effected below ~600Hz. So You wonīt come around using some kind of equing.
Using less mechanical tension lowers the resonance freq, but doesnīt help with P-C. P-C is a phenomenon of panel size/baffle size only.
Since it is not difficult to build a panel the size You wish, be it larger or smaller, it is always beneficial to build as large as possible. Wings are just dead area (acoustical wise). Having active membrane area instead is far better. When You build ītransparent designsī a larger panel looks better than a solid wing too.

What the dots do:
Putting dots between stator and membrane raises stiffness. As result You get a higher Fs and a rather lower Qt. The higher stiffness is beneficial in that way that You can drive the panel with higher signal voltages and the point when it comes to an overload situation where the diaphragm hits the stator is raised.
What it doesnīt do:
It doesnīt kill Fs or high Qts. To lower the Qt You need damping. That is one of the reasons why most fullrangers are not transparent. The damping mats would look rather ugly.

The silicone dots used by Audiostatic introduce not much damping, because silicone has rather low damping values.
So, with regard to Fs and Qt the two ways -using high tension, or using lower tension and dots- lead to similar results.
When placing the dots it should be kept in mind, that they reduce the maximum diaphragm travel and output. This isnīt a real problem with hybrid panels, but could be one with fullrangers. So a certain minimum distance between the dots has to be supplied for. This minimum distance could be reduced only if the dots feature some compressability, like foam does.

jauu
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Old 9th July 2007, 02:19 PM   #14
jnb is offline jnb  Australia
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Quote:
Originally posted by MJ Dijkstra
Hopefully the equalizer can be avoided by the wings, but we can only know after measurements.
In theory, phase cancellation becomes more complete at low frequencies. It seems impractical to EQ, but there is a good word for dipoles here http://www.linkwitzlab.com/

I think I'd like to try an infinite baffle by extending the wings across the room corners and put a lid over it, which I can put my mid/top panels onto.
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Old 10th July 2007, 04:01 PM   #15
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Hi Calvin

I can't agree with you.
The silicone dots DO a lot of damping. They do this by spreading (breaking up) the single large resonance to a more distributed resonance.
Tap on the membrane without dots, you hear doommmmmmmm
Now add the dots on the same panel, you hear domm.
This is a simple experiment anyone can do and you can hear the difference very easy.

With regarding phase cancellation I have yet to see measurements which show me that a panel of 30 cm width with some wings of 15 cm at both sides, need equalizing above 300 Hz. I think they don't unless beaming of mids and highs are uncontrolled and make bass relatively weak.
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Old 11th July 2007, 09:44 AM   #16
Calvin is offline Calvin  Germany
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Hi,

I doubt it First, siliconeīs damping values are quite low and second should You notice a considerable raise in Fs. This might sound as if the high Q is lowered, but in fact it isnīt.

With regard to measurements. I did that with a 10" panel and 4" Wings and there is still a considerable drop out at 300Hz.

jauu
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Old 11th July 2007, 09:55 AM   #17
Calvin is offline Calvin  Germany
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Hi,

I doubt it First, siliconeīs damping values are quite low and second should You notice a considerable raise in Fs. This might sound as if the high Q is lowered, but in fact it isnīt.

With regard to measurements. I did that with a 10" panel and 4" Wings and there is still a considerable drop out at 300Hz.

jauu
Calvin
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Old 11th July 2007, 12:24 PM   #18
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Quote:
Originally posted by Calvin
Hi,

I doubt it First, siliconeīs damping values are quite low and second should You notice a considerable raise in Fs. This might sound as if the high Q is lowered, but in fact it isnīt.

With regard to measurements. I did that with a 10" panel and 4" Wings and there is still a considerable drop out at 300Hz.

jauu
Calvin

Hi

The damping properties of silicone dots are irrelevant. You could get the same thing with hard dots. If it would seriously raise Fs, all the full range esls of audiostatic would have a big problem. They wouldn't be able to generate low bass and they would resonate at a higher freq. This is not the case.
I would suggest that you try this experiment yourself. Seeing and hearing it is better than 1000 words.

The measurement you did, was it an electrically divided esl?
The mirror drive of audiostatic (used to compensate phase cancellation) starts to operate below 300 Hz. Final 1.2 starts to drop below around 300 Hz as well.
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Old 11th July 2007, 12:48 PM   #19
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Hi Folks,

see picture. It shows measurement of a 33cm ( red) wide ESL. In comparison same ESL but 60cm (black) wide, made with two additional wings on each side.

Capaciti
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File Type: gif 33zu60cm.gif (16.0 KB, 297 views)
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Old 11th July 2007, 02:01 PM   #20
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Hi Capaciti

that looks like a plot from a fairy tale with a happy ending.

Can you give more details, such as, size of panel, size of baffle, mic placement, anechoic or in-room etc etc....

I dream of getting such plots.

Regards

Ed
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