Idea from ESL noob

[Calvin]

Hi,

@Emiel
oh my gosh...and I was thinking I were crazy designing a hybrid with a panel of 70x200cm and a dipolar bass tower with 12 drivers per side
But doing this in wire!!! Well....if You´ve really done that successfully, I promise I´ll only call You Mr. Ironman ESL from that day on

To give You an idea of a successfull(?) implementation of that:
have a look at MLs archives for the original old Statement. They claim it to be crossed over at 120Hz and I´m not sure if they used a filter-Q more or less than 1 (probabely >1).

"..(total diameter 1.1mm) at a distance of 2.5mm hart-to-hart" Does this mean +-0,7mm maximum excursion of the diaphragm or +-1,25mm or +-2,5mm??

If You´d use a frame made of 3mm thick spacers, stiffened by lets say horizontal aluminium bars to which the wire would be glued in a vertical manner, You´d end up with 1,9mm excursion. (Think of the Audiostatics! and have a look at the pic).
Using 2.5mm thick spacers and a double sided sticky tape (TESA for carpets, ~0,1mm) You end up at ~1.5mm. This is the easiest way to build and gives a higher efficiency and should just be sufficient for the needed excursion levels.
You could have a stiffening bar every 150mm in height, so You can place diaphragm dampers in form of a small foam strip or a silicon dot right under those bars. But You might need more stiffening for such thin wires, so double the number of bars count (but not the damper count!) In this case You won´t even need to tension the diaphragm mechanically. You can tension it thermally which has some advantages, eg. less material stress, consistancy in parameters and ease of production and will give You a resonance of app. 60-80Hz.
I´d place one wire per 2mm, i.e 1,1mm wire and 0,9mm spacing. That gives You an covered/open-relationship of 55/45 (acoustically, electrically it´s just 25/75). The prob with this wires is, that the electrical coverage-ratio and therefore efficiency is quite bad, because of the thick PVC insulation. This is countered a bit by the dielectric constant of the insulator (which should be high for efficiency reasons, but unfortunately isn´t with most plastics. Luckily PVC as well as polyamides like Kynar range quite high amongst plastics)
Kynar-isolated wire-wrap-wires have thinner insulations which allows for more wires in a more dense fashion (better ratio) and closer proximity of the copper to the diaphragm (remember EVERY 1/10mm counts). Even better are the magnet-wires, because they have the thinnest insulation. Additionally You can get rectangular magnet-wire which allows for even higher field density/strength.

My own old panels were 24x140cm with 30mm spacer-width, 4mm thick. I ended up with app 18x120cm free membrane area. I used H07-VU wire which is PVC-coated with an dia. of 2.8mm. This leaves 2.3mm of excursion after glueing with tape. Thermal tensioning of the membrane gave a Fs of app. 60Hz. Efficiency with a 1:100 trannie was at 80dB/2.83V/1m. Dynamics were still impressive because the maximum SPL was way above 100dB (but the fuses of my Rotel which is capabel of some 300W blew quite often )
Only slight equalizing was needed within the filter to linearize freq-response. It gave some people on a DIY-fair something to think about how a speaker could reproduce if not built with dynamic drivers in the midhighs
But compared to my new metalsheet panels they loose in each and every way.

@dstockwell
not to be over critical, but it would ease my work if You could calculate dimensions into the mks-system, that the rest of this world uses for good reason btw.

AWG14..what is it??? single? stranded? Useful are the outer diameter or insulation thickness and the copper-core diameter of the wire. AWG 14(1) is 1,6mm coreD and probabely 2.8mm OD. It seems to be quite a similar wire as the before mentioned H07-VU. It should work but today I´d opt for a thinner wire like H05-VU (2.0mm) or the Kynar-wire-wrap-wire in AWG30..AWG24
(Infos about that: http://www.eupen.com/images/download...dardCables.pdf
and www.Farnell.com (wire-wrap)
Calculate wires per width such that the covered/open-ratio is between 50/50 to 70/30. Too calculate the electrical coverage-ratio (which is the copper core diameter versus width. This value should be as high as possible (100/0 means a massive metal sheet and highest field density, 0/100 means no metal and no field at all)
For calculation of additional spacers/dampers use L=70 to 100x d/s
with loosely tensioned membrane use 70, for harder tensioned membranes use up to 100. For a d/s of 0.04 use between 2.8 and 4.0. Building for e.G. 7" wide You could use one vertical damper-strip positioned at 3,3"/3,7" or several horizontal strips or points positioned between 2.8" an 4" apart in height.

jauu
Calvin

[dstockwell]

Thanks Calvin I will remeber the mks in the future. What about the attached circuit, is it correct.

[Calvin]

Hi D,

the circuit is corrct so far. Just leave out one of the series resistances (3.3 or 2R2). But keep in mind that just the topologie can be correct for many ESLs (it surely is not Mr. Right for each and every panel) but the component values depend on the ESL´s impedance and surely they must be redesigned for Your panel

jauu
Calvin

[Emiel]

Hi all!

Calvin, you've convinced me of using perforated sheets for my first ESL, so I've started looking around for the right sheets.
The place where I used to work has some sheets lying around which I can use for free. They're probably not the best sheets (see the specs below) but I think I could use them for some testing and buy the right sheets later on.
These are the specs:

Thickness: 1.5mm
Hole size: 8mm
Hole distance: 12mm
Hole/material ratio: 40%
Powder-coated RAL9001

Please post your comments on the use of these sheets for a test model!

Kind regards,
Emiel

[AW]

Calvin,
On the 18-10-2005 you added a pix of a curved panel ESL at the bottom of your reply - is this a commercial panel and if so can you provide me with a URL etc?

If you don't want topost this directly in the forum, can you email me privately?

aw (at) vacuum state (dot) see oh m. Of course, close up the spaces and convert the phonetics

Thanks, Allen

[Calvin]

Hi,

@Emiel
one of the advantages of perforated metal sheets is the possibility to build panels with small d/s spacings with high efficiency. Efficiency is on the other hand a function of field strength, which is the higher the more ´closed´ the stator is and the more equal the conducting material of the stator is distributed over the diaphragm area. Even though a 8/12mm hole/spacing has a netto openness of ~40% the distribution of conducting areas is too far away. This leads to uneven forces on the diaphragm, hence distortion. There will be high forces exactly below the stator and nearly no force under the midst of the holes. As long as the d/s is higher than the hole diameter this is no problem, but with d/s spacings around 1mm the effect should be kept in mind, because here the hole diameter will always be bigger than the d/s. So use smaller holes and hole distances. 4/6mm is a standard pattern with equal openness as 8/12mm but gives higher efficiency. But there has a minimum hole size to be considered, which depends on the thickness of the sheets! Shortly said: the holes should look like holes not like small tunnels, or anther way: the smaller the holes the thinner the sheet has to be. I use 3/4mm in 1.5mm thickness with app. 1mm d/s. If You plan to use even smaller holes You should consider that an insulative coating on the stator reduces openness (more with small holes than with big holes!). Recalculate openness for the coated case. Coated it should always be more than 25% openness..the more the better.

@Allen
write to You soon ;-)

jauu
Calvin

[smunie]

Originally Posted by Calvin

Hi,

famous last words!!

"...easy-to-build wired stator"

"...I think I've got it all figured out, there's only one thing need to know:" :-)

Just kiddin......don´t be upset.

Follow the link Ping Calvin - diyAudio
and have a closer look to the frequency response of the raw panel (Multidioc 1. Panel is 125x25cm). You´ll see that above the strong resonance at 180Hz (Fs) the response curve shows a clear dip (250-700Hz). This is due to acoustic phase cancellation and can only be countered electronically (filter) and/or mechanically (much greater width of the speaker by using wider panels or an open baffle)
This is a typical response curve for an open planar speaker and shows the problem of very low crossover points.
Your specs will be hard to achieve. I actually believe You can´t reach them with Your concept at all without throwing a helllot of work into the panels!

Solutions for this panel size:
- higher crossover freq of min. 250Hz
- reduce d/s from 2 to 1.5mm (with >250Hz 1.0mm)
- take a higher transformer ratio 1:100 or more
- use thin wire (best should be Kynar-isolated wire-wrap-wire of AWG24, AWG26 or AWG30)
- even better, though very hard to get in small quantities is corona resistant magnet wire (not the standard types!!) that are intended for inverter use etc. (wires leave You with the not so trivial prob to get between 300 and 800 of them straight and I mean really really very very straight )

Solution II same crossover:
- bigger panel with min 400mm width
- 2mm d/s
- higher transformer ratio
- use even more thin wires (600 to 1.600) or
- spare the work and use metal sheets
- use massive electrical equalizing

Solution tip:
- work with metal sheets on Your first project (there are enough probs left that can ruin Your nerves)
- restrict freq-range to >200Hz
- keep things simple and work procedures easy
- listen to those humorless grey-haired old men even if their advices sound a little screwed (guess where they lost humor and gained grey hair? )

jauu
CAlvin

Calvin,
I'm very impressed with your depth of knowledge of electrostatic speaker design. You raise issues that make me wonder how the old Acoustats worked as well as they did. I still have my old II+IIs and love the sound. Of course they have their deficiencies and maybe that's part of teh reason they're not around any more. Still, the sound is great yet they break most of the rules that you've outlined.

Does anyone make a full range electrostatic now? Are hybrids truly superior to a full range design? I am more of an enthusiast and work in Healthcare IT but previously was a biomed engineer and can handle a tool with the proper motivation. Can you point me in the right direction to learn more?

-steve

[Calvin]

Hi,

thanks for the praise. It took me many years to learn and much more hair But I´m happy to hear that You can still handle Your tool with proper motivation *hmmh hmmh*
That my dimensional suggestions are different to those Acoustat used stems simply from the fact that a Fullranger´s demands differ from that of a Hybrid.
If I were faced with the task of building a large FR I doubt that my solution would be much different from Acoustat´s.
I´d surely use a wire stator -probabely rather a system with a few horizontal braces like Audiostatic does instead of the egg crates of Acoustat- and a not too thin wire, for example the PVC insulated H07VU to keep the needed amount of effort reasonable low.
I´d beef up membrane size and keep the d/s below 3mm and would think about a transformer interface that boosts low fequencies like both above mentioned companies use. The stator would be of segmented type, segmentation done using simple resistors. I´d use some stuffing for dampening purposes. As such it would not be an open transparent design like Audiostatic but a closed one like Acoustat, Quad et al.
The reason I don´t build FRs is that I believe that a Hybrid can be superior in almost any field if done properly. The design of my systems allows for a seamless integration of ESL-panel and dynamic bass, which represents the firstmost design problem and main reason of refusal of Hybrids by Fullrange fans. For Fullrange fans this one problem outweighs the deficiencies/disadvantages FRs suffer from.
I always liked ESLs in the midhighs, but was never really confident with their bass- and lowermids performance, the restricted dynamics and often to find difficult drive requirements.
For both schools there are excellent examples for the good as well as in the bad meaning. I´d surely opt for a good FR over a bad Hybrid. But nothing fits my taste as well as a good Hybrid.

jauu
Calvin