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Old 20th December 2006, 02:52 AM   #1
thadman is offline thadman  United States
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Default DIY super high efficiency/frequency ESL line array

I have been intrigued with the idea of building a personal line array for quite some time, and after recently purchasing a book on DIY ESLs i've decided they are the ticket.

Im going to be running them on an open baffle crossed over to a stack of dynamic cone drivers (probably 8-12 Dayton RS180s) around 1500hz. I have a Behringer DCX2496 available for all crossover duties, and will be purchasing a DEQ2496 for equalization and measurements.

I'd like the line to match the sensitivity and height of the RS180 array, so im aiming for a 7' by 1" line for maximum displacement. After researching ESLs, ive come to the conclusion that stator to stator spacing will determine the efficiency vs displacement (wider spacing=bad efficiency, but better displacement and likewise)

How wide should my stator to stator spacing be to maximize efficiency and dynamics/output in the >1000hz range? I'd like to match the distortion and dynamic performance of the RS180 stack if at all possible.

I'd like to avoid beaming if at all possible and have concluded that 1" wide diaphragm would disperse quite evenly. Is that a good width to aim for?

How much $$$ in materials should these cost to construct?

Where do I purchase a transformer? What do I look for in them?

All comments/questions are welcome
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Old 20th December 2006, 03:36 AM   #2
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Try Russ at Just Real Music - I've been thinking of trying to get him to help me do almost the exact thing your looking to do for a while now. His power supplies and step up transformers are very nice. His panels are a bit shy on efficiency though - he wants to produce bass

I'm game if you want to start a project - 1K up and 100 db/w/m is what I'm looking for. Russ lives a few miles from me. It seems he doesn't see a 'market' for such a driver - I DO!!! All we need to do is build the panels themselves and use his electronics and trannies.

Russ- Just Real Music Stats

I just sent him an email and invited hiim into this discussion
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Old 20th December 2006, 04:04 AM   #3
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I think that 1-2 mm stator to diaphragm spacing would allow you to make a pretty sensitive driver for that frequency range. It's probably best to make a few test drivers to be sure. Since your final drivers will be only 1" wide, you can make full sized test drivers. The expense will be very low.

I_F
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Old 20th December 2006, 04:06 AM   #4
thadman is offline thadman  United States
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Yeah, I'd definitely be down for a project!

The efficiency of lower midrange/fullrange ESLs isnt...THAT bad (80-90dB im guessing) and efficiency is determined by the square root of the distance of the stator to stator spacing so small distance differences can equate to much higher efficiency. With this in mind, I believe 100dB+ is quite achievable im just a noob at ESLs at the moment.
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Old 20th December 2006, 04:28 AM   #5
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I'm a newbe too but have built lots of speakers using off the shelf drivers. I'm hoping Russ will join in here cause he can turn us on to what we'll need to get started seeing he's been building them for years.
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Old 20th December 2006, 05:46 PM   #6
Calvin is offline Calvin  Germany
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Hi Folks,

a ESL should be run in open baffle mode to sound best, but since You need a certain width of the speaker anyway, it´s good -with regard to nearly every aspect of the design- to size up the diaphragm area (width) as much as possible and to size down the ´inactive baffle´ area. You can roughly say, that a width of 100mm (4") is good for frequencies >800Hz with the use of a baffle and 150mm (6") without -the baffle or a simple bracing should give a width of 8" to 10" to cope for the phase cancellation. For frequencies above 1kHz a diaphragm travel of <0,5mm (~0,02") is sufficient. Add some safety margin against building tolerances and acoustic coupling and You get a d/s distance of max. 1mm (0.04"). I´d opt for just 0.5mm as a starting point, if You´re able to build with small tolerances in such small dimensions.
Forget the idea of high efficiency and small width! You can´t have both! If You need good dispersion character with an ESL but don´t want to sacrifice completely on efficiency, You should think of electrically segmented ESLs (wire or rod or PCB-stators come to mind). Simple metal sheet stators won´t work for this. Efficiency or good dispersion...not both!

But still You will probabely not get even close to 100dB/W/m!!!!!
As a line source of such great height (7´) the SPL will rise as distance increases and will reach its maximum at 3-4m (10´-13´) distance. Above this range SPL will fall, but with less than the 6dB/doubling of distance of an monopolic working driver.
When You get to collect experience with ESLs You´ll learn that measuring on a distance of 1m will give rather useless results with a very high degree of possibility. Nearfield measurements (1-4" distance) and ´in-room-at hearing-distance´ are a way to go. And since the impedance of most ESLs varies greatly it´s common use to measure SPL normalized to 2,83V.

I agree with Russ that such a thin strip ESL has no real market chance, since this is the territory where magnetostatic drivers shine.
Those can be build cheap but with excellent results and high efficiency and are usually a better choice!
If You allow for a greater bandwidth (lets say from ~300Hz on) You come to the field where electrostats reign. With an panel of 8" to 10" or even more width You may start from 300-400Hz with good efficiency and high SPLmax and You make use of the superior sound quality and the extremely low distortion of the ESL against dynamic drivers in the mid and upper frequency range.

So my recommendation is:
If You stay with Your concept of a crossover freq of ~1kHz, You will be better and easier off with a megnetostatic line source like Bohlender et al.

If You´re open to a lower crossover point, You could think of an ESL- panel of ML Sequel size (10"x50") crossed over >300Hz.
The dimensions of both speaker solutions would be quite similar.

jauuu
Calvin

ps. Solution nr. 2 could look like this.
Click the image to open in full size.
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Old 21st December 2006, 12:01 AM   #7
thadman is offline thadman  United States
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High Efficiency and small width...I dont think id be sacrificing diaphragm area at all? The line should have a diaphragm area that is several orders of magnitude larger than a conventional dome tweeter or those BG Neo drivers, how would I be sacrificing anything? A 7' line that is 1" wide would have a surface area of 542cm^2 (thats more than most 12s)

Im open to any options really, as long as I meet the criteria of low distortion, high sensitivity, and cheap and easy to construct. How would I go about building a magnetostatic driver? (ESLs sound like a piece of cake to construct compared to other transducer types)
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Old 21st December 2006, 05:08 AM   #8
Few is offline Few  United States
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I share your enthusiasm for the basic idea of a woofer array coupled to an ESL, but I also second Calvin's comments. I've been designing something very similar to the project you described, but based on experience with previous ESL construction projects, I'm aiming for a lower crossover point than you're suggesting. I intend to use a vertical array of 8" Dayton woofers crossed over to an ESL panel at 300-400 Hz. As I see it, the lower crossover point has significant advantages.

The woofer array and ESL panel will always have some spatial separation between them. As a result, near the crossover frequency there will be two spatially separated sources radiating the same sound. This leads to interference---non-smooth variations in frequency response as a function of listening angle. This problem can be addressed by reducing the distance between the two sound sources, or by reducing the crossover frequency (increasing the wavelength at the crossover). Since there's a lower limit to how closely you can position the woofer array and ESL panel, reducing the crossover frequency can be quite helpful. At 1 kHz sound has a wavelength of a foot or so. A typical woofer array-to-tweeter distance is therefore going to be at least half a wavelength. If the crossover were at 300-400 Hz, then the woofers and tweeter would behave as if they were almost coincident (they'd be something like one seventh or one eighth of a wavelength apart instead of one half).

Also, if you rely on very small diaphragm-to-stator spacing for high efficiency, you start to run into difficulties keeping the diaphragm from touching the stators. It's impossible to make things perfectly flat, and if you rely on something like a 1/32" spacing---or even smaller, given your sensitivity target---you're going to have a tough time avoiding sparks. I tried making some prototypes with 1/32" spacing and it was a real drag. I'm confident that with more careful construction a high efficiency panel with 1/32" spacing could be made, but you mentioned that you were looking for something easy to build. Panels with very small diaphragm-to-stator distances don't fit into that category. The construction becomes much more finicky as the spacing drops below 1 mm.

In addition, you'll find you need some sort of frame to hold the ESL stators, and it needs to have some thickness in order to be sufficiently stiff. If you use, for example, 3/4" thick MDF and cut a 1" slot in it to accommodate your ESL tweeter, you introduce a nasty cavity resonance. Even if you bevel the edges it's still going to have a major influence on the panel's response. If the panel were six or ten inches wide, the same 3/4" frame thickness would cause far fewer problems. You can still, as Calvin pointed out, use a segmented design to maintain good directivity characteristics. Just put a very narrow tweeter strip down the middle of the panel so that it's several inches from the nearest obstruction.

Finally, one of the advantages of the ESL panels is that they exhibit very low distortion over much of their operating range. Why not take advantage of that over a wider frequency range, as long as you're building one? The woofer will act pistonically below 1 KHz or so, but if you look at the frequency response of almost any 7"-8" woofer you'll see the first glitches start to appear at 1-2 KHz. Those glitches are not going to be supressed by much if you use a 1 KHz crossover frequency. If you cross over an octave or more below that point (300-500 Hz) you end up with a dynamic woofer operating at the frequencies it handles best, and the ESL operating at the frequencies that it handles best. Granted, virtually all dynamic speakers cross over higher than 1 KHz and get away with it. But with an ESL covering the upper octaves you have the freedom to use the woofers only in the range in which they behave nearly ideally. It seems a shame to throw away that freedom. Besides, increasing the radiating area of an ESL panel has very little impact on the cost or complexity of the construction. The same can't be said of most other speaker technologies.

Any way you cut it (or cross it over) I agree that an array of OB woofers mated with an ESL panel has lots of potential. I'll be very interested to see how your design progresses. Best of luck!

Few
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Old 21st December 2006, 05:31 PM   #9
Calvin is offline Calvin  Germany
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Hi,

just btw: the woofers of the ESEL in the above pic work in OpenBaffle mode
------ I rather refuse to say OB because over here in Germany O.B. is a brandname for a tampon
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Old 22nd December 2006, 08:49 PM   #10
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Why cross so high? You'll be mostly listening to the woofers, not the hard to build expensive, and good performing, ESL portion.

Think about the cavity and diaphragm resonance issues with a 7' x 1 inch cavity. the 1 inch part will make the resonance pretty high, even crossing it over like it's a tweeter, you may still have to notch that resonance out.

Based on my experiments, I didn't like crossing my panels over as high as 300 Hz, and by 500Hz it wasn't sounding very good at all. IT was exhibiting that weird phasey sound that ML speakers tend to have. I prefer to push the crossover as low as I can. I use a 132 Hz crossover point, but my panel is 20" + frame wide.


Sheldon
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