RTR electrstatic speakers

Hi Sean, The e-stat panels used in the Crown ES 212 are about 5.625" x 5.625". There 12 of these panels (4 wide x 3 high) used with 2 - 10" woofers. Years ago Don at Crown told me that he thought they were crossed at around 350hz and had a sensitivity about 85 db. He wasn't there when they came out, so he said to take the info with a grain of salt. The 350hz sounds about right, but they are a lot easier to drive than the Maggies or Acoustats that I have owned, so I think the 85 db is of a bit. I am trying to use them in a Nearfield Line Array configuration similar to the Linus Array. They will be used along side 9 vertical 6½" midbass drivers. The two major concerns are the sensitivity and horizonal dispertion. The sensitivity can be designed around, but with stacking 12 RTR panels vertically, the desired horizonal dispertion has to be inherit of the design of the speakers. Sean, thanks again for your time and if anyone else has any specs for the RTR panels, it would be nice to hear from you. Thank, Brian

Working from memory, the RTR panels that i have are 3" x 5.75" or so. The panels that you have are obviously different than what i've got and almost twice the size, hence the greater amount of low frequency displacement. Even with the greater size, i would cross them measurably higher than what you mentioned. This will lower distortion through reduced excursion, increase power handling, improve transient response, improve "transparency", etc...

As to the efficiency level, that sounds much too low for that quantity of panels. While bandwidth limited and actively crossed, i was seeing figures that were WAY, WAY above that. Most of these that i have came from Mike who posts as Magnetar over at AA. He had used several of these stacked in parallel as supertweeters and was seeing VERY high SPL's out of them. The fact that he was using them with 109 dB horns should tell you something. If i can recall correctly, i think he mentioned a figure of appr 111 dB's @ 1 watt when used above 10 KHz. I don't know how many of these smaller panels he had wired up though, so i'm not much help there. The fact that you want them to go MUCH lower in frequency is going to drastically reduce their average sensitivity, so keep that in mind.

To get around the displacement and excursion limitations on these little panels, i've got two different sets of midrange panels that i was tinkering with. One set is 1' x 6' tall and the other set is 2' x 6' tall. Each panel is actually 3' tall with one stacked on top of the other. Each panel was driven by it's own channel of amplification, keeping the load on the amp very reasonable. Since i was mono-blocking this set-up, that meant 6 stereo amps with all 12 channels being used.

Depending on how things go once i move, i've been thinking about using both sets and moving up to active quad-amping rather than active tri-amping. This would mean two more stereo amps for a total of 16 channels driven, but it could give me even more dynamic range with improved transient response ; )

As far as the Crown's go, if you can find me the appr years of production, i might be able to find more specific info for you on them. Sean
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Sean, although I remember seeing the Crowns on the sales floor in the late 70's, it seems that they came out in 73 or 74 and were produced for 2 years. Albert Porter could answer that question. As far as cross over points, I plan to cross at about 1000hz between the panels and the 6½" drivers. This should help the panels quite a bit. A subwoofer will be used mainly to lighten the load on the 6½'s allowing them to keep up with the speed of the panels. The highs produced by the RTR's sound very nice to me, but it has been suggested that the surface area of my panels is a little big to get the placement right at the highest frequencies. I'm not quite sure if this is a problem, but would hate to push forward if additional tweeter panels should be used. Thanks for your time, Brian

I looked through the info that i had on hand and here is what i came up with.

As listed in 1975, the RTR ESR-6 was an add on E-stat tweeter array. It was listed as covering from 1500 Hz up to 30 KHz with a sensitivity of 88 dB's @ 1 watt / 1 meter. Nominally rated at 8 ohms and a size of 14.5 x 14.5 x 12 inches and weighing in at 23 lbs. I don't know how many panels were included in each cabinet, as there is not mention of that. One might guess that there were four panels i.e. two high and two wide judging by the dimensions that you listed above.

The RTR ESR-6 as listed in 1976 is shown to be 16.5 x 16.5 x 19.5 in size, which is measurably larger. The weird thing is that this bigger box is still rated at 23 lbs. The size of each ES panel is shown to be 3.1" x 5.75". This would appear to be the panels that i have. Their sensitivity is rated at 90 dB's 1 watt @ 1 meter and a nominal impedance of 8 ohms. Frequency response is shown to be the same as the 1975 model ESR-6 i.e. 1.5 KHz up to 30 KHz.

The Crown info that i have shows their model ES-212 as having the E-stat's coming in at 375 Hz and extending out to 30 KHz. These were rated at a 4 ohm nominal load. Unfortunately, there is no rating on their sensitivity. This is the same info as listed in both 1975 and in 1976.

I don't know of how much help this is to you as the RTR info only confused me. None the less, this did somewhat confirm your appr 350 Hz crossover point ( 375 Hz factory rating ) and states that the panels that you have are rated out to 30 KHz.

As far as being easier to drive than Maggies and Acoustats, i don't doubt that. Using measurably fewer RTR drivers than i had set up, Mike aka Magnetar had told me that he was easily able to hit 110+ dB's with these panels at 10+ KHz. Bare in mind that this was with the smaller 3 x 5.75 inch panels, not the larger 5.625" x 5.625" panels that you have. With the larger surface area and quantity of panels that you have, i don't doubt that they will make a good amount of noise.

Obviously, the more that you limit bandwidth, the louder that they will play with lower amounts of distortion. Having said that, crossing them over right in the meat of the midrange seems to be a mistake to me. If you can get them down around 400 - 500 Hz and actively cross them at 24 dB's, you should be great. You have to remember, they were running them down to 375 Hz and crossing them passively with what was "probably" a much shallower slope ( 12 - 18 dB's most likely ). As such, the ES panels were probably seeing and having to dissipate a measurable amount of power below the crossover point.

By using an active crossover AND a sharper slope, you not only reduce the amount of low frequency energy / excursion that the panels will see as compared to the original design, but their thermal dissipation is also reduced due to crossing over prior to amplification instead of after amplification. On top of that, transient response should be improved due to clearing out some of the clutter between the amplifier / ES Panel interphase. The end result would be greater dynamic range and lower distortion than the original Crown implimentation of these panels without having to resort to a much higher crossover frequency.

So long as you have the means to experiment with the crossover frequency used, and given that your 6.5" drivers could easily go up much higher than 400 - 500 Hz, this might be a good place to start. Depending on your listening level and personal preferences, i would think that this "should" be capable of very satisfying performance all the way around. Otherwise, moving up higher on the crossover frequency may give you greater dynamic range capacity, but it "might" come at the expense of driver blending problems. On top of that, the higher that one runs the 6.5" drivers in frequency, the more potential there is for comb filtering to take place.

If you're looking for excellent resource info on Line Array's, Jim Griffin's research is available for all to view. He not only worked with Rick Craig on the Linus Array but did a lot of research and gathering of facts on his own. I know this as i had seen / read some of his work long before the Linus was ever created. I had posted links to Jim's website on Agon several years ago. Whether or not one can still find this info in Agon's archives would be a good question. As a side note, much of the info that he had previously posted on his website was obtained from JBL professional research papers.

Out of curiosity, what type of cabinet are you going to run the 6.5" drivers in? Are you going to run them open backed to duplicate the ES dipolar radiation pattern, sealed, vented, etc ???

What you're thinking about doing is something similar in concept to Albert's Dali Megalines, except those use a ribbon rather than ES panels. I think that the Dali's are crossed at about 1 - 1.5 KHz also, so there might be some validity to what you originally wanted to do. As is true of most projects like this, a bit of trial and error will probably be in order before you're fully satisfied with the results. Good luck and keep us posted when things start rolling. Sean
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Sean, thank you for all the research work on the RTR e-stat panels. That was the most info I’ve seen so far, the verification of 375hz crossover point was an import piece of the puzzle. I had been swapping speakers in and out of my system with known specifications trying to get a handle on where the RTR’s were in comparison.
Keeping the crossover point between the panels and the dynamic drivers lower has raised some very good questions. Hopefully some of it can be sorted out before they are fired up, but as you suggested the rest can be dialed in with the crossover.
As far as the over all design, I didn’t start out building line array speakers, talking with Albert Porter started all that. He also suggested talking with Danny at GR Research (gr-research.com), who provided some very useful information.
I had drawn up speaker plans before talking to Albert and Danny, but decided to learn more about line array speakers before going any farther. It was becoming apparent that the RTR panels would excel in this configuration if certain obstacles could be overcome.
Someone had suggested James Griffin’s paper, which is a “must read” if you are going to build anything close to a Near Field Line Array speaker. Finding out that by placing drivers within the sound radiation pattern of another driver increases the overall sound pressure level (SPL) is where I decided to take Albert’s suggestion and post on Audiogon. The efficiency of the RTR panel became a major issue when it was learned that the SPL of the dynamic drivers would rise from the mid 80’s to the mid 90’s.
As for the speaker box, the dynamic drivers will go in a sealed box. The drivers could have gone lower in a ported box, but a sub will be used below 120hz. It would have been fun to figure out a good way to “free air” the drivers to match RTR’s dispersion, but for now it looks like a sealed box for the drivers and free air for the RTR panels. Building another box later to experiment with is a possibility.
Sean the info you provided answered a lot of important questions. It was funny to see that you suggested Griffin’s publishing’s on the Linus Array; it’s kind of the foundation that this project is now based on. Thanks for the help, Brian