505 Electrostatic Loudspeaker Panel

 (See below for pix)

Yes, we’ve made some more changes to the 505 panels. After gaining a lot of experience with the 505 panels and listening to suggestions from end users we have made further changes to the 505 panels. The gap between the diaphragm and the stator has been increased by 50% allowing the panel to deliver lower frequencies. The EHT supply has increased output to accommodate this change and to maintain the same sensitivity (more or less). This allows the panel to take advantage of the revised transformer with a low frequency response down to 150Hz, this makes matching the panel with a bass driver / sub-woofer easier.

Due to customer requests we have discontinued the direct plug in banana sockets and 12v connector that were mounted on the board, instead we have installed screw terminals. This makes internal connections easier and less costly for the constructor. Output to the panel is via a header plug and socket.

The rear connections on the earlier panels were a bit flimsy but were the only connectors that would go through 2 layers of stators. So, we’ve changed the stators to accommodate terminals with 2 pins to make them more sturdy and now have a solder through link to connect the front stator to the rear screw connector. The panels carry their own surface mount filter resistors, this has 3 benefits. First there are no wires leading to the front of the panel making for a neater installation, Second, due to the resistors now being on the panel there are only 3 wires leading to it. Third, we have installed more sturdy screw connectors for the wires so there is no soldering to be done at the panel end.

As we had to re-design the stators while we were at it we added a second internal charge rail, this is what transfers the bias voltage to the diaphragm. While one charge rail works very well we now had the ability to create another rail on the opposite side of the panel, this ensures charge gets on the diaphragm evenly.

As well as the change to rear connections we have provided connections at the top of the panel that require a short link to the next panel when stacking. Again, these links are only necessary on the rear of the panel.

The power supply board was also redesigned to accommodate a PCB mount transformer with a 30% thicker core. This allows the transformer to go to lower frequencies before saturation sets in.

Some rearrangement of the circuitry gave us sufficient room to provide a space for an on board inductor so those that are using a passive crossover can choose either a first order or second order filter and mount the inductor on the board instead of off the board in a less convenient position.

The same improved electronics remain and provide room for a high quality on board crossover capacitor and an adjustable bias voltage for the panel. This features a 25 turn trimpot so the voltage applied to the panel can be very finely adjusted. Protection for the panel from over-driving or accidental spikes is provided by a series arrangement of VDR’s (Voltage Dependent Resistors) across the panel. These are essentially out of circuit until they conduct and have no effect on the sound but will shunt the signal when the cut off threshold is reached.

Rob from Australia has had good success using an SB Acoustics Satori bass driver and a single 505 panel, follow this link to see what he has achieved.

The panel is supplied ready built with assembled and tested electronics, you only have to connect the panel to the power supply and provide music. You do have to solder the connecting wires to the plug that plugs onto the power supply board as we can’t predict how long you want to make them, however, this is an easy task.

What does it cost?

AUD $949.00 

What do you get? 

You get 2x ready made and tested ESL panels, 2x power supplies, 2x step-up transformers with a first order filter to prevent bass being applied to the panels and 2x regulated 12vdc multi region mains adaptors.

The transformer and power supply are ready assembled and tested. This is truly a connect it up, provide power and play some music system!!

 For those that are after something a little different we can supply ready made 505 panels without the power supplies to enable stacking of multiple panels without the additional cost of multiple unnecessary power supplies. See below for suggested applications.

 A single ready to use 505 Mini ESL Panel without a power supply

AUD $310.50 

We’ve made the user notes available on our website go HERE to view them.

Bass system to suit the 505 panel.

Integrating a dynamic driver with an ESL is fraught with problems due to the speed of the panel versus the slower response of the dynamic driver. This coupled with the panel being a dipole and the bass driver being a mono pole can cause a noticeable sonic difference between the bass and mid / treble of the speaker.

We have a small stock of 8 inch good quality alloy basket with paper cone bass drivers. These drivers work extremely well into a 15 litre sealed box and integrate very nicely with the 505 panels. The combination gives excellent performance and not just in small rooms, they can go loud and clean.

We can supply one driver for a 2.1 system or a pair of 8 inch drivers for traditional stereo.

Driver cost is AUD $79.00 each.

 Shipping thick MDF around the word is expensive, freight costs for cabinets, even in flat pack form, are often many times higher than having cabinets made locally. We are happy to provide drawings for a suitable cabinet (the one shown above or a more simple conventional box) that is proven to work well and will suit the aesthetics of the panel.


505 Electrostatic Loudspeaker Panel


505 Mini Panel specifications

Dimensions             505 x 150 x 5 (H x W x D in millimetres)

Sensitivity                     86dB for 2.83v input

Frequency Response          200Hz to 20kHz + or - 2dB

Frequency response, impedance and polar plots are below.


Suggested applications

Mid / treble driver in a 2.1 system or a full stereo system. The panels can also be used as AV rear / side effects or as a centre channel speaker when positioned on its side. For larger home theatre set-ups 2 mini panels can be used on their sides to give a 1 metre wide centre speaker. The electrical segmentation of the 505 panel will give excellent vertical dispersion.
Panels can be set at a 5% angle to each other or fixed in a slightly curved frame to give optimum horizontal dispersion.

505 panels can be stacked as a very high quality line source. Two stacked panels can be driven from a single power supply, more than 2 panels need a larger transformer, see the Acorn mid / treble transformer on the ELECTRONICS page. This coupled with a quality dipole dynamic bass arrangement will give remarkable performance.

Some dynamic bass types that will integrate with ESL’s in (our) order of preference.

Some ported cabinets and transmission line systems can sound as if they are half a beat behind the panels or slow and confused. While we do have clients that use these successfully you need to be sure that the design you want to use will work well with the panels.

 Feel free to contact us if you require advice or further information. info@eraudio.com.au


505 panel power supply1

Power supply board showing audio transformer, input crossover capacitor, EHT supply and protection circuit. Note, the red and black banana sockets have been replaced with large screw terminals. The 12vdc input socket has also been changed to a screw terminal.

505 mini panel shown as supplied above. The pictures to the left and right show the panel mounted in a picture frame enclosure.

The panel enclosure is a simple picture frame mounted on the top of a 15 litre sealed bass enclosure.

 The electronics are mounted inside the box keeping everything away from prying fingers. The panel circuit board is wired separately to the bass system allowing bi-amping if desired.

The low voltage 12vdc plug pak connection is made through a 2.1mm socket in the speaker connector plate.

The box design is for illustration purposes only, as long as the internal volume is 15 litres (for this driver) the shape and dimensions are less important

The 505 panels can be used as the satellite speakers in a very good 2.1 system or on top of or built into the front baffle of a standard stereo speaker. It is a simple procedure to extend the front baffle of the bass box to act as the panel mount. Grille cloth of any colour can be used over the panel to complement matching or contrasting frames.

We are using a modest 20 + 20 watt hybrid tube amp to drive the speaker shown above. The bass circuit is a simple second order filter comprising of a 5.6uf inductor and a 65uf shunt capacitor. Performance is excellent, especially when the total system cost is considered.

The panels can be driven remotely from the power supply as long as correct high voltage cabling is used. This allows you to mount the panels on a wall without the bulky power supplies alongside them. The panels can be as far away from the power supplies as 4 metres without any loss of performance.

505 new bass box 002
505 new bass box 006
505 new bass box 001
Capture 2
Capture 4

 For those that are after something a little different we can supply ready made 505 panels without the power supplies to enable stacking of multiple panels without the additional cost of unnecessary power supplies.

Typical applications are for rear or side home theatre effects, centre channels for home theatre, 1 or 2 panels can be placed horizontally to suit the size of the screen. Addition to a large flat screen TV
 (this gets you away from the typically poor sound quality most TV’s have).

 A single ready to use 505 Mini ESL Panel without a power supply

AUD $310.50 

We received this note below from a 505 customer, you may find the information useful.

Hi Rob,I finally got round to making the video about building my hybrid speakers, I've attached it.

My feeling is that there is a level mismatch so that the JBLs are probably 6db too high. But then I like a lot of bass. Not too sure about the neighbours!

Feel free to use it if it is useful to you.   Hybrid speakers.mp4



505 pic for website 1

Front View

Rear View
showing new style screw connectors

Also take a look at Greg’s Project. This is a stacked pair of 505 panels, wall mounted with bass drivers and excellent sub’s from Rythmik. This is a stunning combination. Click HERE


Martin in Australia recently finished his 505 project using the 8” bass drivers supplied by E R Audio, see HERE for pics of his project.

Take a look at Matt’s new 505 project Capture

Fine Audiophile Equipment

Designers and Manufacturers of Electrostatic Loudspeakers and Fine Audiophile Equipment

E R Audio Pty Ltd. ACN: 120 797 775, ABN 48 120 797 775


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