Posts filed under: Blog

Technically Speaking – Dec 2021

Season’s Greetings to everyone! I can’t believe we are already at the end of 2021. Don’t we all feel that somehow, we have a year and a half hole in our lives? On the positive side we are returning to live meetings and getting to hug and shake hands with colleagues again. Let’s hope that by March, we can talk about Corona in the past tense.  

In recent conversations with customers the term “accessibility” is becoming more and more of a theme. The most common type of accessibility measures used in planetariums the past years have been architectural features like ramps and handicapped seating. But specifically for the hearing disabled, there are a number of technologies in use. 

 You may have seen this sign in various shops or theaters. You can find out more about the origin and use of this sign here:

When you see this sign, it means that an inductive loop or “T-Coil” is available with audio that is compatible with hearing aids that support the function. It also serves as good PR for the facility that has made this service available. Unlike other portable headphone or other listening devices, the T-Coil works with a person’s own hearing assistance device, which is often tuned and setup specifically for the individual. Also, one does not need to borrow or remember to return a borrowed device. 

So how do they work? Let’s focus here on theaters like planetariums, and how this technology is implemented in such venues. The simple explanation is that a “loop” is installed around the perimeter of the theater. The loop is simply a copper wire, or tape, and an electrical current is passed through this loop which generates a magnetic field which is modulated by the audio program. Usually, the audio is just a narration, or spoken commentary in order to avoid complex audio signals like music, which can cause audio confusion with many suffering hearing disabilities. 

Here is a simplified illustration of a hearing loop system in operation. Those having a hearing aid that support the T-Coil function, simply need to be within the loop and they can receive the broadcasted audio program. The T-Coil is like a mini-antenna, and it converts the magnetic signal into a small electrical signal with the audio information that then fed to the hearing device. For those not having a hearing aid with T-Coil function, there are wearable accessories like headphones with an inductive receiver, that most venues supporting this technology have available to loan. Hearing Loops are actually mandated by law in many countries, especially in new construction that is for the public. 

The loop itself is often installed as a copper tape and put under the carpeting if the floor is available before carpeting is completed. Sometimes in a round room, a flat tape is a bit difficult to lay and in such cases one can also use a suitable gage copper wire. I’ve often tucked a copper wire at the junction between floor and wall, just tucking the wire under the carpet edge and using hot glue at various intervals to ensure it stays put. 

As the signal being generated is magnetic, there can of course be complications. If there is a lot of metal in the floor construction or theater walls, this can interfere with the signal and cause drop out. Often it is useful to make some tests by simply laying the wire on the floor around the theater and testing operation. I haven’t experienced any interference from projection domes, and I would expect that the newer aluminum domes don’t cause as much interference as they are non-ferrous.  

It’s possible to run the loop also around the theater wall, at about head-height. Many theaters with coves have a fascia or other architectural element at an elevated height that might provide an easy place to tuck a wire behind. You can even have 2 loops in parallel. One on the floor and one at head level in order to increase strength. While installation is easy and the materials are not so expensive, its best to leave the supply and installation to professionals with sufficient experience. The cables feeding the loops need special attention, and there are dozens of factors that effect performance than only a seasoned professional can evaluate and make the right choices. 

Feeding the loop are special amplifiers that work by generating a current in the copper loop, thus creating the magnetic field. The amplifiers used to be a pure analog technology but the newer models on the market now accept digital audio and there are even Dante networked audio models now available. The amplifiers must be selected based on the length and characteristics of the copper loop. Again, it’s best to work together with a professional to ensure the best solution. 

If you have an inductive loop system it is good to keep a headphone or other testing device at the console so that you can make regular checks that everything is ok and functional. The worst is to advertise that you support such devices, and then deliver a poor or disappointing experience to your visitors. 

If because of architecture or other restrictive situations you are completely unable to install an inductive loop system, there are other possibilities. Infra-red (IR) and radio frequency (RF) transmitters can provide suitable coverage and performance for listening devices. Newer systems are emerging now that work via Wi-Fi, and allow visitors to use their own tablets or smartphones to receive broadcast audio. I haven’t any experience with these up to now, but I’ll report back later if I find something interesting. 

These alternatives are really not a substitute for a proper inductive loop and if legally mandated you will need to find a solution. However, any efforts to accommodate visitors with special needs will certainly be appreciated by those visitors. 

Please feel free to respond with any comments by writing to the editor. I think that feedback regarding any of the various articles and columns in The Planetarian would be welcome. Especially if you are sharing your own experiences or helpful tips. 

Images used by permission from Ampetronic Ltd.


Glenn Smith
General Manager
Sky-Skan Europe
Munich Germany

Technically Speaking – Sept 2021

Greetings to planetarians world-wide! The torch has been passed and now I will carry on the tradition of trying to shed light on the more technical aspects of our industry. Technologies used in planetariums have gone through amazing evolution over the past 20-30 years. Some advances have been adopted and brought our systems and presentations to new levels of quality and performance, and others not so much!

I’ve just returned from the Fulldome Festival Brno in the Czech Republic, where the latest productions and uses for our domed canvases were shared in person! Being the first live conference in over 18 months, and it was great to see, chat and interact with colleagues from all over the world again! Many unfortunately could not make it due to local regulations but we still managed to have about 100 individuals convene and watch 4 packed days of fulldome content and works in progress. Let’s hope things keep improving and we can count on more such meetings soon. 

Moving on to more technical matters, it wasn’t so long ago that many of us were wrestling dozens of slide and special effects projectors in order to Spice 😊 up our presentations. The first video projectors that allowed the background to be adjusted to deep black brought our special effects to life, and slewing video projectors inspired us to dream of covering the dome with moving images. 

After a few years of philosophizing over whether planetariums were becoming cinemas or not, most of us have accepted fulldome video and computer-driven visualization as the norm today. Even the word “Planetarium” has taken on a new meaning where not only astronomy and the cosmos, but any range of science topics can be presented in full immersion. And why not also a bit of entertainment too?

Years ago, almost every planetarium had a different type of sound system with the most common similarity was the traditional and authoritative “voice of God” at the zenith. 

Fulldome video has also grown in depth and resolution since its emergence in the late 90s, and now lamp based projectors have evolved to solid state sources like LED and laser so lamp changes and the constant struggle to keep the projection channels balanced is slowly fading to a memory.  

And now active display domes made entirely of LEDs are beginning to appear and with them a whole new set of challenges. The contrast barrier has been broken and it’s exciting to see the first glimpses of the future of dome theaters. Prices will be inhibitive for most for the foreseeable future, as it was also when fulldome projection technologies first emerged, but I think no one can deny that we are now looking at what will eventually be the standard for all new planetariums. 

LEDs are everywhere today. We have amazing colorful LED cove lighting, LED monitors on our consoles, and LEDs now permit wonderful indirect aesthetic lighting for planetarium interiors and the surrounding spaces. LED light sources have also brought our cherished opto-mechanical planetarium projectors into the 21st century with crisp bright white light that faithfully represents the true color of the stars without all the heat generated by previous incandescent or xenon arc-lamp sources. As a result the star projectors have been reduced in size and become less intrusive to the planetarium interior. However I think we all, along with the public, still have a nostalgic feeling for the traditional giant “ant” or as the Germans say “Knochen” (bone) that used to tower above us in the center of the theater. 

In the coming issues of The Planetarian, I will look forward to answer questions and explain in more detail, how all of these technologies work, and what various aspects of their features should be considered or appreciated for use in the planetarium or other fulldome theater settings. Please feel free to send me a message with your comments or questions to  mentioning “Technically Speaking” in the subject line, and I’ll do my best to answer them along with explaining in more detail how many of the technologies we use today actually work. 


Glenn Smith
General Manager
Sky-Skan Europe
Munich Germany