12 minute read
cockpiT audio: parT ii
Technical
Can you hear me?
In Part II of how best to deal with audio issues in the cockpit, Ian Fraser looks at intercom systems…
Audio systems seem to be an avionics function that has been left by the wayside in the trend to equip our aircraft with modern new radios (I know, we didn’t have a lot of choice with that one), and fancy glass instrument panels and navigation systems.
‘An intercom is just a way of connecting the headsets together, and the cheaper the better’ is a philosophy that too many recreational pilots adhere to. However, audio is becoming an important part of the modern avionics’ infrastructure, the quality, capability and flexibility of which is essential for the function, safety and indeed, the value of your aircraft.
Old technology
Many older aircraft are still equipped with very basic intercom systems, which can be significantly inferior to a modern system, yet you can (and people still do) buy them today. I am sure that we have all experienced noisy intercoms or heard very noisy and near incoherent transmissions, and that is indicative of a poor intercom or Above Old basic intercom miss-set squelch. It sounds a bit like an old movie cliché, but it doesn’t have to be that way.
Audio advances
As with most electronics today, there have been major strides forward in the functionality and quality of audio systems and that can make major improvements to the cockpit experience and, in turn, reduce pilot workload.
Before you build or upgrade your aircraft audio system think it through carefully. Make it reliable, flexible and as future proof as possible. In other words, make it as good as you can afford to, not as cheap as you can get away with! You will appreciate it every time you fly your aircraft because good audio not only makes flying a more enjoyable experience, it will look after your ears, and it is becoming ever more essential to support cockpit activity into the future. As airspace becomes more restricted and traffic increases, we are becoming dependent on an increasing amount of information in the cockpit. Even the CAA is advocating the use of navigation devices (e.g. SkyDemon) for infringement avoidance and traffic
awareness, and their use is likely to become part of the PPL syllabus. But, if we are not careful, this could become counterproductive as we are tempted to be more ‘heads down’ in the cockpit, peering at small displays, searching for even smaller and more complex features within them – the very devices we have to help us could actually exacerbate the problem.
Commercial aircraft already use audio alerts to draw attention to information that may need action, and many of our current gadgets that produce visual data can already also generate audio warnings, either in straightforward language or attention-grabbing tones. We must harness this if we are to remain safe and flying is to remain fun.
What is missing from many of our aircraft is a way of connecting and controlling these secondary audio signals. ‘Simple’ say some, just connect the warning source into the intercom or headset music input (if it has one) and you have a solution. That could work but has limitations, which will become apparent as we progress.
However, there are many other options that should be considered, and their use will make the cockpit a much better and less cluttered place.
Decide on functionality
Top left Intercom with auto squelch and individual volume
Top right Audio mixer to connect more inputs
Above Headset music connection use the aircraft. Do you plan for the aircraft to carry passengers? Do you fly long distances or just short local sorties? Is the flying shared? If passengers or a co-pilot are part of your flying plans, then you need a good and flexible intercom. If you are threading the needle of UK open airspace then you need traffic and airspace awareness. A modern intercom is a completely different device to the old traditional ones. They come in various forms from a function built into your radio to a sophisticated audio switching panel, full of all sorts of exotic features.
A complex requirement
It is important to remember that voices, ears, headsets, environment and the intercom’s task are almost always different and vary continually. The modern intercom is the device that has to bring this complex array of audio together effectively, whatever its source, and present it coherently to all listeners. You and your passengers need to be able to hear all your gadgets comfortably, so it needs to be matched to the environment and the task you are asking it to do.
Auto squelch
Starting at the basics, we’ve all used squelch, the knob that adjusts the threshold of sound that ‘opens’ the microphone, supposedly only when you are speaking. In
an old-style intercom, that is a compromise and often demands eternal fiddling to get it set just right for the combination of variable background noise and different microphones in the aircraft. In some cases, setting it correctly is virtually impossible, but if it is not set correctly then background noise is much worse than it needs to be, or voices are clipped or even suppressed.
By far the most important development in intercom systems is the auto squelch function, which constantly adjusts itself to the individual microphone, position and background noise. They only open the microphone when the sound they pick up is a voice, and they don’t need adjusting. They don’t all use the same method (algorithm) and some work better than others, but they are all much better than the old manual squelch system. This development has made an important contribution to quieter cockpits.
Volume control
Volume control is an often overlooked but important consideration when specifying an audio system. An intercom internal to a radio may only have one volume control covering radio and both channels of its intercom and setting it will always be a compromise based on the pilot’s need to hear the radio clearly. That setting may not be good for the intercom and co-pilot. While there are relative radio / intercom volume settings available in some ‘set-up’ menus, you shouldn’t really have to go there every time you need an adjustment.
With a separate basic intercom, the radio volume is independent so that the pilot can set it to what he needs but the intercom volume for both the headsets are still a compromise adjusted by a single knob. As long as both pilot and passenger headsets, voices and ears are the same, no problem, but normally they are not. Ideally an intercom should have a separate volume control for each operating crew member. Of course, some headsets have a built-in volume control, but it is important to realise that it is a volume attenuation (reduction) control, not a true volume control. Auto squelch and individual volume controls are available in many modern types of intercom.
Warning audio
Multiple warning audio inputs to the crew headsets are a Above Miniature audio panel
Below Combined audio panel / radio
‘must have’ thing of the future, indeed audio warnings for angle of attack (AoA), navigation, traffic, airspace, terrain, obstacles, altitude, autopilot and engine management etc. are already available from many modern gadgets common to our aircraft. So, what are the options to enable connecting them to the headset? While it may be theoretically possible to connect some directly into the headset socket or in parallel with another audio input, there are many engineering reasons why you should not do that.
And getting back to the earlier mentioned option of connecting to a music audio or auxiliary input on your radio, intercom or headset, this is also not ideal. If you need more than one input you can add an audio mixer (e.g. Gretz GA AM, or Flight Data AP60) to your music or auxiliary input but, having got the audio in, the next issue you need to think about is how to control it. With all these warnings available there are some points in a flight where they will become a distinct nuisance. In the circuit for example, other traffic and your altitude are well within the warning limits and your various alarms will be chattering or hooting away incessantly.
Control what you hear
Also, although using the music or ‘aux’ input on a radio or intercom can work for warnings, it has other serious drawbacks. Most intercoms automatically mute the music input when the radio is receiving. So, in a busy circuit, just when you might want some important safety warnings, the radio (while receiving ATC messages) turns them off. Some devices allow you to inhibit this ‘radio priority’ function (it is buried in the set-up menus), but if you do, the reverse problem occurs with a variety of lower priority traffic and terrain warnings swamping the incoming ATC radio. It is important to be able to control (without distraction) the lower priority warnings such as nav, obstacles or terrain, while retaining the important ones such as AoA or engine management.
As is often the case, there is more than one way to do this. The simplest is a switch in the audio lead of each warning. Another way is to use the various inputs on a modern audio panel (e.g. PMA4000, GMA245 or TMA44 etc.). Despite the labelling of functions as Com, Nav, Aux, Music etc., that is nothing more than ancient convention, they are just input selection switches – the
inputs are all the same aviation standard (600 Ω) and can be used for anything you like. They have some permanent selected inputs and some selected by the associated Nav / Com etc. buttons. For example, you could connect your tablet or smartphone audio to Nav 1 and a portable GPS audio to Nav 2, which means you have a selective way of suppressing them in the circuit while key warnings such as angle of attack or engine remain always connected. Another benefit of this solution is that the illuminated annunciator on the audio panel will always indicate which devices are selected.
We must not overlook that some headsets can connect to a navigation tablet, through either wire or Bluetooth, but that normally only provides one input and is suppressed (not controllably) by radio or intercom traffic – not a very robust input for warnings. It is mostly intended for phones and music. Also bear in mind that the next generation of iPhones may not have wired audio.
Multiple radio capability
For continental touring, one of my personal concerns is a radio failure – it can be a show stopper. When I built my RV-6 I included a mini audio panel (DC500) providing me with an easy way of connecting a second (handheld) radio to my intercom, headset and PTT. Unfortunately, the audio panel failed, was obsolete and I replaced it with a simple intercom. That was one of the biggest mistakes I made in my 25 years of aircraft ownership and I have now had to put it right. Unless they are set up as the primary radio, handheld portables are not easy to use in a busy cockpit and, if you connect to them independently, you lose intercom and warning functions. Failsafe switching for a second radio in the cockpit is complex and it is not a simple task to do with ‘off the shelf’ switches.
Audio panels
Audio panels are the answer to switching radios and they are available with various levels of capability. Pictured opposite (bottom) is an audio panel combined with a radio, and top (inset) is a 57mm instrument hole mini audio panel. Both provide all the extra functions discussed so far.
Just add a socket for the handheld and you have a box 2 but, be careful in selecting the audio panel for this Below State of art full function audio panel function. If you want a Box 2 function, decide exactly what you want it to be able to do, i.e. just replace Com 1 or allow pilot and copilot to use either. Audio panel Com transmit switching functions are not all the same.
Other features
Having looked at the essential features of a modern audio system, there are several other attributes available which might help you choose one above another. The picture (below) illustrates such a full function example.
Last message replay is a function that has appeared in some radios and audio panels – the push of a button will replay the last message received on the radio, a very useful device.
Bluetooth is also becoming a more common feature on some more sophisticated audio panels (and some of the more expensive headsets). Bluetooth has three main purposes; connecting a phone or tablet, connecting music and, in the case of some audio panels, outputting cockpit audio to an ‘action cam’, although not all at the same time. Mostly they are single channel devices.
S t e r e o . Some headsets and intercom systems now offer stereo capability, but its primary purpose is to support music systems. There is no aviation reason for this, aviation radio is all mono.
However, one clever feature offered by some stereo panels allows the apparent position of sound sources to be synthesized in the audio, such that radios and passenger voices seem to come from the left, right or centre depending on how they are physically positioned.
I L S m a r k e r s . Unless you aspire to IFR flight, don’t bother with marker beacon functions.
Finally…
Audio will become more important in the future cockpit so plan ahead, don’t cut corners on a cheap solution. If you get it right and use a modern standard type of intercom or audio panel, it should last for as long as we are still flying avgas-powered aircraft. This article is not a product review and I am not recommending any device, but I hope that it provides food for thought for anyone planning to build or to update their avionics.
In Part III we will look at audio systems installation and noise reduction headsets. ■
