Not so long ago-in the days when the comm blared over a cabin speaker cranked up somewhere above the threshold of pain-no one cared about audio quality. Heck, if you could understand the words, what more did you need?
Headsets have changed that. Everyone wears them and like everyone else, were bothered when an airplane checks onto a busy ATC sector with scratchy or fuzzy audio. How can you tell if an airplane has a poor audio system? Listen to one with good audio.
And believe us, there’s plenty of good audio out there in the form of state-of-the-art navcomms and, recently, intense competition in the audio panels that tie all this stuff together. In days of yore, an audio panel was just a gang of switches to sort out transmitter and receiver functions. Not anymore. New audio panels incorporate all sorts of features, including marker beacon receivers and intercoms, perhaps to include some features you don’t really want or need.
If you have an older Bendix/King KMA24 audio panel, it probably sounds fine. But if youre making do with a bunch of toggle switches instead and your audio sounds awful, an upgrade is worth considering. Good audio is not just pleasant, its a safety issue with regard to ATC communications and fatigue on long flights.
All of the major systems are competitive in installed price and are comparable in construction and installation considerations. But there are some definite differences and price variations of several hundred dollars, at least. Heres a survey of whats out there. Basically, the major choices are four: Bendix/Kings KMA24 or 26, Garmins GMA340 and PS Engingeerings PMA7000M/S. (A fourth option is Apollos SL series, which are made by PS Engineering for Apollo/UPS Aviation Technologies. They have similar features as PS products so we wont address them separately.)
KMA24
The popular KMA24 audio panel is a tough act to follow. Users can attest that it has clear, no-nonsense audio quality packaged in a durable box. The KMA24 has an audio amplifier, integral marker beacon receiver/lights, speaker/phone switchable selection and the much-appreciated AUTO mode, which allows you to control comm receive/transmit selection with the panel microphone selector switch.
The KMA24 has a deserved easy-to-use reputation, with we’ll labeled, durable switches and knobs. Splitting audio is possible but you cant isolate pilot and co-pilot transmit functions.
The only serious feature missing is an integral intercom, reflecting the fact the KMA24 was designed before intercoms were standard cockpit equipment. (The KMA24H helicopter model has a built-in five-station ICS of the hot mic variety, which is good for high-noise environments but not so good for airplanes. Also, it has no marker beacon.)
The KMA24 is still current production, as is most of the plain-Jane Silver Crown series of radios from Bendix/King. Does that mean its dated? Well, yes. But if you already have a quality panel-mount intercom, such as a PS Engineering PM1000 series or an NAT, the KMA24 is still a worthwhile choice. In our view, it continues to be the most straightforward and reliable audio panel out there. But if you want a high-level feature set, it will come up short.
KMA26
Enter the KMA26, which is becoming available after being recently limited to only new Cessnas, as part of the Silver Crown Plus avionics package. It does all the basic audio tricks that the KMA24 does, plus it has an emergency bypass mode, which eliminates the audio amplifier and connects the pilot mic directly to comm 1 in case of an audio failure.
As with the other audio contestants, the KMA26 has six-place ICS with dual music source input. There’s one intercom master squelch setting control and its automatic. (Its not nearly as sophisticated as the PS design, however.) One push of the volume rotary knob and intercom voice sensitivity is set.
Experience has proven that there’s a squelch sensitivity difference between pilot and co-pilot microphones, even using same model headsets.
No other adjustments are available to the user so this problem is likely to be addressed with a service mod. Independent volume control for pilot and co-pilot allows custom settings and there’s pilot and crew isolation for privacy and choices of music play.
Keeping with Bendix/King tradition, the KMA26 has a quality feel and rugged design. Well-annunciated controls leave no question as to what mode the unit is in. Nighttime backlighting and dimming are first class but we thought the outer marker lamp was too dim. During one approach, with sunlight bathing the panel, we couldnt see OM passage without incoming audio playing.
Users weve surveyed seem content with the KMA26 operation, with limited gripes, most of which may relate to quality control issues. And therein lies a major rub. Bendix/King has been having lots of turnbacks for various failures and until they get this sorted out long term, we cant strongly recommend the KMA26 over the PS and Garmin offerings, which each respective company is pushing hard with lots of promotion. To its credit, Bendix/King always gets things straightened out eventually, but the others are doing it out of the box. (Mostly.)
Garmin GMA340
The accepted wisdom these days-and really, for as long as we can remember-is that any avionics manufacturer who wants to make a splash has to have a complete product line, from navcomms, to audio panels to DME to ADF to autopilots.
Garmin is playing that game only by degree. Its established itself as the leading GPS company and has salted many of its products with first-rate VHF comm gear. Having positioned itself as a progressive manufacturer, Garmin hasnt looked back at DME or ADF but it has looked forward at audio systems, offering the GMA340 audio panel.
This box was obviously designed to compliment Garmins popular GNS 430 electronically and aesthetically, but the 340 is certainly a practical choice for anyone shopping for a new audio panel. It competes toe-to-toe with PS Engineerings PMA7000 and has most of the same critical features.
Incorporated into the GMA340 is an excellent six-place stereo intercom with independent volume and squelch controls for pilot and co-pilot. Crew isolation modes allows left and right seat communications without interruptions from rear seat passengers. Pilot isolation allows left seat privacy, which is always handy for copying clearances and declaring emergencies. Music input capability is there too, with two independent channels.
Heres how it works: A music input jack is installed, allowing the rear seat passengers to plug in a portable CD player or Walkman-type device via patch cable.
If the rear seaters are rocking away, the pilots can switch off the noise using the isolate mode. In addition, they have their own music input jack for a separate source. In our experience, this feature works quite well, especially if an owner has kids who want to listen to Head Banger rock while the parents prefer soothing jazz.
The GMA340 also has a split comm function, meaning the pilot can talk on comm 1 while the co-pilot talks on comm 2. This split audio-which PS Engineering also offers-is a welcome addition to cockpits, in our view, especially if there are two capable pilots aboard. One can do the ATC chores, while the other fetches weather or files a flightplan. Whether the typical owner will rise to the occasions that split audio offers remains to be seen, but we like the choice of having it.
The GMA340 also has a remote comm swap function. This allows remote switching (via yoke mount button) of the comm transmitters without depressing the mic button on the panel. While shooting a busy ILS, for example, we had the approach frequency set in comm 1 and the tower on comm 2.
When shipped from approach to tower, punching the swap button on the yoke automatically switched the transmit function. Gilding the lily, you say? Perhaps, but we think its a good feature.
Other GMA340 features include integral marker beacon receiver and lights with mute and auto-rearm features. One thing we didnt like is that the marker beacon receiver can be turned off entirely, not just muted. No biggie, but it could prove confusing at some point.
There’s also a cabin audio/PA mode that allows you to yell…er, brief passengers over the cabin speaker, just like your airline buddies and, of course, there’s a failsafe mode that couples the pilot mic and PTT directly to comm 1 in the event of audio panel failure.
One feature unique to the GMA340 is tone annunciation when a button or mode is selected, confirming that the unit has done what youve asked. It also has a transmit indication to advise the pilot which radio is being keyed to transmit. This is a nice back-up to the transmit indicators on navcomms, some of which arent especially conspicuous, in our view.
Garmin has been out with the 340 for some months now and thus far, reliability appears to be good. The few problems weve encountered relate to the selector button and the swap feature, but Garmin has provided quick turn around support on these issues. Overall, no complaints. Construction of the unit is first rate, with surface mount technology throughout.
Cosmetically, we think the GMA340 is the best of this group, with a dark charcoal faceplate and robust, well-labeled buttons. To entice potential Brand X customers, Garmin also offers a faceplate to match Bendix/Kings existing Silver Crown line.
PMA7000M/S
The PMA7000M/S is second-generation and the Mercedes Benz of audio selector/ICS combos; the companys flagship product. Its obvious that PSs background is in intercom design. Since the birth of the highly successful PM1000 four-place intercoms, PS has been striving to perfect auto VOX (Automatic Voice Activation). In the PMA7000, PS has what it calls IntelliVox, which uses a trio of microchips to sample each microphone station and decide whats unwanted noise and whats speech. The result is a daring concept: No user adjustable squelch control. Leave it to the internal microcontrollers to automatically boost squelch when your passengers breathe heavy on take off and back it off when they whisper a nervous question about that oil streak on the left engine.
Frankly, we were skeptical of this design, since automatic controls for such fine functions rarely work consistently in the rough-and-tumble of the cockpit. But the IntelliVox design performs largely as claimed. We tried the PMA7000M/S testing in a quiet environment, without engine and other sources of noise. There was no trace of even a subtle background white noise.
Voice activation is smooth and the unit was happy with every voice personality we could emulate-loud, soft and everything in between. It consistently adjusts squelch threshold with accuracy. We fired both engines on a 58 Baron and opened the cabin window, the intercom circuitry maintained a comfortable squelch threshold. Impressive.
A three-position intercom mode switch allows selection of ALL, placing all headsets on a party line, hearing aircraft radio, music input and intercom. ISO isolates the pilot from the other stations and the music for privacy. CREW mode allows pilot/copilot communications while all other passengers have music and intercom.
There’s capability for dual, true stereo music input, allowing separate, simultaneous sources for front and back. Soft mute automatically mutes the music input (when in ALL mode) to background level, which is less distracting when the radio and or intercom becomes active. Get this: There s a selectable Karaoke mode, allowing sing along without muting the music. As for the audio function, the PS can manage three comm radios and one switched audio input (AUX selection). The split audio function is similar to the Garmin but goes one step further. There are two modes for the front seat split: COM1/2 allows pilot to talk on comm 1 while the co-pilot works comm 2. COM2/1 makes comm 2 available to the pilot and gives the co-pilot comm 1. SWAP mode is for the remote transmit selector operation, switching transmitters with one hit via remote yoke-mounted button. A swap annunciator glows when this mode is engaged.
Another first we like is the interface with the headsets and a cellular phone through the audio panel, anticipating when the AirCell airborne system gets into high gear. The PMA7000 is AirCell ready, with full audio distribution to all stations, working in conjunction with Pilot ISO, Crew and ALL modes.
Also, PS offers optional interface cables between certain portable cellphones and the panel for ground operations.
As for buttons and knobs, the PS lags behind the Garmin and Bendix/King units, in our view. Initial units were shipped with white buttons that, in our opinion, looked somewhat homebrewish. New units have been improved with charcoal-color buttons but compared to the Garmins robust military styling, these still feel fragile. The two small toggle switches-for ICS mode selection and marker mode-are just too tiny for easy manipulation. Also, The units on/off switch is shared with the main volume knob and is push-on type, which we simply don’t like for cockpit power controls. We do like the marker beacon design, which can be armed with audio off. Garmins GMA 340, on the other hand, lacks this feature.
The PMA7000s lighted controls and annunciation work we’ll with photo-electronic dimming sensors for low-light conditions. Silver faceplate trim is available to color coordinate with new King Silver Crown styling.
Other features: Digital Recording Aural Warning System or DRAWS, which accepts audio input from popular engine analyzers. Six inputs are available to audibly alert via a pre-programmed message (FUEL LOW or OIL PRESSURE LOW and so on). Clever, but we can hear the technicians bellyaching about the wiring already.
Speaking of which, PS got slick when it designed and marketed the PMA7000. The idea of making the unit a direct plug-in for the KMA24 will get the attention of potential customers due to the perceived ease of installation. A caveat here, however: The number of features the PMA7000 has makes the idea of plug and replace unrealistic.
The KMA24 has no intercom nor many of the other features outlined here so connectors must be accessed and reworked to accommodate wiring for these bells and whistles. don’t be surprised if your shop adds a healthy sum to the invoice to accommodate these details.
We recommend doing a complete audio rewire when replacing an audio system with this caliber box. Experience shows that a number of audio installations don’t work as we’ll as they should due to poor wiring.
Worth mentioning is the PS Engineering PMA6000, available with and without marker beacon. This was somewhat of a breakthrough product for both PS and the market, combining a full-up audio panel with an intercom.
The PMA6000 had some growing pains with marker beacon problems, a confusing marker self test, backlighting and photocell issues. In our view, the selector buttons are too small, especially for use in turbulence. The PMA6000, however, did set the stage for the much-improved and feature-rich PMA7000.
PS Engineering says the PMA6000 has been improved and is offered as part of its new line. Its bugs have apparently been addressed and the unit is still on the companys marketing horizon. Also, it does have a true stereo intercom, a PM2000.
We wonder, however, why a customer would select it over the PMA7000, which is newer technology and only $200 more. And against the Garmin GMA340, which sells for $400 less than the PMA6000, we don’t see much value. The PMA6000 is now available in a hot mic version, matching the KMA24H, which may be the only reason to consider it.
Conclusion
All of the products reviewed here do the mundane work of audio switching. Topping our list in value are the Garmin GMA340 and the PS Engineering PMA7000. But there’s a $600 price Delta here in Garmins favor and that aint chickenfeed, given capabilities that are very closely matched.
If youre not a gadget freak, the KMA24 from Bendix/King is still out there and soldiering along. But again, its $100 more than the Garmin, so it, along with the PMS6000 strike us as being at the bottom end of the value scale. Yeah, they work. But the GMA340 and PMA7000 work better and, in Garmins case, for less money.
We think the PS PMA7000 enjoys a razor thin edge in ICS quality, with its IntelliVox circuitry. Its long feature list is a two-edge sword, however. You may want those tricks, you may not. In any case, the wiring and connectors will add to the install bill. Further, we wish PS would take another stab at improving the look and feel of its buttons. To PSs credit, theyre very responsive to suggestions from the field and there’s clearly a dedication to quality.
For overall ease of operation and durability, we think Garmin enjoys the edge. Its buttons and switches are we’ll designed and labeled and it doesnt have those tiny switches we found to be a nuisance on the PS product.
Whichever you select, don’t be surprised if the audio quality is less than expected, unless you attend to the all-important re-wiring, a check of mag and alternator shielding and, of course, decent headsets. Even the best audio panel in the world wont live up to its potential if you listen to it through lousy headsets.
Also With This Article
Click here to view the Audio Panel Checklist.
Click here to view the Audio Panel Features & Prices.
Click here to view “Yet More Stuff from PS and NAT.”
Click here to view “Garmin’s GNS 430 Fix.”
-by Larry Anglisano
Larry Anglisano is a test pilot and avionics consultant at Exxel Avionics in Hartford, Connecticut.
