October 27, 1999 LightSPEED Technologies' 25XL Active Noise Reduction Headset

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by	Mike Busch
	AVweb Editor-in-Chief

About the Author ... Mike Busch is editor-in-chief of AVweb, a member of the technical staff at Cessna Pilots Association, and in a prior lifetime was a contributing editor for The Aviation Consumer and IFR Magazine. A 6,000-hour commercial pilot and CFI with airplane, instrument and multiengine ratings, Mike has been flying for 36 years and an aircraft owner for 33. For the past 14 of those years, he's owned and flown a Cessna T310R turbocharged twin, which he maintains himself. In his never-ending quest to become a true renaissance man of aviation, Mike's on the verge of earning his A&P mechanic certificate. Mike and his wife Jan reside on the central coast of California in a semi-rural area where he can't get DSL or cable TV. MBusch@AVweb.com

Also see Mike Busch's review of LightSPEED's lower-priced ANR headsets, the 15K and 20K.

LightSPEED 25XL

I was really excited when I first discovered the LightSPEED 20K headset in June, 1997. After decades of flying with green headcrushers from David Clark, I was definitely looking for something that offered more quiet and comfort. I'd flown a few trips with a borrowed Bose active noise reduction (ANR) headset and it certainly was impressive, but as a matter of principle I was defiantly unwilling to spend the $1,000 that Bose was asking. Sorry, folks, that was simply too much — waaay too much — for me to plunk down for any headset!

The LightSPEED 20K promised similar quiet and comfort for a shade over $400, which was well under half the price of a Bose and only about $100 more than DC's top-of-the-line H10-80 passive that I'd been using for years. A test flight proved to me conclusively that the 20K lived up to its promises. In fact, I actually found the LightSPEED to be more comfortable than the Bose, and very nearly as quiet. I was hooked, bought a second 20K for the copilot position of my Cessna 310, and have been flying with the LightSPEED 20K almost exclusively for the past two years.

LightSPEED 20K

In July 1997, I wrote a glowing review of the 20K for AVweb. A few months later, a similarly effusive review appeared in The Aviation Consumer, and word spread through online aviation forums and newsgroups. Soon, pilots started ordering 20Ks in droves. LightSPEED was taken by surprised by the demand, and for awhile pilots who wanted a 20K found themselves waiting a month or more for delivery. But LightSPEED ultimately ramped up production to meet the demand, and the 20K has been the industry's best-selling ANR headset ever since.

Since then, I've become totally addicted to my 20Ks. Like most first-time ANR users, I was worried whether the active cancellation would keep me from hearing sounds that I really needed to hear — gear, stall and autopilot-disconnect warnings, clattering valve lifters, that sort of thing. I quickly found out that I could actually hear these sounds a lot better than before with the low-frequency prop and exhaust noise actively cancelled out.

Not long after I switched from David Clark H10-80 (DC's quietest passive) to LightSPEED 20K (ANR), I started hearing a funny "gravelly" sound that I couldn't identify, mostly during taxi, takeoff, and rollout. Soon, I realized that the noise stopped when I lifted the nosewheel on takeoff, and reappeared when I lowered the nosewheel after landing. I disassembled the nosewheel, used solvent to remove all the grease from the wheel bearings, and discovered a frozen roller in one of the two Timken roller bearings! I bought a new bearing, regreased both bearings, and reassembled the nosewheel. On my next flight, the "gravelly" sound was gone ... and I was irretrievably hooked on ANR!

A Hard Act to Follow

The following year, spurred by LightSPEED's obvious success with the 20K, a number of other headset makers entered the fray by introducing new low-cost ANR headsets in the $400 range. This included firms who were already selling higher-priced ANRs (e.g., Telex and David Clark) and others who were entering the ANR arena for the first time (e.g., Pilot Avionics and FlightCom). Most of these new entrants offered credible noise-reduction specifications in the 20-ish decibel range, and some included novel features (like Pilot's relocation of the batteries into the headset itself). I tried some of these, but I was hard pressed to find anything that felt as comfortable on my head as the LightSPEED. (Keep in mind, however, that comfort is a highly subjective matter — you really owe it to yourself to try as many different makes and models as you can before you make a choice.)

Meantime, I started hearing rumors that both Bose and LightSPEED would be introducing new models at EAA AirVenture 1998. As the story went, the new LightSPEED 25K was to be an evolutionary enhancement to the 20K providing some additional active noise cancellation, extended battery life, and an nifty-sounding automatic shutoff feature that would save the batteries from exhaustion if the user forgot to turn the power off at the end of a flight. (As someone who was frequently guilty as charged, this latter feature seemed particularly attractive to me.) The new Bose headset, referred to somewhat mysteriously as "Model X," was reportedly a radical clean-sheet design featuring greatly reduced weight and abandonment of Bose's signature breast-implant-like silicone gel earseals.

Bose Aviation Headset X

I called both companies to see what I could learn. Bose wasn't talking. LightSPEED admitted that they were working on a new 25K model, but they weren't sure whether or not it would be ready for Oshkosh.

At AirVenture 1998, Bose announced the new "Bose Aviation Headset X" and demoed it, but didn't have any production units to sell at the show. AVweb's Joe Godfrey — a hardcore Bose afficionado — ordered one of the $995 X-sets at the show with the promise of "shipping within 30 days." In late August, he was told to expect "mid-October delivery." Joe finally received his headset in December, and you can read his detailed review here on AVweb.

LightSPEED's announcement of the 25K headset at AirVenture '98 turned out to be even more premature than Bose's. LightSPEED had no demo units at the show, and said that shipments of the $599 headset would begin in early October — a prediction that turned out to be overoptimistic by nearly ten months! As it turned out, meeting the originally announced active noise cancellation target of 30 dB proved insurmountable (LightSPEED now claims a more realistic 25 to 28 dB of active cancellation), and getting the automatic shutoff feature to work reliably turned out to be much tougher than expected (although it now seems to work quite well indeed). And by the time the headset finally made it into production in July 1999, its name had changed from "25K" to "25XL" (more on this later).

LightSPEED also generated a lot of attention at AirVenture when it announced a unique and unprecedented trade-in program for current owners of LightSPEED 20K headsets. For $200, owners could trade in their 20K headset for a brand new 25XL. By the time the 25s started shipping in August 1999, well over 1,000 owners were wait-listed to trade their 20Ks. (What the company plans to do with all those slightly-used 20Ktrade-ins remains unclear.)

Flying the 25XL

LightSPEED had a very limited number of the new 25XLs at AirVenture 1999 and were guarding them like the crown jewels, but LightSPEED's Alan Schrader was kind enough to liberate one of the new headset for me to test-fly. My first opportunity to try it out came immediately after AirVenture, on a 3+30 IFR flight from Oshkosh to Charlotte, N.C. Since then, I've flown with the 25XL on several shorter East Coast hops, including a relatively high-workload day-trip into and out of (ahem) Ronald Reagan Washington National Airport (DCA). During these flights, I also had my trusty old LightSPEED 20Ks aboard, and was able to do some "A-B testing" to get a better handle on precisely how the new 25XL headset differs from its 20K sibling.

Physically, the two headsets are virtually identical. The only real way to tell them apart visually is by color — the 25XL headband and earcups are dark charcoal gray, while the 20K is light gray. The 25XL also comes with two interchangable sets of earseals: standard "soft" seals identical to those on the 20K, and optional "ultra-soft" seals as used on the 15K. I tried both, and found the ultra-soft seals a tad more comfortable, although using them sacrifices a bit of noise cancellation and may not provide adequate room to accommodate large-eared folks. In any case, I think that having the choice is a nice touch.

The big difference lies in the 25XL's all-new electronics, something that is immediately apparent when the headsets are first powered up. The 20K ANR cuts in immediately ("sucking the noise right out of your head"), while the 25XL's seems to take a second or two to become effective ... a first tip-off of the new "adaptive" cancellation circuitry. The 25XL also has a slightly different "sound" compared to the 20K — a bit more emphasis in mid-range frequencies, and a bit less in highs and lows. Also, the 25XL has more receive gain than previous LightSPEED headsets in order to improve compatibility with non-LightSPEEED headsets when several different brands are being intermixed in a single cabin intercom system.

During cruise flight, I tried repeatedly switching back and forth between the 20K and the 25XL to determine how their noise canceling qualities differed. The 25XL is definitely quieter, but I found the difference in noise cancellation more subtle than I expected, given the rather large 3 to 4 dB difference in the factory specifications. (The 20K spec says 22-24 dB of active cancellation, while the 25XL spec says 25-28 dB.)

A more obvious difference in my "A-B testing" was in microphone equalization. Again, the 25XL seemed to emphasize the mid-range frequencies and tone down the highs and lows, compared to my 20K. I found this to be a noticeable improvement, both in better speech intelligibility and in reduced transmission of cabin "air noise." One of my pet peeves with the 20K has long been that its mic picks up too much air noise, to the point of breaking intercom squelch during high-IAS descents. I found the 25XL was much improved in this regard.

However, in discussing this observation with LightSPEED, I was told that the factory modified the microphone preamp equalization in 20K headsets manufactured from about January 1998 on, and my 20Ks are older than that. So it's quite possible that improvement in microphone response that I noted in the 25XL would also be found in late-model 20Ks. At this point, I can't be sure.

LightSPEED claims considerably better battery life in the new 25XL: more than 50 hours from a pair of AA-size alkalines, compared to 30 hours for the 15K and 20K. To be honest, I simply haven't been able to get enough flight time yet with the 25XL to verify this, but I have no reason to doubt it because LightSPEEDs have always offered exceptionally long battery life.

I was able to verify the 25XL's auto-shutoff feature, however, and found that it works remarkably well. Even in a noisy cockpit in flight, I found that if I removed the 25XL from my head and set it on the glareshield or seat cushion, the ANR would automatically turn itself off after roughly three minutes. (To reactivate the ANR after an auto-shutoff, you cycle the power switch off and back on.) My experience over the past two years has been that running down batteries by inadvertently forgetting to turn off the power is a big problem — even if I remember, my copilot might not. Consequently, I'd expect that the 25XL's auto-shutoff feature is likely to be a big battery saver.

That goes at least double for folks who carry their headsets with them rather than leaving them in the airplane the way I do. I've heard a fair number of gripes from folks who say that it's awfully easy to bump the power switch accidentally while the 20K is being carried around, resulting in a nasty surprise and a scramble to find fresh batteries at the start of the next flight. That should be pretty much a think of the past with the 25XL.

One other 25XL feature worth mentioning is its improved immunity to RFI. The 20K had some problems in this area — its ANR would not work with an ICOM IC-A22 handheld radio, for example, and some problems were reported in Bonanzas and Barons equipped with comm antennas immediately above the pilot's head. LightSPEED says that the 25XL does not suffer these problems. (I have not had an opportunity to verify this independently.)

I can tell you, however, that LightSPEED has not completely eradicated the proclivity of their headsets to "chirp" slightly when in close proximity to an ATC radar antenna. The 20K does this, and during my flight to and from DCA, I found that the 25XL does, too. The muffled chirps are not loud enough to be especially annoying or distracting, but they certainly can be puzzling until you realize what's causing them. (This was a much more serious problem in early 20Ks until LightSPEED came out with a fix in late 1997.)

Tech Talk: How It Works

It's not at all surprising that LightSPEED had a tough time squeezing an additional 3 or 4 dB of active noise cancellation out of the 25XL, because doing so is no simple task. It's not just a matter of cranking up the gain on the ANR circuitry, because doing so will invariably cause the headset to go unstable and force it into oscillation — very much like what happens when someone turns up the mic gain on the public address system in an auditorium ... ouch! Traditionally, engineers have experimentally increased ANR gain to the verge of instability, then backed it down by a "safety margin" to account for various operational factors that might trigger oscillation — such as receiving an ATC transmission, the wearer clenching his teeth, or having an imperfect seal around the temples of the pilot's sunglasses.

LightSPEED came up with a different and clever approach for the 25XL: add logic to the electronics that allow the headset to continually readjust its own ANR gain to be as high as possible without actually going into oscillation. When some external factor threatens to push the headset into instability, the 25XL circuitry reacts by automatically reducing the ANR gain to prevent oscillation. When the factor goes away, the ANR gain is gradually increased again. The result is a headset that constantly operates as the maximum possible level of active cancellation at any given moment.

If this sounds tricky, it is. LightSPEED isn't saying much about exactly how it acomplishes this automatic ANR gain control, and has applied for a patent to protect its technology. But you can actually hear the circuitry at work if you know what to listen for. For example, if you lift an earseal from your head in flight (say, to don an oxygen cannula), you can hear a brief, transient "growl" as the ANR starts to become unstable, but the oscillation is nipped in the bud almost immediately as the headset compensates by turning down its ANR gain. When you put the earseal back into place, you can hear the noise cancellation increase as the headset slowly restores the ANR gain to its previous value.

The 25XL's auto-shutoff feature is actually a byproduct of this automatic ANR gain control. If you remove the headset from your head, you create a profoundly unstable acoustic condition because the earcup cavity is no longer closed. Some ANR headsets actually start to squeal audibly when removed from the head with the ANR turned on (I've had this happen with some Telex ANR models, for example). The 25XL doesn't oscillate in this situation — at least for any more than a split second — because its automatic logic cranks the ANR gain way down. At the same time, it says to itself, "this acoustic condition is so unstable that the headset must be off the wearer's head." If this condition persists continuously for two to three minutes, the ANR module powers itself down to save the batteries. LightSPEED has applied for a patent on its auto-shutoff technique, too.

What's in a Name?

Naturally, I was curious to know why LightSPEED decided to call its latest headset model 25XL instead of 25K. After talking to the company, I must confess that I'm still not quite sure. LightSPEED says only that the 25XL is the first of what is expected to be a new "XL" product line, but it's not at all clear what additional members of the XL family might be coming down the pike.

One could certainly speculate, for example, that the existing 15K and 20K might someday be superseded by new 15XL and 20XL models. It would be a fair guess that such models might share the 25XL's increased battery life (maybe "XL" stands for "extra life"?), higher receive gain, and improved resistance to RFI. But let me be quite clear — these are just wild, irresponsible guesses on my part. LightSPEED's not talking.

What to Do, What to Do?

Okay, okay, so the new LightSPEED 25XL is a thoroughly delightful headset chock full of the very latest in bleeding-edge technology ... but is it worth $140 more than the 20K ($599 vs. $439, list)? Or $200 more, if you're a current 20K owners looking to trade up?

That's a tough question.

The 25XL is definitely an improvement over the 20K. It's quieter, but subtly so — enough to notice, but not enough to make you cry "Wow!" The equalization is a little better in terms of fidelity and intelligibility. Battery longevity is greatly improved, particularly if you consider the unit's auto-shutoff feature that is bound to save a lot of batteries and "expletives deleted."

On the other hand, if you're expecting the extra $140 or $200 to buy the same magnitude of improvement that you got by going from a $300-ish passive headset to a $400-ish ANR, you're going to be sorely disappointed. This is by no means a criticism of the 25XL, so much as acknowledgement that the 20K is already a phenomenally good headset and mighty hard to improve upon.

Let's face it: The 20K offers every bit as much comfort as the 25XL (physically, they're identical twins), every bit as much passive noise reduction (same earcups and earseals), and is no slouch in the active cancellation department, either. The 25XL's auto-shutoff is a great feature, but then again you can buy a whole lot of AA batteries for $140!

So, bottom line, would I spend $599 to buy the new 25XL? Yes, I might ... but the 20K would be a mighty tempting alternative (especially at a "street price" around $400 that you can sometimes get from discounters like Avionics West when they get temporarily overstocked and put the units on sale).

Will I shell out $200 to trade my 20K in for a new 25XL? The verdict isn't in on that one yet, but I'm certainly not in a big hurry to do so. Nothing against the 25XL, mind you — it's quite a marvel of acoustic and electronic engineering. But I'm still mighty happy with my 20Ks, and I fully expect to be flying with them for years to come.

But then again, I own three automobiles, and the newest of those is a 1985 model. Not to mention that I'm typing this article on an old notebook computer with a slow-poke 166 MHz CPU. So you may want to get a second opinion.

Better yet, find a way to test-fly the headsets for yourself. As I mentioned earlier, choosing a headset is an extremely subjective matter, and you should never make a purchase decision solely on the basis of someone else's evaluation. Even mine. Especially mine!

Where to Buy

LightSPEED has a web site where you can review the features and specifications of LightSPEED ANR models, read answers to frequently-asked questions, learn a great deal about the theory and design of ANR headsets in general (and LightSPEED's in particular), and order the headsets online.

LightSPEED ANR headsets are also available from a number of dealers, some of whom offer the headsets at small discounts from list. (There's not a lot of dealer margin on these units, so don't expect big discounts.) One of LightSPEED's "preferred dealers" is Avionics West, Inc., who maintains an online site and accepts online orders for all LightSPEED headset models (as well as a number of other brands).