8-Ohm Aviation Headset

wanttaja

wanttaja

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Ron Wanttaja
I've got an ICOM handheld installed in my panel as the only radio in the open-cockpit aircraft. It has an 8-ohm output impedance for the headphone portion.

This summer, I've been using ear buds underneath my leather helmet. With the approach of fall, I've switched back to using my Flightcom Denali ANR headsets. With cooler weather, it's more comfortable with a traditional headset holding the helmet flat against my head rather than the "airscoop" effect that otherwise occurs.

But I got spoiled this summer. With the 8-ohm earbuds on the 8-ohm output, I had very good volume and sound quality. Using the standard 300-ohm aircraft headset for the first time this year really highlighted how much volume the mismatch costs.

So...I'm looking at some options, to regain the impedance match in a traditional headset. So far, I'm thinking:

1. Buy a non-aviation set of ANR headphones and add a mike boom. I like this approach, but am concerned about passive noise attenuation...am worried commercial headphones won't get anything near the attenuation one can get from even a non-ANR headset.

2. Buy a headset configured for US military use (9-ohm speakers). These use a different plug, but I can probably find an adaptor or replace the plug. I believe I'd have to replace the mike, too.

3. Buy a non-ANR headset, and get a Headsets Inc ANR adaptor for a military headset. These come with the lower-impedance speakers.

4. Buy an aviation ANR headset that includes an 8-ohm MP3 input to the headphones, and wire the aircraft radio to that connector instead.

The last option would let me use the headset for those rare occasions I fly in an airplane with a conventional radio (just BFRs, mostly).

So...any other ideas? Suggestions?

Ron Wanttaja
 
Try the one from ICOM. OPC-499 HEADSET ADAPTER CABLE

My YEASU with their adapter worked fine when I came back from Baja after an alternator failure.
 
Ron:

I'm pretty new to this stuff, so you might want to PM @weirdjim, but one of these might work:

http://makearadio.com/misc-stuff/t-725.php

Looks to me like you could connect the output from your panel to the two pink wires and then connect your headphones to the red & black ones.

These are like 10 bucks on Amazon.
 
wanttaja said:
I've got an ICOM handheld installed in my panel as the only radio in the open-cockpit aircraft. It has an 8-ohm output impedance for the headphone portion.
Ron Wanttaja
Click to expand...

Here you go: http://www.jameco.com/z/42TM013-RC-...ry-Resistance-200mW-Power-Rating_2210511.html

$4 plus shipping. About the size of a D-cell cut in half. Stated impedance ratio is 8 ohms to 1000 ohms, but the primary is center tapped, which ought to be a reasonable match to your headset.

upload_2016-9-28_8-33-2.jpeg
Jim
 
weirdjim said:
Here you go: http://www.jameco.com/z/42TM013-RC-...ry-Resistance-200mW-Power-Rating_2210511.html

$4 plus shipping. About the size of a D-cell cut in half. Stated impedance ratio is 8 ohms to 1000 ohms, but the primary is center tapped, which ought to be a reasonable match to your headset.
Click to expand...
My apologies to you all; I hadn't seen the response until just recently. I thought I'd posted this to a different area on the forum.

I did try an impedance matching device, using a Radio Shack 1000CT:8 ohm audio output transformer. Didn't notice any improvement.

One guy suggested that the 500 ohms might still be too high; I found a 250:8 and a 200:8 transformer on Mouser and they should be in today or tomorrow. Once cost $2.50, the other $20, so you can guess which one I'm rooting for.

I have turned this into a bit of a science project, exploring several different routes. I've got an non-ANR aviation headset on order from Rugged Radios. They carry 8-ohm speakers that I assume will fit, so I'll try to swap out the speakers. If it works at that point, I may try a Headsets Inc. ANR kit; they have one for a military-style headset (which I understand use the lower-impedance speakers).

One aspect of the science project is getting some measurable results. With my Flightcom ANL headset connected to the radio, I have to turn the volume all the way up and some transmissions are still hard to hear, in flight. With a cheap consumer 8-ohm headset, I have to hurriedly back down on the volume. But...that gives me only the two end points.

Last weekend, I dug up my old sound meter and attempted some measurements. I plugged in a set of headphones into a second ICOM handheld, turned the radio on, and basically turned the squelch off to give a nice steady roar. I then stuck the meter into an ear cup and took a reading ("C" weighting).

The cheapie consumer headset read 104 dB, a cheap aviation headset was 94 dB, and my Flightcom ANLs were 95 dB with the ANL on...and 89 dB with ANL off, which kind of surprised me.

When I get my new transformers and headset in, I'll try again. Need to come up with a more reliable way to position the meter's mike.

Ron Wanttaja
 
wanttaja said:
I did try an impedance matching device, using a Radio Shack 1000CT:8 ohm audio output transformer. Didn't notice any improvement.
...
Last weekend, I dug up my old sound meter and attempted some measurements. I plugged in a set of headphones into a second ICOM handheld, turned the radio on, and basically turned the squelch off to give a nice steady roar. I then stuck the meter into an ear cup and took a reading ("C" weighting).
Click to expand...
Strange. I came across the adaptor I'd made a few months ago, and decided to give it a try using the measurement setup. This time, I got a measured increase of ~9dB. And it did seem louder, too. This adaptor used the Radio Shack 273-1380 audio transformer, about $4.

Wonder if I had left the ANL off on my brief test, earlier. That does make ~6 db of difference.

Anyway my Mouser cheapie transformers came in, and they're about a quarter of the size of the Radio Shack ones. I'll test 'em to see how well they work, then try to come up with some compact packaging.

Ron Wanttaja
 
I'm a little surprised you used a mic and a sound meter instead of just measuring voltages either RMS or peak/peak, but either way, you measured and found your differences and had a baseline for your changes. Engineering... yay. Ha.
 
denverpilot said:
I'm a little surprised you used a mic and a sound meter instead of just measuring voltages either RMS or peak/peak, but either way, you measured and found your differences and had a baseline for your changes. Engineering... yay. Ha.
Click to expand...
The sound meter probably provides a better indicator of audio power, as that's what the headsets' attenuation is usually spec'ed at. Besides, "db" is easier to write than "Peak to Peak." :)

Though dB are a bit weird. Decibels are logarithmic, and a 3dB increase in level actually means twice as much sound energy. However, the ear doesn't *perceive* that 3dB as being "twice as loud." A good example is the ANL switch on my Flightcoms. Turning the ANL switch off in flight certainly produced a higher noise level, but the 5 dB loss in audio power wasn't that apparent.

The adaptor gave a 9dB improvement. I had the headset lying on the worktable when I changed plugs, and even sitting ~2 feet away, the additional audio strength was apparent.

The fun bit now is working out how to implement the adaptor in the airplane. I don't want to hang another box on the headset cable. I may modify my radio install, so that the 1/4" jack is connected to the radio through the transformer and add a 1/8" jack for a direct connection when using my ear buds. You can see the jack installation on the lower right, there's room for a 1/8" jack.
rad_struct.jpg


Ron Wanttaja
 
wanttaja said:
Though dB are a bit weird. Decibels are logarithmic, and a 3dB increase in level actually means twice as much sound energy. However, the ear doesn't *perceive* that 3dB as being "twice as loud." A good example is the ANL switch on my Flightcoms. Turning the ANL switch off in flight certainly produced a higher noise level, but the 5 dB loss in audio power wasn't that apparent.

The adaptor gave a 9dB improvement. I had the headset lying on the worktable when I changed plugs, and even sitting ~2 feet away, the additional audio strength was apparent.

Ron Wanttaja
Click to expand...

When old man Bell (Alex, late of Nova Scotia) did his pioneering work on sound, he called an apparent doubling of volume the "Bell", modest person that he was. Engineers found this too large a quantity, so they divvied it up into tenths, giving us the deci-Bell. Humans being what they are, they morphed it into the deci-Bel. (dB is the correct abbrvtn, db is not.) Human perception of "just a little louder" or the threshold where sounds are perceived to be louder than one another is taken generally to be about 5 dB to 6 dB, or 4 times the "sound power". Twice as loud is one Bel, or 10 dB. The ear, too, is nonlinear. Just HOW nonlinear was the life's work of the researchers Fletcher and Munson, whose Fletcher-Munson curves regarding the sensitivity of the human ear have stood the test of time.

There are actually three F-M sets of curves. One is the "average", one is the male, and one is the female. The male is skewed towards the lower end of the frequency range, the female to the higher. Without being sexist in the least, one theory says that males (the hunters) needed to hear the low pitched growls of prey (or predators) and females needed to hear the high pitched sounds of babies. Just one theory. There are others.

Jim
 
weirdjim said:
When old man Bell (Alex, late of Nova Scotia) did his pioneering work on sound, he called an apparent doubling of volume the "Bell", modest person that he was. Engineers found this too large a quantity, so they divvied it up into tenths, giving us the deci-Bell. Humans being what they are, they morphed it into the deci-Bel. (dB is the correct abbrvtn, db is not.) Human perception of "just a little louder" or the threshold where sounds are perceived to be louder than one another is taken generally to be about 5 dB to 6 dB, or 4 times the "sound power". Twice as loud is one Bel, or 10 dB. The ear, too, is nonlinear. Just HOW nonlinear was the life's work of the researchers Fletcher and Munson, whose Fletcher-Munson curves regarding the sensitivity of the human ear have stood the test of time.

There are actually three F-M sets of curves. One is the "average", one is the male, and one is the female. The male is skewed towards the lower end of the frequency range, the female to the higher. Without being sexist in the least, one theory says that males (the hunters) needed to hear the low pitched growls of prey (or predators) and females needed to hear the high pitched sounds of babies. Just one theory. There are others.

Jim
Click to expand...


Just learned something new.. Time to go home.
 
weirdjim said:
When old man Bell (Alex, late of Nova Scotia) did his pioneering work on sound, he called an apparent doubling of volume the "Bell", modest person that he was. Engineers found this too large a quantity, so they divvied it up into tenths, giving us the deci-Bell. Humans being what they are, they morphed it into the deci-Bel. (dB is the correct abbrvtn, db is not.) Human perception of "just a little louder" or the threshold where sounds are perceived to be louder than one another is taken generally to be about 5 dB to 6 dB, or 4 times the "sound power". Twice as loud is one Bel, or 10 dB. The ear, too, is nonlinear. Just HOW nonlinear was the life's work of the researchers Fletcher and Munson, whose Fletcher-Munson curves regarding the sensitivity of the human ear have stood the test of time.
Click to expand...
That was stupendous, Jim. Thanks!

It makes me feel better about my results, too... my 9 dB increase is almost a full Bell. That would be what ol' Alexander considered an apparent doubling of volume. Which is EXACTLY what I felt it sounded like.

Got an idea how to Siamese-twin an inline 1/4" jack and a plug with a transformer in between. Will post pictures of the construction.

Ron Wanttaja
 
Ok, just about done with this. I got all engineer-y and set up some Test Sheets to collect data in a methodical fashion. My results varied a bit from previous, probably just due to vagaries of the setup.

To recap the issue, aviation headsets have speaker impedances of 300 ohms. Many low 'n slow airplane owners, including myself, use ICOM or other standard handheld aircraft radios. These have output impedances of 8 ohms, the same as most commercial equipment.

Most handhelds include an adaptor to use a standard aviation headset. However, this adaptor does NOT match the impedance. The combination of an 8-ohm output impedance into a 300-ohm headset is inefficient, which manifests itself as a reduction in audio power. This can be relieved to a great extent by using a small transformer to match the impedance.

For my test setup, I used an ICOM handheld and a cheap set of consumer headphones as my baseline. I used a Radio Shack sound meter (set to "A" Weighting) as my measuring device. The ICOM squelch was set to zero so it "hissed" all the time. The volume was set to produce either 100 dB or 110 dB at the consumer headphones. Then I compared the result with the aviation headsets and several transformers that might be used as adaptors.
av_test_setup.jpg

I had three aviation headsets to test:

1. A generic $100 headset
2. A Flightcomm Denali ANL headset
3. A newly purchased RA200 aviation headset from Rugged Radios (http://www.ruggedradios.com/)

First, let's consider the sound level that is produced by the various aviation headsets connected to the 8-ohm-output ICOM without any sort of impedance matcher (the way most folks operate them).

Reference power level: 100 dB (sound level at the 8-ohm headset)

Generic headset: 89 dB
Denali ANL: 85 dB (with ANL off)
Denali ANL: 94 dB (with ANL on)
Rugged Radios RA200: 92 dB

An increase in 3dB means twice the sound energy, but this is not necessarily perceived as twice as loud...in fact, you might not even hear it. But the scale is logarithmic, so the 6-10 dB we're seeing here starts getting significant. As Jim Weir told us, Alexander Graham Bell defined a "Bell" as the difference in power level that would perceived as twice as loud. So you can see how the volume might seem lower with these.

I tried three different transformers: An Xicon 42TL-004-RC, with a 200:8 impedance ratio (both sides centertapped), a Hammond 148G with a 250:8 ratio, and a Radio Shack 273-1380 with a 1000:8 ratio. Both the Hammond and the Radio Shack's primaries were centertapped. I didn't use the feature on the Hammond, but I did on the Radio Shack to get a 500:8 impedance ratio.

For the most part, the transformers performed about as well. The Denali ANL and the Rugged Radios RA200 got results almost identical. The Generic one actually worked a bit better with the Xicon and the Hammond, but the Radio Shack results were about 4 dB down.

I did experiment with the center taps on the Xicon and Hammond, and found the performance slipped in most combinations.

Costs? The Radio Shack unit was about $4, the Hammond was $20, and the Xicon was $2.50. Plus the Xicon was smaller than the other two, and would be easier to either build into a headset or make a small adaptor.

The results with the Xicon with a 110 dB input were about the same; all three headsets were within 2 dB of the target value.

So... the Xicon is my choice in the future. Good thing I ordered five of them. Ordering information:

http://www.mouser.com/ProductDetail/Xicon/42TL004-RC/?qs=/ha2pyFaduidXMr7No1%2bnwCR7U7rD%2boXR2h0pObUz18=

The Radio Shack unit is a fine fallback if you don't want to through the hassle of ordering a $3 part online.

I've already bought a couple pairs of 1/4" plugs/inline jacks, I'm going to see if I can cobble together an adaptor. In the long term, I'm going to add a 1/8" jack to my panel and add the transformer to the existing 1/4" jack. That way, I can plug aviation headsets into the 1/4" jack and ear buds into the 1/8" without futzing with external adaptors.

Today's other experiment was based on the Rugged Radios headset. When I looked at the site, I noticed the parts section sold replacement speakers in both 8 ohm and 300 ohm varieties. When I ordered the headset ($65) I also ordered a set of 8-ohm speakers ($22 total), betting that the speakers would fit the headset. Thought it was a very good chance, as Rugged Radios probably uses the same headset shell in a lot of applications.

The bet paid off...the speakers were a direct replacement. Removal/replacement was relatively easy.
av_speakers.jpg

At the end, with a 110 dB reference power level, I measured 107 dB.

Why 3dB less, with the same impedance? Two reasons, I think. First, the "Reference" 8-ohm headset was being plugged directly into the radio, and the Aircraft headset had to go through a kluged-up set of wiring. Might be just enough losses.

Second...these are extremely flat speakers, not much more than a half-inch deep. The cheap commercial headset has traditional-style speakers, since it doesn't have to try to pack sound deadening material into the ear cups. I think the old-style speakers are probably more efficient.

One thing...the Rugged Radio headset seems to have excellent passive sound attenuation. May help, since it doesn't have ANL.

Anyway, the speakers are installed. I've done a momentary test transmission in the airplane, and it seems like a decent volume. I've got the modified headset mounted on my helmet, and if the weather's good tomorrow, I'll give it a shot.

Ron Wanttaja
 
Last edited:
wanttaja said:
Anyway, the speakers are installed. I've done a momentary test transmission in the airplane, and it seems like a decent volume. I've got the modified headset mounted on my helmet, and if the weather's good tomorrow, I'll give it a shot.
Click to expand...
And...just got down, and the new headset works perfectly. Transmissions are nice and loud, very understandable. The Rugged Radios headset has some good attenuation, especially with the optional gel ear pieces. Absolutely no trouble.

About ten years ago, I bought a "Special Price" headset for $100. It was about what I expected for a "special price" headset. The Rugged Radios RA200 also sells for $100*, but is a sturdier, better quality headset. I was impressed with it, even before doing the speaker conversion.

I will probably still be looking into the adaptors, but what I've got now is perfectly usable. So there's no rush.

Ron Wanttaja

*$105 list price. However, I bought mine from their "Clearance" listing...just $65.
 
I just happen to have an adaptor for military headset to civilian radio. PM if you want it, for cost of shipping.
 
bluerooster said:
I just happen to have an adaptor for military headset to civilian radio. PM if you want it, for cost of shipping.
Click to expand...
Headset impedance match would be about right, though you'd want to avoid the mic impedance match part (~5 ohm vs. 150 ohm in the aviation headset). It'd need a new plug, too, but those are cheap especially since you won't have to worry about the mic.

Guy emailed me last week, had volume problems on an LSA. He bought a Y-cable splitter at Radio Shack, cut off one the arms, and put the transformer on the remaining line. Works good....

Ron Wanttaja
 
Ron, if you like the earbuds (I'm using Plugfones earbuds under my leather helmet), why not just use the earbuds under a set of passive headphone style hearing protectors like those used for shooting sports?
 
Dana said:
Ron, if you like the earbuds (I'm using Plugfones earbuds under my leather helmet), why not just use the earbuds under a set of passive headphone style hearing protectors like those used for shooting sports?
Click to expand...

Considered that. The problem is, I don't really *like* wearing things in my ears. I do it in the summer since it frees my head up nicely and is a lot cooler. But I seem to have small ear canals, and have some problem getting them seated properly. Probably need to get some custom units.

Ron Wanttaja
 
Built my plug-in adaptor, it works.

Used a 1/4" plug, a 1/4" inline jack, and one of the small transformers on a little bit of circuit card.
av_adapt1.jpg

Next step was to use casting resin to make a solid one-piece adaptor. As before a pill bottle was used.

The jack, as you can see, is enclosed. However, there were slits on the base end where the terminals came out. I sealed them with super glue. Into the pill bottle, pour in the resin, wait 24 hours.

This is how it looked right out of the mold.
av_adaptor.jpg

I stuck a spare plug into the headset end to verify that the jack was indeed clear of resin.

Ron Wanttaja
 
I used a similar technique to make a dual plug adapter for my Icom A24. Mounted both plugs to an aluminum plate and potted the wires on the back side with epoxy.
 
Hi...the impedance in an aircraft headphone system is 600 ohms, yours are probably 32 ohms or less, this means that you're putting too high load on the system.
Second, the microphone amp is normally fed, not always, with power from the aircraft system, so it's a special design. Not necessarily expensive, but again built not to interfere with the rest of the system.
Third, buy yourself a headset built to be used in an aircraft, probably cheaper in the end.
 
@TeraWales - Nice start. A 2.5 year old necro post!

When you saw that red banner that said this thread is over 1 year old, what compelled you to click the box and continue?
 
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