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Thread: Making an A-11, WWII Flying Helmet operational

  1. #11

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    Well after some comparison flight tests I find that the A-11 (and AN-H-15 for that matter) rubber earcups do not block cabin noise as well as a decent set of passive noise reduction headphones.

    So my next experiment is to remove the rubber earcup/receiver holders from an AN-H-15 and replace it with plastic oval earcups that are roughly the same size and shape.

    My question is this:

    Is there any sound absorption material places inside the plastic "cans" of modern headsets? I don'e mean the earseal, but, rather, between the speaker and the plastic can the seals are mounted to.

    Thanks!

  2. #12
    rwanttaja's Avatar
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    I think the interior soundproofing might vary by brand. When I swapped speakers in a Rugged Radio headset a couple of years back, I don't recall any major stuffing in the cups. Looking at pictures, I see a sort of doughnut-shaped foam ring that went behind the speaker. Don't recall anything else. You can see the ring on the top left of this picture:


    You can see the ring around the speaker in the cup.

    You could try stuffing some sound-deadening material inside the cups. It's probably the easiest way to go, as long as you can find a place that'll sell small quantities. I once used little blocks of dense temperfoam to try reduce the noise level. Seems to help a bit, but never did a scientific measurement.

    The second approach is to remove the speakers ("receivers") and install a set of ear buds, instead. Check out this picture:

    If you look carefully at the bottom center, you'll see the ear buds that dangle out of the original ear cups. These dangle down about ~5 inches below the helmet...set the helmet lightly on your head, insert the buds, and pull the helmet down gently over them.

    Now, civilian ear buds don't have the right impedance, so you need an adapter. This is just a simple, tiny audio output transformer with a 300-600 ohm primary and an 8-ohm secondary. Used to be able to buy them at Radio Shack, but online places like Digi-Key and Mouser electronics sell them for ~$4 or so. Here's the diagram to make it work:

    The part number that I use is right on the drawing....XICON 42TL004.

    These transformers are small, and easily built-in to tiny boxes. You can build a separate adaptor as show above, or just build it into the headset itself. If you can't find one, drop me a message and I'll stuff a couple of spares in an envelope and send them to you. I made a lot of runs to Radio Shack before it closed. :-)

    The photo that shows the ear buds has the transformer located between the lining of the helmet and the leather, right at the nape of the neck. This is also the helmet that I stuffed the dense temperfoam into the cups to add to the passive attenuation.

    The neatest thing about this approach? They make ANL ear buds! But I use Plugfones, which are foam ear plugs with speakers inside. They have 24 dB of passive attenuation (same as a passive headset) and cost $25 a set.

    Ron Wanttaja

  3. #13

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    Quote Originally Posted by rwanttaja View Post
    I think the interior soundproofing might vary by brand. When I swapped speakers in a Rugged Radio headset a couple of years back, I don't recall any major stuffing in the cups. Looking at pictures, I see a sort of doughnut-shaped foam ring that went behind the speaker. Don't recall anything else. You can see the ring on the top left of this picture:


    You can see the ring around the speaker in the cup.

    You could try stuffing some sound-deadening material inside the cups. It's probably the easiest way to go, as long as you can find a place that'll sell small quantities. I once used little blocks of dense temperfoam to try reduce the noise level. Seems to help a bit, but never did a scientific measurement.

    The second approach is to remove the speakers ("receivers") and install a set of ear buds, instead. Check out this picture:

    If you look carefully at the bottom center, you'll see the ear buds that dangle out of the original ear cups. These dangle down about ~5 inches below the helmet...set the helmet lightly on your head, insert the buds, and pull the helmet down gently over them.

    Now, civilian ear buds don't have the right impedance, so you need an adapter. This is just a simple, tiny audio output transformer with a 300-600 ohm primary and an 8-ohm secondary. Used to be able to buy them at Radio Shack, but online places like Digi-Key and Mouser electronics sell them for ~$4 or so. Here's the diagram to make it work:

    The part number that I use is right on the drawing....XICON 42TL004.

    These transformers are small, and easily built-in to tiny boxes. You can build a separate adaptor as show above, or just build it into the headset itself. If you can't find one, drop me a message and I'll stuff a couple of spares in an envelope and send them to you. I made a lot of runs to Radio Shack before it closed. :-)

    The photo that shows the ear buds has the transformer located between the lining of the helmet and the leather, right at the nape of the neck. This is also the helmet that I stuffed the dense temperfoam into the cups to add to the passive attenuation.

    The neatest thing about this approach? They make ANL ear buds! But I use Plugfones, which are foam ear plugs with speakers inside. They have 24 dB of passive attenuation (same as a passive headset) and cost $25 a set.

    Ron Wanttaja
    Hi Ron,

    Yeah if you look at the Oregon Aero upgrade kits, they give you a foam pocket into which you slide the speaker, and the speaker is suspended in the foam ear ring. They don't mention anything about any sound absorbing foam in the plastic cup. I have some high density but thin foam laying around I may put a couple layers in the plastic cup.


    How difficult , and expensive, would it be to add a pot to that circuit so that you'd also have some volume control?
    Last edited by Saville; 03-17-2018 at 04:39 AM.

  4. #14

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    Quote Originally Posted by rwanttaja View Post
    I think the interior soundproofing might vary by brand. When I swapped speakers in a Rugged Radio headset a couple of years back, I don't recall any major stuffing in the cups. Looking at pictures, I see a sort of doughnut-shaped foam ring that went behind the speaker. Don't recall anything else. You can see the ring on the top left of this picture:


    You can see the ring around the speaker in the cup.

    You could try stuffing some sound-deadening material inside the cups. It's probably the easiest way to go, as long as you can find a place that'll sell small quantities. I once used little blocks of dense temperfoam to try reduce the noise level. Seems to help a bit, but never did a scientific measurement.

    The second approach is to remove the speakers ("receivers") and install a set of ear buds, instead. Check out this picture:

    If you look carefully at the bottom center, you'll see the ear buds that dangle out of the original ear cups. These dangle down about ~5 inches below the helmet...set the helmet lightly on your head, insert the buds, and pull the helmet down gently over them.

    Now, civilian ear buds don't have the right impedance, so you need an adapter. This is just a simple, tiny audio output transformer with a 300-600 ohm primary and an 8-ohm secondary. Used to be able to buy them at Radio Shack, but online places like Digi-Key and Mouser electronics sell them for ~$4 or so. Here's the diagram to make it work:

    The part number that I use is right on the drawing....XICON 42TL004.

    These transformers are small, and easily built-in to tiny boxes. You can build a separate adaptor as show above, or just build it into the headset itself. If you can't find one, drop me a message and I'll stuff a couple of spares in an envelope and send them to you. I made a lot of runs to Radio Shack before it closed. :-)

    The photo that shows the ear buds has the transformer located between the lining of the helmet and the leather, right at the nape of the neck. This is also the helmet that I stuffed the dense temperfoam into the cups to add to the passive attenuation.

    The neatest thing about this approach? They make ANL ear buds! But I use Plugfones, which are foam ear plugs with speakers inside. They have 24 dB of passive attenuation (same as a passive headset) and cost $25 a set.

    Ron Wanttaja
    Ron I love our work. Have you ever thought about doing a workshop at Oshkosh on things like this? You have done a lot of specialty projects for your Experimental that are just awesome. Maybe you have done this already and I am way behind. Keep up this great work and thanks for sharing what you have done. That hand held radio mounted in a panel. Leaves me speechless. As does all your work.

  5. #15
    rwanttaja's Avatar
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    Quote Originally Posted by Saville View Post
    How difficult , and expensive, would it be to add a pot to that circuit so that you'd also have some volume control?
    You can buy inline volume controls for ear buds pretty cheaply... just enter "volume control" on Amazon. Not sure how they'd work on a 300-ohm aircraft set, but it'd be easy enough to try.

    When I mounted my ICOM in the panel, I added a simple potentiometer for volume control. You can see it in this diagram:

    However, I have not been too pleased with it. IIRC, it's a 5000-ohm pot (lowest I could find locally in the physical size I wanted) and it has no real dynamic range... headphones are silent until it gets to the last few degrees of adjustment, then you have to adjust it carefully to get a particular setting. Fortunately, I usually run it at full volume anyway, and flick it down only when I'm away from the airport and don't want the distraction.

    After more than ten years of use, it's started to get a bit scratchy and finicky. I recently bought a selection of small LOGARITHMIC pots. Next step is to use my test setup in the shop to experiment and come up with something that works a bit better. I'm contemplating some electrical changes to my airplane, and it would be the perfect time to take care of this.

    Ron Wanttaja

  6. #16
    rwanttaja's Avatar
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    Quote Originally Posted by 1600vw View Post
    Ron I love our work. Have you ever thought about doing a workshop at Oshkosh on things like this? You have done a lot of specialty projects for your Experimental that are just awesome. Maybe you have done this already and I am way behind. Keep up this great work and thanks for sharing what you have done. That hand held radio mounted in a panel. Leaves me speechless. As does all your work.
    Thanks, Tony. I don't come to Airventure very often...every ten, fifteen years or so...and I suspect that a forum on accident statistics might be more of an attraction. Or as someone once told a writer friend of mine when he held a forum, "We came to see if you're as funny to look at as you are to read."

    Ron "Funnier in my case" Wanttaja

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