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 Post subject: Sound powered headphones
PostPosted: Jun Tue 15, 2021 8:53 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Florence, Al. U.S.A.
I have a pair of restored U.S. Instrument Corp. P030 headphones. How do you check to see if the sensitivity is up to anuff?


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Wed 16, 2021 2:55 pm 
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Location: Roanoke, VA
The standard approach uses a dummy head with calibrated microphones in the ears and a calibrated audio input to the headphones.

Dale H. Cook, Retired Chief Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Wed 16, 2021 10:20 pm 
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The shortcut approach is to listen to them while touching the leads together. You should hear a distinct click. 2000 ohm magnetic headphones will click, too, just not as loud.

If you've age-related or other hearing loss, you may not hear the click. Another simple uncalibrated test is to use one SP element as transmitter, the other as receiver. The signal should be quite audible. You might put a noisemaker like a small radio at the transmitter in a sound proof enclosure like a stack of pillows.


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Wed 16, 2021 10:25 pm 
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Macrohenry wrote:
The shortcut approach ...

The OP was asking about sensitivity, and that is a quality that must be measured.

Dale H. Cook, Retired Chief Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 12:03 am 
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Location: Florence, Al. U.S.A.
Thanks, Dale, I was asking to see how much better these would be for a foxhole radio.


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 12:34 am 
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Carl Neidert wrote:
Thanks, Dale, I was asking to see how much better these would be for a foxhole radio.
Night and day.


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 2:00 am 
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Dale H. Cook wrote:
Macrohenry wrote:
The shortcut approach ...

The OP was asking about sensitivity, and that is a quality that must be measured.

That's your interpretation of the OP's question. Here's the question, bold added by me:

Carl Neidert wrote:
How do you check to see if the sensitivity is up to anuff?

I interpreted it differently: Sounded to me he wanted to CHECK whether the SP element is working optimally. There's more than one way to skin a cat. You can CHECK to see if an AA cell is fresh by either measuring under load or by bouncing it on a hard surface. Either is an acceptable method that tells you whether it's fresh if that's all you want to know.

This is learning forum. Not everyone has broadcast quality equipment like you've prescribed before for other measurements. Some of us don't even have a full complement of professional equipment, but that doesn't mean we shouldn't try with what we do have available.

Your admonition reminds me of the question whether a member should even bother to weigh in with additional contributions after an authority has already answered the OP's question to the OP's satisfaction.


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 3:31 am 
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The sensitivity of a transducer is defined as the ratio of the output to a given input under given conditions. For headphones that is sound pressure level in decibels divided by input voltage in millivolts. Note that this is not the same as efficiency, which for headphones is sound pressure level in decibels divided by input power in milliwatts. In both cases the reference frequency is 1 kHz.

This is not a matter of interpretation. For more than 40 years I have made my living in part by making measurements of electronic equipment, sometimes in order to satisfy Federal regulations.

Dale H. Cook, Retired Chief Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 3:34 am 
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Macrohenry wrote:
Your admonition reminds me of the question whether a member should even bother to weigh in with additional contributions after an authority has already answered the OP's question to the OP's satisfaction.

You can weigh in whenever you want to at any time on any subject. I was simply providing a technically correct answer.

Dale H. Cook, Retired Chief Engineer, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 3:56 am 
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Welcome back, I'm sure.


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 5:09 am 
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I needed to run some tests on headsets. I thought: "how hard can it be"

It turned into a deep rabbit hole. You learn about all kinds of fun stuff: IEC couplers, head and torso simulators, pistonphones, etc.

Like so:


Attachments:
Headset testing.JPG
Headset testing.JPG [ 512.42 KiB | Viewed 1045 times ]
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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 12:32 pm 
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Location: Utica, NY 13502 (USA)
What are "sound powered" headphones? I thought all headphones need audio in the form of an electrical current to produce sound. I tried to find a picture of what you have. I'm thinking this is not it.

Attachment:
Dutch Acoustical Headphones.png
Dutch Acoustical Headphones.png [ 294.41 KiB | Viewed 999 times ]


Dave


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 2:47 pm 
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Dave Doughty wrote:
What are "sound powered" headphones? I thought all headphones need audio in the form of an electrical current to produce sound. I tried to find a picture of what you have. I'm thinking this is not it.

Attachment:
Dutch Acoustical Headphones.png


Dave

To check them must they be measured?


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 Post subject: Re: Sound powered headphones
PostPosted: Jun Thu 17, 2021 11:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Florence, Al. U.S.A.
It's too bad that Curt Reed is not still around. Think I learned what I need to know.


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