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Message-ID: <011c01ccdd57$d6de06f0$4001a8c0@lark>
From: "Alan Melia" <alan.melia@btinternet.com>
To: <rsgb_lf_group@blacksheep.org>
References: <CAHAQVWP_9KdqZ1NjzmJqB3O2mrb-GfJfZBf_D7CY0Y8FAasC3Q@mail.gmail.com>
Date: Sat, 28 Jan 2012 00:27:05 -0000
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Subject: LF: Re: OT: Headphones
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Hi Roger, you are talking about kit from the good ol' days when things had
to be made sensitive :-)) I think those uints have a quite high impedance (5
to 10k??) a fairly narrow range cetainly no more than telephone bandwidth,
and I believe some were even tuned to favour morse tone frequencies. I think
I have heard of ops loading the diaphram to peake them lower in frequency.
Most if not all modern headphones are made for "HiFi" and use small low
impedance speakers in the muffs. It might be possible to make a sensitive
one by swapping these for piezo units like used in singing birthday cards
:-)) They are obviously very high impedance, but most seem to be driven from
single batteries, and do not have the aid of the muffs to channel the
sound.......Just a though for someone who wants to experiment :-))

Alan G3NYK
----- Original Message ----- 
From: "Roger Lapthorn" <rogerlapthorn@gmail.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, January 27, 2012 10:29 PM
Subject: LF: OT: Headphones


> Slightly OT but people like Mal and Jim may have an answer.
>
> Is there a "modern" (i.e. can you buy it new today?) headphone set that is
*
> extremely* sensitive in the same way that the old DLR5 headsets were in
> terms of efficiency converting AF to sound pressure in the ear?
>
> I believe Jim M0BMU claimed 2uV audio power could be heard using DLR5
> headsets in his passive mechanical SAQ receiver. As DLR5s are more
> difficult to find these days I was wondering if there is anything as
> sensitive, or more so, around "new".
>
> 73s
> Roger G3XBM
>
> -- 
> http://qss2.blogspot.com/
> http://g3xbm-qrp.blogspot.com/
> http://www.g3xbm.co.uk
> https://sites.google.com/site/sub9khz/
>