27 Jan 2012

How sensitive can headphones be?

Having made several short-wave crystal sets in my time I have nearly always used the little "deaf aid" very high impedance crystal earpieces as the acoustic transducer. I thought these were very sensitive being able to copy HF AM signals down to around -55dBm to -60dBm. However I recently read somewhere that with the old WW2 DLR5 low impedance headsets one could hear an applied audio signal as low as 2uV (-101dBm), which is remarkably low.  

So, I began to wonder just what ARE the best headsets to use if one is after the maximum efficiency converting an audio frequency electrical signal into sound pressure in the ear?

This graph (from Wikipedia) shows the sensitivitity of typical humans at different ages. Someone of my age (63) is likely to be less able to hear as low as someone aged 30 years.

As some of these old military surplus headphones can be hard to find nowadays in good condition, I wonder what is the most sensitive headset/earpiece that can be bought new "off the shelf". Any ideas please?


LY2SS said...

Wow! Nice find Roger!
First find in Google regarding DLR-5 show amazing sensitivity comparing to crystal earpiece


Results are in picowatts (at the very bottom)


LY2SS said...

It seems that sensitivity was achieved after home rewinding though...

Anonymous said...

Hello Roger,
if you want something really new,
look for ST-3 from Japan Radio company.
Mike/AA1TJ has used them with great sucess in all kind of gain-less receivers e.g.:
A czech OM managed to find them on the web a year or so ago.
Not that new, nor cheap, but in good shape one can buy Racal elements here:
They are as good as DLR-5, but a bit smaller, so they fit fine into a standard 2x2000Ohm holder with
little milling work to do -
measured 50fW(-103dBm)for a minimum detectable signal at 1kHz and used them with good sucess in several gain-less and low gain
minimalist receivers.

Roger said...

Thanks for all the comments. This is a fascinating thread and I am amazed just how good (sensitive) some headsets appear to be.

Anonymous said...


China military headset, got one, still have to use them.
And i have modified them to make them comfortable.