Introducing FC-HDS4 headset

Mychaela Falconia mychaela.falconia at
Thu Nov 11 20:25:01 UTC 2021

Hello FreeCalypso community,

I have a follow-up regarding the venture to produce our FC-HDS4 wired
headset.  First let me start with some pictures:

These photos are of the two headset sample pieces which JWH (the
Chinese manufacturer) sent me.  The photos were taken by JWH themselves
before these sample pieces were shipped to me - it is good that JWH
folks took these pictures, as my own camera skills are abysmal.

If you look at the stretched_out.jpeg photo, you will see that I got
two sample pieces with different wire lengths between the earpiece and
the inline microphone housing: on one piece this wire length is 135 mm,
and on the other piece it is 210 mm.  Naturally I need to decide on
this wire length for the full production run, hence the present

As a bit of background, when I asked JWH to produce this custom headset
for us, they took one of their existing designs as the starting point.
This previous design had a micro-USB connector (yes, analog signal
wires on a USB connector, a total hack, but many historical phones
once used this peculiar arrangement, just to save an extra connector)
and a 16 ohm earpiece speaker - thus the change from JWH's previous
design for unknown other customer to our FC-HDS4 consisted of changing
the earpiece speaker from 16 to 32 ohm and changing the connector from
micro-USB to 2.5 mm TRRS, in our custom pinout copied from iWOW.

In JWH's previous design for unknown other customer, the wire length
between the earpiece and the inline microphone housing was 210 mm.
But when I measured this wire length on the historical headsets from
Pirelli and iWOW, both were found to be in the 13 to 14 cm range.
This 13 to 14 cm wire length makes sense when the headset hangs from
the user's ear but is otherwise loose - in the hanging-from-ear use
case, this ear-to-mic wire length puts the microphone right at the
level of the user's mouth.  OTOH, JWH's choice of 210 mm wire length
never made much sense to me - reasoning that they are a professional
headset manuf and that they must have *some* good reason for their
design choices, I asked them for their reasoning, but they never
answered this line of questioning - who knows, it could be some
previous customer's private design.

Because I wanted to get a practical feel for both ear-to-mic wire
length options, I asked JWH for one sample piece of each length, and
they delivered.  The 135 mm versions works as I expected: I insert the
earpiece speaker into my ear canal, the headset hangs loose from my
ear without any other securement or attachment, and as it hangs there,
the inline microphone ends up right at the level of my mouth.  When I
tuned Calypso+Iota audio settings for this new headset (see
fc-audio-config Hg repository, aud-caramel directory), I used this
135 mm version.

The other 210 mm version does not make much sense if the headset hangs
from the user's ear and is not attached at any other point - in this
mode of usage the microphone ends up a few cm below the user's mouth,
needlessly attenuating your speech during calls.  Instead the only way
I can see how this longer version might work would be if the headset
is secured with a clip to the wearer's shirt, blouse or other clothes,
as opposed to hanging loose from the ear.  Depending on where the
clothes-grabbing clip is placed, it may be possible to secure the
microphone at some fairly fixed position near the mouth, and in that
case a longer wire span between the mic housing and the earpiece would
allow more slack in that wire piece.

I am currently leaning toward the 135 mm option, based on familiarity:
Pirelli's headset features the same ear-to-mic wire length, and I have
practical experience using it in the role of an end user, talking on
the phone while driving my car.  I never had any problems with the
microphone position being wrong, neither using Pirelli's headset as an
end user in my car, nor using iWOW's headset (same ear-to-mic distance)
during FC development work.  Furthermore, Pirelli's headset came
equipped with a clip that allows it to be secured (anywhere below the
microphone) to the wearer's clothes, and I successfully used that clip
many times while wearing the headset in my car and driving with it -
thus the shorter ear-to-mic wire length does not preclude the use of
clothes-grabbing clips.

However, if anyone else in our community has other ideas, the time to
speak up is now!

Hasta la Victoria, Siempre,
Mychaela aka The Mother

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