Which microphone on a smartphone is usually enabled for hands-free
speaker operation?

My Moto G7 uses only the microphone at the very top of the phone, when
the speaker is turned on during a phone call.

The top mic seems a strange choice as it points into the room or street.
Do other handsets use a mic in a similar position for speakerphone?

As background, the Moto G7 has three microphones

(1) one at the very top (2) one at the bottom of the screen (3) one at
the rear

Pamela <pamela.private.mailbox@gmail.com> wrote:
> Which microphone on a smartphone is usually enabled for hands-free
> speaker operation?
>
> My Moto G7 uses only the microphone at the very top of the phone, when
> the speaker is turned on during a phone call.
>
> The top mic seems a strange choice as it points into the room or street.
> Do other handsets use a mic in a similar position for speakerphone?
>
> As background, the Moto G7 has three microphones
>
> (1) one at the very top (2) one at the bottom of the screen (3) one at
> the rear

No knowledge for sure but I'd guess they use all of them and some signal
processing to cancel background sounds. They don't know which way the phone
will be pointing when in speakerphone mode so the signal processing will try
to discriminate the speaker who is close to the handset compared with sound
sources further away. They may be able to establish the direction of the
speaker and adjust gains appropriately.

The audio mix could be different in speakerphone mode compared with video
recording mode, where you're pointing the rear camera at something, or video
call mode where you're using the front camera.

Theo

On 18:25 18 Mar 2024, Theo said:
> Pamela <pamela.private.mailbox@gmail.com> wrote:
>>
>> Which microphone on a smartphone is usually enabled for hands-free
>> speaker operation?
>>
>> My Moto G7 uses only the microphone at the very top of the phone,
>> when the speaker is turned on during a phone call.
>>
>> The top mic seems a strange choice as it points into the room or
>> street. Do other handsets use a mic in a similar position for
>> speakerphone?
>>
>> As background, the Moto G7 has three microphones
>>
>> (1) one at the very top (2) one at the bottom of the screen (3) one
>> at the rear
>
> No knowledge for sure but I'd guess they use all of them and some
> signal processing to cancel background sounds. They don't know which
> way the phone will be pointing when in speakerphone mode so the signal
> processing will try to discriminate the speaker who is close to the
> handset compared with sound sources further away. They may be able to
> establish the direction of the speaker and adjust gains appropriately.

A handset on a call in speakphone mode would often be placed on a flat
surface, such as a desk. In such as case, the active mic on my phone (at
the top) is pointing away from the user, which means it would pick up
room acoustics.

In most situations on a call using speakerphone, it seems better
acoustically to use the front-facing mic at the bottom of the screen.

> The audio mix could be different in speakerphone mode compared with
> video recording mode, where you're pointing the rear camera at
> something, or video call mode where you're using the front camera.
>
> Theo
Above, I'm considering only the microphones used during a phone call.
Recording audio using a voice recorder app or a video app might well use
a different combination of mics.

On 25/03/2024 15:13, Pamela wrote:
> A handset on a call in speakphone mode would often be placed on a flat
> surface, such as a desk. In such as case, the active mic on my phone (at
> the top) is pointing away from the user, which means it would pick up
> room acoustics.

If only a single microphone is in use, the response will be
omnidirectional. Mobile phone microphones have single, very small,
apertures, so a effectively point pressure sensors, and pressure is a
scalar quantity.
>
> In most situations on a call using speakerphone, it seems better
> acoustically to use the front-facing mic at the bottom of the screen.

If you are operating in speakerphone mode, you want the microphone as
far away from the speaker as possible, to give echo cancellation a
change, and, at least on mine, the speaker, in this mode is at the
bottom of the phone. I presume that is to make it unlikely you will put
it directly to your ear and deafen yourself.