How to turn off the internal speakers while connecting headphones

[ZZZzzzO_O]

I have recently received my new desktop in my office. However, when I connect to my headphone to either the front or the rear port, the internal speaker still works, which is embarrassing in a public premise. So how do I silence the internal speaker and leave only the headphone working?

[BeemerBiker]

Your audio dialog boxes may look different as the drivers may be different.

Basically bring up sound settings by selecting the speaker icon and set the volume of the "speakers" to 0  

Be sure to click on "apply" or "ok"  after making any changes.

You should first type "manage sound devices" in windows search box  which should pop up the following.  It shows speakers disabled and options for NVidia or headphone. 

If the above does not show up then the following:

Sound setting for headphone (front panel connector)

Sound setting for rear (or speakers)

[itsmyname]

@ZZZzzzO_O  -- in addition to what @BeemerBiker wrote, be sure that you are inserting the headphone "jack" as fully as possible. 

Pushing that jack FULLY into the socket should cause a mechanical action, like opening a "switch', similar in concept to:  SPST-diagram.png (460×166) (learningaboutelectronics.com)

If you don't push the jack far enough, the switch stays "closed", and sound is still directed to the internal speakers.

Since you get the same "non-action" from both the front & rear sockets, I doubt that it is a mechanical problem with both of the sockets on the motherboard.

Maybe, try a different headset ?

Finally: do you work in a large office, where there is an official I.T. Department where you can get help with the new computer?  Or, do you work in a smaller office where one employee is the "in-house computer wizard" ?

I hope this helps.

[ZZZzzzO_O]

I am sure that I have fully push the jack in. Actually, my headphone is able to work normally. The problem is that both the internal speaker and my headphone work simultaneously. If I disable speaker in sound setting, both the internal speaker and external headphone become silent togather. I want to disable the internal speaker and let my headphone work exclusively.

[ZZZzzzO_O]

There is only one output device option when headphone is connected into the socket. The strange thing is the internal speaker and my headphone work simultaneously. If I disable speaker in sound setting, both of internal speaker and headphone cannot work simulteneously. It seems the two devices are bound together.

[BeemerBiker]

It seems the device has not had a driver assigned to it.  Either the internal speaker or the controller for the jack.

Clarification: exactly what is the "internal speaker". ?  Most internal speakers I  have seen are tiny and all they do is beep.

Does the monitor you are using have speakers?  The intel GPU routes video and audio out the DP or the HDMI. Are those speakers, if any, being used?  What is your monitor model?

This is your system here (I selected win10 build /version 2004)

https://support.hp.com/th-en/drivers/selfservice/hp-z2-small-form-factor-g5-workstation/34407171/mod...

Please check your OS to see if 2004 or not and download and install the correct audio driver.  Unless both devices show up you will be unable to control them independently.

I looked at another problem as suggested by @itsmyname .  Your system spec shows the audio jack has CTIA & OMTP support.  Is your headset compatible?  I assume you are not using an Apple headset.  There is a discussion of the problem in below url.  The jack must be is 4 conductor as it is designed for mike and stereo.  If you have headphone (3 conductor) and not headset then possibly the audio is not being transferred properly just to the headset as suggested by @itsmyname 

https://support.headsetbuddy.com/hc/en-us/articles/207970396-Smartphone-Headset-Standards-Apple-iPho...