Cancelling echo in a recycled phone microphone-speaker set

Question

The speaker and microphone of my Android phone have stopped working, but the headphone jack still works. I don't want to always use a headphone, so I removed everything from a discarded non-smart phone, and soldered a headphone jack to its speaker and microphone, in order to use it as an extension to the phone.

Now I can comfortably use it, but people calling me can hear their own voice as an echo.

People at the other end speak -> my speaker -> my microphone catches it -> they hear their voice back

I tried lowering the speaker's volume to minimum, but that does not stop the issue. I am not even using the ringer speaker. I also tried putting some cotton on the speaker and the microphone, but that does not help either.

This is how the phone looks after removing the top cover.

The issue persists irrespective of whether the top cover is there or not.

How can I prevent this from happening?

Answer 1

Two points to consider: the acoustical path and the electro-magnetic path. Most handsets put a block of soft dense foam between the speaker and the mic. Cotton is too acoustically transparent. For the electro: use shielded cable for the microphone. If that doesn't work, confirm the type of microphone.

Answer 2

The mic is an electret condenser mic which is extremely sensitive to vibrations of the housing in which it is mounted. You will need to isolate the mic from the housing with soft foam, and also do the same with the speaker mount.

Answer 3

I found the following article that deals with an echo similar to your question. The problem is that the echo is from the other end; however, if you substitute "yours" for "theirs" you should be well on your way to solve the issue. A few different ways are mentioned here. I would freely exchange handset for headset, your speaker for their speaker, and so forth.

You could be hearing your own voice through a headset for a variety of reasons. Identifying and solving the problem is largely a process of trial and error. Fortunately, none of the common fixes are particularly difficult to implement and avoiding the frustration and distraction the echo should prove well worth the effort.

Others' Speakers
The simplest and most likely cause of an echo is not even caused by your microphone. If the people you are speaking to have microphones of their own and are receiving your voice through speakers, their microphones can pick up the sound from their speakers and send it back to you. An easy test is to ask that your friends momentarily turn their speakers off. If your friends' speakers are causing the problem, ask that they move farther from the speakers, reduce their volume or use headphones instead.

Other Devices
You may have more than one recording device activated. Many laptops and webcams come with an integrated microphone. If you computer is using both your headset and another recording device at the same time, it can create an echo effect. To disable other recording devices click the "Start | Control Panel | Hardware and Sound | Sound." Click the "Recording" tab in the window that appears. Right click on any device listed that is not your headset and select "Disable" from the pop-up menu.

Microphone Boost
Some sound cards employ a Windows feature called "Microphone Boost" that Microsoft reports may cause an echo. To disable the setting return to the Sound window as described in the previous section. Click the "Recording" tab, and then right click on your headset and select "Properties." Click the "Levels" tab in the Microphone Properties window and uncheck the "Microphone Boost" tab. Click "Apply," and then close the window.

Mic Monitor
Some headsets deliberately send some of the user's voice back to the headset in order to help users know how loud they will sound to others. Depending on your Internet connection and the programs you are using, there may be a slight delay between your speaking and the sound being played back. Return to the Microphone Properties window for your headset as described in the previous section. Click the "Listen" tab and make sure that the check box next to "Listen to this device" is left blank. If it is checked, click the box once to remove the check mark, then click "Apply" and close the window.

For what it's worth, any one of these might give you some ideas to pursue.

Good luck.