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Articles - Sony MEX-BT2500 mic tuning

Publication date: 01/21/08

How to improve a quality of microphone sound in Sony MEX-BT2500 stereo

I bought a Sony MEX-BT2500 stereo some time ago, which has a really cool set of features (including Bluetooth and MP3 player) and worked great for me. The only complain was about an awful quality of microphone sound while using my cell phone over the Bluetooth. The other party was always complaining about bubbling and noisy voice, coming from my side, while I had a pretty clear sound from them.

I started troubleshooting the problem and found, that the reason was in technically improper position of a built-in microphone, hidden behind of detachable face (at the right upper corner). I suspect it can only catch low frequencies at this location. I don't know why Sony came up with this dumb decision, but mixing my voice with the sound of engine and air blower make it really horrible.

The first thought was to drill a hole in detachable face, but it turned out, that stereo has the "Eject" button right at this place, so the idea was rejected.

The second thought was to move a microphone into some other position, which would be directly accessible for the voice. Left side of a face plate, which I had to get in order to install stereo into my Nissan Sentra seemed to be a right choice. So, I decided to go for it.

DISCLAIMER: Procedure below describes my experience and is intended for technically experienced people only. I DO NOT TAKE any responsibility for any kind of damages, caused by it. Make sure, you also know, that WARRANTY ON THIS STEREO WILL BE VOID right after you take it's cover off.

Be careful, don't use too much force.

1) Take the cover off by unscrewing (1). You may need to use a screwdriver to "unlock" it from sides to pop the cover off.

2) Unscrew (2) and (3), then you should be able to take a CD reader out. Right after that you will see a microphone at the right side and it's twisted wire, coming across the board.

3) Unscrew (4). Microphone should pop out. Unplug it from the left side and take it out for now. Also, take out a small metal holder - you won't need it anymore. If you leave it inside, it may drop and make a short circuit somewhere, which may potentially burn a whole device.

4) Take a measure of microphone holder and then drill 2 holes in a face plate accordingly. One will be for the microphone diaphragm (5), the other one is for the holder's screw (6).
I used 9/64 and 5/64 drill bits, but cannot guarantee, that you would have the same type of microphone and a holder. Exact location is completely up to you. Make sure you put a thin piece of rubber between microphone holder and face plate to damp off possible vibrations.

5) Put wire through one of the vent holes at the left side and plug microphone back to the board. Make sure this wire won't affect your stereo mounting.

6) Put everything back in a reverse order.

Your callers will notice, that sound from your side became if not perfect, but at least much better, than before.

Juan G Castro Baiz replaced a built-in microphone with an external one, further improving a sound quality

I just wanted to thank you for your detailed instructions on how to make the BT functionality of the Mex BT2500 work. It has a terrible design flaw, by having the mic behind the panel! I bought mine a year ago, and people couldn't hear me, so I found your site and followed your instructions. The hands free feature now worked, but I had to lean towards my dash and speak in a loud voice, as the internal mic has a very short wire, which forced me to place it very close to the radio; far away from my mouth. I wanted to share with you an upgrade I just performed a some minutes ago. I called two friends and they told me they couldn't tell that I was on speakerphone. I cut the internal mic and soldered the wires to a female 3.5 jack which I removed off an old computer sound card. I drilled an 1/4" hole on the back of the radio and placed the connector there. Then, I bought a standard "genius" computer mic which comes with a very long wire. I placed it on the A pillar of my car (a '94 626 Mazda) and routed the cable behind the dash.

The 3.5mm jack has 3 connectors (ground, left and right). As per an instruction sheet I found online, I soldered both L and R to the red wire from the radio, and G to the black wire. The jack I used is 1.1cm deep. Any longer, and it will interfere with a bracket from the CD player, so please advice the readers to keep this in mind when deciding where to drill the metal backplate. I had to erase the radio from my phone's bluetooth list (BB Storm) as it wouldn't connect after reassembling the radio. I followed the procedure to pair again, and it worked flawlessly on the first time...

I am very happy with the outcome, and couldn't have done it without your webpage! A very big thanks from Colombia, South America!