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Volume Limit mod for Kids BT Headphones
Volume Limit mod for Kids BT Headphones
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Old 30th December 2017, 08:30 AM   #1
felixW is offline felixW
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Join Date: Dec 2017
Default Volume Limit mod for Kids BT Headphones

Hello !

New member here and i need advice !

I have purchased a set of NIA X2 Bluetooth headphones for my kid which are very convenient.

However, my advice for lowering the volume is constantly bypassed, so i would like to mod them in order to decrease the maximum volume to a safest level.

I have disassembled them as you can see in the attached photo.

I was thinking of adding a suitable resistor in line to each speaker's input.

Do you think that it will do the job ?

I have measured speaker resistance and it is about 38Ohm.

Would a 5Ohm resistor suit for a 15% volume drop ?

Or should i connect a larger (e.g. 200 Ohm) resistor in parallel with each speaker ?

Thank you in advance for your help !


Regards,

George
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Last edited by felixW; 30th December 2017 at 09:09 AM.
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Old 30th December 2017, 10:26 AM   #2
brig001 is offline brig001  United Kingdom
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Join Date: Jan 2009
Hello George, you could use a single resistor, but since we don’t know much about the circuit that drives the headphone, better to use an L pad (two resistors instead of one). This will keep the impedance that the amplifier sees at 38 ohms and still reduce the power to the headphone. There are lots of calculators on the internet like L pad calculator - attenuation dB damping impedance decibel loudspeaker speaker voltage divider - sengpielaudio Sengpiel Berlin

I would try 10 dB for a start as this is subjectively half as loud

Hope that helps,
Brian
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Old 30th December 2017, 11:46 AM   #3
felixW is offline felixW
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Join Date: Dec 2017
Thank you Brian !

Very helpful link, i just returned from the electronics store with resistor supplies.

I will try with single speaker first to see if 6db is enough, if i am not satisfied i will increase damping.

Fortunately, she has not realized her headphones are missing, so i have plenty of time to work on them.
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Old 30th December 2017, 05:38 PM   #4
felixW is offline felixW
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Join Date: Dec 2017
The resistors i got were measured 10, 6 and 2.5 Ohm (bought them thinking that i would connect in series)

I ended up with the following :

Attenuation=9.7dB

R1=26 (2x10 + 1x6)
R2=18.58 (1x10 + 1x6 + 1x2.5)

Fortunately, the resistors had space to fit inside the headphone shell.

Now the maximum volume is normal level, but not high enough to damage her ears.


Thank you again Brian for your help !
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Old 31st December 2017, 07:34 AM   #5
brig001 is offline brig001  United Kingdom
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Join Date: Jan 2009
You’re welcome George, glad you got it sorted. I’m sure that your child will thank you in years to come too
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