As the title states, I am having trouble interpreting the specifications for a Bluetooth audio board I have to determine what kinds of speakers I need, or if I need an amplifier circuit between my speaker and my bluetooth audio board.

For reference, the specifications of the Bluetooth audio board I used are here, and the specifications of the speaker that I am using are here.

I'm assuming that the important specifications for the audio board are the sensitivity and the frequency range, and that the only important specifications for the speaker are the resistance and the power rating. But like I said, I have no idea how to find out if they are "right" for each other.

  • 2
    \$\begingroup\$ Look at the pictures at the bottom of the page, any solution with speakers uses an amplifier. That's because the BT module only provides a "line level" output. That has barely enough drive to drive a very sensitive high impedance headphone. It is not powerfull enough to drive any speaker. So yes, you will need an audio amplifier. Stop worrying about sensitivity and frequency range, you don't know what it means and actually it does not matter. Get a cheap amplifier module, it will just work. \$\endgroup\$ Jun 7, 2016 at 14:05
  • \$\begingroup\$ How much power can the BT audio module output? How much power do you need? \$\endgroup\$
    – Andy aka
    Jun 7, 2016 at 14:08
  • \$\begingroup\$ The data sheet clearly states that the Bluetooth module has built-in power amplifier intended for driving small speakers. If you supply 5V power, it is rated at 3 watts into 4 ohms. But that equates to 375mW into 32 ohms. Ref: electrodragon.com/w/… \$\endgroup\$ Jun 7, 2016 at 14:22
  • \$\begingroup\$ @FakeMoustache - I have seen other people not use amplifiers before when trying to do the same thing (most notably this person). So I thought it was a possibility. Andy - The spec sheet says that the transmission power is 4 dbm- but I can't find any specifications that list the output power in watts. \$\endgroup\$
    – Tri
    Jun 7, 2016 at 14:24
  • 1
    \$\begingroup\$ transmission power is 4 dbm That is the RF (2.5 GHz) output power from the antenna. It has nothing to do with audio. Indeed there is an audio amplifier on the board like Richard says but geez, is that hidden in the spec. So indeed you can use your 32 ohm speaker directly with the module but it will not be very loud. For more volume, choose a 4 ohm speaker. \$\endgroup\$ Jun 7, 2016 at 14:29

1 Answer 1


Because the Bluetooth board operates on such a low voltage (3.3V), it needs a LOW impedance speaker in order to produce any useful sound volume. All of the information on the specification page you cited shows using 4 ohm speakers.

But the speakers you are asking about are 32 ohms. Using speakers with such a HIGH impedance will produce very low sound volume from that Bluetooth board.

You do not mention what you are trying to do here? Are you trying to make something that will produce sound that will be heard by many people? In a large room or outdoors? Or are you trying to make your own personal headphones?

Those 32 ohm speakers are more suitable as personal headphones than as "speakers" that will be heard by several people.

  • \$\begingroup\$ Yeah, I'm making personal headphones. If by "low sound volume," you meant that it would be a low volume for big speakers but not too low for headphone speakers, then I think you have answered my question. \$\endgroup\$
    – Tri
    Jun 7, 2016 at 14:28
  • \$\begingroup\$ There is also a "3-wire" output from the Bluetooth module. That output is designed for typical earbuds or headphones which typically have 32 ohm impedance. You may get more sound volume out of the "3-wire" headphone jack than from the differential outputs designed for low-impedance drivers. Or simply select lower-impedance speakers. \$\endgroup\$ Jun 7, 2016 at 14:30

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