Why do we hear less sound volume when adding more magnets?

[deleted-411499]

We did this below project of making the speakers using paper plates, and we used the neodymium magnets as written in the project description. Once we tested the speakers, we started noticing that the higher the number of magnets used, the less sound volume is generated. Any explanation as to why we are hearing less sound when more powerful or count of magnets are used? Below is the link the project... Any help is greatly appreciated as we are not observing why we are seeing this phenomena. Our Science fair is due this Thursday (Dec 1st 2016), we would greatly appreciate a quick answer/advice.

Thank you.

Finio, Ben. "How Loud Can Paper Speakers Get?" Science Buddies. Science Buddies, 24 Oct. 2015. Web. 27 Nov. 2016 <https://www.sciencebuddies.org/science- ... p101.shtml>

[rmarz]

sohanpavan - Interesting observations. I'm going to make some guesses only on explaining the phenomena you are seeing. Basically, the coil attached to the paper plate, or diaphram, moves as the varying current in the voice coil acts within the magnetic field of the permanent neodymium magnets. The field is extremely strong already, so the voice coil currents are already converting to mechanical movement very efficiently. There is an optimum point where the permanent magnet field, and the moving coil field can react in a most efficient manner. By adding more magnets you are changing the shape of the magnetic field, perhaps reducing the effective movement of the voice coil. In addition, the only way you may increase movement is increasing the current in the voice coil. Have you reduced the number of magnets in the stack? You might even increase sound output for all the reasons suggested above. Just guesses, but probably reasonably correct.

Rick Marz

[bfinio]

Hi sohanpavan,

Another guess with a more physical explanation - for the speaker to work, it's important that the paper tube can move up and down without sliding against the magnets. This will introduce friction, decreasing the movement of the speaker cone and decreasing the sound volume. If the paper tube and magnets are not perfectly aligned, then as the stack of magnets gets taller, the odds that they will rub against each other increase. To rule this out, you could try making another speaker with a slightly larger diameter paper tube, and double check to make sure that it does not bump up against the magnets at all when you assemble the speaker.

Hope that helps,

Ben