Speaker design for portable devices

HiVi M4N with a TN25 and Parallax EmbeddedBlue BlueTooth Board
HiVi M4N with a TN25 and Parallax EmbeddedBlue

Speakers are surprisingly simple yet can be made very complex with the addition of crossovers, self-amplification, and source control.

At Weburban, we decided to come up with the ultimate high end mass production prototype for something that would sound good with a portable device — for example, an iPhone.

We started with a look at speakers. We needed something small in size and wide in tonal range. The HiVi M4N 4 inch midrange speaker looked like the best candidate. We coupled this with HiVi TN25 tweeter at just 1 inch. We were astounded at the optimum box size for the M4N at a mere 0.17 cubic inches.

The passive crossover circuit we used can be seen below. Basically, this high pass crossover removes low frequencies from the sound going to the tweeter. It’s passive, so no additional power is needed other than what is coming from the amplifier. The HiVi has an amazing range so we didn’t think a low pass was necessary. But that might change depending on how muddy it might end up sounding.

Simple custom crossover circuit
Simple custom crossover circuit

I used male/female 0.11. x 0.020 terminals to connect the wires together so I could swap out the crossover if it didn’t sound good. Soldering the crossover was pretty straight forward. Don’t forget to swap the positive and negative terminals on the end of the crossover.

Finished high pass passive crossover
Finished high pass passive crossover

For amplification we ended up going with an off the shelf circuit design for a Tripath battery driven chip amp. It produces amazing sound out of an amp the size of a pack of gum. Stay posted for some pictures of our really rough prototype.

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