The Talk Box

[TXSidewinder]

In the Process of searching for a DIY talk box online, I discovered two things. Almost no one out there has built a really good one, but also how few people even get the concept of how it works.

Simply put, it's a speaker with no cone in a closed box. In place of a paper speaker cone it has an outlet in the box that moves a column of air inside a tube of some diameter and length. That column of air is pushed into the mouth of the user through the plastic tube. The mouth of the user forms the acoustic chamber and shapes the envelope of the sound while proximity to the tube modulates the frequency range of the sound (to a given extent). Typically, this tube would be attached to the side of a standard vocal microphone. It's the microphone that 'hears' the effect of this, not the guitar. The guitar makes the note, the talk box driver and the tube create the pressurized column of air of limited frequency response and the microphone reproduces the tone the mouth of the user is forming. Depending on the talk box design, the onstage amp may not be affected.

In the simplest design, the talk box is connected like an extension speaker to the amplifier head in the guitar set-up. You send the speaker line from the head to the talk box and back out to the onstage speaker cabinet. An on board foot controlled switch selects the driver receiving the amplified signal from the head. That is to say, EITHER the talk box driver is powered OR the onstage speaker cabinet is powered. I'm sure more complex offerings would have line level in/out capabilities for use in Combo amp set-ups but that's the gist of it.

To build a good one you need to use a good quality fairly large diaphragm driver to avoid blow outs and have reasonable low roll off characteristics. You also need switching that can handle the potentially high output of the amplifier. I would go 3/4" into an aperture of 1/2" and make sure the driver is at least 50W. It's important to also note the impedance of the driver your using. Most horn drivers are fairly high impedance, in the 8-16 ohm range. Be sure not to load down the output of the amplifier if both drivers are engaged. Further to that I would recommend building in a passive choke to prevent potentially damaging low frequencies from reaching your compression driver. Position the outlet tube exactly centered above the compression driverand epoxy a small nylon screen over the outlet opening. This helps keep the gum out. Screw your box together and attach your thin walled plastic tube.

Your ready to 'Doobie-Wah'!

[nochtanseenspecht]

yes nice explanation!
i've been experimenting with this and you need quite a lot of output ,like 50 watt indeed.
it is fun a talkbox