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Plane Wave Tube


JohnA

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Jon,

I'm not for sure I know what this is, but was thinking that I'd seen something like this in the Bose Bass Cannon. (no joke). It is a 12 inch woofer installed in a 12 inch dia PVC tube.

Is this the kind of device you are thinking about?

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A plane wave tube is a measurement device that provides a standardized air load for testing horn drivers. The response curves shown by manufacturers for horn drivers are almost all made with such a device since most drivers can be used on many horns. It is not meant to be part of a loudspeaker system.

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This is what I found via a quick Google search in "Images"...

High-power plane wave tube. Paul Spranger used to tell a yarn about this

contraption. . .they put a mouse in a cage at the business end, and opening

it after found only a grease spot - t.u.

post-15109-1381928440901_thumb.jpg

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A plane wave tube is a measurement device that provides a standardized air load for testing horn drivers. The response curves shown by manufacturers for horn drivers are almost all made with such a device since most drivers can be used on many horns. It is not meant to be part of a loudspeaker system.

I saw one of these in the lab at the Klipsch plant in Hope. It is a very cool instrument.

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The plane wave tube that I know about is indeed a device used to measure the performance of compression drivers without any horn attached. As the horn modifies the mechanical impedance shown to the compression driver, testing the horn/driver combo does not provide information about the driver alone. The plane wave tube is a long piece of plex that has within it a long, skinny foam wedge. The compression driver is attached at one end and the tube provides a purely resistive load for the driver. In the ones we have, a small diameter measurement mic is placed just in front of the driver, inside the tube. Think about this something like an anechoic chamber for a compression driver. The analogy is not precise but may help convey the concept.

As you can tell, I don't know a great deal about this. But there you go.

I've never heard of the rodent-destroying type of plane wave tube, but a certain bearded engineer here at Klipsch must have.

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I did not notice the foam filling in the PWT in the lab at Hope.

I was hoping I could use one to cause a threaded compresson driver to

throw a laser-like beam some distance. I've noticed the narrow

angle, long throw horns are long and thin. I made the leap to

thinking the PWT might act like an audio laser.

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Well you still need the flare for a long throw waveguide otherwise diffraction at the mouth will effectively widen the polar response.

The key to high directionality is actually a very large mouth...it's the same principal as the beaming of high frequencies on larger transducers. At least that's my limited understanding of it all...

What kind of application and bandwidth are you looking to achieve? Perhaps something like the parabolic wave guides are more along the lines of what you're after?

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