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2 Pi tower [message #92736] Sat, 05 December 2020 15:18 Go to next message
rcanglinwastaken is currently offline  rcanglinwastaken
Messages: 2
Registered: December 2020
Esquire
Hey Wayne
I've been enjoying my 2 Pi Bookshelf's in various setups & houses for about 15 years. Thank you for sharing your designs!
I'm thinking about rebuilding them as towers to use in a 2 channel setup w/o sub in a new space. Please send 2 Pi Tower plans.
Re: 2 Pi tower [message #92737 is a reply to message #92736] Sat, 05 December 2020 18:10 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
Messages: 17937
Registered: January 2001
Illuminati (33rd Degree)

You've got mail!
Re: 2 Pi tower [message #92955 is a reply to message #92737] Sat, 16 January 2021 00:43 Go to previous messageGo to next message
rcanglinwastaken is currently offline  rcanglinwastaken
Messages: 2
Registered: December 2020
Esquire
Thanks Wayne! Couple of questions about modifying the tower design (slightly?). 1.) What are the impacts / concerns if I were to make the box narrower & deeper but keep same volume? 2) ...impacts of moving the port from back to the front?
Re: 2 Pi tower [message #92960 is a reply to message #92955] Sat, 16 January 2021 11:13 Go to previous message
Wayne Parham is currently offline  Wayne Parham
Messages: 17937
Registered: January 2001
Illuminati (33rd Degree)

I wouldn't suggest making any change to box dimensions in this model. It "rides the line" between being a transmission line and a bass reflex design. There are both internal standing waves and Helmholtz resonance in play in the bass region, so any changes in dimensions will alter the pattern of internal standing waves and may affect performance.

When I designed this model, I started by using the traditional alignments based on Helmholtz frequency and box volume. Then I used Martin King's spreadsheets to analyze the cabinet's standing wave modes, and the positions of the midwoofer and the port. Then, when I was satisfied with the simulations, I built a physical model and measured that.

This is the subject of several discussions on this forum. You can find some of them in the Pi Speakers FAQ, in the "Cabinet Design" section. Specifically, look at the content in the links called Cabinet design, port placement and internal standing waves, Damping material placement and Altering dimensions.

Basically, this issue potentially affects any physically large two-way loudspeaker, one where the woofer acts as a midwoofer and is used up through the midrange band. Midrange wavelengths are shorter than bass, so the larger boxes start becoming close to wavelength scale. Then what you have acts sort of like room modes inside the cabinet, with hot and dead spots. You don't want a hot spot in the midrange to align with the midwoofer or the port.
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