Linkwitz Pluto ... sewer pipe omni-directional loudspeakers

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So many good things has been said about this Linkwitz experiment ...

One say it gets too uncomfortably close compared to Orion Dipole ($8,000 system!). I am curious to see how it will compare to my OB speakers.

Importing a pair of Auras is not an issue ($60), but the woofers are too expensive for me. So I substituted them with a pair of Dick Smith woofers laying around. The base uses paving block readily available in the garden. PVC pipes and rubber coupler are available in Bunnings (Australia).

As usual, breadboard implementation. Easy, no soldering. The electrons don't mind.

Halfway build. Very easy, very cheap. $50 worth of PVC from Bunnings.

Update 13/6/2008 - The Verdict

So I've been living with the Plutos for few weeks now. These are my impressions about this amazing little speakers.

  • First, it is very small and slender. Visually appealing and cocky. I ended up not painting the PVC pipes as the beige colour is very nice.
  • Bass is amazingly deep. But it does not have that dipole speed and transparency. Slam is better than dipole.
  • It sounds lively like a dipole. There is no "narrow" box sound.
  • However they are very prone to positioning. While initially were intended for small room, I found out that they are less tolerant too, which somewhat defeats the purpose. They ended up in my larger living room where they can "breathe" more freely. I found dipole is much more tolerant even in smaller rooms.
  • In summary they sound like something in between dipole and box speaker, with leaning towards dipole.

Update 11/11/08:

Schematics posted on request. This is the same schematics available at LinkwitzLab. The greyed ones are not necessary, assuming you have a pair of stereo amps. I also removed the green ones because it sounds better subjectively without those. The green ones are tweeter phase delay and woofer notch filter. I'm not saying I know better than SL, just what I hear in my setup and my room.

(c) LinkwitzLab

I added a shelving low-pass on the woofer circuit to give deep bass. But can't play too loud (it's loud enough for 5x6m room). No need for subwoofer. Use the non-inverting circuit.
(note: removed and replaced with Linkwitz Transform circuit in next update)

Small clip is available at YouTube. Pardon my digicam's limitations and the fact that they only take 30-second clips.

Update 16/2/09

Revisited the equalization, and modified the Linkwitz Transform down to 20Hz. See design and conclusion here. In short, the low-frequency is extended but room modes issues still exist and manifest in boomy room sound.

Update 8/09

A friend came over to hear the speakers. He was very impressed, in his own words "I didn't know speakers can image like that." Hence, he is currently building his Pluto2 (real one).

Damping is an interesting topic. This is my final damping fill using polyester fibers. There is also an extensive discussion about the topic here. Note that I am using readily-available Polyfill, not the more exotic acousta-stuff.

Update 27/6/09

The pluto "imposter" was demo'ed at SNA Melbourne get-together (GTG). This is one of the comments:

"Now those little Plutos with some tracks had no right to sound as good as they did.Especially with that vocal track by Angelique Kidjo "Blewu" Amazing what you can make with some dunny pipes!!" -Joz

Update 6/8/10

I am on business assignment for a few months in Switzerland. I brought the Pluto clones and their small footprint and light weight make them a great pair of travelling loudspeakers!

Update 2/1/2011

Directivity plot, indoor, normalised at 0 degrees.

The Pluto maintains omni-directional pattern until 4khz where it starts to transition to forward-directional. The transition is excellent with minor widening around 15khz.

Stealth OB

Looks like stealth fighter. Can dissapear.