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Omnidirectional columns 8 years 3 months ago #9402

I recently designed and built a pair of omnidirectional tower loudspeakers.

They are biamped using MiniDSP for crossover and equalization, inside a custom amp built from an inexpensive class-T amp board.


I have built a fair number of speakers in the past; these are far and away the best yet.

The woofers are Seas L16RN-SL, the same as used in another famous DIY speaker with a similar form factor. The tweeters are Vifa TC6FC00-04, six per channel, arranged on the faces of a hexagon.


Compared to that other famous DIY speaker, they:
  • Have a higher spousal acceptance factor, being made of wood instead of plumbing supplies
  • Are omnidirectional at all frequencies, instead of becoming directional in the highs
  • Are less expensive to build, primarily due to the much lower cost of the amplifier and associated signal processing. The total material cost for a pair is about $750.
  • The amp is easier to build, requiring no soldering
  • The MiniDSP equalizer can also correct for room response
On the other hand, the woodworking is more complicated that the pipefitting necessary for that other speaker.

As you can see from the graph, these speakers measure quite well.


A friend of mine (who has even better woodworking skills than me) is building another pair based on my instructions.

A similar design, with slightly less bottom end and reduced dispersion, could be built for $200 less per pair; I am planning to build such a pair to use as rear speakers for surround sound.

More pictures can be seen at:
www.facebook.com/media/set/?set=a.520392...&type=1&l=faeeb4ecd5
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Omnidirectional columns 8 years 3 months ago #9405

  • john.reekie
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Very nice work! What crossover frequency are you using?
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
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Omnidirectional columns 8 years 3 months ago #9408

I am crossing at 700 at the moment. I also tried 1000 but settled on 700 because it seemed like a zone where both the LF and HF drivers were comfortable. With six HF drivers, none are working particularly hard at the low end.

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Omnidirectional columns 5 years 5 months ago #24783

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These look really nice (woodworking) and I bet they would sound great too (design)!

I'm a huge fan of the TC6 drivers. Bet you could cross them lower, but maybe that's just not necessary?

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Omnidirectional columns 5 years 5 months ago #24801

I'm sure I could cross them lower. The tradeoff is which drivers have to take the power in the midrange. Both the LF and HF drivers sound good through a fairly wide range in the crossover region, and the dispersion is similar for both, so there is a lot of flexibility.

I have also done a version with Silver Flute W17RC38-04 as the LF and 6x Aura NSW1-205-8A for the highs. Also a variant with 4x Aura NSW1-205-8A plus a Dayton Audio AMT Mini-8 tweeter. All the variants sound about the same to me. The AMT version measures better in the extreme high register but I can't hear the difference. Younger people might be able to.

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Omnidirectional columns 5 years 5 months ago #24823

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Having not tried an upwards firing midrange, I was only worried that the orientation of the driver might become apparent with such a high crossover - but then again, 700Hz is what SL uses so I have to assume its OK. To reflect on the theory of why this isn't a problem... Speaker Off Axis and Driver Diameter .

From the datasheet for the SEAS driver, its radiating surface has a 4.5" diameter. That would mean that it is completely omnidirectional (90 degree response is the same as on-axis) up to 475Hz. At 950Hz it starts to beam. At 1900Hz the 90 degree response is -6dB down from on-axis. A LR2 crossover at 700Hz will not cause any problems in this respect.

Plus, the distance between the center of the "jewel" and the center of the SEAS driver appears to be 6", which is within a quarter-wavelength at 700Hz. Nice one!

PS. Those Dayton AMT tweeters really sparkle but its mostly distortion. I have yet to find a use for them...

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Omnidirectional columns 5 years 5 months ago #24829

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Plus, the distance between the center of the "jewel" and the center of the SEAS driver appears to be 6", which is within a quarter-wavelength at 700Hz. Nice one!


Hi, quarter wavelength at 700 Hz is 12 cm. With that said, I'm curious about your observation - is it related to the first half-wavelength cancellation and the crossover frequency, or...?
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?

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Omnidirectional columns 5 years 5 months ago #24832

The center-to-center distance of the drivers is about 5", but one wonders if that is the right way to measure it. With the up-firing driver hitting the sloped underside of the "jewel", the edges of the driver might dominate the wavefront. In that case the measurement is about 4", i.e. 10 cm. In the Silver Flute + Aura NS1 builds, it's even closer, because the jewel is shallower owing to the smaller HF drivers.

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Last edit: by [email protected]. Reason: typo

Omnidirectional columns 5 years 5 months ago #24833

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Oops, my math was a little off there! Yes, its about half-wavelength cancellation affecting the off-axis response (and therefore, the power response).

Anyway, the 1/4 wavelength driver spacing is just a rule of thumb for avoiding off-axis interference lobes around the crossover frequency (where the distance between the LF and HF drivers isn't the same). At a position directly above the speaker (90 degrees off axis), the HF driver is 6" closer than the LF driver. If the two drivers were a half wavelength apart, you would have a complete null at this position.

Since in this case the two drivers are (roughly) 1/4 wavelength apart, they will sum coherently (+6dB) even at 90 degrees off-axis. At one octave higher (1400Hz) where there is a half wavelength spacing, the LF driver is attenuated -12dB, so the null is quite mild and has basically no effect on the power response. Again this null only occurs at 90 degrees off-axis. This isn't taking into account phase shift due to the crossover, but this paper does .

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Omnidirectional columns 5 years 5 months ago #24838

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Ah. Thanks guys, I was jumping on the wrong horse there, thinking about the (horizontal) distance between the various fullrange drivers. It's all very intriguing, I need to think some more about it.
I am not miniDSP support.

"You must ask the right questions." - Dr. Alfred Lanning's hologram.
-> Have you read the User Manual??
-> Have you drawn and posted a diagram?
-> Have you posted a screenshot?
-> Have you posted your config file?

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Omnidirectional columns 5 years 5 months ago #24920

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Great project indeed! Thanks much for sharing with us~!
Is it OK for us to publish it on the project library?
miniDSP, building a DSP community one board at a time.

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Omnidirectional columns 5 years 5 months ago #24961

Yes, please do publish it on the project library. I can supply kits for the hard-to-cut wooden parts that comprise the top "jewel" assemblies.

So far 6 pairs of these have been built by myself or others.
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