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Old 21st November 2014, 03:52 AM   #111
Tesserax is offline Tesserax  United States
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MuddJester, you raise excellent points about stiffness. R. Buckminster Fuller would have had comments about the stiffness (tensegrity etc). When you put these things together out of thin panels they are hilariously floppy until the last couple of pieces go in...then they are really tight and strong.
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Old 21st November 2014, 04:47 AM   #112
oculi is offline oculi  Australia
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Quote:
Originally Posted by Tesserax View Post
Apologies if I misunderstood your post, Oculi. The cuboctahedron is the dual of the rhombic docedahedron. They are easy to tell apart when the RD is non-truncated...but when you square-truncate the RD it can look from some angles like the cuboctahedron.

Cuboctahedron - Wikipedia, the free encyclopedia

Rhombic dodecahedron - Wikipedia, the free encyclopedia
I was going off this photo Click the image to open in full size. which looks like a Cuboctahedron to me, does a Rhombic dodecahedron have zero square faces?

My method (of making a Cuboctahedron wouldn't work anyway as unless you were prepared to do a lot of work (and it looking very untidy) it would end up being a truncated hexahedron.
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Old 21st November 2014, 04:49 AM   #113
xrk971 is offline xrk971  United States
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Hypercube Loudspeakers
Default Foam Core Hypercube with TC9FD

This speaker is perfectly suited for foam core: fast and easy to make, and hardly uses any material. The shape of the speaker uses very little foam core that I think a 30in x 20in sheet could probably make 4 or 5 speakers. I am using the Vifa TC9FD which I know the response of very well in a variety of cabinets. I made the square baffle 4.62in and all the other edges 4.00in. I made 2 patterns: a triangle and a rhomboid then used them to cut 4 triangles and 8 rhomboids, then a square. I added a triple-ply cardboard layer behind the baffle for screws to mount the driver. Cutting the pieces took about 15 minutes, hot melt gluing them another 30 minutes. The speaker was done in under an hour. Like Tesserax says, it is a floppy contraption until the last few panels are glued in place and then it is very stiff. Hot melt glue is the way to go - very fast and easy - only 2 sticks needed.

Here is a photo of the completed speaker - it has a nice flat for resting on surfaces. I wish one of the surfaces would allow it to slightly tilt up, but no luck there. It tilts either down or is level.

Hypercube Loudspeakers-hypercube-photo-jpg

Measurements were made at 0.5m distance, amp is custom TPA3116D2, mic is Dayton UMM-6. Software is REW 5.0 with HP Mini110 netbook. Here is the measured frequency response and harmonic distortion at 0.5m away with no stuffing, there is a resonance peak that is not normally there with other cabinets. I think this looks a lot like a good sealed cabinet, and a lot like the Nautaloss in smoothness, but the Nautaloss is smoother. You have about 4 or 5 dB baffle step loss below 1kHz, and the diffraction effects appear to be minimal:

Click the image to open in full size.

Here is the measured frequency response and harmonic distortion with loose polyfill stuffing - smoothed out some of the peaks and dips. The stuffing really does reduce the harmonic distortion levels though, which are excellent and typical of the TC9FD:

Click the image to open in full size.

Here is a comparison of the response with and without stuffing - the no stuffing case is very similar to with stuffing - not too bad. The cabinet does indeed do a good job of controlling major typical boxiness resonances internally:

Click the image to open in full size.

Here is the response (no stuffing) showing the phase - which shows a dip at 1.7kHz that causes a phase discontinuity because the phase was so close to 180 deg already, the dip is flanked by a couple of large peaks, with the bigger one at 2.2kHz (this level would be audible with certain songs). This must be the cabinet's characteristic resonance frequency. Probably latex caulking and a second layer of foam core for constrained layer damping would clean this right up:

Click the image to open in full size.

Here is the impulse response with stuffing (without looks the same) - very clean:

Click the image to open in full size.

How does it sound? Very nice - similar to the Nautaloss in character, but a lot easier to make. The claim that this speaker does not need any stuffing is valid. I would use it just to reduce the distortion though. I find the sound to be very pleasing and would be great if used in a FAST with a subwoofer crossed at say 200Hz. A fun build, highly recommended! Great desktop speakers to use with a sub.

For reference, here is the TC9FD in a Nautaloss II:
Click the image to open in full size.
Attached Images
File Type: jpg hypercube-photo.jpg (34.9 KB, 2016 views)
File Type: png hypercube-no-stuffing-hd.png (133.0 KB, 1919 views)
File Type: png hypercube-with-stuffing-hd.png (149.9 KB, 1522 views)
File Type: png hypercube-no-stuffing-phaase.png (86.6 KB, 949 views)
File Type: png hypercube-stuffing-compare.png (72.3 KB, 1007 views)
File Type: png hypercube-with-stuffing-ir.png (47.8 KB, 949 views)

Last edited by xrk971; 21st November 2014 at 05:13 AM.
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Old 21st November 2014, 04:59 AM   #114
Tesserax is offline Tesserax  United States
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Oculi, the rhombic dodecahedron normally has only rhombi (12 of them) except when you truncate it. When you truncate back one of the 4-edge (pyramidal) points it makes a square baffle plate. You can see from #113 that the rhombi can appear to be squares when seeing them from a slant instead of straight on.
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Old 21st November 2014, 05:04 AM   #115
oculi is offline oculi  Australia
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Quote:
Originally Posted by Tesserax View Post
When you truncate back one of the 4-edge (pyramidal) points it makes a square baffle plate.
cheers, that explains why the photo looks the way it looks, the baffle looks like a square because it is a square!
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Old 21st November 2014, 05:16 AM   #116
Tesserax is offline Tesserax  United States
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In a word, wow, xrk971. I have never used foamcore and had no idea it was such a fast prototyping material. Obviously I need to get out more often. Can I ask your opinion of what differences, if any, you have noted with speakers in the past between wood and foam core in terms of sound quality?

You can tilt it up though. When I make this shape, I like to situate it so the woofer is facing up at a 45 degree angle similar to the effect caused by the speaker stands I remember seeing. Granted, with light cabinet materials it can be unstable with the weight of the driver tending to roll it if jostled. But the woofer can also be faced parallel to the floor as your picture shows.

Click the image to open in full size.
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Old 21st November 2014, 05:34 AM   #117
xrk971 is offline xrk971  United States
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Quote:
Can I ask your opinion of what differences, if any, you have noted with speakers in the past between wood and foam core in terms of sound quality?
I am biased as I have only made speakers out of foam core (except for one which used a masonite front baffle). I think they can sound excellent if braced, and in some cases, if constrained layer damping (CLD) is used. For CLD, I use 2 foam core layers and latex caulking in between. This can substantially reduce resonances that lead to harmonic distortion. You can see from my measurements that the HD is quite low above 200Hz. Below 200Hz, the foam core can buzz more - but a lot of that is also the driver having lots of distortion due to large cone movement. My tractrix synergy (Trynergy) horns sound amazing:-55dB HD from 200Hz on up and 110 dB sensitivity. Those have to have CLD to work right though.
http://www.diyaudio.com/forums/full-...x-synergy.html
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Old 21st November 2014, 08:23 AM   #118
gpapag is online now gpapag  Greece
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Quote:
Originally Posted by ticovski View Post

The scientific paper is here for those who can comprehend such things (I donít)
http://arxiv.org/pdf/1404.4369v3.pdf


xrk971
excellent 'light-speed' foam service to the community as always

George
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Old 21st November 2014, 10:31 AM   #119
Scottmoose is offline Scottmoose  United Kingdom
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Indeed. Curious thing though -I'm not seeing that big sensitivity gain claimed for it.
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Old 21st November 2014, 10:32 AM   #120
xrk971 is offline xrk971  United States
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Thanks, George.

Thanks for the arxiv link to the teleportation paper. I had not seen this one yet done with solid state crystals and diode lasers - much more amenable to miniaturization for a quantum computer. Back in the day, they did this with complicated Bose Einstein condensates and finicky optical traps.

I like the look of the Hypercube and feel that this project deserves the matching stereo pair. Given that it consumes only 1/4 of a sheet of FC and another TC9FD, and one hour of time. I think it's a no brainer to make two and bring to the office as my desk speakers. It is a great conversation piece if anything.
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