Fri, 11 Jul 2014 21:12:42 -0400, Ronald C.F. Antony wrote : > There's a laser distance measuring device from Bosch with built in > incline measuring aka electronic level. Not too expensive and useful > for many other things as well. > > http://www.amazon.com/gp/product/B005AZZNXE/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=B005AZZNXE&linkCode=as2&tag=cubiculumsyst-20&linkId=BE6RN3HLUWWGVJYK > > There's also a bundle with an aluminum bar that turns it into a > level, but for this purpose the device tripod-mounted would be good > enough, as long as the tripod head has markings for the horizontal > angles. > > Ronald
The Bosch tool is nice and affordable, but maybe difficult to use. One (overkill) option would be to use a theodolite: https://en.wikipedia.org/wiki/Theodolite Some theodolites have an integrated laser pointer, like the Topcon DT-209L, but it is very expensive. A much cheaper (DIY) solution: a (large enough) dodecahedron made of cardboard could work as a guide for a laser pointer, by cutting holes at the vertices and faces. Inserting the laser pointer in two opposite holes would project a dot in the desired direction. The appropriate laser pointer should be in the form of a long tube; a small laser pointer could be inserted at the end of a tube. Even if not precise, the resulting laser pointer could be rotated to project a circle, its centre being precisely the right spot. In order to register (and remember) the centre position in the room, I suggest to first find its projection on the floor and mark it. Then find its projection on the ceiling using a plumb-line, and attach a hook to later suspend the plumb-line at the same position. Do the same on two side walls, using a level meter, and attach hooks for a string. The intersection of the vertical and the horizontal strings is a reference. On 11 Jul 2014, at 20:43, I wrote: > First you need the angular positions of the loudspeakers from > the listening spot. It shouldn't be too difficult to calculate for > your layout, knowing the properties of the dodecahedron (and some > trigonometry). Angular coordinates are usually required to design Ambisonics decoders. Here's how to find them from the cartesian coordinates: https://en.wikipedia.org/wiki/Dodecahedron#Cartesian_coordinates It's a matter of converting the cartesian ratios to polar coordinates (azimuth and elevation) in degrees, using the arctangent (inverse trigonometric) operation. According to: https://en.wikipedia.org/wiki/Ambisonic_decoding "The coordinate system used in Ambisonics follows the right hand rule convention with positive X pointing forwards, positive Y pointing to the left and positive Z pointing upwards. Horizontal angles run anticlockwise from due front and vertical angles are positive above the horizontal, negative below." So in the picture of the dodecahedron vertices (on Wikipedia), z becomes y and z becomes y. The golden ratio is phi, After conversion to polar coordinates, the angles for the green, blue and pink vertices are: a=31.7 and b= 58.3. The angle for the orange vertices (the cube) is (obviously) c=45. Here's the conversion from cartesian to polar coordinates: For the green vertices (0, +-phi +-1/phi): (90,a), (90,-a), (-90,a), (-90,-a) For the blue vertices (+-1/phi, 0, +-phi): (0,b), (0,b+2*a), (0,-b), (0,-b-2*a) For the pink vertices (+-phi, +-1/phi, 0): (a,0), (-a,0), (180-a,0), (a-180,0) For the orange vertices (+-1, +-1, +-1): (+c,+c), (+c,-c), (3*c,+c), (3*c,-c), (-c,+c), (-c,-c), (-3*c,+c), (-3*c,-c) I hope there's no mistakes; it's easy to double-check... Steve wrote: > Of course, but not sure how easy this may be in practice. > Would I use the first golden rectangle on the smallest plane, and > intersect the others with that. Then use each rectangle corner as a > line from centre until it hits reaches a wall and then mark the > speaker position? The problem I have is the room has a sloping > ceiling, low at front and then high at the back. I would prefer to > extend the angles and attach speakers to the boundaries rather than > build a frame to hold them, as that would use up space and become > an obstruction. It is also easier to attach to walls and ceiling. > I was thinking of having the face of a Dodecahedron on the floor. > This way there will be less obstruction in the room and I will > only have to embed one speaker in the floor (i'm using both the > vertices and faces of dodecahedron). Calculating the positions of the described layout, rotating it to get a pentagonal face on the floor, is left as an exercice. ;-) But I would not recommend it, because it would mean more speakers on the floor, with more possible obstructions from the listening chair and listener's body. Worst: it would make the calculation and placement more difficult and counter-intuitive. I would simply rotate the hexagon by 90 degrees (horizontally), in order to get only two speakers on the floor and two on the ceiling (the blue vertices), on the right and left sides of the listener. The speakers on the side walls would on the pink vertices. The front and rear speakers would be on the green vertices (leaving room for a possible television/computer screen). The other speakers are on the cube formed by the orange vertices, and could be installed further apart. Think of the vertices as elastic sub-layouts; each of them is a valid Ambisonics layout. That said, I don't know how much elasticity is allowed by decoders. > Does anyone know of a simpler and maybe more accurate method? Another solution is to create an irregular layout with three horizontal layouts (middle, upper, lower), with more resolution for the middle layout. > Thanks > > Steve Good luck! -- Marc _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
