Low-cost Spherical Speaker Array

Step 6: Cut and adjust the speaker holes

Again with the dremel cutting bit, cut along the lines you drew in step 5. There is quite a bit of inaccuracy introduced by trying to draw a flat template onto a curved surface. The first hole you cut is going to be too small. Test fit the speaker, and cut out more material where it rubs against the speaker. Don't worry about ragged edges, they will be covered by the speaker flange.

NB: This might be a better time to do step 13.

Comments

[mje]

Actually, any speaker will radiate omnidirectionally at frequencies whose wavelength is greater than 4x the diameter of the speaker. So 4" speakers will radiate omnidirectionally at all frequencies below 2.5KHz. Stil, an interesting project, and one that would make a pair of neat computer speakers.

[mzed]

I think the wavelength of a 2.5k sine tone is only about 13.7 cm, so in your formula a 3.4 cm speaker would radiate omnidirectionally below that frequency. I'm looking here:

http://www.sengpielaudio.com/calculator-waves.htm

A 4" loudspeaker speaker driver would have a diameter of 1/4 wavelength at around 850 Hz. Then,I think there's some further interaction between the driver's radiation and the enclosure in which it's mounted.

But these are details. The important concept that you are telling us is that it would be fine to make this project with tweeters, and pair it with a (single) subwoofer. Not only are speakers not as directional at low frequencies, but our auditory system does not localize low frequency sound as readily.

[mje]

Sound travels at 1000m/s, so an 850Hz tone has a wavelength of 1000/850, or roughly 1.18m. A quarter wave is .295m, or 11.6 inches. You may have made a units conversion error. But yes, it's not a bad idea to do this with smaller speakers and use a single woofer. And yes, you can't really localize a sound with a wavelength that's large compared to the distance between your ears, as you can't detect the phase difference.

[mzed]

Sound travels at ~ 344m/s (which is approximately 1100 *feet*/s) at sea level at 21 degrees Celsius. If you don't believe me:

http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe.html
http://en.wikipedia.org/wiki/Speed_of_sound

[mje]

BTW, the idea of a polyhedral or spherical speaker enclosure is an old one. There have been commercial cabs like this going back to at least the 60s. One of the the best way to make a cabinet "disappear" and appear as a point source is to get rid of early reflections- those coming off the face of the cabinet. One way of doing this is to caver the area surrounding the speaker cone with something that absorbs sound, like heavy felt.

[mje]

You're right, I was wrong, what was I thinking? Mea culpa.