multiple mini full-ranges in a spherical enclosure?

[boris81]

So since a sphere is the most preferable sound source why aren't spherical arrays explored? It's obviously costly and complex to build but are there any other factors limiting this design?

I'm proposing an array of small full-range drivers (Hi-Vi B2S) held together in a Dodecahedron formation.

Let's not worry about coverage under 400Hz for now. What I'd like to achieve is:
1. low non-linear distortion.
2. flat frequency response
3. a polar uniformity to at least 5Khz

1) If I understand correctly, playing an array of drivers at lower levels introduces less distortion than playing one driver loud. So my biggest worry in terms of distortion is sealing the enclosure well and damping the inside to make sure internal wave reflections don't come in contact with the cone.

2) EQ can help toward a flat frequency response but I don't have a good understanding of how a spherical baffle with relatively close positioned point sources will interact with each other. I know dipoles exhibit some not very nice effects with baffle interaction.

3) The million dollar question: How bad will directivity in high frequencies be for such a design? Will there be a comb filter effect bad enough to discourage such a design?

Are there any other considerations that I'm not aware of?

[planet10]

Design Acoustics built a commercial dodecahedron, and i have see at least one diy article form the 60s (?).

The general concensus is that the 3" drivers are better in all respects than the 2" drivers.

dave

[boris81]

I considered both and I am leaning towards the 2" because i'm assuming it will handle the high end frequencies better. I suspect it won't beam as much and the FR looks smoother.

Maybe I'm wrong?

[Studio Au]

Heres a cheap solution I stumbled on a while ago, its even in your colour. link below.




Low-cost Spherical Speaker Array

[Don Hills]

Use Google to search for the file "aes102.pdf". It describes the modelling, construction and measurement of a dodecahedron enclosure speaker. The speaker is also used as an example in Akabak, a simulation program used for speaker design. The paper and Akabak are by the same author.

[CLS]

This was shot in a local restaurant years ago. Quite interesting. There're 32 boxes in total. It didn't play when I was there, so no info of how it sounded. Severe diffractions and interferences I guess.

[planet10]

Originally Posted by boris81

I considered both and I am leaning towards the 2" because i'm assuming it will handle the high end frequencies better. I suspect it won't beam as much and the FR looks smoother.

Maybe I'm wrong?

One would think that would be the case... but Zaph's survey of small drivers has the 3" outperfoming in all ways.

dave

[planet10]

Originally Posted by Don Hills

Use Google to search for the file "aes102.pdf". It describes the modelling, construction and measurement of a dodecahedron enclosure speaker. The speaker is also used as an example in Akabak, a simulation program used for speaker design. The paper and Akabak are by the same author.

http://www.wvier.de/texte/aes102.pdf

dave

[boris81]

Originally Posted by Studio Au

Heres a cheap solution I stumbled on a while ago, its even in your colour. link below.

Low-cost Spherical Speaker Array

i have seen this before and i partially draw inspiration for this idea from it. unfortunately the driver positions don't look very uniform and there's no measurements.

Originally Posted by CLS

This was shot in a local restaurant years ago. Quite interesting. There're 32 boxes in total. It didn't play when I was there, so no info of how it sounded. Severe diffractions and interferences I guess.

this is interesting indeed and i'm very curious to know how it sounds. unfortunately i agree that the lack of common baffle will cause lots of problems.

Originally Posted by planet10

One would think that would be the case... but Zaph's survey of small drivers has the 3" outperfoming in all ways.
dave

i understand that the 3" is an overall better driver. i should've mentioned this earlier but the main reason i was looking at the 2" is because i have plenty of spheres on hand of about 5" diameter.
anyway, i will not make a final decision for a driver until i do some preliminary testing.

Originally Posted by Don Hills

Use Google to search for the file "aes102.pdf". It describes the modelling, construction and measurement of a dodecahedron enclosure speaker. The speaker is also used as an example in Akabak, a simulation program used for speaker design. The paper and Akabak are by the same author.

i read the pdf but i still can't get a strong feeling pro or against the dodecahedron model. he says that it achieves an omnidirectional radiation which is what i'm after but he reports a lot of diffraction from the baffle and time smear because of the multiple sources.
the software will be useful to run simulations of different drivers. i'm particularly interested in knowing at what frequency a particular driver becomes uncomfortably directional in this setup. can you guys help me translate the driver parameters that they are using?

|Drive unit, type: Bose B901
Def_Driver 'Drv1'
dD=9.35cm dD1=30mm tD1=11mm fp=4.5kHz
Mms=4.95g Cms=0.6e-3m/N Rms=1Ns/m Bl=2.1Tm
Re=0.93ohm Le=120uH ExpoLe=0.618

[Don Hills]

The answer to the directionality of a driver is, "it depends". The general assumption is that the driver will start to beam noticeably above the frequency where half a wavelength equals the diameter of the driver. So for a 9.35 cm driver, that would be about 3.6 KHz. The frequency at which it becomes "uncomfortably directional" will depend on many more factors.

You can use Akabak to help understand the driver parameters.
Start Akabak.
Select File --> New Script
Above the 'System' line, paste in the data you quoted in your post.
Put the cursor in the middle of the data,
Select Def --> Def_Driver...
A data entry window will open that describes the values.