10 speakers in series/parallel? Dodecahedron design.

[crinklecut]

Hi all! I'm a relative newb to speaker building, my only work being refurbishing and swapping out parts of an old Philco tombstone radio to play modern music!

I've been looking to build an outdoor party speaker, and this design really inspired me:

http://www.instructables.com/id/A-Dodecahedron-Speaker-for-Desktop-Printers/

The design calls for 12 8ohm speakers, which once arranged in series/parallel, line up nicely with what seems to be an even balance of power across all the speakers.



The circuit diagram from the instructable

However, I want to modify the design so the speaker can stand on its own two feet, and with a knob/button cluster on the top. This means I need to wire up 10 speakers.

Therein lies the problem - whichever way I try to cut it, I can't seem to get an ideal balanced configuration for power distribution.

What're my options?

• Should I add a resistor to balance things out?
• Will the resistor overheat?
• Is it alright to leave the imbalance of power as is?
• Will an amp rated for an ideal 8ohms have trouble powering a roughly 10ohm load?
• Am I a blithering idiot?

Thanks in advance!

[tyger23]

Re: 10 speakers in series/parallel? Dodecahedron design.

Not sure how you're going to wire 10 speakers to get a 10 ohm load. However, if you do, your amp should be fine.

You might be best off using just 9 speakers. Wire 3 sets of 3 speakers in series (24-ohm load for each set), then wire all three sets in parallel. Total impedance seen by the amp will be 8 ohms.

[crinklecut]

Re: 10 speakers in series/parallel? Dodecahedron design.

Not sure how you're going to wire 10 speakers to get a 10 ohm load. However, if you do, your amp should be fine.

You might be best off using just 9 speakers. Wire 3 sets of 3 speakers in series (24-ohm load for each set), then wire all three sets in parallel. Total impedance seen by the amp will be 8 ohms.

Hi, thanks for the quick reply. The 10ohm figure I just grabbed from the instructables 12 speaker design. Sorry I wasn't being clear.

I'd love to go for an even split with a 9 speaker design, but one of my faces would then be empty. Apart from aesthetics, would that impact sound significantly? Can I get away with it?

[craigk]

Re: 10 speakers in series/parallel? Dodecahedron design.

if the speaker is on a stand you will need one empty space, and with 9 speakers one more is not going to make or break the deal.

[crinklecut]

Re: 10 speakers in series/parallel? Dodecahedron design.

The 10 speaker array already takes into account an empty top and bottom face. There are 12 faces, so an empty top and bottom leaves 10. I guess one empty face wouldn't hurt. I could leave for aux input or something.

On another note, I'm thinking of equipping the speaker with an internal amp and battery. I've done some searching, but I can't quite find a suitably small board that'll support 9x 3W speakers, and run off a low voltage. Any recommendations? Apologies if I'm asking too much.

[Wolf]

Re: 10 speakers in series/parallel? Dodecahedron design.

Ping! cptomes

I bet he'll be able to help you....
Wolf

[MGrant1957]

Re: 10 speakers in series/parallel? Dodecahedron design.

The instructables design has his mount at the apex of 3 baffles. If you keep the dodecahedron, you could mount yours on a pole at the bottom apex between 3 drivers and use your the 3 top baffles or 3 bottom baffles for mounting your input jack, on-off switch, and tone control/whatever. This way you won't be wasting power driving speakers that are pointed up at the ceiling or down at the floor. It would also allow you to use 9 drivers 3 parallel sets of 3 series drivers... I.E. 8 ohms.

[crinklecut]

Re: 10 speakers in series/parallel? Dodecahedron design.

That's an interesting idea. I'll think about that I'm just afraid I won't be able to build a sturdy enough pole/stand for the job. It's meant to be quite rugged for outdoor use.

The idea I had was to have an empty top and bottom face, for button clusters and a stable rubber/silicon base. This would leave 10 facets for speakers.

Taking into account a 9 driver design, I could leave another down facing face empty for input/charging/etc.

My only concern with my idea is if there's any impact on sound quality with one of the drivers not having an opposing driver on an opposite face. Thanks for the suggestion, though!

[blur]

Re: 10 speakers in series/parallel? Dodecahedron design.

You could reach 10 ohms using 10 four ohm drivers. A series of 5 drivers makes 20 ohms, paralleling that with another group of 5 makes 10 ohms nominal. Don't know if this helps...

[joeybutts]

Re: 10 speakers in series/parallel? Dodecahedron design.

Ping! cptomes

I bet he'll be able to help you....
Wolf

Def.

[jhollander]

Re: 10 speakers in series/parallel? Dodecahedron design.

You could reach 10 ohms using 10 four ohm drivers.

+1, also the original 12 plus a threaded rod and 1 inch PVC stand. If your driving with a a battery powered amp may want to consider something less than 10 ohms.

[crinklecut]

Re: 10 speakers in series/parallel? Dodecahedron design.

I'll have to find a suitable amp/speaker pairing! Till then, I think I'd prefer an array of 9 speakers, with 3 empty faces for controls, inputs, stand/base, and a handle. I kinda want the finished product to have a carry-around boombox feel, great for outdoor bbqs and the like.

Are there powerful enough little amp boards for a 9x 3W load? I guess I could place battery packs at the bottom of the unit, resting on the silicon/rubber base for stability.

[ngjockey]

Re: 10 speakers in series/parallel? Dodecahedron design.

Do omni's need BSC?

[jhollander]

Re: 10 speakers in series/parallel? Dodecahedron design.

The PE t- amp in the podzuma would work

http://www.parts-express.com/dayton-audio-dta-2-class-t-digital-audio-amplifier-module--300-385

There’s also a video at PE for using the t-amp
Podzuma link for battery info

http://www.parts-express.com/project-gallery-speaker-project-the-podzuma

3 parallel groups of 3 series- 4 ohms woofers results in 4 ohm.

The will be some BSC as the woofer is not a perfect point source and this not a perfect sphere. I think that’s worthy of measuring as many people are looking for a full range no x-o option.

With an open facet this could get a port… I’m starting to like this project.

[crinklecut]

Re: 10 speakers in series/parallel? Dodecahedron design.

The PE t- amp in the podzuma would work

http://www.parts-express.com/dayton-audio-dta-2-class-t-digital-audio-amplifier-module--300-385

There’s also a video at PE for using the t-amp
Podzuma link for battery info

http://www.parts-express.com/project-gallery-speaker-project-the-podzuma

3 parallel groups of 3 series- 4 ohms woofers results in 4 ohm.

The will be some BSC as the woofer is not a perfect point source and this not a perfect sphere. I think that’s worthy of measuring as many people are looking for a full range no x-o option.

With an open facet this could get a port… I’m starting to like this project.

Those are some really useful links, thanks!

I'm not sure what the impedance of my speakers will be - I haven't found suitably efficient 3" full ranges that fit my budget.
I'm not going to splash nearly a hundred on speakers I don't have confidence will work out.

On that note, how would you suggest splitting the two 15W channels across 3 parallel sets of 3 series?
Any recommendations on cheap and cheerful drivers, even if they're not from PE?

All the help is incredibly encouraging (: I'm glad I joined this community. Thanks loads!