Please help me choose the components for my dodecasub

Greetings to all,

I am a noob to DIY subs, but an adventurous one. I have looked at tapped horn, sonotube and other types but a dodecasub is just so strikingly appealing to me and therefore I have decided to build one. As you can see, achieving the max SPL and the lowest octave is not necessarily the goal here. But the question is rather how to get the best performance out of a dodeca box. May I please get your kind help in choosing the drivers, the equalizer and the amp to complete my build?

As far as building the box, I spent/waisted the 1st weekend "working out a procedure" to cut the pieces w/o any success. The 2nd weekend was a total success as I was able to cut 14 (only need 12) perfect pentagons which were 99.9% identical to each other and with the beveled sides being 99.9% accurate. This weekend I am planning to make the holes for the biscuits and cut the braces that are needed for assembling the box. I will then be able to do a dry fit and see what the box looks like. I have cut - and can now easily cut - the pentagons using ONLY a $100 table saw from Home Depot (and of course, a cordless drill and a hammer). If you're interested in seeing how I did it please show me how to attach pictures and I will show you how.

Anyway, the next step is where I need your help. The internal sides of the pentagons came out to be 11 5/8" long (external is 12 1/4") which gives an internal volume of 6.97vt^3 or 197L. If I were to use 10 eD 11kv2 they would occupy roughly 52L and the net volume would become 145L. The Q (...uhum...according to my noob calculations) will be 0.66 with an Fc at 58.4Hz. Please note that in a dipole configuration there will be a steep 12dB/oct roll-off at this 58.4Hz Fc. In choosing the components I have 3 questions for you:

1) the drivers: I have my eye on the 10" 11kv2 because this is what eD is installing in their D1. Are there any other drivers that give me better performance/price ratio and also better other factors (whatever they are)?

2) the amp: is the popular EP2500 what I need/want? How will it integrate with the choice of eq below?

3) the Eq: this is where a noob like myself gets hit hard. First, I know I have to compensate for the 12db roll-off at Fc so do I absolutely have to have an LT? Second, do I also need an SSF (or HP?) and/or LP? I ask about LP because my pre/pro sends out the full range signal when it does LFE+mains. Is the DCX2496 or DSP1124P or SMS-1 what I need/want? Are there other choices?

4) amp with built-in eq: can I use something like a Dayton 1000W instead of the combo from 2 and 3 above? Can this amp's built-in eq satisfy my requirement to fight the 12dB roll-off?

Anyway, please help me put the puzzles together and educate me wherever you can. Also note that the sub will be running in dipole almost all of the times. But sometimes I would also run the sub in monopole (maybe with just 5 front drivers?) to get a different kick out of it so the 3 choices will have to support this option, even if it's not a high priority one.

So please start the suggestions and comments. Thanks.

Thanks for replying; it is so thrilling for a noob to get the first response

I see, with an ~infinite volume the driver's Q becomes the system Q. So, with Fs in the mid 20s, for example, the sub will just need a little boost in the low end and an LT will NO longer be needed? Could you, or anyone, please give examples of 10" drivers with high Qts (> 0.28) and low Fs (<24.8Hz)?

With that said, the choices for #2 (amp) and #3 (eq) are still there to be made. Pls help me out.

BTW, 11.625" is the straight edge, of the internal surface. I am using 3/4" MDF and so the external straight edge comes out to be 12.25". The smallest width of the box - which is the distance between any 2 opposing surfaces - will be 27.25" and I think that will fit thru a standard-size door. I've got a spreadsheet with ALL the geometric parameters for pentagon and dodecahedron but I don't know how to post it.

Thanks again.

Thanks for replying LTD02. I certainly agree with you on the 'form follows function' part. But, FWIW, due to WAF my semi-big box will also have to look good. So, if I said I had a ~7ft^3 box that I would like to run in dipole and I was looking for help on choosing the components for it, would you be able to help then? BTW, the pieces of incoherent pieces of info I threw out on the 1st post are prolly more confusing then providing background info. So please just discard them and assume I know nothing. Thanks again.

Looneybomber,
That is an awesome suggestion on the DLP10 and I have made inquiry to them. Thanks.

Meanwhile, if we forget about monopole then what would be a good software to do modeling on dipole?

Thanks for the link. I've spent quite a bit of time reading over there at icix. Tough part for a noob is the pieces of info are there but scattered everywhere and it's hard to filter out what you need or don't need to know. Guess that's why a lot of people would go with a popular and proven design.

Thanks guys. I'll start reading...hmm...after work.

Hi all,

Sorry for bringing up an old thread but I just wanted to give it a closure.
The dodecasub has been finished for almost half a year and I am finally
finding some time to collect the pictures and describe the build.

On the equipment side, I ended up with ten Exodus DPL-10 drivers, an
SMS-1 for eq and an EP2500 for power. The drivers were 10lbs each and
the box weighed in at some 40lbs, so the total was a little bit below 150.

As far as wiring goes, the drivers were divided into 2 groups of five. The
fives within each group were wired in parallel giving a nominal impedance of
1.6ohms and putting the 2 groups in series resulted in 3.2ohms. The leads of
the 2 groups were connected to a set of 4 spring-loaded connectors so that
I could easily switch between dipole and monopole (by shorting out different
pairs of connectors) in like a minute.

Fortunately, my pre/pro had balanced sub-out so there were no problems
hooking up the SMS-1 and the amp with XLR cables. The finished sub is still
in its temp location today, but I did eq it for both dipole and monopole
configurations. The SMS-1 came in real handy as it was so simple to
operate and I could just use preset 1 for monopole and preset 2 for dipole
(=> no mix-ups). It also had discrete remote codes so integrating it into the
system was a breeze. BTW, the sub is cross-overed at the customary 80Hz
point.

01 Ten Exodus DPL10s


02 Dodecasub in temp location


As far as performance goes, in dipole, it sounds gorgeous! "Gorgeous" is
because the low bass is just so tight and clean and very non-fatigueing.
There is plenty of bass and no boominess at all. In monopole, though, the
slamming and authority really come in and I could feel the vibration in my
marble coffee table. I've been leaving it in dipole most of the time. For the
occasional gatherings, I set it to monopole as my friends like to see things
get a pounding. Once I've made some room on the left wall I can move it
there and hopefully find the optimal spot to make it sound even better then.

Coincidently, the Exodus DPL-10's have now been lowered to $45 apiece. I
might just build one more for my other room or whoever wants it.

Anyway, I am gonna go ahead and explain how I built the box. To be able to
repeatedly cut 12 identical pentagons with slanted edges I had to device a
jig. The picture below shows what it looks like.

03 Jig on wood to be cut


The jig looks like a pentagon itself but it does not have to be (it was just the
result of my prior failed attempt at cutting a pentagon). Its main features
are the 2 holes (1 at center and 1 at corner) and the guide (the strip of
wood). The wood to be cut will have 1 center hole and 5 corner holes. The
idea is to stack up the jig and the wood, insert a pin (a nail, really) thru the
centers of the jig and wood, a 2nd pin thru the jig's corner hole and one of
the wood's corner holes. Run the stack of jig+wood thru the table saw and
cut a side of the pentagon. Move the 2nd pin to another corner hole and
another side of the pentagon can be cut then repeat the process. The
next shots show the hole markings on the wood and how it's run thru the
table saw.

04 Nail holes on wood to be cut


05 Cutting the wood


06 Cutting the wood Close-up


To mark the holes on the pieces of wood to be cut you can use a paper
template. How well you draw a pentagon on the paper template will decide
the precision of your work (I actually double- then triple- checked the
markings). Also, jig's guide has to fit the slot on the saw really well so things
won't wiggle when running the wood thru the saw blade.

Well, before anything can be cut the saw blade has to be tilted at the
correct angle. The dihedral angle (the angle between 2 pentagons) is
116.565 deg so the tilt will be 58.28 deg. The next pictures show how that
was accomplished. Notice I use the straight yellow ruler to extend the
radius of the blade, and tilt the blade until there is no gap between the ruler
and the angle paper.

07 Setting saw blade angle


08 Setting saw blade angle Close-up


Once the tilt is set (and tightened really hard) all the pieces should be cut at
once. I cut 2 extra pieces just in case and that was a good thing. It only
took me about 2 hrs to cut 14 pieces.

09 After 2 hrs of cutting


10 The aftermath


Then I proceeded to make the biscuit holes and 30 braces out of 1x4 wood.
The braces were needed during the glue curing process because how the
heck would I clamp this dodecahedron thing? Anyway, #10 biscuits were
about right for this job and 2 were used on each side.

11 Making biscuit holes


12 Biscuit holes and braces


Before the drivers arrived I couldn't help but try dry-fitting everything:

13 Dry fit 1


14 Dry fit 2


15 Dry fit 3


During the wait, I went ahead making the feet, drilling the connector holes
on, and painted the bottom piece. Eventually, it was time to assemble the
box and I enlisted a buddy's help. Within 20mins we had to glue 2 halves
separately and then glue them together. This is what it looked like 12 hrs
after glueing:

16 Box assembled with feet


Honestly, there were some gaps in a few of the seams so I just ran the left
over glue on all of the inner seams to plug the gaps. On the outside I just
used wood filler. The braces were also removed because I reckoned they
would be a liability more than help. The next few evenings and a weekend
were then spent to apply 2 coats of primer, 2 semi-thick coats of paint and
2 very light coat of spay-polyurathane. The sub was going to be used in a
projector/screen room so I wanted an orange-peel look and did not want it
to be shiny at all. Prolly these are the least interesting pictures:

17 Box primed


18 Box painted


I've been thinking about buying/making the grilles for them but not gotten
any good ideas yet. If you know of an economic way of buying/making ten
grilles please let me know.

Again thanks to those that have helped and a big Happy New Year to you all.