Please help me choose the components for my dodecasub - AVS Forum
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post #1 of 41 Old 06-05-2009, 12:29 PM - Thread Starter
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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.
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post #2 of 41 Old 06-05-2009, 01:13 PM
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In dipole, your internal volume becomes infinite. If you're primarily going to run it in dipole, maybe find some drivers with a fairly high Q and a fairly low fs because the driver's parameters will be the Qtc.

When you say the pentagons came out to 11.625" long, is that each strait edge, or from a strait edge to the point perpendicular to it, or from one point to the longest point across from it (longest part of the pentagon)?

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post #3 of 41 Old 06-05-2009, 02:27 PM - Thread Starter
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Quote:
Originally Posted by Looneybomber View Post

In dipole, your internal volume becomes infinite. If you're primarily going to run it in dipole, maybe find some drivers with a fairly high Q and a fairly low fs because the driver's parameters will be the Qtc.

When you say the pentagons came out to 11.625" long, is that each strait edge, or from a strait edge to the point perpendicular to it, or from one point to the longest point across from it (longest part of the pentagon)?

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.
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post #4 of 41 Old 06-05-2009, 11:37 PM
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your plan seems to be designed around a "design goal" rather than a "performance goal"...as such, i (and many others) will be at a total loss to offer advice.

linkwitz has written on dipoles (but uses a monopole sealed for the bottom end), audio artistry was a company that built on his principles for the most part, but is dead now.

if your goal is a subwoofer flower with a pink cupcake sitting on top, we can't help. if your goal is 125db from 25hz on up, in room, we can readily spec a system for you.

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post #5 of 41 Old 06-06-2009, 05:48 AM
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Quote:
Originally Posted by XJ6 View Post

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)?

Wow, a .28Qts, which equals a .28Qtc is really low. I was thinking something closer to .5-.7. Looking at a few options, Exodus makes an OB/dipole sub with a .76Q that's on sale for $65/ea! (8 for 600)
http://www.diycable.com/main/product...3b97a0bc005797

Ask around to see if this will work for your application, but this should be a formidable driver.

In monopole, your Q will jump up quite a bit. I've not modeled it to see what it'll do, but if it jumps up to 1, 1.1 or over, you'd need quite a bit of eq to mellow things out in the 40-60hz area. I'm guessing it wouldn't perform at all like what you'd want...but that said, Bossobass always builds high Q sealed enclosures and LT's them down to a lower Q, so maybe you'll be just fine.

For amp choices, I've not modeled it, but you can model 10 of whatever driver you choose isobarically (5 pairs of 2) in an infinite box and see how much power it takes to reach xmax. In monopole, your power handling will jump dramatically

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post #6 of 41 Old 06-06-2009, 06:40 AM
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post #7 of 41 Old 06-06-2009, 11:37 AM - Thread Starter
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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.
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post #8 of 41 Old 06-06-2009, 11:45 AM - Thread Starter
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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?
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post #9 of 41 Old 06-06-2009, 11:55 AM - Thread Starter
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Quote:

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.
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post #10 of 41 Old 06-06-2009, 12:09 PM
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That was just mean! I read that whole thread only to get let down at the end That would have been something to see/hear!!!!
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post #11 of 41 Old 06-06-2009, 12:12 PM
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XJ6, I'm having trouble reconciling your description of the design with the comment that it will be a dipole speaker. You should have enough posts now to attach pictures via the "management attachments" button at the bottom. Can you add some drawings or sketches?

Keith
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post #12 of 41 Old 06-06-2009, 05:28 PM
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Quote:
Originally Posted by HornsKeith View Post

XJ6, I'm having trouble reconciling your description of the design with the comment that it will be a dipole speaker. You should have enough posts now to attach pictures via the "management attachments" button at the bottom. Can you add some drawings or sketches?

Keith

The five drivers facing the front are in phase. The five drivers in the rear are out of phase. It's the same as having five drivers on an OB, but this is with 2 motors per driver so to speak.

Another way to think about it. 5 isobaric pairs on an OB.

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post #13 of 41 Old 06-06-2009, 10:07 PM
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Quote:
Originally Posted by XJ6 View Post

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.

i don't recall having seen any dipole subs around here. i forget what his name is but if i recall the brother of one of the principals at audio artistry built some really nice dipole subs around the dayton titanics. they were pretty good looking too if i recall. i'll see if i can find a link for you.

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post #14 of 41 Old 06-07-2009, 06:09 AM
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Quote:
Originally Posted by LTD02 View Post

i don't recall having seen any dipole subs around here. i forget what his name is but if i recall the brother of one of the principals at audio artistry built some really nice dipole subs around the dayton titanics. they were pretty good looking too if i recall. i'll see if i can find a link for you.

I think you're thinking of Monekay. Here's a link to his project age for the dipole you're talking about:
http://www.mfk-projects.com/dipole_s...tanic_mkii.htm

Here's the link to his projects page, it's quite a list!
http://www.mfk-projects.com/my_projects.htm

And a link to his Line Source project page, in the pictures you can see the stacks of dipole subs:
http://www.mfk-projects.com/theatre_main_speakers.htm

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post #15 of 41 Old 06-08-2009, 12:11 AM
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yes lennon_68...thanks! after quite a bit of searching, i couldn't find the build. you nailed it. monte kay.

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post #16 of 41 Old 06-08-2009, 09:59 AM - Thread Starter
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Originally Posted by LTD02 View Post

yes lennon_68...thanks! after quite a bit of searching, i couldn't find the build. you nailed it. monte kay.

Thanks guys. I'll start reading...hmm...after work.
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post #17 of 41 Old 12-31-2009, 08:25 PM - Thread Starter
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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.
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post #18 of 41 Old 08-13-2012, 07:59 PM
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Quote:
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.

Now there's at least one other person who can't put into words the difference between monopole and dipole Dodecasubs!

I built the cabinets on the eD website and the ICIX forums.

We tried to sell them for some time, and they are just weird enough that no one wants to buy any. As you know, the cost is in the drivers.

We tried your option for making pentagons, we discovered that a different method was easier and faster. Your method relies on putting six holes in twelve pieces of wood in exactly the right places. Making twelve pieces is one thing. Making sixty at a time is another.

I strongly recommend two dipole Dodecasubs in stereo. We had two smaller units running a few years back in dipole and it is pretty amazing. I think the work some others have done on velocity vs pressure nodes/antinodes tells the story. In any room you get standing waves at bass and low bass frequencies. Most people only think of the pressure nodes/antinodes. But it turns out that the velocity nodes/antinodes play a big part in bass perception. On-axis, a dipole "fires" a pressure and velocity pulse at the listener. Of course, it's rolled off pretty steeply because it's a dipole. You might have noticed that with ten long-excursion drivers, you've got plenty of output at the box. We cracked the drywall in the old eD offices with the original proof of concept Dodecasub in monopole. ~150dB on a Termlab sensor at ~50Hz iirc. So what, throw away 12dB/octave and another ~20dB for distance and another ~10dB for power compression and you're still in the ~90dB range at 25Hz at 15'.

My latest Dodecahedron. NOT a sub. Custom full range project...

LL

Smaller ones work great for full range use. I got tired of having rectangular prisms around...
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post #19 of 41 Old 08-13-2012, 09:08 PM
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i love the presentation of the dodecasub.

just out of curiosity, is there a relatively simple way to give this sub a cardioid radiation pattern?

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post #20 of 41 Old 08-13-2012, 10:11 PM
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Quote:
Originally Posted by LTD02 View Post

i love the presentation of the dodecasub.
just out of curiosity, is there a relatively simple way to give this sub a cardioid radiation pattern?

Set it on the ground. Rotate it so you can see five drivers.

Wire the five drivers you can see in phase. Wire the five you can't see out of phase. You now have a dipole Dodecasub. It behaves very close to a true dipole (a sphere moving front to back). Most of the time a dipole is approximated using two monopoles a set distance apart, one 180 degrees out of phase.

The size of the cabinet sets the natural frequency, one wavelength around the circumference. Below this frequency the front and rear waves will begin cancelling pretty rapidly with distance. This is why most dipole woofers use H or W frame cabinets, to increase the path length from the front of the cabinet to the rear. On the Dodecasub, we use lots of displacement.
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post #21 of 41 Old 08-14-2012, 10:07 AM
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that arrangement creates dipole radiation. i was asking about cardioid radiation.

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post #22 of 41 Old 08-14-2012, 11:01 PM
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Originally Posted by LTD02 View Post

that arrangement creates dipole radiation. i was asking about cardioid radiation.

Sorry, dipole on the brain.

From vague recollections you get a roughly cardioid pattern from a U frame open baffle.

I've never thought about it but I suppose if you didn't have symmetrical front and rear arrays you'd end up with a field that's not symmetrical.
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post #23 of 41 Old 08-15-2012, 07:49 AM
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Quote:
Originally Posted by LTD02 
just out of curiosity, is there a relatively simple way to give this sub a cardioid radiation pattern?

Using two channels of amplification, one for the front half and another for the rear half, place an adjustable all pass filter on one channel. This won't affect frequency response, but will introduce a frequency dependant phase shift ranging from zero degrees to 180 degrees. Above some frequency, the two halves operate out of phase in dipole fashion. Below some lower frequency, the two operate in phase in monopole fashion. Between is a gradual transition passing through a range of cardioid-like patterns. By adjusting the center frequency and width of the filter, you can control where the transition from dipole to omnipole begins and ends.

Best of both worlds? Maybe. I corresponded briefly with Linkwitz about this topology. The dodecasub may be a great candidate for application of this technique. Never could decide what to call it though.


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post #24 of 41 Old 08-15-2012, 08:09 AM
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Hm. I just realized I have two DCX2496 and two 6-channel amps. Might be time for some test and measurement. I knew I assembled an extra dodecahedron for a reason... I think I even have 12 identical drivers lying around that are appropriate for the task.
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post #25 of 41 Old 08-15-2012, 10:14 AM
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"Sorry, dipole on the brain.
From vague recollections you get a roughly cardioid pattern from a U frame open baffle."

no problem. i was kind of wondering with all those drivers if there would be some way to wire this thing up to create a cardioid. just thinking out loud here, but maybe wire all the drivers in phase except the one on the back or something oddball like that. anyways, it will be interesting to see what you do.

...

interesting idea bigus, so if there were some sort of frequency dependant phase alteration a full range cardioid could be created?

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post #26 of 41 Old 08-15-2012, 01:37 PM
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Originally Posted by LTD02 
interesting idea bigus, so if there were some sort of frequency dependant phase alteration a full range cardioid could be created?
If the phase offset is somewhere between zero and 180 the radiation pattern will be cardioid-like. If you wanted to preserve that pattern you would need frequency INdependant phase shift, ie delay. Just as two monopoles separated by some distance only approximate a dipole source, so too is this case.

IMO, the transition region is a means to an end, not an endpoint in itself. What I've provided is a technique for seamlessly integrating dipole mains and monopole subs.

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post #27 of 41 Old 08-15-2012, 01:43 PM
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"...you would need frequency INdependant phase shift, ie delay."

do you know if there is a way to set that up using the filters commonly employed in something like the dcx or the mini-dsp?

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post #28 of 41 Old 08-15-2012, 03:21 PM
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Deleted my previous post - was thinking a simple delay would work. That's variable phase with frequency too... have a headache at the moment, will have to think about that later.

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post #29 of 41 Old 08-15-2012, 03:23 PM
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If the phase offset is somewhere between zero and 180 the radiation pattern will be cardioid-like. If you wanted to preserve that pattern you would need frequency INdependant phase shift, ie delay. Just as two monopoles separated by some distance only approximate a dipole source, so too is this case.
IMO, the transition region is a means to an end, not an endpoint in itself. What I've provided is a technique for seamlessly integrating dipole mains and monopole subs.

I can put an arbitrary delay on any of the outputs of the dcx.

Interesting concept. I think I'm just going to have to try it.
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post #30 of 41 Old 08-15-2012, 03:25 PM
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Sure, a simple delay. But for normal sub sizes we are talking a couple of feet separation at most, meaning sub millisecond delay granularity/adjustability required.

Delay settings on the dcx2496 are in 1ms increments. Normally used for time aligning drivers in an active array that are vastly different depths from the "baffle" (in quotes because many such setups have separate cabinets for each driver). I use delay on my active 4-ways because the baffles slope and the mid is a dome, so the tweeter ends up about ~2" farther from the listener than the mid dome or woofer cone (an 8" Peerless).
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