Jub-Like Drone Build (Jubilee)

[Panacea Engineering]

Tom and Jc,

Tom:

1. While I have not used it yet, my DriveRack 260 came with a microphone and Driveware software that I can connect to my PC. I really appreciate the suggestions and I will look at other RTA programs. You are right, NOW is the time to start setting up for testing, as i will more than likely complete the first cabinet today. I will be adding epoxy and 2" Fiberglass tape to all of the joints for added strength and to seal the seams. Hopefully this will give me as close to air tight as I can get. I will be using silicone caulking where the tops and bottoms intersect with the rest of the cabinet and a good grade of gasket material on the hatch covers, top and bottom.

2. The Kappa 3012's that I purchased came with a very thick gasket which gives plenty of clearence for cone movement. I will address the Drone below.

Jc:

1. You are right about the flames, all I was trying to accomplish was to keep this from becomming any type of argument, as I have seen in so many other build threads. It will be best to get everything out in this thread and hopefully we all can come to some type of consensous as the right way to go.

2. I am using the 4-3/4" x 9-1/4" slots for all three drivers. I did make a template that can change this opening but I have not installed it. The motorboard has three equal openings. The ramps really turned out nice and i took the extra time to sand them smoothe. The Drone ramps are identicle to the other two drivers.

3. You, of course are right, the Drone is the main subject and what will drive the tuning. I had to build a "ring" so to speak to allow the cone movement. It is a 1" spacer that lets the Drone have full movement of the cone so it will not be banging the motor board in extreme excursions. I was surprised at the amount of cone movement on the Drone/Passive.

4. I think djk suggested to start with 400 grams of weight. To me this seems to be a lot and i have a fear of doing damage to the KP-12 with that amount of weight. But, like you, I have never tuned a Drone so I will have to rely on other's suggestions. It would be nice to see some type of weight to frequency chart if one even exist to get a starting point. I totally agree that the drone should be tuned down to at least 30 Hz, if this requires 400 grams, so be it.....

5. I will go back and re-read the 260's manual today, as I have not used them since the event last May and I set the parameters up sometime in March for the MCM's. I have several options for testing...I can test in my HT room as I know the accoustics are pretty good there or I actually set up a seperate room for just this one speaker. Also, can do testing outside but the noise level sometimes gets hectic as I am very close to the airport and right next to (25 feet) from a major NS rail line. Of course, I do know the train schedule as it even affects the inside of my building. Talk about LFE let a 150 car 20,000 ton train come by at 25 feet and see what you feel. They are true building and ground shakers.....!

Thanks for all of the input and keep it coming,

W. C.

[PrestonTom]

WC,

Quick question during my lunch. I now notice that you are not using the K-31 drivers, but rather the Kappa 3012.

If it is handy, could you post the following T/S values for that driver.

Vas

Qts

Fs

These would be on the data sheet for the driver. I just wanted to do the calculation for the throat area and back volume. Nothing urgent...

-Tom

[Panacea Engineering]

Tom,

Here is the Eminence PDF: http://www.eminence.com/pdf/Kappalite_3012LF.pdf

Vas = 106.65 Liters/3.77 cu/ft

Qts = 0.32

Fs = 37.02 Hz

Hopr that helps.

W. C.

[DrWho]

At small signal levels, there are 3 main design parameters to consider when tuning a passive radiator:

1. Mass
2. Suspension Stiffness
3. Self-resonance

Classically, a passive radiator uses a suspension stiffness that is
equal to the impedance of air moving through a port, and then the moving
mass is equal to the mass of that trapped volume of air. In the real
world, the moving mass is much greater than the trapped volume of air,
so the suspension also needs to be a lot stiffer (which it is). This has
the effect of increasing the Q of the resonance.

Also, the tuned
passive radiator will naturally want to vibrate at a certain
frequency...which means it takes very little external energy to get it
to vibrate at this rate. Because the front and rear pressure of the
active driver are out of phase, this causes the passive radiator to
create a big suckout at its natural resonance (keep in mind that this
natural resonance is different than the "port tuning" of the passive
radiator).

With this in mind, it is important to keep the natural
resonance of the system much lower than the passband you're interested
in. Adding mass to the passive radiator pushes the Fs lower, which is
important to keep in mind (since the stock TC Sounds passives have a
relatively high Fs). I would try to keep the Fs a minimum of 1 octave
below your intended tuning frequency. The lower the better though.

When
buying passives off the shelf, you're pretty much limited by the
suspension stiffness that the manufacturer chose. This means that the
only tuning you can do is by altering the mass on the passive...

Increasing the mass on the cone causes the tuning frequency to move lower, but also causes the Q to increase.

You can also modify the tuning of the passive by changing the volume of the rear chamber. Two things are going on here:

First,
the rear volume acts like a capacitor, which means it takes time for
the rear wave of the active driver to increase the pressure in the box,
and then it takes time for that pressure to cause the passive radiator
to move (inductance). The goal here, is you want the motion of the
passive radiator to be delayed by 180 degrees of phase - which is needed
to get the inverted polarity of the rear wave in phase with the next
cycle of the front wave from the active driver. When they're in phase
and equal in amplitude, you'll get a perfect +6dB of summation at the
tuning frequency. You can actually get more than +6dB from a
vent/passive radiator, but then it takes more than one cycle to ramp up
the motion of the passive radiator.

Secondly, there is also the
propagation delay of the pressure generated by the active cone itself.
So if the rear enclosure were infinitely big such that there was no
capacitance from the trapped air, then the passive radiator would still
get moved by the pressure wave eminating from the front and rear of the
active driver. If the passive radiator is acoustically close to both
sides, then the passive radiator moves opposite of the active driver -
this behavior is why you see the response fall-off below the tuning
frequency faster than a normal port: it's basically a big hole in the
box.

The reason I bring up the propagation delay is because the
pressure in front of the passive radiator is going to be higher in a
horn than in a normal vented box. The "pressure" or acoustic impedance
in front of the driver is going to be a function of the compression
ratio (size of the slot) and the acoustical load presented by the horn.
Because the mouth of the horn is undersized, you get reflections
travelling back down the horn which will create a time-varying
(frequency varying) acoustic load on the passive radiator (it also
affects the active drivers too).

Increasing the acoustic load on
an active driver makes the active driver more efficient because it gets
to push more air. Imbalancing the acoustic load on a passive driver will
cause it to move. Also, if the passive driver is close to the active
driver, then the motion of the passive is going to change the acoustic
impedance seen by the active driver. All that to say, the reflected wave
travelling back from the mouth of the horn is going to be time-delayed,
and cause the passive radiator to move. It is for this reason that I
believe you need to play games with the phase/propagation timing from
the rear wave of the active driver as it pertains to the timing of the
reflected wave from the mouth of the horn affecting the motion of the
passive radiator. Ideally, you want the passive radiator trying to
offset pressure reflection from the mouth of the horn.

In the
Jubilee design, the rear volume is fixed, and then the suspension
compliance is only adjustable by choosing different passive radiators.
This means for a given bandwidth, there is going to be very little fine
tuning available as it pertains to the effects of the varying acoustic
impedance presented by the horn. Getting the passive radiator to tune
without the horn is a piece of cake, and is where I would start by
trying to figure out what mass to start with. However, what I think you
will find is that either the passive radiator causes less LF output,
and/or you will see a dip in the response just above the tuning
frequency.

Roy had access to changing both the mass and compliance
of the passive radiator - and could have even modified the rear volume
if he wanted to as well, but wasn't able to get the drone version to
offer the desired performance enhancement. I don't know if this is
because he didn't have enough time to spend on the project, but my gut
feeling is that it has to do with the size and logistics of the rear
volume. The math of a vent into the throat of a horn is actually very
similar to the math behind a tapped horn, and what you find in the
tapped horn is that the phase of the rear wave from the active driver
has a complicated interaction with the front wave. When using a passive
radiator instead, you have an LC time constant providing a phase
rotation that shifts with frequency, but you also have a low passing
effect which reduces the cancellations you normally see in a tapped
horn.

In other words, if you could magically increase the distance
between the active driver and the passive radiator, then you could
account for the delay of the mouth reflection.

Anyways, I'm just thinking out loud.

Btw, re the braces....I
may have seen a prototype where the braces were streamlined. I do know
the production of the Jubilee was modified to now have totally different
braces that are much longer and fill more space in order to make it
easier to build. It's like small shelfs now instead of just bracing if
I'm remembering correctly.

[Guest " "]

I would focus less on the power handling and more on the frequency response and the FS spec's. 46hz as a useable bottlemend on this driver makes putting them in Jubilee's point less and an fs spec of 37hz would make the drone a non participating player. The 3012lf starts to dip at 100hz and by the time it gets to it's usable bottom end it's down 20dbs. That makes the spl at 46hz about 75db's,

Tom,

Here is the Eminence PDF: http://www.eminence.com/pdf/Kappalite_3012LF.pdf

Vas = 106.65 Liters/3.77 cu/ft

Qts = 0.32

Fs = 37.02 Hz

Hopr that helps.

W. C.

[jwc]

I would be interested in seeing what the 3012LF does.

The K31's are available to you when you feel you want to mess with them.

Again.....I would love to hear the GPA drivers in there. They spec out to that horn "well". Such as annul and throat "requirements". It doesn't have the SPL of the K31.....but worth trying...esp for this drone/jubelike.

http://www.greatplainsaudio.com/downloads/3124.pdf

jc

[Panacea Engineering]

Mike,

Thanks for your very detailed explination and I truly appreciate your expressing it in terms that I understand. If you wrote that from scratch I am truly amazed at the level of detail that you included. I certainly have no doubt that you did. If you will keep this level of participation I will feel more comfortable in this undertaking and i am ready to try all of the combinations that WE can come up with to see if this is a workable project. Time will tell and I am certainly in no hurry.

Thanks again for your valuable time in trying to help me understand the operations of the Drone/Passive,

W. C.

[Panacea Engineering]

Fritz,

Power handling was never part of MY equation on choice of woofers. These were reccomended and I found them on a great deal. I am sure that if they do not work in this application, they will be used elsewhere or at the very least, I can recover my investment on eBay. Thanks for your input and if you have speaker suggestions for this application, please feel free to advise.

Thanks for your time,

W. C.

[Panacea Engineering]

Jc,

I'm certainly not adverse to ordering a couple of the GPA's for testing purposes. At this point it looks like we are going to need to try several drivers to find the (and I use the term very lightly) Perfect combination for this application.

Is it the general thought that the K-31's are the best speaker for this?

W. C.

[DrWho]

Is it the general thought that the K-31's are the best speaker for this?

Well
the K-31's are a known reference point that performs very well. To my knowledge, I've
not seen any other drivers compared so it's hard to say "best". They
are definitely very good.

If you'd like, I've got a pair of B&C 12NDL76 drivers that you could borrow too:

http://www.bcspeakers.com/product.php?id=178

As far as measuring, how in depth were you planning to go? Basic
impedance and frequency response would be big first steps, but it would
also be interesting to see some distortion comparisons too.

Btw, I
believe the latest hornresp has some tools for predicting the response
when porting into the throat. Extrapolating those predictions into a
passive radiator tuning should be relatively straightforward. Life has
been very busy lately (so much so that I've not been on my home computer
for several weeks now), but when I have time, I would be willing to
crunch the dirty numbers and at least help you get into the ballpark -
or at the very least, if we can predict the outcome, then we can
validate the simulation if it doesn't turn out as nice as we might hope.

It might also make sense to start with a way simpler horn that makes
all the modifications way easier to deal with (like varying rear chamber
volume, easier swapping of drivers, variable injection point into the
horn, varying rear pathlength, etc...).

[Edgar]

Well
the K-31's are a known reference point that performs very well. To my knowledge, I've
not seen any other drivers compared so it's hard to say "best". They
are definitely very good.

...

Btw, I
believe the latest hornresp has some tools for predicting the response
when porting into the throat.

A basic Jubilee Hornresp model can be found here. I haven't experimented with porting into the throat, so you're on your own there.

Also, attached is a hornresp.dat file (I had to append ".txt" in order to attach it; just remove that) containing data for several 12" woofers, for your simulation pleasure.

Greg

Hornresp.dat.txt

[Panacea Engineering]

Mike,

I am certainly open to any suggestions. One question is, if we steer away from the basic jube design, how will we get accurate information since the horn folds the way it does. i am at a stage that the dog house volume can certainly be adjusted but this will also affect all of the other deminsions unless I am missing something. Are you talking about constructing a simple three fold box? If you are talking about porting out of the dog house, that can also be accomplished as i have not glued anything yet except the ramps and parts B, D and E. Everything else has been aligned and screwed but at this point I have not glued anything further so this gives US a lot of flexability.

As to the use of your speakers and also Jc's 31's, I will be more than glad to pay the shipping both ways to get the use for testing as i feel that this experiment will certainly be benificial in the future. hell, we may come up with something great...! I use the term WE as this is a community build, I just have the time and tools to be able to experiment. I just ordered another twenty sheets of the baltic Birch as I have a few other cbinets I want to build. I also want to replace my center La Scala with a custom built Belle to fit my entertainment center.

As to the ease of geting to the speakers for changing, I am going to have hatches on the top and bottom so access should be "Kinda" easy. The center Drone will not be as bad as I thought as long as the woofer on either end is removed for access. I will be cutting the top and bottom tomorrow.

If you guys have the patience for all of the testing that needs to be done, I have the time and resources to make it happen.

Hope all of that made some sense. Anyway, here is the template for the top and bottom.

[PrestonTom]

WC, you may have mis-interpretted what Mike (Dr Who) was advocating. My 2 cents is don't try and change the back volume. The Jubilee has a volume of 37 liter per driver. My impression is that the protype drone build had a comparable volume. As you have noted, trying to change the back volume would change too many other things. Personally I would not do anything that alters the back turn. I believe this turn is critical to getting the bandwidth that the Jubilee has (that is another discussion).

One trick to make the back volume "appear larger" is to add open cell foam to cavity. The effect wil not cause huge changes, but it will help and its effects can easily seen when you make the impedance measures. The production model has foam in the back cavity for instance.

[Panacea Engineering]

Tom,

I understand about the "stuffing" effect to increase aparrent volume. I really am not planning on changing anything structural to the design. I am just at a point, if everyone feels strong enough about it, some minor changes could be incorporated in the design. The jube Like drone will be built as origionally designed.

I may have missed something but i thought Mike was speaking of building just a relatively simple box with adjusted volumes for testing purposes only. That is something that can certainly be done relatively easy.

Anyway, tomorrow is the day for the tops and bottoms.

W. C.

[jwc]

What you are doing is perfect for the start. Equal ramps for the drone and the actives and same sized slot. Don't change a thing....march forward. Can't wait to see more pics.

jc

[michael hurd]

Whoa, just reading along here, and if you haven't planned for using the TC Sounds VMP passives, they have a VERY different frame size than anything else on the market. They use the LA style ( Lightning Audio ) frame, that was built from the ground up to accomodate high excursion. The industry standard 12 spoke baskets are smaller in diameter.

If you can wait a day or so I can get you accurate measurements of my LA 12" frame, otherwise check the Parts Express website link, or call their tech line. I see you already have T-nuts in place for a frame, but they won't be in the right place for the TC Sounds frame. Sorry for not catching that earlier, and letting you know.

Here's the frame specs: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=293-680

If you need more accurate measurements, I can take one to work and measure it. ( 12" LA basket )

[seti]

This is very exciting....! ! ! ! ! It will be interesting to see test results for all the different drivers in the LF.

[michael hurd]

I just dug up some more info on the VMP baskets, the bolt circle is 8 on 11.7 inch diameter, ( radius is 5.85 inch ) and the holes drilled in the basket are .220 inch before powdercoating. They are designed to be used with the internal hex screws supplied, and they work well. You would have to fashion up a gasket and a spacer for rear mounting.

Hope this helps. The surround should fit through the same size hole as what the rear of the basket cut out is ( 11.16 inches ) but if you need a more accurate number, I can measure it for you.

[Panacea Engineering]

Michael,

I would have to make a 2" adapter ring for it anyway so not to worry about the T nuts installed. I'm more concerned about the depth and if it will even fit in the dog house. At 12.6" diameter that only leaves 1/16" clearence for the basket and with a 2" adapter I don't know if it will be enough room to install it with the angles of Parts F. Part E is only 4-3/4" inside. It looks like the back side of the "Silver" frame may be an issue. That would be the measurements that I need, the diameter and depth of that part of the passive.

Thanks,

W. C..

[Panacea Engineering]

How about some thoughts on this pasive. Says it has a max moving mass of 1200 grams, fully adjustable.

http://www.solen.ca/pdf/css/apr.pdf

Has anyone used Jeff Babgy's software to design for passives? Here is some information from the Pats Express Forum:

http://techtalk.parts-express.com/showthread.php?t=209863nt

I am on a hunt to find some type of information on tuning the passives. If someone has any ideas it would be a great help. The above APR 12 will take up to 1200 grams and can be loaded from the front. It may be easier to add or subtract weight by removing the front panel rather than trying to reach down through the top hatch. Or a possibility would be to add a front access panel in front of the passive that will just remove the splitter for the passive....Just some thoughts