Enclosures made of CARBON FIBER laminates ???

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JinMTVT

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Joined 2004
as i am working with carbon fiber right now for R&D purposes ( structural unidirectional prepeg stuff ..
not fenders and decorative products )

i thought about using some CF prepeg + core sandwiches for enclosure ...
i am pretty sure that i can make an enclosure of regular subwoofer size that will take as much power to flex as a few inches think concrete box would ...

all this for probably 1/10th the weight of the wood box


anyone ever used such material ?

the only drawback i'd see, would be the movement of the box on floor when energized because of it's low weight ???? ( could be overcome by fastening it nah? )

just a quikc thought ...


CF used to be really expensive ... now already make alum or balsa core sandwichs with woven prepeg can be purchased quite cheaply ...
 
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JinMTVT

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Joined 2004
my Mirage BPS sub is of push-push arrangement ..

i believe that this is a very good design for control ..
but does it work only good at a certain freq depending on the distance from the 2 drivers??or it works at all freq ? is there any disadvantage to push-push ?
 
J

JinMTVT

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Joined 2004
nice :)

yes of course, carbon wire is very conductive :)


what is the radiation pattenr of push-push drivers?
i am pretty sure i've seen a few graphs around here,
but i can't remember in wich thread ...


is the radiation affected by the distance between the 2 drivers ??


is guess there is not limit to how many pairs could be used side to side on an enclosure
 
planet10

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It is a subwoofer. All subs have an omnidirectional radiation pattern* whether they have 1, 2, or 10 drivers. Doesn't matter what side of the box you put them on either as far as that goes. Within the confines of a house you would be hard pressed to build any practical sub that had the drivers too far apart.

In a push-push sub, maximum benefit is had when the woofers are close coupled, and this is easiest to do if they are in close proximity to each other.

*(not strictly true if one considers dipoles and some of the cardioid pro-subs)

dave
 
planet10

planet10

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buggsson said:
Could you expand a bit on this issue please? More care in what part of the building process?
Click to expand...

You need to design in -- and build -- a structure into the box that tightly couples the drivers.

In this example the horizontal brace and the outer shell work to couple the drivers (2 x CSS SD12):

push-push-SD12-woofer.gif


and this takes it a step or 2 further:

pushpushPR2.gif


dave
 
planet10

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OzMikeH said:
That's easy if you have drivers with vented pole pieces but the large chunk of aluminium would cost as much as the drivers!
Click to expand...

Worse than that the drivers have to be specially made. Note that the basket envelopes the motor (so you don't tear the magnet off when tightening the bolt), and the thru hole is purpose made for this ap -- the designer hates vented pole pieces (and with good reason IMHO)

I was understating "a step or 2 further".

These drivers are in excess of $200 each (if you can find any)

pr2_bass.jpg


http://www.t-linespeakers.org/drivers/pr2_woof.html

Does the threaded rod through the middle have to be non-ferrous?
Click to expand...

I think they were designed with a ferrous bolt in mind.

dave
 
Magura

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Variac said:
CF could probably also work well as a case for a preamp, etc. as it would conduct electricity. So if you grounded it, would be a Faraday cage.. With Neodymium drivers, what a great portable PA it would be!!
Click to expand...


This is actually what I have done in my latest case for a power amp. The beauty of CF is that it is not only electrically conductive, but also sports heat conductivity close to what is found in copper. On top of that you get very fine EMI/RFI shielding, which is about twice what you get from aluminum. All in all a fantastic material, counting out the price that is.

Magura :)
 
J

JinMTVT

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Joined 2004
buggsson said:


Could you expand a bit on this issue please? More care in what part of the building process?

About the original purpos of the thread, what about using alu. honey comb material in between, they would not add that much weight, would they, and they are supposed to be stiff?
Click to expand...


aluminum is really nice and stiff
but i guess that i would go with Balsa for this application since it is not much more heavy,almost as strong and doesn't have the same effect on resonnance and sound than thin aluminnum foils making small close chambers in all the walls of the enclosure

loading the drivers together is not that hard
just make a wood or carbon bar that will be just a tad too long to sit in between the 2 drivers..it should be exercing some good pressure between the 2 drivers then they'll both be tight!!


Dave : what if someone would be to use a few pair of drivers, inside the same enclosure,
will it work correctly or will the multiple source affect the cancellation of the waves ??

so talkin for talking , a push push configuration is one that has almost no drawback other than requiring 2 drivers??does it exhibit any box coloration ?

net pressure within the box is near 0 all the time ?
so no back loading of the drivers?
does it work agains't freenes of the driver to operate, and adds distortion to its movement ?

having 2 drivers of the same size in a sealed box effectivly double the output VS the same sealed box with only 1 driver ??
3db increse ??
 
T

tinitus

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Most quality woofers/subs will have the vented polepiece, so you will just have to remove the dustcap to do this, only problem is that you then wont have the vented through polepiece

Fore easy construction I would mount the drivers on their frontplates and "magnetbaffle" with the connection, and the build the rest of the box around it using screws

I suppose that the connection between the magnet dont have to be aluminium, but could be a box filled with sand, it will just have to be very precisely made and tight around the connection rod, so you dont get sand into the woofer

Remove the drivers to give it a nice finish ... but ofcouse this is with MDF or something and not a sophisticated carbone construction
 
planet10

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JinMTVT said:
what if someone would be to use a few pair of drivers, inside the same enclosure,
will it work correctly or will the multiple source affect the cancellation of the waves ??
Click to expand...

No. Wavelengths are really long on a sub

so talkin for talking , a push push configuration is one that has almost no drawback other than requiring 2 drivers??does it exhibit any box coloration ?
Click to expand...

almost no drawbacks. The beauty of push-push is that it actively cancels most of the energy that would otherwise go into the box and cause box coloration so way less box coloration. You only need worry about changes in pressure in the box.

net pressure within the box is near 0 all the time ?
so no back loading of the drivers?
Click to expand...

No. Both drivers push the air in the box the same way.

If you had the drivers wired for 0 pressure differential you would have no bass (actually an expensive dipole)

having 2 drivers of the same size in a sealed box effectivly double the output VS the same sealed box with only 1 driver ??
Click to expand...

A box for 2 drivers needs to be 2x as big as for one. With 4 drivers 4x as big.

dave
 
planet10

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I would not use the vented pole-piece to try to bolt 2 drivers together. The key with that is the basket outside the motor. The driver needs to be designed for this kind of ap and those are very few & far between.

In practise you build something like the 1st illustration. Taking it a step further would use ready rod as common bolts for the drivers -- i have not yet taken one of these woofers that far.

dave
 
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