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Old 21st August 2007, 07:44 PM   #11
JinMTVT is offline JinMTVT  Canada
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i would have to dig it up ..
we make our sandwiches and all ourselves ...

i'll try and get my bookmarks from the shop
see if i can post a few here
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Old 21st August 2007, 08:48 PM   #12
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Quote:
have to take a bit more care in the build to maximize the benefit.
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?
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Old 21st August 2007, 09:32 PM   #13
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Quote:
Originally posted by buggsson
Could you expand a bit on this issue please? More care in what part of the building process?
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):

Click the image to open in full size.

and this takes it a step or 2 further:

Click the image to open in full size.

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Old 21st August 2007, 11:01 PM   #14
OzMikeH is offline OzMikeH  Australia
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That's easy if you have drivers with vented pole pieces but the large chunk of aluminium would cost as much as the drivers!
Does the threaded rod through the middle have to be non-ferrous?
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Old 21st August 2007, 11:20 PM   #15
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Quote:
Originally posted by OzMikeH
That's easy if you have drivers with vented pole pieces but the large chunk of aluminium would cost as much as the drivers!
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)

Click the image to open in full size.

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

Quote:
Does the threaded rod through the middle have to be non-ferrous?
I think they were designed with a ferrous bolt in mind.

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Old 21st August 2007, 11:27 PM   #16
Magura is offline Magura  Denmark
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Quote:
Originally posted by Variac
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!!

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.

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Old 22nd August 2007, 02:26 AM   #17
JinMTVT is offline JinMTVT  Canada
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Quote:
Originally posted by buggsson


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?

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 ??
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Old 22nd August 2007, 02:50 AM   #18
tinitus is offline tinitus  Europe
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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
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Old 22nd August 2007, 03:40 AM   #19
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Quote:
Originally posted by JinMTVT
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 ??
No. Wavelengths are really long on a sub

Quote:
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 ?
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.

Quote:
net pressure within the box is near 0 all the time ?
so no back loading of the drivers?
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)

Quote:
having 2 drivers of the same size in a sealed box effectivly double the output VS the same sealed box with only 1 driver ??
A box for 2 drivers needs to be 2x as big as for one. With 4 drivers 4x as big.

dave
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Old 22nd August 2007, 03:43 AM   #20
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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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