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Old 23rd March 2017, 05:18 PM   #11
bob4 is offline bob4  Germany
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I'd advise against butchering any of the stuff you have, since it all is in working condition.

New cabs for the csx70s are a good idea though, building to a more vertical form factor instead of the awkward original shape.

Then build some subs to stack the csx on. Two single 18" Reflex or tapped horns per side. You should be able to cross over quite low (80-100 Hzish).
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Old 25th March 2017, 12:15 AM   #12
dokkodo is offline dokkodo
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Thanks bob, sounds good as well, if I can implement all these things sounds like I might end up with a decent system.

Done some googling, and PPSL sounds intriguing, but as a layman it also looks like I'll need a degree in acoustic engineering to work out a PPSL cabinet design... I saw one djk post mention a 4x12 PPSL design but i cant find it any more. Would you have any pointers for a place to start?
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Old 25th March 2017, 11:46 AM   #13
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Quote:
Originally Posted by dokkodo View Post
as a layman it also looks like I'll need a degree in acoustic engineering to work out a PPSL cabinet design...
its less complicated than you think. You dont have to actually design from the ground up. The main goal is to keep the internal cabinet volume and tuning frequency the same, while changing the shape of the box.

PPSL is really just a twin driver reflex box with a specific physical arrangement. The dimensions of the 12inch lowmid drivers determine the size of the slot. You want to make the plenum (chamber inside the slot that contains the drivers) as narrow and shallow as possible. You have to keep in mind that the volume of the plenum has to be subtracted from the cabinets internal volume in the design process.

Wish I had more time to help you with the design.....
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Old 25th March 2017, 11:51 AM   #14
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Thats a good start, many thanks
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Old 25th March 2017, 01:42 PM   #15
bob4 is offline bob4  Germany
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much obliged

I did some quick napkin calculations concerning the internal volume. The factory cab is about 260 litres external (calculated from dimensions), 221 litres internal (info on datasheet). The 40 litres difference is the volume taken up by the enclosure (including bracing), loudspeakers and fittings. To allow for PPSL mounting in a plenum while maintaining internal volume, you will have to increase the cabinet size a bit.

The plenum size will depend on slot width, but lets assume a 6 inch slot, 12 inches deep and 24 inches high. That would add up to roughly 27 litres. Taking the factory cab external dimensions, a total external volume of 287 litres would be required to accomodate the plenum and keep the internal volume (which is important for the reflex tuning).

If you reshape this to 1,2 m high, 0,5 m wide and 0,5 m deep, you end up at 300 litres. If you take that as a starting point, you can think about where to shave off a few cm/inches.

Its going to be a big, heavy box regardless, but a lot better to stack, and the PPSL loading might improve the sound as well by a) reducing distortion b) bringing drivers closer together, and thus improving summing between the woofers and mid driver. If you look at the datasheet, there are two nasty dips in the frequency response around the crossover frequency, 700 Hz.
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Old 25th March 2017, 01:47 PM   #16
bob4 is offline bob4  Germany
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.......and all these considerations are made under the assumption that you want to replicate the factory box tuning..... you could of course experiment with smaller cab volume and different tuning if you are adventurous.......
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Old 22nd April 2017, 10:45 PM   #17
dokkodo is offline dokkodo
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Sorry to revive this thread but i have some time coming up and some spare money which is rare so I think im going to give these a go. so, one more round of questions!

to clarify, im going to rebuild the cabinets with the same internal volume as before, but adjusting for the extra volume of the plenum (the slot).

whats the difference between the plenum and the slot? and i suppose slot width is dictated by the depth of the drivers, as one magnetic structure will be in the slot, but i remember reading that closer is better.

does the volume of the slot matter?

is one driver in each pair is wired out of phase?

also, seeing as I will be using four 12s per box, i assume it is ok to have a single plenum for both pairs, two above two?

and lastly, does it matter how and where I mount the remaining compression and horn drivers?

i think with these questions even vaguely answered I can get drawing! thanks for all your help!
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Old 22nd April 2017, 11:26 PM   #18
dokkodo is offline dokkodo
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just so you can see if im on the right tracks...

Click the image to open in full size.

Click the image to open in full size.
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Old 27th April 2017, 09:56 PM   #19
bob4 is offline bob4  Germany
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Hi Dokkodo,

nice to see you're going ahead with this project! Sorry for the delayed response.

Quote:
Originally Posted by dokkodo View Post
whats the difference between the plenum and the slot?
the way I see it (I might be wrong!): the plenum is the volume that contains the drivers, enclosed beyond the slot. The slot is the opening in the front baffle that couples the airmass around the drivers to the surroundings


Quote:
Originally Posted by dokkodo View Post
and i suppose slot width is dictated by the depth of the drivers, as one magnetic structure will be in the slot, but i remember reading that closer is better.
both correct. Measure the depth of the woofer from back of magnet to front of gasket. Assuming you want to avoid additional access panels on the sides, you would want to make the slot just wide enough that you can insert the drivers. Remember to take the rim/gasket of the non-inverted driver into account, or countersink the driver so that it doesn't stick out.

Quote:
Originally Posted by dokkodo View Post
does the volume of the slot matter?
only in the sense that if you want to replicate the original box volume and tuning, you have to account for it. You could for example cut the back corners of the plenum to reduce volume. If your carpentering skills are up to the task, you could make the plenum trapezoidal (narrower at the back, wider in the front). That way mounting might be a bit easier, and you could get the drivers closer to each other than with a rectangular footprint plenum. But that would be a lot more work, and you would probably have to build a mockup to get it perfectly right.

Quote:
Originally Posted by dokkodo View Post
is one driver in each pair is wired out of phase?
correct, the inverted drivers need to be wired out of phase

Quote:
Originally Posted by dokkodo View Post
also, seeing as I will be using four 12s per box, i assume it is ok to have a single plenum for both pairs, two above two?
yes, should be ok. someone has done a 4x12" sub with single plenum


Quote:
Originally Posted by dokkodo View Post
and lastly, does it matter how and where I mount the remaining compression and horn drivers?
I suppose i would make most sense to mount the horn directly above the slot.


Quote:
Originally Posted by dokkodo View Post
i think with these questions even vaguely answered I can get drawing! thanks for all your help!
good luck with your build! And please report whatever you come up with, I'm highly interested My partner in crime just bought a second pair of csx60's, and I'm itching to eventually do something similar to what you are attempting

did you check this thread?
http://www.diyaudio.com/forums/subwo...nclosures.html
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Old 27th April 2017, 10:49 PM   #20
dokkodo is offline dokkodo
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Amazing, no worries for the delay im just grateful for the advice. I will definitely report back!

im going to have to read that thread and your definitions a few more times just to get it clear in my head!
i have found that thread before and have read bits of it, theres a lot to absorb and as I said, a lot of technical talk that melts my brain, but useful info to chew through

I am a carpenter by trade luckily so I have a technical mind and a workshop, but audio engineering is a whole world for which I need a new dictionary.

I quite like the idea of trapezoidal because there is something quite strange looking about a rectangular speaker cab with a rectangular cavity in the middle! Might give this a go http://www.diyaudio.com/forums/attac...led_back_2.pdf

In fact, I dont see why you couldnt get the drivers basically touching, i suppose you want to leave room for cone travel but if you mount them into the panels and then build the panels in you could get them very close indeed.

This Click the image to open in full size.

seems to suggest a port, but I have also read that sealed is fine too, and i guess the original boxes were sealed so Ill stick to that. I guess it would make sense to tweak the tuning of the box etc but as I am an amateur ill leave that for now!
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