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Old 3rd February 2009, 04:41 AM   #1
the joz is offline the joz  Australia
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Default Twin 12" driver sub...but?

Ok can anyone see amy major problems with using two 12" drivers in one box (sealed )...Oh! I must add that i'd have one driver forward facing and one rear facing..

The reason being to keep the front small on the sub.

I'll be using two boxes like that,so thats 4x12" drivers

The reason being that I plan on putting my mid/bass+tweeter in a box on top.
So really I don't want to go too large for the subs but want enough LF extension and SPL.
really wanting a solid response down below 30hz (20 would be nicer) in a very large room.

Tossing between Exodus Shiva 12"s or Peerless 12"s.
With Winisd the Peerless is needing about 100Litres as oppossed to the Shivas with nearly 200litres.

The smaller boxes would be preferable but I'm stuck with understanding the difference between gain and spl on the Winisd charts.
The Peerless looks better on the SPL chart but the Shiva looks better on the gain chart???

The system will be all active with EQ in the bass aswell.


So some help would not go astray..

Thanks!
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Old 3rd February 2009, 05:13 AM   #2
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Two woofers push-push (ie like you plan) is always a good idea IMHO... make sure you have a good solid brace between the magnets to tightly couple the drivers. You will get active cancellation of the newtonian forces and very little will be transferred to the box.

dave
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Old 3rd February 2009, 05:27 AM   #3
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Two drivers mounted back to back also seem to behave as if the box is bigger than it's actual volume, but I confess to ignorance as to why, but when playing around with this concept I found I could make the box 20/30% smaller.
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Old 3rd February 2009, 05:44 AM   #4
the joz is offline the joz  Australia
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Sorry Dave I might not have made myself clear but Moondog has got what I was contemplating.

The magnets were to be facing each other,not a push pull type setup.

I didn't know that that bit of info Moondog.Interesting that it would make the box seem that much larger..

I am just a bit concerned with the way the rearward facing driver may interact with the room and give me any problems.

Still wondering about the gain and spl graphs though??
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Old 3rd February 2009, 05:53 AM   #5
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I'm talking about same set-up as Dave, push push, working in phase with each other, except Dave takes it to a higher level with back plates coupled.

Big gain as no baffle step.

Why not pick up some cheap cars woofers to try first, Sunday Market stuff?? or from Darn cheap auto @ $39 each ( for the 8 inch last time I walked in the door )

It is what I am doing with the 10 inch woofers I'm chasing

Australia Wanted sale or swap

Test boxes can save big dollars by showing mistakes early.
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Old 3rd February 2009, 06:06 AM   #6
the joz is offline the joz  Australia
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Oh dear,now I'm feeling like the numpty now!

Its just that I didn't think that push pull was having the magnets facing each other.
I suppose because I had an M+K dual driver push pull unit which had one driver with its cone facing into the box from the bottom,while having the other facing forward..
Sorry got confused..

So are you suggesting both drivers in phase or out with each other??

Sorry if this sounds basic but this has just been introduced to me and I'm a bit confused.


Doh! (really must read replys more thoroughly) edit: just read the inphase bit MD55 and push/push Dave..

Sorry can you please explain baffle step or in this case no baffle step??
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Old 3rd February 2009, 06:22 AM   #7
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Quote:
Originally posted by the joz
The magnets were to be facing each other,not a push pull type setup.
I did say push-push... magnets facing each other, cones pointing to the outside world.

I don't have access to the good pictures, but maybe these will help...

Click the image to open in full size.

A snapshot from this pdf attached

http://p10hifi.net/tlinespeakers/FAL...ube-woofer.pdf

dave
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File Type: gif push-push-extremis-cube.gif (22.0 KB, 186 views)
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Old 3rd February 2009, 06:36 AM   #8
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Bass from front meets bass from back as the signal wraps around the box,
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Old 3rd February 2009, 06:40 AM   #9
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Yes Dave you did.
I was just very silly racing through your reply and not reading it properly.
And your right, about the vibration cancellation that's a very appealing reason to do it that way.


But somewhat concerned about the rear facing driver and how it will sound as opposed to a front firing one or in conjunction with it ??
As pointed out by Moondog the slightly smaller volume is also a bonus,as it gives me more 12" drivers in one box without having the two 12" facing forward making the front baffle too large.
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Old 3rd February 2009, 06:42 AM   #10
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I actually have the drivers here for my unfinished "Tardis" woofer/sub-woofer box if you want to buy them from me.
Two sets of drivers
2 * 10 inch plus 1 * 12 inch,
all rewired to 24 ohm nominal good performance in a 90litre box excellent performance in a 120 litre box I would think.
I only built one test box of 90 litres and never measured or anything.
being 24r all in parallel it is a nice easy load for any amp.
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