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My SMT212 CP755TI / SN12B

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wafflesomd View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 6:45am
So I'm actually trying to figure out what type of driver works well in this cabinet.  

I'm trying to actually understand QTS and how it plays a role in this.  I tried finding drivers that match the specs of the P.Audio you used.  It's kind of hard to find a qts of .16.  

Can't seem to find any drivers with a similar BL either.  Not to many with the same VAS either.


Edited by wafflesomd - 05 November 2008 at 6:59am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 7:38am
Ok.

Turns out my issue was that I was running the 12's way to high.  I had them crossed at 2.5khrtz to meet my current tweeter.

Plan is to buy a midrange, and run a 3-way with this cabinet.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LunchieTey Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 8:13am
Don't forget the whopping 10db spike in response on the deltas between 1 and 2k translating into harsh sounding mids Embarrassed Many eminence drivers have the same problem so don't feel bad!
www.eminence.com/pdf/delta-12a.pdf, see that huge peak from 1.8 up? That will rip ears too unless you eqWink you will also need a good highpass, 2.4mm x-max.
I've been looking thoroughly at these plans and might just build a pair(15mm ply is literally piled up where i work and I mean 2000 sheets or more! and is free!) I have a pair of bmd-750's ph-4528 horns, and 4 sn-12mb's. I want to ask a maybe silly question... Is the open void behind the compresison driver used by the 12's or is it only the airspace behind the baffle itself?
edit, have looked at other post with build pics, can see horn area is closed off Wink




Edited by LunchieTey - 05 November 2008 at 8:31am
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wafflesomd View Drop Down
Young Croc
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 7:16pm
The tweeters chamber is seperate from the woofer.  It's seperated by piece F.  Which is too long.  It should not be 388mm.  You'll have to figure out how long it needs to be.  It depends on the thickness of wood you used.

So my plan is to run the 12's from 80-500, then a mid range from 500-3.5k, then the compression gets the rest.

Has anyone modeled the 12" section in hornresp?


Edited by wafflesomd - 05 November 2008 at 7:29pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djtecthreat Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 9:08pm
Originally posted by wafflesomd wafflesomd wrote:



Has anyone modeled the 12" section in hornresp?


As far as I know;  No.

I believe hornresp wont do mid range freq.  Plus the SMT isn't really a horn, it's a wave-guided reflex.

-Tec
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 9:35pm
Hornresp has it's limits - but you need to know them accurately (do a search on power response). Lots model mid on hornresp...

THs SMT212 is a reflex design - the waveguide is there to lend a bit of directivity and wavefront control.

It's old school design which I've touched upon in the past - there's a thread that mentions the altec VOTT which has some info in for anybody wanting to know how to design a mid 'flare' as opposed to a horn.
Away on extended leave.
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wafflesomd View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 10:24pm
so I should be treating this like a reflex?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 10:53pm
Treat it as a direct radiator if that keeps it simple. Hornresp can do the low end response - how high the double twelve section goes will be determined by individual driver response which you can't model. Check manufacturer's driver's plots - it is best to cross below driver breakups (easily spotted on the FR plots) and below when the 12" starts beaming (see polar plots - otherwise this is around 1k2 for most 12").
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 05 November 2008 at 11:00pm
I should be fine running the 12's from 80-500 then.  The drivers I used peak up at around 100, then dip down about 10db at 400hrtz for some reason. 

They'll be replaced soon.


Edited by wafflesomd - 05 November 2008 at 11:24pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2008 at 1:46am
Is there a reason why the rear chamber was made so small for this cabinet?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2008 at 4:43am
Did you ever get around to measuring them and checking for peaks and dips.

I may just be ditching these cabinets and going for something else.  It seems like there will always some annoying resonances just based on the cabinets design.


Edited by wafflesomd - 06 November 2008 at 5:11am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LunchieTey Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2008 at 8:10am
Originally posted by wafflesomd wafflesomd wrote:

Did you ever get around to measuring them and checking for peaks and dips.

I may just be ditching these cabinets and going for something else.  It seems like there will always some annoying resonances just based on the cabinets design.


It may just be your choice of speaker, you said you tried it with drivers that have a qts of 1.3 and the deltas(if you have them now) have a big response peak and also don't like small boxes! Maybe if you decide to bin them, open up the extra space behind the compression driver?Or put in the ports(hole sawWink) might lower the resonant frequency of the cab as you didn't port yours(high q alignment with the deltas will give you a big resonance at fb) Also try stuffing the rear chamber if you stay sealed.
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