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My SMT212 CP755TI / SN12B

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Paulo Duto View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Paulo Duto Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2008 at 10:34pm

OK Deadbeat

Follow beside my comments refer to compression of 4,3dBs at 0 dB and qt 0,61.
 
Experience with that driver in Selenium horns similar to MT102 always indicate failure due to the absence in play low mids, when people try to eq it;
Play some sims with it BR and you will have a preview.
 
Regards,
 


Edited by Paulo Duto - 06 November 2008 at 10:36pm
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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 10:52pm
I don't think they make the wpu 1209 anymore.

This is kinda why I would rather build the x12.  Four really.  I can make four, good sounding x12's for the price of one good sounding SMT212.  


Edited by wafflesomd - 06 November 2008 at 11:31pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Paulo Duto Quote  Post ReplyReply Direct Link To This Post Posted: 06 November 2008 at 11:57pm

Hi

At Seleniuns site they are apparently in production;
 
Everyone knows what he can spent and what hope with the investment. Would only advice you before waste money with 12PW3...
 
Only referred 1209 as Deadbeat was indicating Selenium drivers and it is a good one; Here in Brazil these WPU1209 are not cheap (R$380,00 =>> before crash rate was R$1,70 = US$1,00 now R$2,10 = US$1,00;
 
Regards,
 
 


Edited by Paulo Duto - 07 November 2008 at 1:02am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2008 at 1:14am
I'm just going to build four x12's and four g subs.

I think this cabinet is bad by design.  There will always be standing waves in the front section of the cabinet.  Placing padding in the rear of the cabinet will help, but you would still need to absorb waves in the front.  That's going to significantly reduce SPL.


Edited by wafflesomd - 07 November 2008 at 4:29am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LunchieTey Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2008 at 9:14am
Originally posted by wafflesomd wafflesomd wrote:


I think this cabinet is bad by design.

Only they way you are doing it, it's fine if built how it is specified.

When I get around to it, I will be building a pair and will post results, may be a few weeks yet though Big smile These will be with p-audio sn12mb's(slightly different specs but oh well-that's what eq is for)
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Paulo Duto View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Paulo Duto Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2008 at 12:59pm
Hi
 
That's your choice.
Remember diffraction loss that occurs when you lift the boxes from the ground plane..
 
Have you added all the braces of the project?
If you nit made it BR it would not play low mids at all
Take a look at Pi forum at the for the driver of Pi project:
 
Also value take a look at BF forum to the speaker indicated for the Omnitop12; following it plans you will find out a way to extend response of the 12", without adding phase plugs, and so turning the HF drivers life easer.
 
Good luck!
 
Regards,
Paulo Duto
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2008 at 1:07pm
Standing waves aren't as much of a big deal in a design like this. The small rear chamber means that the drivers will be in the way of any standing waves. The front isn't as affected as much either - and if you lay down the foam - all you are doing is padding down the top end of the driver response which won't matter since you're crossing to the comp. One of my favourite quotes is actually from Siegfried Linkwitz, on standing waves - I can't find it atm so never mind..

2 X12s and 4 GSUBs is a good plan though Thumbs Up
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Post Options Post Options   Thanks (0) Thanks(0)   Quote wafflesomd Quote  Post ReplyReply Direct Link To This Post Posted: 07 November 2008 at 5:52pm
Yes, x12's and gsubs will be a lot easier for me to control and use.  They should put out a great deal of sound as well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote djtecthreat Quote  Post ReplyReply Direct Link To This Post Posted: 09 November 2008 at 7:16pm
For the record-

Delta-12A under Selenium D210ti sound incredibly good for $205 a cab.    I'm impressed and happy and cant wait to finish all 4 of my SMT's.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 29 November 2008 at 8:16pm
Originally posted by Deadbeat Deadbeat wrote:

Haha. In that case all our speakers are flawed.

Anyway. Tell your friend that he is right in noticing standing waves in a cabinet caused by parallel sides.

The distance from Piece F to the bottom is 680mm. This is the wavelength of 500hz - he's done the math right. Unfortunately, the driver's chassis and cone are in the way of nary a standing wave Wink. Besides - any standing waves formed would be chased away if you stuffed and lined the boxes properly when finished.


Damn! I hate it when I post at odd hours.

I am wrong here, and so is wafflesomd's friend.

Box resonances occur at half wavelengths at parallel walls. They cause notches in the response.

344/0.68/2 = around 250hz. There would be additional resonances at 750hz, 1250hz, etc.

However, there is a major flaw in this....er....it hardly has an affect in this horn in real life conditions.

The back chamber is full with speaker cone and magnet, so one won't have resonance there.
The front waveguide is too short to really create any ridiculous resonances imo.

If you calculate resonances obsessively, nearly all designs are crappy LOLWink.

Resonances from ports, boxes, etc, become apparent in FR graphs. You should also be able to hear them If they ain't there, they ain't!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote WmAx Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2008 at 5:59am
I am wafflesomd's friend that was mentioned previously in this thread.

The main resonances of this cabinet will be in relation to the front section, with the substantial near-parallel sides on both sides of the midbass drivers. This is going to cause substantial resonances and cancellations in the lower to upper mid-rand band if left bare. Of course, I realize this is no hi-fi sound reproduction system, but instead, simply a P.A., but none the less, is an issue that will be addressed if maximum fidelity is so desired.

BTW, standard dampening foams are near useless in many cases. The standard 1" acoustic foam has virtually no action under 1200Hz, and the staneard 2" acoustic foam has little action under about 600Hz. If it is a premium grade foam like Auralex(and most are not near this quality), then those figures are approximately halved(600Hz, 300Hz). A better and cheaper material is 6-8# mineral wool board. In 2" thick, it has a very high absroption co-efficient at 250Hz, for example, before it starts to reduce in effectiveness.

Cabinet panel resonance also reduces fidelity substantially, but again, that is probably not that big of a deal in P.A. systems. I have actually never noticed any P.A. system with low resonance cabinet panels. Heck, most so-called hi-fi high dollar speakers have relatively high resonance panels. It's not really feasible in most cases to prevent this problem, especially in P.A., due to the usual side effect of very heavy cabinets that result in substantially reducing resonance with standard methods that are highly effective. There are relatively low weight solutions, but this would likely result in very complex cabinet construction which translates to very high cost or very high labor(in the case of DIY).

-Chris
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Deadbeat Quote  Post ReplyReply Direct Link To This Post Posted: 30 November 2008 at 11:55am
Hi,

Measure the speaker and see whether this is true in practice. It all comes out in the graphs.

Standard acoustic foam (30ppi open cell) is useless in this place. What I am however referring to is closed cell foam which does help. I've measured it affecting FR. The mentioned wool will help. Sorry for any confusion.

The 30ppi foam, is good, as I have maintained, for absorbing any higher order mode distortion. But that's a different topic.

The main point was that such resonances will happen in half wavelength, not full as specified. In practice, the extent will be revealed by measurement, and then you apply fixes. We all strive for high fidelity.

Resonance in panels, eh?
I've got a link to measurements of energy transference in loudspeaker cabinets of different materials. Somewhere...

Here's a short bit I wrote a bit earlier on material.
'Resources: diyaudio.com and some personal experimentation in the past, Ron Clake for my sentence or two on damping.

Well, the object of a speaker cabinet material is to not affect the sound of the cabinet.

Sound travels faster in solids. The issue with panel resonances and all of the other talk around that factor is to do with energy storage, and release. You want to control this so it achieves the objective, as it is impossible to stop any resonances happening. What you do is stick the panel resonance up or down relative to the cabinet passband. Option one- using MDF, HDF, hewn granite, (whoops) is to whack the resonance down low. Whack one of these and it is a low ring you hear. You do this by choosing the material and making it as thick as possible. If I went with this method, I would use 1.5 inches of HDF just to be sure. Now for the opposite approach, using ply, aged woods, laminate, fibreglass, metal etc. What you have now is the situation of attempting to push resonance high above the upper cutoff of your cabinet. This works just as easily, but you don't need all the material as stated. By the way, there are other lesser known materials that work apart from BB ply and the other staples, I also favour aged woods, metal honeycomb, and bamboo ply for the latter effect. I had a subwoofer a while back made of aeronautical grade metal honeycomb.

Now for more detail:

MDF breathes. You car audio guys should know this, it breathes, and you have to paint both sides to stop it.

Energy loss in laminated enclosures. Ron Clarke:
One of the good reasons for the application of ply in enclosure applications is the fact is thats its a laminated medium. Any energy has to encounter several interfaces, every time an energy encounters an interface of different values it gives up greater energy than a monochromatic singular medium due to the loss at an interface.
Simply put, the more interfaces an energy has to encounter the greater the loss of energy, thus the more damping.

My final point. Stiffness. Stiffness can be checked by Young's Modulus.
MDF and chipboard aren't stiff at all.
Fir ply is stiff. BB is even stiffer. You can google for average Young's Modulus values of whatever material.'


Siegfried linkwitz once mentioned that his speakers were boxy because any resonances created would be easier to notch out if they appeared, than curvy ones. That's not an exact quote.

Nice to have you on board.

Omar
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