Midbass/subbass Plenum? - Page 2 - diyAudio
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Old 28th February 2014, 04:57 PM   #11
T3mpest is offline T3mpest  United States
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Quote:
Originally Posted by Djim View Post
Hi T3mpest,

If you turn the inside enclosures around you can make a Push-Pull configuration which helps to suppress distortion (even harmonics). You need to make the 'plenum' as small as possible if you want to cross high. There are many posts about PPSL here on DIY forum if you need more info.

Click the image to open in full size.
Yeah I looked at a few designs like that to help figure out duct sizing. However that wouldn't work well for the effect I'm trying to achieve which is having my midbass in stereo and spaced as far apart as possible. In your drawing ports on each end would be my low frequencies, but then my midbass wuold be in mono because the plenum in the center would have all the upper bass information. Perhaps if I had enough money for 4 of those B&C's I could combine the ideas, but that's not in the budget

However, when you say make the plenum small in what dimension are you referring? It's depth, height or width of the opening? Again that's the part I'm trying to figure out. If I have the woofer cone f firing into a small opening like both of our drawing depict , how does the dimensions of the space effect the woofer?
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Old 28th February 2014, 05:05 PM   #12
Djim is offline Djim  Netherlands
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Hi T3mpest,

The larger the volume of the plenum the lower it's resonance (in frequency). In your case I would make it small enough that you can fit the driver.
You can make it smaller but than the high-cut as result of the Bandpass will start to drop. You can use Atc/Vtc in Hornresp to simulate the effect.
If you make the opening exactly the same as the Sd of the driver (effective cone area) you should still have sufficient bandwidth.
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Old 28th February 2014, 05:19 PM   #13
T3mpest is offline T3mpest  United States
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is vtc the total volume of the duct and atc the surface area of the opening? That was the part of hornresp I couldn't figure out, was how to simulate the plenum
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Old 28th February 2014, 05:25 PM   #14
Djim is offline Djim  Netherlands
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Hi T3mpest,

That is correct.
Btw you have another configuration option;


Click the image to open in full size.
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Old 28th February 2014, 05:29 PM   #15
T3mpest is offline T3mpest  United States
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Quote:
Originally Posted by Djim View Post
Hi T3mpest,

That is correct.
Btw you have another configuration option;


Click the image to open in full size.
Very nice! I hadn't though about that, but it would be MUCH easier to build.. I may mess with that and see if I can get something workable.. That does force the higher frequencies to exit to the far left and right.. It would also be MUCH easier for me to build removeable baffles until I get a response I like.. The old guess and check may be far from perfect, but it always works eventually If the response doesn't come out the way I want it, I could always turn it back into a flat wall without messing with much other than pulling that front most panel off.

I wonder how far I would need to mount that wall away from the woofer before back pressure became an issue? I mean I need 2inches or so just for mechanical clearances of the woofer.. That duct would be approx 10-20inches wide and 2inches deep in that case, give or take a bit obviously..

Last edited by T3mpest; 28th February 2014 at 05:46 PM.
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Old 28th February 2014, 05:39 PM   #16
Djim is offline Djim  Netherlands
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Hi T3mpest,

The pressure is not a problem for such a (monster) driver but the bandpass filtering might be. Since the B&C is able to produce quiet some force the stiffness of the slot-baffle will give you the most trouble...

The space between baffle and driver should be enough to realise Xmech.
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Old 28th February 2014, 06:41 PM   #17
T3mpest is offline T3mpest  United States
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Quote:
Originally Posted by Djim View Post
Hi T3mpest,

The pressure is not a problem for such a (monster) driver but the bandpass filtering might be. Since the B&C is able to produce quiet some force the stiffness of the slot-baffle will give you the most trouble...

The space between baffle and driver should be enough to realise Xmech.
Yes, the baffle will likely be at least 2 layers thick of .75inch mdf and I may brace it if that isn't sufficent to stop the panelfrom moving.. Xmech on that driver is 30mm, but it's essentially impossible to reach that, suspension is just too stiff.. I'll try playing with hornresp and see what effects making the volume larger and smaller is.. I know my exit area will be approx the SD of my woofer, so that really leaves my main variable to be my distance from the cone to the baffle. Thanks so much for the help
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Old 28th February 2014, 06:59 PM   #18
Djim is offline Djim  Netherlands
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Your welcome...

If you calculate the 'cavity' volume do not forget to count for the volume in the cone, since it will be part of it.
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Old 28th February 2014, 07:13 PM   #19
T3mpest is offline T3mpest  United States
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Originally Posted by Djim View Post
Your welcome...

If you calculate the 'cavity' volume do not forget to count for the volume in the cone, since it will be part of it.

If I flush mount the woofer to the baffle couldn't I ignore that? Since it would out as often as it would be in and it's center position wouldn't really be effecting the airspace much vs not existing, since it's sitting flush..
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Old 28th February 2014, 07:26 PM   #20
Djim is offline Djim  Netherlands
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Hi T3mpest,

Ignoring an acoustic parameter usually means you don't model correctly.
In this case it would not surprise me if the cone volume ends up bigger than the volume of the 'cavity'.
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