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36" X 36" with 10" drivers...question! (Read 5147 times)
Lonely Raven
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36" X 36" with 10" drivers...question!
08/14/08 at 21:07:59
 
It's been a LOONG time since I've done the calculations for any sub-boxes. I could use a hand with this.

I need help figuring out this setup for my home theater, please!

I built the  36" X 36" Wicked One about 8 years ago or so, and just had some junk Rockford Fosgate bottom end 10" drivers in it. A few years ago my Dad got me some JL Audio W7 10" DVC drivers which I put in the box, but really didn't have much use because my neighbors complained a lot about my loud movie watching habbit.   Grin

Anywho, now that I have a house, I'm revisiting this sub with the LJ Audio W7 drivers, and I'm trying to figure out how much air space I should have behind the sub to get some solid sound for home theater use. I want to brace the snot out of the chamber, and once I get it right I'm going to do a satin black lamination all around (to cover up 8 years of spilled drinks, cat puke, and chipped up edges).

Can someone tell me how much airspace I have in the sealed champer of a 36" X 36" Wicket One running 10" drivers, and help me figure out what is optimal for the W7 drivers?

Here are the specs on the driver:

10W7 DRIVER SPECIFICATIONS  
  10W7-3
Free Air Resonance (Fs):  30.6 Hz
Electrical “Q” (Qes):  0.578
Mechanical “Q” (Qms):  7.647
Total Speaker “Q” (Qts):  0.537
Equivalent Compliance (Vas):  1.28 cu. ft. / 36.1 liters
One-Way, Linear Excursion (Xmax)*:  0.9 in. / 23 mm
Reference Efficiency (no):  0.171%
Efficiency (1W/1m)**:  84.3 dB SPL
Effective Piston Area (Sd):  59.8 sq. in. / 0.0386 sq. m.
DC Resistance (Re):  2.75 ohm
Nominal Impedance (Znom):  3 ohm
Thermal Power Handling (Pt):  750W
Driver Displacement:  0.09 cu. ft. / 2.5 liters
Net Weight:  30 lbs. / 13.6 kg




Any and all help is greatly appreciated!  8-)
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chuck827
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Re: 36" X 36" with 10" drivers...question!
Reply #1 - 08/29/08 at 15:24:32
 
Hey Raven,

I have a spreadsheet setup to design chamber volumes for 4th order bandpass boxes, based on a desired Fl (lower 3 dB cutoff frequency).  The output gives the Fh (upper 3 dB cutoff frequency), Fb (resonant frequency of vented chamber), net volumes of both vented and sealed chambers, and the gain of the system.

You could also solve for the Fl and Fh, for a given desired gain, but I dont have a calc sheet setup for that...

See - http://www.diysubwoofers.org/bnd/4thord1.htm for formulas

Anyway,  assuming you want to design a system with a 0 dB bandpass ripple (S=0.7), and say, an Fl of 30 Hz:

Vf (volume of vented chamber) = 20.4 liters = 0.721 cu ft = 1245 cu in
Vr (volume of sealed chamber) = 28.27 liters = 1.0 cu ft = 1726 cu in
Qbp (Qtc of sealed chamber) = 0.81
Fb (resonant frequency of vented chamber) = 46.2 Hz
Pa (gain) = 2.19 dB

Let me know if that if these numbers are usable to you.  Id be glad to run new numbers if have any constraints such as for the sealed chamber volume.
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chuck827
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Re: 36" X 36" with 10" drivers...question!
Reply #2 - 08/29/08 at 16:16:16
 
Raven,

I also forgot to mention that the sealed chamber volume for the 36 x 36 wicked one is around 2054 cu in, assuming 3/4 in material and 12 in interior depth for 10 in woofers.  (For 8 in woofers and 10 in interior depth, the volume is 1712 cu in.)

Dont forget to subtract the volume displace by the driver magnet and cone inside the chamber.

Chuck




Chuck
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Lonely Raven
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Re: 36" X 36" with 10" drivers...questi
Reply #3 - 08/29/08 at 17:51:21
 
Thanks Chuck. It's been about 10 years since I've done any calculations...I'm going to have to brush up on it as I only understood about half of what you gave me.

Since I'm using this for home theater, I want to tune it as deeply as possible. But it's sounding like I may need bigger chambers considering how much displacement my subs have.

Am I right in thinking that?

For example, lets say I wanted to tune it to 15Hz or 20Hz, how much space would I need in the front and rear chambers?



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« Last Edit: 08/29/08 at 17:55:08 by Lonely Raven »  
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chuck827
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Re: 36" X 36" with 10" drivers...question!
Reply #4 - 08/29/08 at 19:49:14
 
Raven,

Consider this, and then tell me what you think:

From my calculations for the 36 x 36 x 12 in interior depth, the volumes for the vented chamber is 1456 cu in, which is somewhat close (17% higher) to the calculated volume I gave you at Fl =30 Hz which was 1245 cu in.  You said you were going to brace it to 'heck', so I suspect the bracing volume displacement can bring the net "real" volume closer to the 1245 cu in.  I say close enough...

And...similarly,  the volume of the 36 x36 x 12 in sealed chamber is 2054 cu in, without any reduction for speaker magnet, and the volume I calculated at the Fl =30 Hz, is 1726 cu in, about a 328 cu in difference.  Again, if you estimate the volume of your speaker magnet and cone inside the chamber to be close to that 328 cu in, I'd say that's an ideal design already.   Both chambers appear to be at the design volumes for the assumptions I made - 12 inch depth (I'm assuming for your 10 in speakers), S=0.7 and Fl=30Hz.

Remember, these calc'd volumes are for a true 4th order bandpass, but this cabinet adds the horn component, which may inherently extend the tuned frequency to below the 30 Hz cutoff.  Anyone comment to that statement??

But that's really beyond my understanding.  :-?  

Actually, I don't completely understand all of the theory behind these design formulas either, but the math is easy for me to follow, and I can build a sheet to compare numbers on 'paper', making changes and corrections simple.  I love Excel.  I also cheat using Autocad to sketch the layout in a jiffy, and then it can automatically calculate the areas (and volumes) for each chamber.

But, if you want to really to see what's required at Fl=20 Hz... Wink

Vf (volume of vented chamber) = 20.4 liters = 0.721 cu ft = 1245 cu in (same as before)
Vr (volume of sealed chamber) = 118.7 liters = 4.19 cu ft = 7242.5 cu in (HOLY COW...a little too large??  :-/)
Qbp (Qtc of sealed chamber) = 0.61
Fb (resonant frequency of vented chamber) = 34.9 Hz
Pa (gain) = -2.65 dB (not ideal to drop into negative here...)

It appears to me that your speaker drivers don't work well for Fl of 20 Hz.  I dont even have to rerun the calcs to show that 15 Hz wont work either...

However, Fl=25 Hz gives a Vr volume of 2885 cu in, which you could achieve by increasing the interior depth to 16.85 inches.  You can decide if that make sense for you or not... Cool

Let me know what you end up doing.  Take care.



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Lonely Raven
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Re: 36" X 36" with 10" drivers...question!
Reply #5 - 08/29/08 at 20:23:11
 
Well, I'm not about to build out the chamber bigger, so it sounds like it's best if I just hold at 30Hz.

I'm thinking I may want to build a Sonosub as well eventually, which I could tune to 15Hz and the deeper bass I'm looking for.

Thanks for your calculations.
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