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Old 28th May 2010, 04:08 PM   #1
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Default 50 year old old fart building a bandpass sub

I want to design/build a 4th order bandpass box for my son's 2001 cavalier. I've looked over many posts and read Dickason's chapter on bandpass and have a couple questions.

What is a good vent tuning freq and bandpass to shoot for? Music selection is mostly rap but I'm trying to give my son a sub that will make him proud but meet my requirements for being at least semi-musical. Fronts will be 6" comps rolled off around 80 hz I guess.

How large of a driver do you really need? I've been playing with specs for 12" drivers and get fairly large encosures. My price point is $150 or less. I need something he can't easily destroy.

Does the vent need to be sealed to the rear deck?

I've built all types enclosures including front and rear loaded horns and tapped horns so don't hold back.

Thanks for the help
Jim
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Old 28th May 2010, 07:58 PM   #2
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Some handy stuff here
The Subwoofer DIY Page - 4th Order Bandpass Systems
The Subwoofer DIY Page - Car Audio Subwoofer Design and Construction
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Old 28th May 2010, 08:02 PM   #3
HK26147 is offline HK26147  United States
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I don't know the size available in a Cavalier.
Because of cabin gain I would not worry about tuning low, with a correspondingly large cab.
If you get a chance to read Margerand's article in the SpeakerBuilder 6/88 issue. It goes into further detail on how a 4th order can be "jammed"for allowable ripple.
I built them back in the 80's and I tended to keep to a S =.7 and Qbp of.7143

Syd

(FWIW: I'm older than you are )

Last edited by HK26147; 28th May 2010 at 08:05 PM.
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Old 28th May 2010, 08:12 PM   #4
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You'll probably end up tuning the box around 60-70hz with an f3 around 40-50hz. In car cabin gain is around 20dB's @ 20hz.
Measuring cabin gain? Need a little advice from the experts. - DIYMA.com
Click the image to open in full size.
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Old 28th May 2010, 09:08 PM   #5
infinia is offline infinia  United States
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Quote:
Originally Posted by Jimmy D. View Post

What is a good vent tuning freq and bandpass to shoot for? Music selection is mostly rap but I'm trying to give my son a sub that will make him proud but meet my requirements for being at least semi-musical. Fronts will be 6" comps rolled off around 80 hz I guess.
How large of a driver do you really need? I've been playing with specs for 12" drivers and get fairly large encosures.


More musical means design for wide band and shallow LF rolloff versus designing for max eff. ie one note bass. If you haven't tried Unibox yet, it is great for getting in the ballpark bandpass designs.
Seems a target size box 40-50 liters using a 10" sub driver s/be enough.
40 Hz -100 Hz

Quote:
Quote:
My price point is $150 or less. I need something he can't easily destroy.


You should also figure on using a line level steep rumble filter for over excursion protection. Depending on max power available use a settable attenuator to limit the power gain at the amp line in? Normal stuff for pro-sound not sure what there is for 12V systems. This may cut in your budget, but surely costs less over the long term. ie replacing burned and and bottomed out stuff.

Quote:
Quote:
Does the vent need to be sealed to the rear deck?


The kids long term hearing health?
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Old 28th May 2010, 11:55 PM   #6
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The kids long term hearing health?
Yes, maybe I need to rethink this.... maybe a standard ported design in the trunk.

Thanks for the help all.

Jim
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Old 2nd June 2010, 08:52 PM   #7
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Quote:
Originally Posted by Jimmy D. View Post
I want to design/build a 4th order bandpass box for my son's 2001 cavalier. I've looked over many posts and read Dickason's chapter on bandpass and have a couple questions.

What is a good vent tuning freq and bandpass to shoot for? Music selection is mostly rap but I'm trying to give my son a sub that will make him proud but meet my requirements for being at least semi-musical. Fronts will be 6" comps rolled off around 80 hz I guess.

How large of a driver do you really need? I've been playing with specs for 12" drivers and get fairly large encosures. My price point is $150 or less. I need something he can't easily destroy.

Does the vent need to be sealed to the rear deck?

I've built all types enclosures including front and rear loaded horns and tapped horns so don't hold back.

Thanks for the help
Jim


It's difficult to tune a ported box without measuring the impedance curve, and bandpass boxes are even harder. (Because missing the tuning by a fraction of an octave can reduce efficiency, or create a huge peak.)

Do you have the ability to measure impedance?

If not, build something else. How about a tapped horn with a pair of diycable Anarchy woofers?

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Old 3rd June 2010, 12:07 AM   #8
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Do you have the ability to measure impedance?
Yes, but I"m too lazy for this excerise.


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If not, build something else. How about a tapped horn with a pair of diycable Anarchy woofers?
You talking about the Exodus woofers? Point me to a thread or resouce for more info?

Jim D.
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Old 3rd June 2010, 12:34 AM   #9
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Originally Posted by Jimmy D. View Post
Yes, but I"m too lazy for this excerise.



You talking about the Exodus woofers? Point me to a thread or resouce for more info?

Jim D.
Here you go.

Reed Exodus Anarchy 25hz Tapped Horn - AVS Forum

Todd built them, I designed and tested them.
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Old 3rd June 2010, 01:48 AM   #10
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Originally Posted by littlemike View Post
Here you go.

Reed Exodus Anarchy 25hz Tapped Horn - AVS Forum

Todd built them, I designed and tested them.
Any FR measurements for that TH?

What's the total volume of the box?

For cars, I usually recommend a simple design - while higher-order designs are efficient ways to use drivers, they're usually not the most efficient way to use space - important when you've only got a limited amount of space to work with.

For example, if that TH takes up ~2 cu.ft., that about the same amount of space two good 12" car audio drivers would take up in a sealed alignment (or perhaps two 10s in vented enclosures).
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