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4th order BP for midbass/ shape check

Old 06-21-2011, 06:58 AM
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4th order BP for midbass/ shape check

We purchased a Beyma midbass to run as our center channel midbass. We have been running it in a sealed .35 cuft box between the front seats/under the storage tray, firing up on an angle off the lower center dash.

The response curve I figured out by ear and then using a box program. We are only getting down to about 300 hz with the power we run. Not really midbass range

Anyhow, using a box program, I figured out the bandpass curve we wanted using a 4th order design. The possible problem I have is the shape. It would need to be 7"x9"x60" !! VF-.76...Vr.87 ..Fb 252.75

With that shape it will fit between the seats, front to back, with the port firing up between the front seats.

Will the long but narrow box work as the numbers say, or is the shape a possible problem?
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Old 06-21-2011, 02:42 PM
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The box won't mind being that long and narrow.
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Old 06-22-2011, 07:10 AM
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Thanks Dukk
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Old 06-22-2011, 02:33 PM
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Originally Posted by Dukk View Post
The box won't mind being that long and narrow.
at roughly 100hz you'd have 180 degree backwave reflection...Just put some foam or something light insulation on the walls of the box.
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Old 06-22-2011, 02:45 PM
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At any given length there will be some frequency of reflection. I assumed the box would be properly damped / baffled but good thing you mentioned it.
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Old 06-23-2011, 06:42 AM
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Originally Posted by mohawkboom View Post
at roughly 100hz you'd have 180 degree backwave reflection...Just put some foam or something light insulation on the walls of the box.
Do you have some more info on this bro. I really don't understand...lol..
I'll need to make the box even bigger if I add anything on the inside, I'm not sure I could get the cubes I need adding anything inside. Its a tight fit already as planned..

How does the reflection change the sound/volume etc?
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Old 06-23-2011, 03:16 PM
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If you are stuck with a rectangular box with parallel walls try putting a couple of angled baffles in it so the sound waves don't have a direct path through the box. Add a little fiberfill too and you should have a nice enclosure.
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Old 06-24-2011, 07:17 AM
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Thanks for clearing that up for me Dukk..
However, maybe you could help me again?
I ran into a problem trying to find the port length. Doesn't matter how I try to find the tuning using a 2" flared port , I always end up with a negative number!! What is a -1.3" port?? lol

I don't know if I use the Vf, Vb or both to tune the port!! Have any advice?

Last edited by SOULMUSIC; 06-24-2011 at 07:41 AM.
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Old 06-24-2011, 02:49 PM
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If your port length comes up negative you have some combination of:

- Too much box volume
- Too high tuning
- Too little vent diameter

The easiest to fix is to use a bigger vent. Try a 3"
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