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help with 4th order bandpass build

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I'm in need of help concerning my first 4th order. I already have two Soundqubed HDS3.1 12 inch subwoofers that are right now sitting in a ported enclosure in a Toyota LC, but the thing is, I have now bought a new car which is a sedan, ported enclosures + sedans isn't the best way to go. After doing my research, I'm planning to build a 4th order bandpass and porting it thru the rear deck. I've done my calculation regarding the subwoofers and they will do a good job in a 4th order bandpass.

I haven't yet been able to design a all around good enclosure, ether the gain drops low, it gets too peaky, the port resonance get to high or the port air velocity peaks very high or the port wants to be too long (over 40 inches'').  (calculating using WinIsd) 


parameters of the subwoofers:

RMS power: 1200 Watt

dual voicecoil: 2 ohm

woofer size: 12''

F(s): 33.65 Hz

Q(ms): 6,19

Q(es): 0,769

Q(ts): 0,692

V(as): 22,13 litres

L(e): 8,62 mH

n(0): 0,10%

M(ms): 364,4 grams

C(ms):  0,06 mm/N

BL: 27.2





Edited by TimNorr
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On 9/11/2020 at 3:05 AM, 1point21gigawatts said:

What’s the available trunk measurements and then what’s the measurements for the cutout of your rear deck?

Trunk measurements: 107 cm long, 31,5 cm high and I'm able to play with the width a bit (at least 100 cm)

I will cut away and strengthen the rear deck for the needed space.

i have calculated a box that's pretty good now, but the only problem is that i get a impedance peak at 30 Hz and 68 Hz. i would want to lower the 30 Hz peak, but I haven't found a good way to do that yet, while playing a bit with the port and ported enclosure measurements I did get it a bit better but then the rest got worse.


Edited by TimNorr
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12 hours ago, TimNorr said:

well of course they work,  but it isn't the best option.

unless you have a seat that won't fold down I don't see why its a problem.



Stock :(


2019 Harley Road Glide:

Amp: TM400Xad - 4 channel 400 watt

Processor: DSR1

Fairing (Front) 6.5s -MMats PA601cx

Lid (Rear) 6x9s -  TMS69


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7 hours ago, TimNorr said:

which i dont.

Cut a whole in it 😈


- I've seen rear seat deletes in sedans, with the wall taking up the entire width of the trunk opening behind the seats, and an interchangeable port in the middle - albeit rectangular or aero or etc.


Pic for reference:


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