Can you use 2x 4th order BP boxes to imitate a 6th order BP ?

[RobWells]

I'm working on a tiny sub to blend in with cabin gain in a car. The perfect option is a 6th order BP rolling off at 24dB/oct from 70Hz down (vehicle has a 20dB boost at 42Hz)

However, I'm thinking the cone will unload below 70Hz and may be a problem so was wondering if I could replicate a 6th order BP with a pair of 4th order boxes, with tiny sealed back chambers. (sealing them will prevent them from over excursion below tuning)

I've attatched a pic to show what I'm trying to achieve.

I guess the pair of 4th order subs would be wired out of phase to act like the 6th order one ?

Thanks,
Rob.

[Zero D]

Hi, i see what you're trying to achieve by using 2 x 4BP

rolling off at 24dB/oct from 70Hz down

I think you mean rolling off from 70Hz up

Why do you think the cone will unload below 70Hz ?

Can you provide the driver Make/Model # & TS ?

I guess the pair of 4th order subs would be wired out of phase to act like the 6th order one ?

Why do say they are or would be wired out of phase ?

[RobWells]

Originally Posted by Zero D

Hi, i see what you're trying to achieve by using 2 x 4BP



I think you mean rolling off from 70Hz up

No - I mean rolling off from 70Hz down - take a look at the graph I posted

Why do you think the cone will unload below 70Hz ?

It's in a vented alignment - below tuning they are unloaded.

Can you provide the driver Make/Model # & TS

Elemental designs 7kv 6" subwoofer. Too late to post all the specs. tbh my question is generic and will apply to all drivers / boxes.



Why do say they are or would be wired out of phase ?

Because in a 6th order box the 2 chambers are driven out of phase to one another.

[Zero D]

No - I mean rolling off from 70Hz down - take a look at the graph I posted

Ahh, right you want 60/70Hz - 100Hz

Ok, not much bandwith there, but sure it'll make a difference to having none

It's in a vented alignment - below tuning they are unloaded.

If you have a HPF in place @ 60/70Hz you'll be fine

Because in a 6th order box the 2 chambers are driven out of phase to one another.

But they will be tuned to different Frequencies, so add rather than cancel Have a look at these links for more info.

but they are 180 degrees out of phase with each other so if you tune them to the same frequency they will almost perfectly cancel each other out. The two chambers have to be tuned to different frequencies so they sum effectively.

https://sites.google.com/site/amateu...holtz/bandpass

phase_accurate Post # 11

6th Order Bandpass Subwoofer (rear & front chamber size?)

[RobWells]

Originally Posted by Zero D

Ahh, right you want 60/70Hz - 100Hz

Ok, not much bandwith there, but sure it'll make a difference to having none


It will be flat in car from 40Hz - 150Hz. That's not a bad bandwidth



If you have a HPF in place @ 60/70Hz you'll be fine

If I use a HPF it will change the response and not blend in with the cars cabin gain Maybe that's why I'm asking the question in the first place



But they will be tuned to different Frequencies, so add rather than cancel Have a look at these links for more info.

I'm perfectly aware of how a 6th order bandpass box works thanks.

[pinkmouse]

Rob, can you use open and close quote strings, ( [/qu0te], [qu0te]), so we make sense of your replies without scrolling up and down please.

[RobWells]

I'll do my best Al,

Any thoughts on my actual question ?

Cheers,
Rob.

[Brian Steele]

Originally Posted by RobWells

I'll do my best Al,

Any thoughts on my actual question ?

Cheers,
Rob.

Measure the t/s parameters of that eD driver before you commit to any design, particularly one that's quite sensitive to t/s parameter variations.

[chris661]

I'd try them wired in phase then out of phase. One will likely sound better than the other. I would be interested to know which one it is (in or out of phase).

It is an interesting question, nothing like what I've seen before. Go for it, and if it doesn't work out, you could always use a generic sealed box (but where's the fun in that?)

Chris

[pinkmouse]

Originally Posted by RobWells

...Any thoughts on my actual question ?

I'm not really an authority on bandpass designs, so can't really comment, but I completely understand your worries about unloading. In my limited experience I would really recommend a high pass filter if you're running them that high. Have you thought about a three chamber fourth order bandpass? That might be easier to get working, and sound more musical than the sixth order.