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-   -   6th order bandpass design - (http://www.diyaudio.com/forums/subwoofers/84075-6th-order-bandpass-design.html)

TheWacoKid 1st August 2006 08:04 PM

6th order bandpass design -
 
Hey everyone, I'm new here (as you can see). I was told to come here with my questions, so here we go! :)

I know it's a tricky job to design/build a 6th order bandpass, but anyway - here's what I've got so far:

Gain:
http://people.clemson.edu/~dbonnie/Box/gain.png

I mapped out my current box (5.2 @ 35), the 6th order bandpass I'm looking at, and a 30 hz tune in the same 5.2 cube box. From this viewpoint the bandpass looks like it's the best in every category of flatness and extension.

Excursion:
http://people.clemson.edu/~dbonnie/Box/excursion.png

That's the excursion of the different setups at 450 watts input. Since I have no subsonic filter, the bandpass box again looks to be the best overall.

Port velocity:
http://people.clemson.edu/~dbonnie/Box/portvelocity.png

The graphs for the 2 ported boxes are with 54 sq inches of port, the bandpass is 36 sq inches for the rear port and 49 sq inches for the front port. The front port velocity can be seen here: http://people.clemson.edu/~dbonnie/Box/front%20port.png

I know admittedly little about designing this type of box, so how's it look so far? WinISD wouldn't calculate the "optimal" box for this so I kinda just played with the numbers till I get a flat curve in the passband that I liked. Group delay for all three boxes is about the same.

All three graphs have a 3rd order (18 dB/octave) 80 hz lowpass filter applied, as that's what my active crossover has. The subs are eD 13Kv.2 D4s, which are 4 ohm DVC. For my setup I have them in series-parallel for a final load of 4 ohms. Full specs can be viewed here: http://edesignaudio.com/product.php?...=Specs&cur=USD

Any insights? I know building this box would be rediculously hard and exacting, but I've been playing with the idea for a while and would be willing to put a lot of time into it tweaking it and getting it right. Space isn't of huge concern, the box I have now isn't exactly small and I can deal with losing a little more trunk space (I don't use it anyway). Everything that WinISD tells me is that the bandpass box is the best for overall output in the passband and overall power handling.

My goals are simply to get more output in the passband without resorting to new drivers or more power while retaining reasonable sound quality. I realize it's not going to be all that flat in my car, but I don't mind the bottom heavy sound that ported boxes offer so I don't think that'll be a problem. I'll soon be replacing my midbasses with a higher-output 8" driver to help blend the sub stage into the front as well.

Any comments are welcome and appreciated! :cheers:

Ivo_Hristev 2nd August 2006 06:29 AM

Hi,
if the port velocity graph is for 2,83V at the input ( as I think ), you will have problems with port noises. Also you will notice strange "out of band" noises. The both problems can be minimised by using flared ports. Reducing the out of badn noises further is acomplished by using sharp low pass filters.

The above is all my thoughts....

TheWacoKid 2nd August 2006 07:45 AM

Those plots are actually with 450 watts running through them. I was planning on flaring the ports as well as using a sharp low pass filter.

e-side 2nd August 2006 09:24 AM

Re: 6th order bandpass design -
 
Why don't you try a 4th order bandpass sub? Calculations for a flat alignment are available.

Quote:

Originally posted by TheWacoKid

That's the excursion of the different setups at 450 watts input. Since I have no subsonic filter, the bandpass box again looks to be the best overall.

Loudspeakers in vented and 6th order BP enclosures become unloaded below the (lowest) tuning frequency. Apparently you're going to play at quite high volumes, so you'll really need a subsonic filter. Closed and 4th order BP systems protect the driver from unloading, because of the enclosed air behind the driver.
Also, you'll probably end with a smaller box when choosing for a 4th order BP.

Bandpass systems need large ports, because all of the system's output goes through it. As with horns, only frequencies from the system's passband should be applied to the system, to reduce distortion, so your lowpass filters could be used for it.

Often vented and bandpass systems sound boomy in cars, because of the cabin gain and usually a (too) low tuning frequency.

4th order BP info and 6th order BP info

just some suggestions :)

Ivo_Hristev 2nd August 2006 11:34 AM

I belive that with such amount of power applied and with these port areas, you will have extra unwanted noises from the ports. But maybe they will get masked by the serious SPL generated by the system.

TheWacoKid 2nd August 2006 03:02 PM

Thanks for the tips! I've actually just contacted a pro designer to design the entire box for me (whether using one or both woofers) to meet my design goals. I'd rather not spend a ton of time/money on the box to find out I messed up the design somehow (which wouldn't be surprising :D).

I'll post here when I get the final plans for the box and see what you think of that.


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