# single 12 4th order bandpass build



## gatwix (Jul 30, 2013)

First things first, I am a newbee. O k so I tried to build my first bp box with port into center armrest of my sedan. I know that most boxes built anywhere from 4 to 1 to 1 to 1 port to sealed. I plugged my 12 inch alphasonik 700wrms specs to a couple free online bp calculator and it put out .866 for ported side and 1.3 for sealed. So I built with a port of 1.25x4x5.75l. I know. Ported side came out smaller. And sounds horrible. Real bad. In need of rescue. Oh and I did add for driver displacement and port.


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## [email protected] (Nov 7, 2010)

The first question I have is, did you seal the trunk airspace off from the airspace of the cabin? ONe way to test this is to play the stereo and open the trunk. If the bass is louder with the trunk open then you are having cancellation problems and need to seal the cabin from the trunk.
It is also very easy to mess up a bandpass enclosure, I would suggest starting maybe with a sealed??


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## gatwix (Jul 30, 2013)

Yes I did try the trunk open and closed and the doors also. I had a sealed box and box anf sounded good, then went to ported sound was way better but tons of rattleing. Not ass much after deadning and foam. But lots of trunk flex and losing a lot of bass trying to come into cabin of sedan. Why I wanted bp porting inside the car.


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## SPLEclipse (Aug 17, 2012)

You only have 5 in^2 of port area, which is not going to be capable of correctly moving the displacement of a 12" sub. That's also really small for a BP, I'd bet that the combination of a 50ish hz lp filter provided by the front chamber and the fsc of the sealed side are really close, which can be beneficial in a pure SPL setup but will severely limit frequency response across the spectrum. BPs can be great enclosures, but I think that one just isn't suited for the sub.


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## Oscar (Jun 20, 2010)

You need to start with accurately measured T/S parameters. It's really not that hard to do, nor is it expensive.....

I should add that it won't necessarily fix your problem, but it is a good habit if you plan to go the DIY route for subwoofer enclosures. The majority of the issues you are seeing likely stem from the incorrect porting. You need to look at vent air speed and keep it below 30 m/s at the very highest, with < 15 m/s being ideal along with flared/roundover ends.


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## gatwix (Jul 30, 2013)

What's are T/S parameters? And if I went to 13^2 inchs of port area what would be my length? Before I trash this box, does anybody have a program that can put out some numbers for me. Driver is 12 inch fs 28, qts .47, vas 2^3ft,


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## Hanatsu (Nov 9, 2010)

The T/S parameters is those values you mentioned; Qts, Fs, VAS for example.

The ones which are most important important are Qes, Qms, Fs, VAS, Sd, Re, Xmax. 

Give me those and I can check how it model. Note that the sub should be burnt in and that even the T/S may very from the manufacturers spec.

Sent from my Samsung Galaxy 3 via Tapatalk.


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## Oscar (Jun 20, 2010)

gatwix said:


> What's are T/S parameters? And if I went to 13^2 inchs of port area what would be my length? Before I trash this box, does anybody have a program that can put out some numbers for me. Driver is 12 inch fs 28, qts .47, vas 2^3ft,


http://www.linearteam.org/download/winisd-07x.exe


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## gatwix (Jul 30, 2013)

Qes 0.5, qms 7.7, fs 28, vas 2^3ft, sd .044, re 3.4x2, xmax +/- (mm) 14.5 Now lets see how bad I was off.


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## gatwix (Jul 30, 2013)

And oscar I've tried downloading winisd and it won't let me open it. I am working off my android phone though.


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## Hanatsu (Nov 9, 2010)

Looks pretty normal to me. No major issues. Power handling goes down below 35Hz pretty quickly.


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## HiloDB1 (Feb 25, 2011)

Hanatsu said:


> Looks pretty normal to me. No major issues. Power handling goes down below 35Hz pretty quickly.


Where is the graph of the port mach velocity?


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## Oscar (Jun 20, 2010)

gatwix said:


> And oscar I've tried downloading winisd and it won't let me open it. I am working off my android phone though.


That's because WinISD is a Windows-based PC program, not an android phone app. 

Hanatsu, that response looks alright. With that curve it shouldn't sound horrible, so it's probably the fact that he's trying to squeeze the output of ~500cm^2 cone through ~42 cm^2, lol.

A 20-25Hz HPF along with a slightly smaller sealed chamber lined with fiberfill and a higher tuning should result in higher mechanical power handling as well as slightly higher sensitivity. The ported chamber can then be adjusted to widen the passband if needed, even if you get a couple dB of ripple.


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## Hanatsu (Nov 9, 2010)

HiloDB1 said:


> Where is the graph of the port mach velocity?


Good thing you pointed that out. Totally missed it and I believe this is the issue here.

Input 37V = 75m/s maximum vent velocity = not good.



Vent is too small obviously. 32,3cm² with the OP's design. He needs approximately 130cm² to keep air velocity below 17m/s (which in my opinion is the maximum point for a non flared port to not create vent noise)


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## Oscar (Jun 20, 2010)

Gatwix as you can see you're way above 30 m/s, let alone 15 m/s for optimum results. Depending on how you actually built the enclosure, you may be able to modify it to get better results. Since you are android phone savvy, we'll be expecting pics of this enclosure from all angles and inside pics. That is, if you want help on possibly modifying it.


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## hurrication (Dec 19, 2011)

Vent velocity is definitely the culprit.

The models so far aren't accounting for cabin gain. When I model it with an estimated cabin gain rise, I see a mountain response curve with a peak at 30hz. I think if you keep the volumes the same but tune your vent to 65hz it will yield a better in car response. 4"x6"x10.5" slot will do for 400 watts.


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## gatwix (Jul 30, 2013)

Ok so it just seams like the first and biggest issue is the port. Way to much velocity. What happened is that I tried to shorten the port so that I didn't have to push my box back. Tomorrow I will remake port and take pics and post tomorrow. I had a feeling this was the issue when I could feel air blowing from bout a yard away. Lol. Thanks guys


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## gatwix (Jul 30, 2013)

I do have the driver in the ported side for better cooling. But way Is it that in my build the ported side has a smaller cubic air space, when usually its something like 2 to 1 ported to sealed?


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## Oscar (Jun 20, 2010)

gatwix said:


> I do have the driver in the ported side for better cooling. But way Is it that in my build the ported side has a smaller cubic air space, when usually its something like 2 to 1 ported to sealed?


you've been brainwashed by yourself if you believe that, plain and simple. There are no ratios that are set in stone that will apply to _ALL _subwoofers. This is because there is no _one_ single way to design a bandpass. All there is are shades of gray. It depends on what you want the final completed product to do---IE: do you want extended low bass and sacrifice the rest? do you want high sensitivity and sacrifice the rest? do you want small enclosure and sacrifice the rest? Bandpasses still obey Hoffman's Iron Law: Small, high sensitivity, low-bass extension----you can only pick two, and once you do, the third one _will_ suffer.

Wanna see what happens when you make the ported section 2x the volume of the sealed chamber for that ridiculous 2:1 ported:sealed ratio??

here ya go: http://www.linearteam.org/download/winisd-07x.exe

spoon-feeding time is over. Time to feed yourself now that you've been taught how to fish.


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## gatwix (Jul 30, 2013)

Ok finally got around to make the new port @ 4x6x10.5. And now it sounds way better. But still a little sloppy and not to much of a punch. Should I fiberfill the port side but shorten the sealed side. I think right now I'm at bout 1.8 db gain. Maybe to much for my couple year old sub? Any suggestions. Or maybe the port a lil to big at 20^2 inches for a .866 cubic ft ported side?


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## Oscar (Jun 20, 2010)

6in x 4in = 24in², not 20.

This port takes up more volume inside your ported section. This affects the final response curve. Did you take this into account? What is your new F3L? What is your new F3U? How much ripple does it exhibit?


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## cubdenno (Nov 10, 2007)

Yeah my single reflex for my 15 has a bigger sealed than ported side. Tuned around 65 hertz for a nice in car flat response. Big port though. 

Rules of thumb are usually wrong.


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## hurrication (Dec 19, 2011)

What's the model# of your sub? One thing that lower end companies are notorious for is fudging t/s specs. This sucks because depending on the margin of error, it could make or break an install - especially bandpass. It could also just be what the sub itself is capable of performance wise.

You could try lowering the displacement of the sealed side by shoving some filler blocks in there and some polyfill in the ported side and vice versa to see how it reacts. The port area is fine - no need to decrease it as you could run into velocity problems again.


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## gatwix (Jul 30, 2013)

It an alphasonik psw612e. How do u post pics off an android?


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## SPLEclipse (Aug 17, 2012)

gatwix said:


> Ok finally got around to make the new port @ 4x6x10.5. And now it sounds way better. But still a little sloppy and not to much of a punch. Should I fiberfill the port side but shorten the sealed side. I think right now I'm at bout 1.8 db gain. Maybe to much for my couple year old sub? Any suggestions. Or maybe the port a lil to big at 20^2 inches for a .866 cubic ft ported side?


Don't stuff the ported section.

Do you know what the new tuning is on the ported side? Having such a large port in a small section negates the point of bandpassing the signal acoustically; you basically made it a sealed box design but with mechanical wave control. The benefit is that you're directing the output from the sealed box into the cabin and probably giving you a little gain across the entire bandwidth just from loading. The downside is that you'll get a nasty spike in the higher frequencies that can make things (especially male vocals) sound echo-y and resonant. That's probably why it sounds sloppy. Do you have any means of EQ? Try crossing the sub at a higher slope/lower point?


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## gatwix (Jul 30, 2013)

No eq. I beleive its at 65 hertzs. Any suggestions on the port?


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## gatwix (Jul 30, 2013)

No eq. Do u have any suggestions of thr port size. Maybe making lil s maller but roundover the ends to prevent port noise?


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## gatwix (Jul 30, 2013)

No eq. Any suggestions on size of the port?


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## SPLEclipse (Aug 17, 2012)

You're really out of options concerning that enclosure IMO. Sure you could spend a bunch of time rounding edges, subtly adjusting placement, and so on, but you would be treading water. I honestly think you could get it to sound good if you had a PEQ to knock down any resonance or at least shelf the high end.


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## gatwix (Jul 30, 2013)

I've had toughts of remaking it with both 12s that I have. What are ur toughts on completly remaking the box. What would u suggest for box volumes and port size?


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## Oscar (Jun 20, 2010)

gatwix said:


> I've had toughts of remaking it with both 12s that I have.


If you're gonna go through the trouble, you might as well measure the T/S parameters yourself. Ain't that difficult, and it would increase your chances of success.


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## gatwix (Jul 30, 2013)

My funds are very limited right now. Where and how would I do this. This would be a different language for me.lol


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## gatwix (Jul 30, 2013)

I think that a big prob of my box is that the port is cut right in front of my magnet and I think u can here noise from the center breather hole.


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## Patrick Bateman (Sep 11, 2006)

IMHO, it's very difficult to get ported boxes to work without a Dayton Woofer Tester 3, or something similar. Unless you can measure the impedance of the box, the port tuning frequency is just a guess.

With a 'regular' ported box, this isn't the end of the world, because if you're off by five hertz the results will still sound alright. But with a bandpass box, if you're off by five hertz the box will sound terrible. Because you can lose or gain two or three decibels of output if you're off by a few hertz in a BP box.

Bottom line - if you're going to build a bandpass box, spend a few bucks on a WT3


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## gatwix (Jul 30, 2013)

Where can I get a wt3, and how little we talkin. And I'm sure not self explanitory, but I'm welling to expand my herizon.


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## Hanatsu (Nov 9, 2010)

Parts express sells them. Search for WT3 or DATS

Sent from my Samsung Galaxy 3 via Tapatalk.


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## Oscar (Jun 20, 2010)

You can measure them yourself if you have a multimeter, test tones, amplifiers, and a high wattage resistor. Well you get the impedance graph actually----then basic math to calculate the parameters. You can easily Google the procedure using your android phone. You may even find the procedure in the "how to" section of these forums.

Do keep in mind that it's very possible that you just happen to own a ****ty speaker and even measuring it's parameters won't magically transform it into an awesome speaker, nor will it guarantee that you'll be able to accommodate what it needs with your current box.

...and yes, placing the port right in front of the backplate vent hole wasn't a very good idea.


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## hurrication (Dec 19, 2011)

Here's the link to the current woofer tester. 

Dayton Audio DATS Dayton Audio Test System 390-806

I have one, and it's by far one of the best investments I've made not only because of getting t/s specs, but it also doubles as a oscope, signal generator, and it can test resistors, inductors, and capacitors!


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