# 4th or 6th Order Bandpass For Sound Quality



## 2MuchRiceMakesMeSick (Apr 6, 2011)

I have a RE XXX 12 and about 3 cuft to put it in a center console I will be building from MDF and then molding over the top with fiberglass.

Originally I wanted a slotted L design box using RE's website with the sub firing down but because I need to allow the 2.25 Inches for the sub to move (+ wave) + 1.5 MDF (double thick) + 0.75 for the top board + 13 sub depth + 2.25 L Port depth + 0.75 baffle for L port makes the box way taller then my 15" target. I'm trying to keep the box between 16.5 W x 15 H x 23 L.

So this leaves me with the sub facing front (or back). The problem is, if I port the box with it facing forward, I will wind up fiber glassing (essentially creating a box) on the front wave of the sub.

I DO NOT want sealed, I never liked the sound of a sealed box (just personal preference I guess) 

I have been playing around with WINISD and I noticed that I can get a much flatter response from a 6th order then a 4th order. I know bandpass is not typical for SQ installations but what are your thoughts on the situation?

Thanks in advance.


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## minbari (Mar 3, 2011)

dont like bandpass. have only heard 1 or 2 that were done right. it is REALLY hard to biuld them correctly. they can be very effective if done right, or they turn into 1 note wonders.


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## 2MuchRiceMakesMeSick (Apr 6, 2011)

Thats not what I want at all but I'm afraid with the way my install has to go I may not have a choice? If i build a console around the front wave, its like a bandpass anyways.


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## Patrick Bateman (Sep 11, 2006)

2MuchRiceMakesMeSick said:


> I have a RE XXX 12 and about 3 cuft to put it in a center console I will be building from MDF and then molding over the top with fiberglass.
> 
> Originally I wanted a slotted L design box using RE's website with the sub firing down but because I need to allow the 2.25 Inches for the sub to move (+ wave) + 1.5 MDF (double thick) + 0.75 for the top board + 13 sub depth + 2.25 L Port depth + 0.75 baffle for L port makes the box way taller then my 15" target. I'm trying to keep the box between 16.5 W x 15 H x 23 L.
> 
> ...


I did my first bandpass box about 21 years ago. One 'trick' to a good bandpass box is to use a really efficient vent. For a 12" sub, I'd be looking at a minimum of a 6" vent, and an 8" or a 10" vent would be even better.

WinISD is a horrible horrible program, and on of it's many flaws is that it doesn't model the losses that you get with vents that are too small. In other words, *WinISD will lead you to believe that the sub will play louder than it really will.*

If small size is a priority, a bandpass box with a twelve is probably not a good idea. Bandpass boxes have a lot of advantages, but size is not one of them. You *might* be able to squeeze a big vent and a 12" driver into that footprint, but if you undersize the vent, you're going to lose output.

As far as sound quality goes, you can definitely make bandpass boxes outperform sealed boxes. It just takes a little work. Bandpass boxes will generally have lower distortion, while sealed boxes will generally have better group delay. Pick your poison - low distortion or low group delay.

In some respects, I think that tapped horns are actually easier to get right than bandpass boxes, and tapped horns generally have better group delay than bandpass, as well as low distortion. They are a very nice solution.

If anyone's curious, the TH has lower group delay because the output from the rear of the cone is only 180 degrees out of phase, while in a conventional vented box it's 360 degrees out of phase.

The group delay of a bandpass box is even stranger, because there's a ton of group delay in the center of the passband, but less on either end.

This is why some bandpass boxes sound like they're "slow."

That's group delay that makes them sound like this.


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## 2MuchRiceMakesMeSick (Apr 6, 2011)

Very nice information. Thank you.

I also have Bass Box Pro that im using for design as well. Is there a better program? How do I design a Tapped Horn box?

What if i make the band huge 20-200hz which produces a pretty flat curve from 30-100hz in a 6th order design? The crossover will be set at 100Hz and lower.


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## 2MuchRiceMakesMeSick (Apr 6, 2011)

Ive done alot of reading about tline boxes (mostly quarter wave) but with my particular application i can only tune the box to 51hz (15x4.75) @ 65 inches long and even thats a very big box. My guess is that a 51hz tline wouldn't sound very good.


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## BuickGN (May 29, 2009)

I had a JL designed bandpass that fired through the ski pass with two 12W6s and it sounded very good, much better than the sealed box with the same subs and louder than the ported box with the same subs. It was crazy just how little excursion there was for the SPL level. It was very musical, not peaky and blended very well with the midbass. The only reason I got rid of it and went infinite baffle was space issues.


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## Patrick Bateman (Sep 11, 2006)

2MuchRiceMakesMeSick said:


> Ive done alot of reading about tline boxes (mostly quarter wave) but with my particular application i can only tune the box to 51hz (15x4.75) @ 65 inches long and even thats a very big box. My guess is that a 51hz tline wouldn't sound very good.


I've honestly never heard a quarter-wave sub that sounded bad. (I consider a quarter wave sub to be any design that's tuned to a quarter wave resonance, instead of a helmholtz resonance. So that would include transmission lines, front loaded horns, and tapped horns.)

The real challenge with quarter wave subs isn't making them sound good, because they all sound pretty good.

The real challenge with quarter wave subs is making them small enough, without making them so small that the added complexity isn't getting you anything.

In other words, as you make a quarter wave sub smaller and smaller, you start to lose the efficiency advantage, and eventually you reach a point where it's basically behaving like a sealed box. (IE, the "line" isn't doing anything.)

But if you're worried about a tline or a tapped horn or a horn sounding bad, it's really not a big concern. It's a hell of a lot easier to screw up a vented box or a bandpass box. Those designs are very susceptible to mistuning.


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## XtremeRevolution (Dec 3, 2010)

Never liked the sound of a sealed box? You obviously had some very poorly designed sealed box, or the sub was not suitable. 

If all you're going for is SQ, the distortion in a sealed box will be low enough because you're not cranking it loud enough to exceed xmax (if measured at 10% distortion). Group delay is another animal in itself, and is one reason why bandpass and SQ don't mix very well *if your primary goal is sound quality.* If you want a little of both, or "SQL," then have at it. If not, see the link in my thread and give me a chance to model a proper box for you. I've modeled well over 75 boxes now and not a single person came back to say that they were disappointed with the results. One guy kind of did a while back, but he ended up finding a massive leak in the prefabbed box he bought and he's since been very happy with it.


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## thehatedguy (May 4, 2007)

<-would like to do a TH for his car but doesn't know how to fit one that will go low enough in his trunk.


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## 2MuchRiceMakesMeSick (Apr 6, 2011)

I wish i knew enough about tapped horn to design one. Its a truck (dodge ram quad cab) and I took the center seat out so i have a little bit of room
16.5 wide total 
15 high
20 depth

I found this tutorial on making one but im stuck on step 6 and 7
Audio Psychosis • View topic - Insanely Easy Tapped Horns

Step 6: Adjust the area of the other segments so that they're a fraction of the mouth
Step 7: Adjust the length of the tapped horn so that it's resonating at the frequency from step 3. For instance, if your number from step 3 is 30hz, adjust the length so that excursion is at a minimum at 30hz.

There isn't a whole lot of information on TH boxes but ill keep reading.


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## thehatedguy (May 4, 2007)

There is a ton of TH stuff on DIY Audio in the subwoofer section.


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## vitvit (May 3, 2011)

XtremeRevolution said:


> If all you're going for is SQ, the distortion in a sealed box will be low enough because you're not cranking it loud enough to exceed xmax (if measured at 10% distortion).


But cone excursion in vented box will be less than in sealed box almost for whole frequency range we give for sub. Low tuned vented will have less distortion than sealed. (you are right about group delay as being different beast)


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> <-would like to do a TH for his car but doesn't know how to fit one that will go low enough in his trunk.


All of my best tapped horns were clones. I'd probably build The Insubnia if I had an excuse to have another sub.

Horns are a bit tricky, cuz they can sound great, but they sure need a lot of space.


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