# Ported Box - Too Big (9cu ft)??



## justinmreina (Nov 3, 2009)

Hello All,
*Question:* Are there any appreciable tradeoffs to this large of a box (9cu ft.), other than pissing of my girlfriend for consuming so much of the trunk? 

*Box/Sub:* 15" Brahma MKII, 9.1cu. ft. [email protected] Hz.

I set out to build a ported box for my 15" Brahma MKII. My install is in a Subaru wagon and I had a lot of space to work with. Long story short (I can elaborate if necessary) I ended up with a 9.9 cu. foot enclosure (9.1 net). My intentions were to finally build a flat box for this sub. The first box I had built for it was an SPL honker tuned to 36 hz. Sure was great for the SPL comp, but musically it was terrible. The second box was sealed 3.3 cu feet. This one lacked the low end to a certain degree. So my goal with this ported box was to finally get a good balance out of the sub!

Thanks,
Justin Reina

*I won't be able to install and test for about 5 more days, and this question has been gnawing at me. 9 cu. ft seems a little much...


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## mvw2 (Oct 2, 2005)

How exactly do you fit that size box in the trunk? I own a Forester and I wonder if you'll actually build it right to magically slide in somehow.

That's a lot of weight on the back of that poor car, something both the springs and dampers weren't designed for. You WILL be riding on the bump stops...all the time.

As well in a car, it's sort of pointless to build a box to play that low. You should have more then enough cabin gain to go low sealed. You don't really have excursion limits sealed either. Best of all, it's only 3 cu.ft. to fit. F3, the -3dB roll off point, is at 40Hz which is pretty appropriate for a car environment.

The problem is ported doesn't really gain you much once the box gets so big. It doesn't really help excursion. It doesn't really improve power handling all that much. You're just adding size and weight.

Also, 9 cu.ft. is a bit big for that sub. According to the T/S specs for it, ported is 6.6 cu.ft. tuned to 22Hz (classic "ideal"). Sealed is 3.2 cu.ft. (classic "ideal"). You could very likely fit it in 2.5 cu.ft. or even 2 cu.ft. well stuffed if you wanted an even more compact configuration.


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## Maglite (Dec 28, 2009)

Can you hear 19 Hz?


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## justinmreina (Nov 3, 2009)

no of course not...

My target was 6.5 cu ft @ 22hz like you mention. However 22hz doesn't look so hot in WinISD @9cu. ft. (about a 3dB peak), so I went a little lower to 19-20hz. This box is 80% fiberglass so it only weighs ~40 lbs minus the sub. I was somewhat dumbfounded when I calculated out the final volume, during my build I never saw it getting that big!

Maybe I can cut it in half and make two boxes ?

Thanks,
Justin Reina


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## justinmreina (Nov 3, 2009)

*@mvw2:* I made my own floor and built a spare-tire well box to make it fit. I laid out the front baffle and the rear amp mount (back of box), and made the box from there. I swear I thought it was going to be 7cu. ft. max!:surprised:


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## Patrick Bateman (Sep 11, 2006)

A 15" Brahma in a ported box tuned to 19hz will be ANYTHING but flat once you factor in cabin gain.


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## ncv6coupe (Oct 25, 2009)

I wish I could hear this beast in your wagon, what do you plan on high passing this at, anything over 40-50 hz is not gonna do it for you!


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## fastlane (Apr 6, 2009)

ncv6coupe said:


> I wish I could hear this beast in your wagon, what do you plan on high passing this at, anything over 40-50 hz is not gonna do it for you!


I assume you mean low pass?


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## ncv6coupe (Oct 25, 2009)

oops< hahaha low pass thats rite thx


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## 94VG30DE (Nov 28, 2007)

I have been looking at weird group delay issues while trying to design a box that I feel like is WAY too big. It is close to double the normal volume, and is tuned ~22Hz. In WinISD the group delay is higher than the graph goes, but it is pretty low in the frequency range. Will something like that be an issue?


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## justinmreina (Nov 3, 2009)

*@ncv6coupe:* Look me up if you're ever in town and you can take a listen.

*@fastlane:* I was confused there too for a second 

*@Patrick:* I simply made my design goal to be less than a 2dB ripple and a cutoff below 35 Hz. Would a good design goal in the future be to first characterize the cabin gain, and then build a box to compensate as much as possible?

Thanks,
Justin Reina


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## chad (Jun 30, 2005)

Patrick Bateman said:


> A 15" Brahma in a ported box tuned to 19hz will be ANYTHING but flat once you factor in cabin gain.


yeah, but it sure as **** would be fun.

And above all efficient, you can always turn down and use less power, but you cannot turn up and use less power


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## ncv6coupe (Oct 25, 2009)

richard clark said to keep the group delay under 25ms at 20hz and you should be golden, i try to keep my group delay as close to a sealed box is in the 45-70 region, thats where those metallica kick drums transients really make people aww at my bass, haha, my group delay peak is right at my 31hz tuning frequency, and it's only 19ms so control is left to sub and amp, I can't tell any sloppiness but the garage door can when I'm listening so some bass heavy reggae!


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## ncv6coupe (Oct 25, 2009)

justinmreina said:


> *@ncv6coupe:* Look me up if you're ever in town and you can take a listen.
> 
> *@Patrick:* I simply made my design goal to be less than a 2dB ripple and a cutoff below 35 Hz. Would a good design goal in the future be to first characterize the cabin gain, and then build a box to compensate as much as possible?
> 
> ...


i JUST left washington yesterday, I was up there doing some work for the weekend. DAMMIT, post earlier next time, :laugh::laugh: JK

and that question to patrick is exactly right, theres a pic somewhere on here that Andy from harmon kardon posted that shows that you can gain more than *20db/octave* down low, SHEESH


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## stickler (Jan 31, 2009)

I would love to check this out also, I'll be in Seatown in a couple of weeks!

What amplifier are you going to use?


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## Patrick Bateman (Sep 11, 2006)

ncv6coupe said:


> i JUST left washington yesterday, I was up there doing some work for the weekend. DAMMIT, post earlier next time, :laugh::laugh: JK
> 
> and that question to patrick is exactly right, theres a pic somewhere on here that Andy from harmon kardon posted that shows that you can gain more than *20db/octave* down low, SHEESH


Someone emailed me about making them a tapped horn and I can't figure out where. I have something like ten email addresses. Was that you?

(I don't live in NYC, that's just a goof. I live in the PNW.)


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## Patrick Bateman (Sep 11, 2006)

chad said:


> yeah, but it sure as **** would be fun.
> 
> And above all efficient, you can always turn down and use less power, but you cannot turn up and use less power


Are you sure?

There are a few different ways to raise the efficiency of a loudspeaker. You can use a big box, or use a lighter cone, or figure out a way to get some of the output from both sides of the cone. Or all of the above.

A Brahma in a big ported box does two of those things. It gets some output from the back side of the cone via a vent, and it also uses a big box to raise the efficiency.

The problem with the design is that it rasies the efficiency _where we don't need it._

We already have GOBS of efficiency at 20hz due to cabin gain. We're getting 20 to 30dB for "free" at 20hz. So raising the efficiency at 20hz is a complete waste of space.

If you want to increase your output, focus on 40 to 80hz. In that octave we're only picking up about 10 to 15dB of cabin gain, so efficiency is a bigger issue in that octave than the octave below it.

Here's an example of what I mean:

Design the sub so it can kick out some serious output at 40hz outside. Let's say you aim for 135dB. Tweak it so the response falls at 12dB/octave. That means your putting out 123dB at 20hz.

Now put it in the car.

Thanks to cabin gain, 135db at 40hz becomes 147dB, and 123dB at 40hz becomes 147db.

Voila!

You now have a sub that's flat, and you're hitting 147dB.

If you aim for flat response outside, you'll end up with a ton of useless output at 20hz, and not enough at 40hz.

Here's a real world example:
















Let's compare a 15" Brahma in a 9cf vented box against a pair of Danley Tapped Horn Minis. The tapped horns take up a little bit less space, a hair under 9cf for the pair. We'll give the Brahma two thousand watts, and each tapped horn will get 1000 apiece.

The tapped horn will put out 104dB at 20hz, 128dB at 40hz, and 137dB at 80hz.
In a nine cubic foot vented box, the Brahma is basically flat to 20hz. It's belting out 112dB at 20hz, 112dB at 40hz, and 112dB at 80hz.

So the Brahma wins right? It has a full 8dB more output at 20hz. *Not so fast  *

Put them in the car, and the story changes.*
*In the car, the TH-Mini belts out 128dB at 20hz, 140dB at 40hz, and 137dB at 80hz.
In the car, the Brahma belts out 136dB at 20hz, 124dB at 40hz, and 112db at 80hz.*

Wild huh? The TH-Mini is flatter and louder in the car. The vented Brahma has too much output at 20hz, and not enough at 40hz. Can you see what I mean about the importance of 40 to 80hz? The TH-Mini is absolutely annihilating the Brahma in that octave, with a whopping 25dB advantage at 80hz. Depending on cabin gain, a single Brahma would need as much as HALF A MILLION watts to make up for a 24dB deficit at 80hz.

_* these numbers use a simplified analysis of cabin gain, with 24dB of extra output at 20hz and 12dB at 40hz. Your results may vary. The only way to be certain is to measure your own car. The point is that it's easy to generate bass in a car from 20 to 40hz. It's above that point where things are tricky._


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## ncv6coupe (Oct 25, 2009)

no that wasn't [email protected], and now I'm REALLY upset, i would have LOVED to hear your car, I'm going into depression now, that would have been perfect to top out a stressful weekend.


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## Patrick Bateman (Sep 11, 2006)

ncv6coupe said:


> no that wasn't [email protected], and now I'm REALLY upset, i would have LOVED to hear your car, I'm going into depression now, that would have been perfect to top out a stressful weekend.


YOU'D love to hear my car?

I would too, it's a pile of parts in my garage right now


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## justinmreina (Nov 3, 2009)

Thanks for the input to all! I love this forum just for this kind of feedback and interaction. I would like to reiterate though that I wasn't shooting for a 9cu ft. box . I can't wait to get my mic and actually get the response in and out of car.

*@stickler:* I have an old Planet Audio TT1250D. Plenty of power to the point that my Subaru tells me 'no more'...

*@Patrick:* I am considering building a parametric EQ (on the RCAs) just for my sub. Not because I have found I need it (yet), but more because I've wanted an excuse to build one for awhile now and the sub seems forgiving enough with regards to noise & interference.

*@all:* So to re-propose the question, there is no significant penalty to the large box?

-Justin


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## ncv6coupe (Oct 25, 2009)

You need lots and lots up upper range bass (50-320hz), what are you gonna handle that range with?


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## justinmreina (Nov 3, 2009)

Could you elaborate a little on your question?

Thanks,
Justin

*As a side note, I'm kind of an SPL wimp. Kind of like my dad's old Chevelle. Sure it has a beefed up 396, but he hasn't taken it over 80 in 10 months... So this Brahma won't get turned up that much.


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## JoshHefnerX (Jun 13, 2008)

Justin, just thought I would add my 2 cents in here, as I have a little experience in similar situation. 

I had an 02 wrx sedan, w/ a mk1 brahma. Dan Wiggins stated to me to use about 3.25 -3.5 cuft tuned low (~29hz). It was sealed from the trunk so that nothing back there vibrated, but in the car my vision would shake.

So that's what I did and it absolutely hammered from about 18hz - ~50hz. At that point it dropped of very quickly to the point where I needed more midbass to make up for a hole. If I did it again I would probably use about the same size box and tune just a bit higher ~35hz. Wagons like to resonate just a bit lower than the sedans also.

I was putting about 1100 watts into it and on long loud passages it would start getting a bit hot.


edit: Now I always wanted to try out a 9cu ft ABC box w/ the brahma. That would be interesting...

Josh


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## JoshHefnerX (Jun 13, 2008)

justinmreina said:


> *@all:* So to re-propose the question, there is no significant penalty to the large box?
> 
> -Justin


Having a very large ported box "generally" gives more of a bump at the tuning frequency - the larger the box the bigger the bump. Works pretty well for spl comps. It also throws off the group delay.

Josh


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## justinmreina (Nov 3, 2009)

Hey Josh,
Thanks for the input about the wagon, I am curious to see how it measures out. That was kind of my guess.

The hard part about my comparisons for this sub is that the last time I had it installed, I was a freshman in college and new next to nothing. Thus my qualitativ interpretations were worth little to nothing. And yet I am basing my current build off of them, go figure 

edit: I still know little-to-nothing, just in a different way now


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## ncv6coupe (Oct 25, 2009)

What other speakers do you have in the car, midbass and midrange? That box is a real"SUBwoofer"
It will not have the high end extension of a smaller box but if you don't really like it loud then u may be ok. But at anything past mid volume, it may be lacking and have more rumble than boom unless you eq it.


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## justinmreina (Nov 3, 2009)

*@ncv6coupe:* Yeah I'm planning on building a dedicated equalizer for the sub box late January, after I characterize it in the cabin. Hopefully I can get away with something very simple, but we'll see.

Speakers - I used to have a set of 6.5" Adire Koda Components, and they were heaven. Until one of the mids failed and Adire happened to be out of business ... Saddest day of my life. And with regards to my new set, I will only tell you if you really really want to know. I am experimenting with a certain brand that is passionately hated on this forum.

Thanks,
Justin


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## ncv6coupe (Oct 25, 2009)

For some reason I think its either "I" or "J". No need to know but hope everything works out for you. Keep us posted on those measurements and feel of those test tones when you put that sucker in!


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## justinmreina (Nov 3, 2009)

what's I and J? Sorry for the ignorance 

-Justin


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## ncv6coupe (Oct 25, 2009)

Abbr for the hated company


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## justinmreina (Nov 3, 2009)

India or Japan? I do hate them because they steal our electronics jobs... ?


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## Patrick Bateman (Sep 11, 2006)

justinmreina said:


> Thanks for the input to all! I love this forum just for this kind of feedback and interaction. I would like to reiterate though that I wasn't shooting for a 9cu ft. box . I can't wait to get my mic and actually get the response in and out of car.
> 
> *@stickler:* I have an old Planet Audio TT1250D. Plenty of power to the point that my Subaru tells me 'no more'...
> 
> ...


The downside of a large box is that it's efficient where you don't need it to be (below 40hz). Putting it in a sealed box with a QTC over 0.707 would increase output above 40hz, so that it would measure flatter in the car. Besides saving a lot of space, it would require less EQ. (I would still recommend EQ for *all* systems.)

Twenty years ago you used to see some giant vented boxes, because woofers tended to offer higher efficiency and lower xmax. So a big vented box was a way to get into the 20s and 30s.

Nowadays a big vented box will get you into the teens, even the single digits. That's because woofers have more excursion, lower efficiency, and lower free air resonances.

In 1985 the typical fifteen had an FS of 35-45hz; now it's something like 15-25hz.


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## T3mpest (Dec 25, 2005)

If he didnt' like the low end output of the sub in 3.3 he ins't going to like in 2 cubes either, which is about as small as he would have to go to add a bit to upper end and actually cut some low end. Anyway I'm modeling a brahma atm and they are very peaky in ported enclosures, how big was your last one at 35hz? Something like [email protected] might be a better compromise between low frequency response and effeciency. This is especially true if your last enclosure was bigger than 3 cubes.


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## justinmreina (Nov 3, 2009)

> If he didnt' like the low end output of the sub in 3.3 he ins't going to like in 2 cubes either,


I was thinking about this today after posting it and realized that my evaluation metrics back then were nonsense. So I guess my answer is I'm not sure what I would think of that 3.3cu. ft. sealed box if I gave it a listen today. Wish I still had it.

-Justin


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## chad (Jun 30, 2005)

Patrick Bateman said:


> If you want to increase your output, focus on 40 to 80hz. In that octave we're only picking up about 10 to 15dB of cabin gain, so efficiency is a bigger issue in that octave than the octave below it.
> 
> Here's an example of what I mean:
> 
> ...




Problem is that when some think car boxes (thanks to kicker in the early 90's) they think shoebox, where the driver is well into falling on it's face at 80 cycles. But hey! We have cabin gain.. so we take an inefficient box and pour assloads of power at it for a "flat response." Which, incidentally is NOT what 95% of the car audio world is going for. So instead of pouring gobs of power at a shoebox let's build a larger more efficient enclosure, that yes, will be more efficient at 40-80 also. THEN attenuate what we don't need. Vola, no more shoving gobs of power at a shoebox. Given a cooperative driver you don't really even need to make said enclosure that much bigger to do this.


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