# Facing a sealed box



## MrLister (Feb 17, 2006)

SQ wise, does it matter if in a sealed box the sub is facing forward or backward. Examples below



OR


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## azngotskills (Feb 24, 2006)

the first picture seems to be an IB setup?


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## bobditts (Jul 19, 2006)

I have found that it does make a difference and it varies from car to car. just experiment with your own to find the best one.


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## coffee_junkee (Jul 13, 2006)

I had mine facing up in the first iteration and facing rear in the second. The response was much better with the sub facing rear. Hope this helps..


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## ocuriel (Oct 7, 2005)

IMO, it usually sounds the best facing the most rear wall, a few inches away from trunk or tailgate.


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## MarkZ (Dec 5, 2005)

There was actually a good discussion on this a while back in rec.audio.car between Tom Nousaine and Eddie Runner (for those of you who might remember it). Yeah, it kinda turned into a flame war, but I think the most compelling point brought up was that aiming isn't as critical as position. That is, rear firing often works better not because of the direction it's facing, but rather because the rear-firing sub cone is typically closer to the back of the trunk. Here's a link to an article that Eddie wrote about it:

http://www.installer.com/tech/aiming.html


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## MrLister (Feb 17, 2006)

Interesting, I really wish there were a few more tests ran with the box facing the back of the car but not a few inches away from the trunk. Placing the box that close to the back is not practical for a presentational purpose. 

Regarding matching up the sine waves, is that something important I should be considering and doing when positioning the subwoofer box in the car?


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## rekd0514 (Sep 24, 2006)

From the threads I have read, the conscensus is that it should be faced towards the back.


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## GrnyEydDvl (Dec 28, 2006)

There are a few ways you can do it. You can fire it forward but if you do you should seal the trunk so everything behind the sub is sealed from the waves emitting from the front of the sub.

You can also fire it towards the rear without sealing off the trunk. The closer to the rear of the car you get the better your output will be.

The reason firing it forward without sealing the trunk does not work well and why moving it closer to the trunk when firing it backwards results in more output is because of cancellation. Or a lack thereof. 

You have waves emitting from the front of the sub and from the back. The waves emitting backwards bounce of the trunk wall and interact with the front waves. When you face it forward (without sealing) you get much more cancellation between the two waves. The closer you move the enclosure towards the rear when firing rearward, the closer you get to zero cancellation, as the wave bouncing off the trunk is only slightly out of phase with the wave that did not bounce off.


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## MarkZ (Dec 5, 2005)

If you seal the rear part of the trunk like that and fire the sub forward, do you get any adverse effects from the cone being close to the back seat? In other words, is it necessary to have a decent chunk of space between the cone and back seat? If so, how much?


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## 89grand (Nov 23, 2006)

GrnyEydDvl said:


> There are a few ways you can do it. You can fire it forward but if you do you should seal the trunk so everything behind the sub is sealed from the waves emitting from the front of the sub.
> 
> You can also fire it towards the rear without sealing off the trunk. The closer to the rear of the car you get the better your output will be.
> 
> ...


That's exactly how I understand this as well. Front firing subs only work well when they fire straight into the interior sealed up againts the rear deck or back seat. I discovered this issue about 17 years ago with my first subwoofer, a Kicker C10. I first had it under the rear deck firing towards a center hole in the rear deck, but not sealed against the deck, it sounded like sheit, no bass at all. Next I faced it towards the rear of the car and bass improved dramatically.


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## GrnyEydDvl (Dec 28, 2006)

To be clear, I did not mean that facing the sub to the rear and having it not close to the rear of the car was a bad idea. 

I have heard many a rear firing substage that was many feet from the rear trunk wall and had very impressive output.

The one thing to almost certainly avoid is firing the sub forward without properly sealing the trunk.


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## khail19 (Oct 27, 2006)

GrnyEydDvl said:


> The one thing to almost certainly avoid is firing the sub forward without properly sealing the trunk.


I assume you are only referring to an IB setup?


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## MIAaron (May 10, 2005)

Just like an IB setup, except with a box. You just seal off the mounting baffle like you would an IB baffle.


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## 89grand (Nov 23, 2006)

khail19 said:


> I assume you are only referring to an IB setup?


A front facing sealed box needs to be completely sealed into the cabin just like IB, if you don't want cancellation problems.


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## 02bluesuperroo (Oct 31, 2006)

khail19 said:


> I assume you are only referring to an IB setup?


I think he means even in a sealed box setup, you don't want it front firing unless you have basically created an IB setup even though the sub is in a box? This is how I understood it.  

What about having it firing up from the floor? 

What about a down firing sub in the trunk somewhere?



Edit: I r too slow ^^^ :blush:


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## khail19 (Oct 27, 2006)

89grand said:


> A front facing sealed box needs to be completely sealed into the cabin just like IB, if you don't want cancellation problems.


I understand cancellation to be the rear wave of the speaker cancelling out the front, causing a dip in the FR. If the rear wave is confined in a sealed box, how can there be cancellation? Maybe I'm off on the terminology.


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## squeak9798 (Apr 20, 2005)

khail19 said:


> I understand cancellation to be the rear wave of the speaker cancelling out the front, causing a dip in the FR. If the rear wave is confined in a sealed box, how can there be cancellation? Maybe I'm off on the terminology.


Read the link posted on the first page.

It addresses that issue exactly, and has some rudimentary drawings to illustrate (particularly the first image, about half way down the page).

Cancellation isn't _just_ the interaction between frontwave and rearwave, but between any two soundwaves. Both could have eminated from the front of the cone, but due to reflections/etc interfere with each other within the listening enviornment.


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## ocuriel (Oct 7, 2005)

MrLister said:


> Interesting, I really wish there were a few more tests ran with the box facing the back of the car but not a few inches away from the trunk. Placing the box that close to the back is not practical for a presentational purpose.


Agreed. not very pretty, but does sounds the best to me. evenso my my sub is molded into the r/r trim panel firing across. Not my favorite position for a sub, but does look good and I guess that's more important to me.


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## khail19 (Oct 27, 2006)

squeak9798 said:


> Read the link posted on the first page.
> 
> It addresses that issue exactly, and has some rudimentary drawings to illustrate (particularly the first image, about half way down the page).
> 
> Cancellation isn't _just_ the interaction between frontwave and rearwave, but between any two soundwaves. Both could have eminated from the front of the cone, but due to reflections/etc interfere with each other within the listening enviornment.


Sort of makes sense to me. So by rear facing the box, basically the sound is all reflected from the trunk back up to the listener. By front facing it, some sound goes straight forward, and some reflects off the back seat/rear deck and causes cancellation. By sealing off the trunk you avoid those unwanted reflections.


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## 89grand (Nov 23, 2006)

Exactly, say you have a sealed subwoofer system in the trunk facing towards the back seat, well some of the sound enters the cabin, while other sound waves reflect off of metal and what not in the trunk. When those reflected sound waves meet the original sound waves out of phase cancellation occurs. This only a subwoofer problem as any other speakers are placed in a door, kick panel or whatever, the front and rear waves are separated by the door, kick panel or whatever, but the front wave fires straight into the listening enviornment with no late reflections.

With a subwoofer in a trunk, you have a sealed enclosure inside another enclosure in a sense, and inside that second enclosure (the trunk) is where the cancellation problems occur. 

I'm even confusing myself, I think the illustration mentioned above will make it easier to understand.


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## MrLister (Feb 17, 2006)

khail19 said:


> Sort of makes sense to me. So by rear facing the box, basically the sound is all reflected from the trunk back up to the listener. By front facing it, some sound goes straight forward, and some reflects off the back seat/rear deck and causes cancellation. By sealing off the trunk you avoid those unwanted reflections.


Wouldn't a rear facing box also send waves back that the back of the sub sent in a similar fashion a forward facing box would?

I also have another quick question when it comes to a rear facing box. (because even with a rear facing box you have waves coming out the front and back, the waves that are aimed at the back of the car, should those be attempted to cancel?

** "reflex back" -> "reflect back"*


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## GrnyEydDvl (Dec 28, 2006)

MrLister said:


> Wouldn't a rear facing box also send waves back that the back of the sub sent in a similar fashion a forward facing box would?
> 
> I also have another quick question when it comes to a rear facing box. (because even with a rear facing box you have waves coming out the front and back, the waves that are aimed at the back of the car, should those be attempted to cancel?
> 
> ** "reflex back" -> "reflect back"*


You will always have incident waves and reflected waves. What has been shown to be common is you have more cancellation from phasing issues between waves when the sub faces forward.

With the sub facing rearward the waves are usually more aligned, therefore less cancellation. If you haven't, as Squeak said, read the link on the first page. It explains things very well.

I would not attempt to prevent the waves from reflecting off the trunk wall. 

Note - I made a mistake in my earlier post saying that the waves that emit from the back of the sub play a role in this discussion. As Squeak pointed out, that is not what I should have said. You have the wave coming from the sub (incident) combining with waves that have reflected off the trunk wall.

As far I know, the only time we should be concerned with waves coming from the back of a sub is in a ported box, where we hear them escaping the port. Hence the approx 3dB increase near tuning.


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## MarkZ (Dec 5, 2005)

khail19 said:


> Sort of makes sense to me. So by rear facing the box, basically the sound is all reflected from the trunk back up to the listener. By front facing it, some sound goes straight forward, and some reflects off the back seat/rear deck and causes cancellation. By sealing off the trunk you avoid those unwanted reflections.


Not quite. Check out the link I posted earlier in the thread. Bass is (mostly) omnidirectional, so it's not just emitting towards whatever direction the cone is facing.  It's being emitted all over. But when you're rear-firing, the cone itself is closer to the back of the trunk which reduces the effect of rear reflections. You would theoretically achieve the very same thing if you kept it front-firing but moved it back more so that the position of the cone was exactly the same in both cases.

But yes, sealing off the trunk with a partition of some sort would reduce the reflections as well.


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## MarkZ (Dec 5, 2005)

MrLister said:


> Wouldn't a rear facing box also send waves back that the back of the sub sent in a similar fashion a forward facing box would?


Yes. That's why the article I linked to said that front- or rear-firing is irrelevant. It's the position of the cone that matters. It just so happens that when you rear-fire the cone tends to be a box width further back in the trunk.


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## khail19 (Oct 27, 2006)

So having a side firing enclosure in the rear corner of the trunk would be better yet?


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## MarkZ (Dec 5, 2005)

khail19 said:


> So having a side firing enclosure in the rear corner of the trunk would be better yet?


It would seem so. But maybe the partition thing would be an even better option.


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## MrLister (Feb 17, 2006)

What about facing the subs up into the rear window?


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## Detune (Jun 3, 2008)

MrLister said:


> What about facing the subs up into the rear window?


I do this with a dual 10W0 JL Powerwedge box, they fire up and forward into the rear deck of my civic, and the rear speakers have been removed. Sounds bitchin. Going to experiment with putting them back at the rear of the trunk, facing rearward, and check the differences.


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## Patrick Bateman (Sep 11, 2006)

Detune said:


> I do this with a dual 10W0 JL Powerwedge box, they fire up and forward into the rear deck of my civic, and the rear speakers have been removed. Sounds bitchin. Going to experiment with putting them back at the rear of the trunk, facing rearward, and check the differences.


Low frequencies aren't directional. 

The reason that it sounds different is due to the fact that moving a speaker even six inches will change the in-room response.


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