# Trunk car - sub placement



## Fields92 (Jan 27, 2014)

This is going to be a little lengthy, but I think I should give as many details about my situation as I can to get your expert opinions. So bear with me.

I had a Sundown SA-12 in the trunk of my 2001 Saturn SL2 (if you aren't famililar with it, it's basically the same thing as a Chevy Cavalier). Originally the sub and port were facing the cabin. Later, I turned it around so that the sub and port were facing the rear of the car, and it gave me the same results that most people get. Most noticeably, a little more low end output.

I bought a second SA-12 and built a new enclosure for the two of them last weekend. It's only the second enclosure I've built, but it turned out really well. 4 cubes net, tuned to 30 hz, 65 inches of port area, and absurd amounts of bracing.

You might see where this is going. The only problem is fitting an enclosure that huge in such a little car. I had obviously taken measurements of the trunk before designing and building the enclosure, but it was a tighter fit than I was expecting. After a half hour of three of us pushing and shoving, we finally got it in.

However, it's such a tight fit that even with both back seats down, the trunk is basically sealed off from the rest of the cabin. Of course, I decided beforehand to have the subs and port facing backwards due to my prior experience with the single sub. 

The overall output is decent, but not what I was expecting. I've never seen the mirrors shake anywhere near this much, but it just doesn't seem as loud as all the shaking indicates that it should be. The low end extension was particularly disappointing. I really wasn't expecting the lows to let me down with these two subs tuned to 30 hz. I used to have a Fi Q 12" in a 4th gen Camaro tuned to 30 hz, and it was exponentially more impressive on the lows.

So my question is (finally!), could this be due to the subs being practically sealed off from the cabin? I know I should just experiment for myself, but I'd really like some assurance that I might get some results before I go and round up at least two friends and we push and shove around the enclosure and throw out our backs spending an ungodly amount of time just to turn the damn enclosure around when I might just decide I like it more how it is now.

Anyone have experience with something like this?

Any input is appreciated.


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## therapture (Jan 31, 2013)

Does your rear deck have speaker holes in it? My G8 has 8" oem spots (no speakers in it now of course) and there is a substantial difference in output, as compared to when the rear deck was blocked off.


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## Fields92 (Jan 27, 2014)

It does, and I have holes cut so that there is nothing obstructing the rear speakers. They're Alpine Type-R coaxials, I don't really want to take them out. But I'll probably give it a shot anyway.


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## therapture (Jan 31, 2013)

Having those "ports" in the rear deck will allow a lot of sound into the cabin.

Unless you like fuzzy, soft focus imaging, I really don't think you will miss the rear fill, especially since you don't appear to be running a DSP?


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## Fields92 (Jan 27, 2014)

I'm not, the rear speakers are really just for passengers in the back seats. 

I'd hate to see the $ spent on the Type-Rs, as well as the MRX-F65 essentially wasted. But I guess that's not the best way to make decisions.

I'll try it out this weekend.

Did you try subs and port forward in your trunk car?


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## therapture (Jan 31, 2013)

I have a small pass through that is blocked pretty solidly by the fold up armrest. I tried the sub far up and facing into the cabin, with the arm rest down, but since I did not have the enclosure sealed off against the trunk/cabin divider, it was sucky.

It was better facing backwards, firing into rear of the trunk.

Now it is mounted in the spare tire well, firing up, while the rear deck ports feed the cabin. 

Even if the sound gets through a thin metal panel, or worse yet a heavily damped and/or thick partition, a TON of energy is wasted doing so. With an open air passage into the cabin, sound and pressure can easily get to the front of the car.


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## amalmer71 (Feb 29, 2012)

I'd recommend checking the polarity of the wires to each sub to make sure they're the same.

If one's switched, the sound waves will be out of phase and you won't hear a lot of bass, but you'll still get a lot of vibration in the car because the speakers are still moving, causing vibrations.


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## jpeezy (Feb 5, 2012)

the port on a vented enclosure at tuning produces roughly the same or more output as the driver, so you'll want to try to keep the vent on the same plane as driver.


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## stevemk07 (Jan 3, 2012)

amalmer71 said:


> I'd recommend checking the polarity of the wires to each sub to make sure they're the same.
> 
> If one's switched, the sound waves will be out of phase and you won't hear a lot of bass, but you'll still get a lot of vibration in the car because the speakers are still moving, causing vibrations.


+1 check it out


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## HertzGuy (Jan 23, 2010)

Ok, so....what did you find out by checking the polarity of your subs?

I am curious to what you find? I am having similar issues with my sub. Tried lowering the rear seats, moving the box forward, aiming box & vent forward & backward, all to no avail! So I said screw it and bought bigger subs. Wondering what you found has worked for ya?!
Cause 2 SA-12s should be Wanging!! I don't think you should be complaining about OUTPUT with 2 of those babies!!


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## Fields92 (Jan 27, 2014)

The polarity was one of the first things I checked. They are in phase as they should be.

I tried taking the rear speakers out, and it made a pretty big difference in output, particularly on the lows, but I still wasn't happy with it.

So I tried turning the enclosure around (subs and port facing the cabin), and the difference was huge. More airflow into the cabin was definitely needed. The low lows, like 30 hz-ish are probably like 4 times louder now.

Unfortunately, they don't sound nearly as good on metal. Having them facing the rear apparently added a lot of punch. Metal is the main thing I listen to, so I'm not sure if I'll keep them this way or not.

Looks like there's going to have to be a compromise one way or another. The best thing would probably be to have them facing the rear, and just cut up the rear deck a lot to increase airflow. But I don't know how I could do that and keep it looking half way decent.

Anyone reading this, thinking about building an enclosure for a trunk car, consider how the airflow is going to get into the cabin!


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## humandrummachine (May 17, 2010)

My buddy put an 18" sub in his impala facing the cabin, seats up, and the sound was terrible. With the seats down or trunk open, it was excellent. Ended up facing the sub backwards, away from the cabin, and it cleaned up all the issues. Loud and sounds great. The box is huge too and blocks off most of the trunk from the cabin, along with the seats up. Still sounds great. Its like the exact opposite of whats happening to you.

Anyways, if you can't find a good solution, maybe try experimenting with a new box. If you listen to metal, build a smaller sealed box that you can flip around easily.


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## ZombieHunter85 (Oct 30, 2012)

I am having similar issues in my car, sounds way better with sub facing toward the trunk, however would it be better to face the port towards the cab, and seal the box off where the sub and port are firing only directly into the front of the car? Where the trunk is sealed off and the sub and port are firing into the cab? very curious about this as this is how I want to install my ported box. Or should I just keep it firing toward the trunk?


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## syc0path (Jan 23, 2013)

Sounds like u've got a couple of different issues here. I'm sure your trunk lid is rattling like hell w/ the subs aimed backwards, and that means a lot of bass is being wasted.

U've also got reflection/interference issues as the sound waves bounce off the back of the car (when aimed backwards) or off the back of the rear seats (when aimed forward). The interference changes depending on the position of the box and the materials that the sound is reflecting off of, so that's why certain freqs sound better in 1 direction and others sound better in another direction.

W/ a box that big in a trunk that small, u probably also have what is basically a bandpass-box effect, wherein the size and shape of the trunk itself is having an effect on the bass response.

And finally, u've got issues w/ the sound actually penetrating into the cabin.

So what to do about all this? Unfortunately it will probably require a lot of trial and error. I ran into a similar issue (thought not nearly as severe) when I built a sub box for my '99 Grand Prix. I intended to face the subs forward, and I built in a gap between the subs so I could still use the pass-thru in the back of the rear seat. It sounded awful, in large part becuz of the bandpass-box effect I mentioned above. Then I turned it around, and it sounded amazing! The bass reflects off the back of the trunk and then travels thru the gap between the subs. It doesn't interfere w/ the rear speakers, and opening the pass-thru isn't necessary. Of course, that was a much smaller box in a larger trunk...


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