# Sub louder with trunk open



## Maylar (Dec 6, 2012)

I finally got around to installing a sub in my 99 Buick Park Ave. It's a Boston G3 10" in the recommended 0.5cu ft sealed enclosure. After setting the amp gain (400W with a -5dB 40 Hz tone), listening to music it sounded really nice. Put away my tools, closed the trunk to go for a ride, and noticed the bass level was lower than before. Popped the trunk and it came back up.

Hmm...

So today I tried to quantify the difference. I played a 40 Hz tone and adjusted volume for 80 dB (I have a meter), opened the trunk and there was no change. In fact if anything it was a bit lower by maybe 2 dB (meter wasn't very steady). But with certain songs, it definitely changes (opening bass line on Floyd's Welcome To The Machine, for instance).

Not sure how to proceed here. Relocating the sub isn't a viable option, since I use the trunk a lot. The sub plays through the cabin filter in my rear seats:










It's mounted about 6 inches back from the seats:










I would expect this to be great coupling into the cabin. Why does the ouput change so much with music?


----------



## qwertydude (Dec 22, 2008)

Try different test tone frequencies. Shouldn't be too hard to test since you have a meter. Then you'll be able to spot which frequencies are getting boosted when the trunk is open.

Also maybe try reversing the phase of the subwoofer. Then again testing the different frequencies.

You may be getting some cancellations between the subwoofer and your rear speakers. Considering you're listening to Floyd but testing with 40hz I'd say you need to experiment with higher frequency tones. What frequency are they crossed over at? It's possible opening the trunk is preventing standing waves from the sub and rear deck speakers cancelling each other in the trunk.


----------



## Kevin K (Feb 11, 2013)

Turn off (fade, etc) the rear speakers like mentioned above and see how that works.
You many need to seal the box to the seats as well so there's no loss thru the trunk.

Looks like you could move the box to one side and fire the sub back, not losing any space.


----------



## therapture (Jan 31, 2013)

Definitely try facing the sub backwards, instead of facing the pass through. In my G8 that has a similar pass through, it was a noticeable difference.


----------



## Changchung (Aug 15, 2012)

What about replace the box for a vented?


----------



## Horsemanwill (Jun 1, 2008)

put a grill on the sub and turn it around


----------



## therapture (Jan 31, 2013)

Changchung said:


> What about replace the box for a vented?


Vented could be louder if done correctly, but it won't solve cancellation or install related issues. When I had a sealed box in the trunk, it had the best response when placed in a corner, facing straight backwards. With that passthrough being the only vent into your cabin, it could also be acting like a bandpass enclosure with a narrow passband.


----------



## [email protected] (Nov 7, 2010)

If you are going to orient the sub like that you have to completely seal the trunk off from the cabin. The enclosure needs to be sealed to the cabin as well. The open trunk test tells me you probably didn't do that?


----------



## Changchung (Aug 15, 2012)

therapture said:


> Vented could be louder if done correctly, but it won't solve cancellation or install related issues. When I had a sealed box in the trunk, it had the best response when placed in a corner, facing straight backwards. With that passthrough being the only vent into your cabin, it could also be acting like a bandpass enclosure with a narrow passband.





[email protected] said:


> If you are going to orient the sub like that you have to completely seal the trunk off from the cabin. The enclosure needs to be sealed to the cabin as well. The open trunk test tells me you probably didn't do that?


I am not a expert on boxes, but I think that he build a good vented box, with a well frequency port he will get better responses and maybe loud with the trunk close...


----------



## thomasluke (Jun 10, 2011)

Bass cancellation

A little deeper than the first...http://www.installer.com/tech/index.php?page=aiming


----------



## [email protected] (Nov 7, 2010)

thomasluke said:


> Bass cancellation
> 
> A little deeper than the first...Aiming a woofer box in a car trunk - bass cancelation -


Yep....


----------



## Angrywhopper (Jan 20, 2010)

Turn the sub to face the trunk. I bet it sounds a lot louder


----------



## [email protected] (Nov 7, 2010)

Angrywhopper said:


> Turn the sub to face the trunk. I bet it sounds a lot louder


yep...


----------



## Maylar (Dec 6, 2012)

Thanks a lot for the ideas, guys. I'll experiment with phasing and try turning the box around and see if that makes any difference. Easy enough to do. Though logically it seems to me that facing the sub backwards would block the passthrough and make things worse.

Sealing the trunk isn't an option, as that would impact air flow through the cabin. This is my daily driver.

I can also use my 'scope and measure what the frequency the bass line is from the Floyd song. Not sure how useful that info will be, but being an engineer wants me to take data...

Some people have recommended removing the 6X9's in my rear deck for better coupling to the cabin. I'll try that as an experiment too, but losing my rear fill would break my heart.


----------



## therapture (Jan 31, 2013)

Maylar said:


> Thanks a lot for the ideas, guys. I'll experiment with phasing and try turning the box around and see if that makes any difference. Easy enough to do. *Though logically it seems to me that facing the sub backwards would block the passthrough and make things worse.*
> 
> *Sealing the trunk isn't an option, as that would impact air flow through the cabin. This is my daily driver.*
> 
> ...


The bass frequencies are so long in length that you can't just block them by turning the sub around. 

Block airflow? You like air conditioning your trunk? Maybe I misunderstand what you are saying...

And yes, having some holes in the rear deck would change things, probably dramatically, and for the better. If you have a solid front stage, with solid midbass, you don't even need rear fill. But in your case, it's a tradeoff, and you have to decide what you want, or what is most important.


----------



## BuickGN (May 29, 2009)

What I've found is if you want to have the sub facing forward right behind the seat it's very beneficial to seal the trunk from the cabin as best as you can. Obviously this is the case with my IB setup but also when I had a sealed setup facing forward it made a big difference especially in the lower frequencies. Also when I had a bandpass with the port through the armrest I got more low end by sealing off the trunk. Obviously it's not air tight, just the big leaks are sealed. 

It would be hard to affect airflow through the cabin if you tried. It's harder than people think. I spent a lot of time sealing mine and air from the AC has no problem making it from the AC vents to the outlet vents in the trunk. I also listened to the change in airflow with the fan on high and doors open vs closed when stock. When I would close the door or roll up a window there was a slight drop in output. After sealing the cabin from the trunk there was no perceivable change.


----------



## therapture (Jan 31, 2013)

As far as sealed in the trunk, facing backwards, with only the passthrough venting into the cabin...my G8 sub response was narrow and peaky. After I opened up the stock 8" holes in the rear deck, it came alive. My sub is now in the spare tire well, facing up, at the far rear of the car, and the response is quite nice. It digs deep and is snappy.

I vote the OP at least try it with no rear 6x9's and see what happens. Easy to try if the rear speakers come out easily.


----------



## jt_buck (Jan 25, 2013)

A few trunk cars are engineered to cancel out road noise coming from the trunk. This can also cancel out your bass. That's why your bass is louder with trunk open is because the frequencies are no longer being cancelled out. This is one of the big reasons people do bandpass through the rear deck or ski hole, or seal off their trunk from the cab.


----------



## BuickGN (May 29, 2009)

therapture said:


> As far as sealed in the trunk, facing backwards, with only the passthrough venting into the cabin...my G8 sub response was narrow and peaky. After I opened up the stock 8" holes in the rear deck, it came alive. My sub is now in the spare tire well, facing up, at the far rear of the car, and the response is quite nice. It digs deep and is snappy.
> 
> I vote the OP at least try it with no rear 6x9's and see what happens. Easy to try if the rear speakers come out easily.


I definitely don't suggest sealing the cabin from the trunk with the subs facing the rear. I would do the same, open up more places for bass to get through.


----------



## therapture (Jan 31, 2013)

BuickGN said:


> I definitely don't suggest sealing the cabin from the trunk with the subs facing the rear. I would do the same, open up more places for bass to get through.


No, it wasn't, I just had the sub in the corner, facing to the back.


----------



## 14642 (May 19, 2008)

No, none of this is correct, not even the links. When you open the trunk or the windows, the cabin of the car becomes a vented box. Because the volume of the car is so big, the tuning frequency is SUPER low and the change in frequency response appears to simply be a rise as frequency decreases. Turning the sub around will reinforce frequencies where the difference between the distance from the driver to the listening position and the distance from the driver to the reflecting surface to the listener is equal to 1/4 wave, but remember, bass radiates in ALL directions. Turning the sub around is NOT a "fix" for less bass when the trunk or windows are closed. If you seal the box to the cabin of the sedan, you'll minimize the bass boost when you open the trunk, but you'll still have more bass when you open the window.

Tune your EQ so the car sounds good with the windows closed. Then, be happy with the extra bass when they are open, or set a second preset to remove the additional bass.


----------



## therapture (Jan 31, 2013)

Andy Wehmeyer said:


> Tune your EQ so the car sounds good with the windows closed. Then, be happy with the extra bass when they are open, or set a second preset to remove the additional bass.


Or have a remote level control for the sub, which I prefer due to the wide range of music I listen to.

Thanks Andy, for more info.


----------



## Maylar (Dec 6, 2012)

Andy Wehmeyer said:


> No, none of this is correct, not even the links. When you open the trunk or the windows, the cabin of the car becomes a vented box.
> <snip>


This makes more sense to me than the cancellation theory. If it was all about reflections and cancellation then putting some sort of sound diffusion on the trunk lid would be the cure. I was actually going to try that...

I have moved the sub around in the trunk and tried facing it backward, all that gets me is reduced output. Fading the rear fill out made no difference.

I'll try removing the rear speakers and see what that does. Thanks again for the input guys.


----------



## therapture (Jan 31, 2013)

As noted, in my G8, what made the big difference was opening up the two, 8" holes in the rear deck. Having only the pass-through open to allow sound in was very narrow sounding and boomy, kind of a one note wonder. 

I guess you can say the sub can breathe now. Definitely much improved.


----------



## Danometal (Nov 16, 2009)

Going with the theme in the second link, I would turn the box around, kick it to one side, and slide it back towards the rear of the car where there's just a few inches between the cone and the rear of the trunk. You should be able to get luggage and such around that small of a box kicked to the side.

I build my boxes to intentionally set the cone within a few inches of the rear of my trunk for the least cancellation. I also had to reverse my sub's phase even with my front stage time delayed to it. And, I removed my factory sub from the back dash which opened up a hole for bass to vent.


----------



## ccapehart1980 (Aug 6, 2013)

okay maybe im an idiot or a smart ass 
but if you close the trunk anything inside that makes sound is gonna be a little quiter 

like if you kidnap someone and put them in the trunk there screaming 
the screaming is going to be alot louder when you open the trunk


----------



## Danometal (Nov 16, 2009)

Bass should be way louder when boundary loaded in a trunk. Trunk open is mostly open air. IMO, the fact that it's louder with the trunk open is proof that a lot of the bass waves are cancelling somehow.


----------



## jt_buck (Jan 25, 2013)

Look at my previous post, it's designed to cancel. You have to seal off your box from the trunk whether it's all firing forward, bandpass blow through style, or IB.


----------



## GlassWolf (May 8, 2010)

I haven't read this whole thread, but in regards to the bass being diminished by having the trunk closed, I wrote an article about this a while back that might help you out a bit:

Why is there more bass when my windows are open?

Also, instead of firing the sub into the cabin, maybe try firing it the opposite direction, or switching from sealed to ported or vice versa.

The short answer is that this effect is caused by the cabin or trunk of the vehicle acting like a second enclosure similar to a bandpass box. Opening the trunk changes the volume of the second [enclosure.]


----------

