Porting trunk

[johnjj728]

I bought two 4 inch ports and im gonna cut holes in the rear deck and try to seal the trunk as best i can and port the trunk into the car to get a lil more bass into the car....anyone tried this before? should it work decent?? P.Si have 2 12 inch Audiobahn alumQ's in a 2.8 cubic foot sealed box and a JBL 1200.1 amp running at 1.5 ohms.

Thanks,
John

 

[Audiowizard]

Originally posted by johnjj728
I bought two 4 inch ports and im gonna cut holes in the rear deck and try to seal the trunk as best i can and port the trunk into the car to get a lil more bass into the car....anyone tried this before? should it work decent??

If you click on my website in my sig, I have dual 3" ports for my a/d/s Reference 10" subs. I had to remove the factory torsion bars and build a gas shock lift system for my deck lid. The results are outstanding and the bottom end is entering the car the way it should. Here is a quick link with pics to my personal page:

Ported rear deck "Audiowizard style"

 

[johnjj728]

ya i want to do something similiar to that except my box is sealed so it would be a little different..you have quite the system wow i wish someday mine will look like that.

 

[mcss383]

I have done exactly what you are describing and wanting to do.....DON'T DO IT!! I got practically no difference in percieved output in the cabin from cutting holes in my rear deck. If you want to get MUCH better bass in cab, then simply remove the rear speakers. I DID notice a big difference in output after doing this and the good part is, you don't needlessly hack up your car.

 

[johnjj728]

ill remove the rear speakers first....but i dont see how it will help any???thanks

 

[Audiowizard]

Originally posted by mcss383
DON'T DO IT!! I got practically no difference in percieved output in the cabin from cutting holes in my rear deck.

Since mine is a direct port (different from what you want), it DOES make a difference and is worth all the time and effort that I did to achieve my goal. I agree with Bradley with just removing the rear speakers first and trying that.

I did a similar design on a Cadillac but I surgically removed the entire rear deck (minus the 3rd brake light) and built a replica rear deck with grill cloth and it hammered like a "MoFo" (just a thought!!)

The open rear deck was vented to the car with the dual 12" Earthquake subs, it was similar to a 4th order bandpass. It is an extreme mod it yielded massive bass like the customer wanted!

 

[mcss383]

Originally posted by johnjj728
ill remove the rear speakers first....but i dont see how it will help any???thanks

It helps by allowing the pressure in the trunk to enter the cabin. Pressure = sound, so the easier it is for the pressure to cross the boundary the more bass that you get. The dual ports just don't cut it for allowing pressure. I didn't really notice a difference when I put the ports in, but a huge diff with the elimination of the rear speakers.

When removing the rear speakers, you are going to want some much better speakers than stock up front or else you will loose all your upper frequency's...just something to keep in mind.


Yep Eddie, your method is great since you have a ported box.

 

[GNandTTA]

I did a similar design on a Cadillac but I surgically removed the entire rear deck (minus the 3rd brake light) and built a replica rear deck with grill cloth and it hammered like a "MoFo" (just a thought!!)

What did you rebuild the deck with. I would think that would lessen the rigidness of the car alot.

Bass notes have a very long wavelength. They are able to pass through most anything. I took out my 4X10's and put in 4" coaxials in sealed pods. The vacated space from the 4X10 opening now lets a "little" more bass in. In reality all it does is let in more of the upper bass notes since they are more directional. Did not help the deep "good" bass at all, as it shouldn't. But it did increase overall volume.

 

[Audiowizard]

Got it covered!

Originally posted by GNandTTA
What did you rebuild the deck with. I would think that would lessen the rigidness of the car alot.

I recomended bracing to him since I was removing some structural integrity. All I did was remove the top sheet metal on the left and right side and left the center in (apx 7" wide for the 3rd brake light mount). I made "X" braces ( just like the ones for the "G" bodies )out of 3/4" conduit pipe, flatened the ends, ground nice edges, drilled 3/8" holes, bent slight center offsets with my pipe bender and bolted them into place. I only charged him $50.00 for the bracing installed since I already had the pipe.

 

[Joe Tiano]

wow..i'm confused....you guys...can actually defy the law's of physics....but.. that seems to be easy in the car auido enviroment......maybe if it ALL really worked...the next concert we go to will have ....10,000 hi frequency drivers mounted all over the place....and of course many, many 5th or 7th order bandpass boxes mounted be hind the seats..with a port directing the bass to the listining area!..

 

[PPI Typhoon]

Yes, for the love of all that's holy, don't go cutting holes in your rear deck without properly finding out what you need.

By just putting ports in that trunk.......you're essentially porting the trunk...which is what...........15+ cu. ft? If you put lets say two 4" ports.........10" long in 15 cu. ft. That would tune it to something like 18Hz. In a bandpass (which is what this would be), it would be awful.

Your best bet is to port the enclosure you have already properly. And keep your ports on the same face as the subwoofers, to help prevent phase cancellation.

If you want.......I can help in the modification of your design. I know I work for Precision Power/Orion, but I'm sure I can get the specs for the subs you're using, and help you out. Just let me know.

BUT DON'T CUT HOLES!!

 

[Joe Tiano]

hey PPI typhoon...I need an orion 400BDG...i have an OLD 2x25 HCCA ...got any ideas???

 

[PPI Typhoon]

You have mail

 

[mcss383]

Joe, its not defying physics in any way. Porting a ported box into the cab of the car WILL net much louder bass. Removing rear speakers with a sub in the trunk will net more in car bass. Physics works FOR this principle not against...

 

[Joe Tiano]

Hmmm...a 50hz wave is how big..crest to trough?....a clue...ALOT bigger than your car!...and the lower you go the bigger it is!....i'm just rambling here...in the car auido world...you can DO almost anything you want!...

 

[johnjj728]

Originally posted by PPI Typhoon
Yes, for the love of all that's holy, don't go cutting holes in your rear deck without properly finding out what you need.

By just putting ports in that trunk.......you're essentially porting the trunk...which is what...........15+ cu. ft? If you put lets say two 4" ports.........10" long in 15 cu. ft. That would tune it to something like 18Hz. In a bandpass (which is what this would be), it would be awful.

Your best bet is to port the enclosure you have already properly. And keep your ports on the same face as the subwoofers, to help prevent phase cancellation.

If you want.......I can help in the modification of your design. I know I work for Precision Power/Orion, but I'm sure I can get the specs for the subs you're using, and help you out. Just let me know.

BUT DON'T CUT HOLES!!

the ports would only be about 2 or 3 inches long what would that be tuned to

 

[PPI Typhoon]

Originally posted by mcss383
Joe, its not defying physics in any way. Porting a ported box into the cab of the car WILL net much louder bass. Removing rear speakers with a sub in the trunk will net more in car bass. Physics works FOR this principle not against...

That's not entirely true. Because of the tuning capabilities, it won't necessarily create more sound, and can cause problems.

If you run the port into the trunk and not into the enclosure, then you're again, making a bandpass. And for it to be effective......you'd have to have a HUGE opening for it to be anything close to a gain. Otherwise, it will actually dampen the output. Because the properties of the bandpass enclosures (4th order), you want the tuning frequency high (like 80 Hz) and cutting two 4" holes will barely get your tuning to 20 Hz IF that.

So remember that when quoting physics laws, you have to observe all the factors. This is why cutting holes just doesn't work. It's best to modify the enclosure itself rather than the vehicle.

If the subs are in a sealed enclosure right now.......that's THE least efficient enclosure subwoofers can be in. You WANT a ported enclosure if want loud, and deep bass. Typically a sealed enclosure will only play down to 55 Hz before rolling off (your power handling rolls off too). Then in ported enclosure, you can play down to the tuned frequency generally without any problems......and has a much lower -3dB point. So if you take the enclosure you have........tune it to 40 Hz with a port......you could get as much as a 3dB increase in efficiency......basically the same increase you would get from doubling your amplifier power. AND you get a better power handling into the lower frequencies. If you're a rock kinda guy......tune from 40-45Hz. If you're a rap/hip hop kinda guy, tune from 30-35 Hz. Keep in mind that the higher you tune, the more SPL you will yield. (It will play higher volumes)

Hope this helps a little. Also helps from hacking your car up only to find that it's not done right.

 

[PPI Typhoon]

Originally posted by johnjj728
the ports would only be about 2 or 3 inches long what would that be tuned to

I'm not sure what the volume of the Buick trunk is, but from a reference of just 15 cu. ft. That would tune to roughly 25.12 Hz.

That's about 50Hz shy of where you want to be. If you wanted to make an effective hole to "bandpass" your trunk at 15 cu. ft. It would need to be an opening.....

20" x 40" and 4" deep for it to be tuned to 70 Hz, which is around what a typical bandpass enclosure is tuned to.

Now just off the top of my head, putting 2 12" subs in a proper enclosure, lets say 3 cubes for both, and have a 15 cu. ft. front chamber with a 20x40 port, 4" long, would give you a playable bandwidth of.....

*drum roll*
13 Hz

Now if you do that with 2 4" round ports, 3" long. That would give you a playable bandwidth of.......

*drum roll*
4.8 Hz

Now I dunno about you. But I'd not hack up my car for 5 Hz of playable bandwidth.

I have pictures and graphs if you want.

 

[Audiowizard]

Originally posted by Joe Tiano
wow..i'm confused....you guys...can actually defy the law's of physics....but.. that seems to be easy in the car auido enviroment......maybe if it ALL really worked...

 

[johnjj728]

so nobody recommends doing the ports??what would be a good idea to get more bass into the car itself??