NEw BOX for the Q18

Fishy · Post by **Fishy** » Mon Mar 19, 2007 8:49 pm

Long answer: To get a 28 Hz tune the port velocity with a pair of 21" long 6" round ports playing in 7.7 ft^3 at 1000 watts, with a 12 dB/oct butterworth hipass centered at 20 Hz maxes out just below 18 m/s(17 m/s being the "limit") at around 26 Hz. :)

Short answer: I think you can get away with just two 6" ports somewhat over 20" long. If you get some of those fancy flared ports(do they make em that big?) you should be completely good to go. Using 3 ports would require them to be over 35" long. Not good.

Once we get the exact airspace figured out we can get more accurate with the predictions, but I think this is a good guess.

subster87 · Post by **subster87** » Mon Mar 19, 2007 8:52 pm

hmm the fancy flared ones are only 17 inches lol so i might have to go with regular pvc which would save me a shit ton on money lol and jesus thats long.. Um where am i putting these on the box in reality the only place to put them with no bends is on the front of the box facing into the cabin or on the back with limited breathing room

subster87 · Post by **subster87** » Mon Mar 19, 2007 9:08 pm

well ill get the full demensions of the box one last time tomorrow to see if my cut list and drawings came out to close to the size of my acutal project to get a really specific enlosure size

Fishy · Post by **Fishy** » Mon Mar 19, 2007 9:17 pm

subster87 wrote:i know firing in the opposite direction of the sub has cancelation or so my local dealer instills on me. I know firing the sub into the cabin without the trunk sealed cancels but i dont know about if its just the port with the sub firing up. I think my best air space would be firing up simplest to get onto the box also. THe demensions within the box are freakin nuts they get complicated quick

Yeah firing up would be "safest", but then you gotta deal with grill cloth and elbows. How much depth do you have right next to the sub? Can you fit two 6" pipes in the corners? Might not need any elbows. They'll be awful close to the driver though.

Awww nevermind. I'm an idiot. You don't HAVE to make the port terminations flush with the top of the box. Let them stick out 6 inches or so on that lower "shelf" between the sub and the rear seat. All it does is change the end correction a bit(unflanged ends). You'll just have to make them wait...... about 3/4" longer. Plus you get the added bonus of preventing things from sliding around on top of your box and falling in! i.e. no need for grill cloth. It'll look industrial cool too, like a couple of velocity stacks. In fact that is EXACTLY what they would be, hehe. The only problem is if you use the flares you might get a little more turbulence w/o a baffle board, but you might not even need them. 1000 watts is a helluva lot of power to be "on" all the time.

To see if this will work all I need to know is the distance between the bottom of your box and your trunk lid at a location about 9" forward of the front edge of your sub. But let me do this tomorrow night. I got an 18 hour workday I gotta get up at 6am for.

:)

Fishy · Post by **Fishy** » Mon Mar 19, 2007 9:20 pm

subster87 wrote:hmm the fancy flared ones are only 17 inches lol so i might have to go with regular pvc which would save me a shit ton on money lol and jesus thats long.. Um where am i putting these on the box in reality the only place to put them with no bends is on the front of the box facing into the cabin or on the back with limited breathing room

Don't they just sell flared ends that slide over the PVC?

subster87 · Post by **subster87** » Tue Mar 20, 2007 4:28 pm

yeah they do but how could that work if im having them up in the air the flared end with just kinda be there lol umm and i have about 15 inchs of depth in the box on the front shelf sooo hmm they would stick up about seven inches lol. And i have lots of clearance from nine inches in front of the box i have 15 inch of box clearance no biggy. and yeah the box comes out to the same volume i already gave oddly enough exactly 8.25 lol. Now add in the cone and subtract the airspace that will be out of the box with the ports.. and perfect lol. Anyways thanks for the help those exact numbers would be great!!!

Fishy · Post by **Fishy** » Tue Mar 20, 2007 7:56 pm

I know it sounds retarded but it would work. Its simply matter of whether you like the idea of a couple "smokestacks" comin out the top of your box. :P

However, I think the simplest thing to do would be to port the thing into the cab, especially if there's no restrictions there. We'll get a more accurate box tuning that way. It'll also give you more cargo space and I don't think cancellations will be an issue with the frequencies the port is playing anyways. I reread this article:

http://www.teamrocs.com/technical/pages/aiming.htm

The wavelength of a 28 Hz acoustic signal in air is over 12 meters. In order to get "100%" cancellation at that frequency the ports would have to theoretically be located 1/4 wavelength or 3 meters(~10 ft) forward of the rear of your trunk so having your ports what, about 4 ft in front of the rear of your trunk? isn't that big of deal. What may be a big deal is that you might get more output from the ports if they were firing up into the trunklid due to reflections there. Its also nice to have the port closer to your driver to keep phase differences between those two outputs at a minimum. Even then lower frequency waves more easily propagate through things such as your trunk(this is one reason why when you hear some guy cruisin down the road jammin with his windows shut, you hear the bass, but not the midrange stuff). As a result of this and shorter wavelengths, cancellation causing reflections are more apt to occur in the upper bass frequencies such as those the driver will be playing(like 60 Hz as is modeled in that article). Unfortunately you're pretty much stuck with your driver placement, hehe.

So what I would do is install a couple flared 6" ports firing into the passenger compartment. Don't glue them in. If you don't like how they sound, just remove them and patch the holes, then try the "smokestack" method. It may not sound any better, but ya never know til you try. Its damn hard to predict. The car enviroment is a real sucky place to be listening to music in.

:)

subster87 · Post by **subster87** » Tue Mar 20, 2007 8:21 pm

no i dont mind the smoke stack idea i think acutally its the only one that will work lol

subster87 · Post by **subster87** » Tue Mar 20, 2007 8:22 pm

but why flared?

Fishy · Post by **Fishy** » Tue Mar 20, 2007 8:57 pm

subster87 wrote:but why flared?

Flared ports reduce chuffing. If you can buy ends I wouldn't even bother with them at first. Just put a couple smokestacks in there and see how it sounds, but don't glue them in. It may sound like crap(I hope not, hehe) and you might want to try porting out of the front of the box.

I'm thinking you might even want to try porting them horizontally on the back even though you've got limited space. Its just that once that box is in there you're not going to be able to remove them without tearing things apart, although you could just leave em in and patch the ends. I dunno. All this technical gobbilygook may not mean squat. The experimental method may very well be the best way to go to get your box to sound good. It may just end up looking a bit ghetto.

:)