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View Full Version : OK idea to start sealed, then maybe port??



drpeeb
04-30-2009, 03:31 PM
Alpine PDX-5 (300W RMS @ 2ohms or 4ohms) feeding two Alpine SWS-1043D subs (4ohm DVC; 300W RMS/ 900W max) in two separate boxes.

I can only get about 0.9 cu-ft for each box*. I was thinking about trying them sealed first, and if I don't like it try adding a PVC port.

I calculate that a round port 5" dia. & 37.06" long, aka tuned to 38 Hz, "should" work.

Good ideas, bad ideas, or ????

Am I thinking right?


* Box size 20 x 18.5 x 6.5 = 0.91 cu-ft. Might get an extra inch one way or the other, but not much more. For under a truck extended cab rear seat.

dappa5
04-30-2009, 04:03 PM
what kind of truck?

hatemonger
04-30-2009, 04:08 PM
they will perform far better sealed at .9, then ported at .75 (after displacement). that is 1/2 what the sub needs ported. it won't sound good. with your space, you're better off doing a single 10 ported on around 1000 watts. or a couple of 8's ported. or a couple of 10's sealed.

drpeeb
04-30-2009, 04:10 PM
what kind of truck?

Nissan Titan King Cab

dappa5
04-30-2009, 04:13 PM
they make sealed boxes for that truck that will give you a little more cubes
then you ca vent them if you don't likje the sound
i did it in my work truck just left it sealed

drpeeb
04-30-2009, 04:14 PM
they will perform far better sealed at .9, then ported at .75 (after displacement). that is 1/2 what the sub needs ported. it won't sound good. with your space, you're better off doing a single 10 ported on around 1000 watts. or a couple of 8's ported. or a couple of 10's sealed.

Hey tks for the input. I will go with the two 10's sealed then.

Just FYI ... the Alpine manual says the volume range (gross) for sealed with this sub is 0.65 - 1.5 cu-ft.

Does this tell us that the 0.65 number is a bottom-of-the-barrel, not-really-very-good number?

drpeeb
04-30-2009, 04:15 PM
they make sealed boxes for that truck that will give you a little more cubes
then you ca vent them if you don't likje the sound
i did it in my work truck just left it sealed

Well, I have the ability and tools, so I'm just gonna make them myself ... part of the fun I guess.

I will probably leave them sealed ... Would be nice to be able to like flip a switch and hear sealed vs ported, though, wouldn't it?!!

hatemonger
04-30-2009, 04:16 PM
Hey tks for the input. I will go with the two 10's sealed then.

Just FYI ... the Alpine manual says the volume range (gross) for sealed with this sub is 0.65 - 1.5 cu-ft.

Does this tell us that the 0.65 number is a bottom-of-the-barrel, not-really-very-good number?

it will do ok at the lower number. it will probably be a little more "punchy", and will lose some lower end also. the high number is usually "optimal", but i wouldn't trust the manufacturer. it should be ran through winisd.

hatemonger
04-30-2009, 04:20 PM
Well, I have the ability and tools, so I'm just gonna make them myself ... part of the fun I guess.

I will probably leave them sealed ... Would be nice to be able to like flip a switch and hear sealed vs ported, though, wouldn't it?!!

waste a little wood and build a couple of crude square boxes first. i've worked with alpines quite a bit, and i can tell you that they will sound really bad in that small of a ported box. you could do some 8's in that small box ported, but not many 10's.

drpeeb
04-30-2009, 04:31 PM
waste a little wood and build a couple of crude square boxes first. i've worked with alpines quite a bit, and i can tell you that they will sound really bad in that small of a ported box. you could do some 8's in that small box ported, but not many 10's.

Yeah ... I'll try the obvious first: Sealed as big as I can possibly make it, and listen to that. If it's bad, I'll just have to start losing space in the back seats for passengers, for either bigger sealed or ported.

DNick454
04-30-2009, 06:24 PM
The problem with sealing a box and then porting is the fact that while sealed, they will have a specific volume. Typically for ported you want more volume than its sealed counterpart. By adding the PVC port, you are subtracting even more volume from the box, making it much to small to perform well. Also, with how small it would be volume wise, you couldn't make the PVC port long enough to tune it how you'd like it without having it sticking like a foot out of the box and looking hella ghey. Just my $0.02

drpeeb
04-30-2009, 06:38 PM
The problem with sealing a box and then porting is the fact that while sealed, they will have a specific volume. Typically for ported you want more volume than its sealed counterpart. By adding the PVC port, you are subtracting even more volume from the box, making it much to small to perform well. Also, with how small it would be volume wise, you couldn't make the PVC port long enough to tune it how you'd like it without having it sticking like a foot out of the box and looking hella ghey. Just my $0.02

I agree with the small-ness problem I have (ouch that hurts to admit) ... but couldn't the PVC make a turn or two inside the box? Should make no difference, might actually even help cut down noise.

Also ... as for porting later, it's all just calculations. Let's say I did not have my small-ness problem (ouch again), I could start with a sealed 1.25 cu-ft box, then if I wanted to port it, all I'd have to do is calculate the appropriate port area and length in relation to how much of the existing box volume it would consume. Might take several runs of trial-and-error port-to-box-volume math calcs, but no reason it shouldn't work, I don't think.

This box volume and port calculator could be used: http://www.the12volt.com/caraudio/boxcalcs.asp

dappa5
04-30-2009, 06:40 PM
porting a 1.25 cube is very touchy gl let us kno how it turns out

DNick454
04-30-2009, 06:41 PM
The problem is, when you curve the PVC port, it still takes up volume inside the box, even more actually. Ontop of that http://www.the12volt.com/caraudio/boxcalcs.asp does NOT account for the actual volume INSIDE the box taken up by the port... So even though you think you're getting a certain port length, it is infact WAY longer and not possible due to the fact that the calculator is not subtracting the volume taken up by the port assembly itself. Sealed is your best and only option, sorry to say. Unless of course you are willing to sacrifice some space in the cab somehow.

dappa5
04-30-2009, 06:42 PM
don't 4 get sub displacement

drpeeb
04-30-2009, 06:45 PM
The problem is, when you curve the PVC port, it still takes up volume inside the box, even more actually. Ontop of that http://www.the12volt.com/caraudio/boxcalcs.asp does NOT account for the actual volume INSIDE the box taken up by the port... So even though you think you're getting a certain port length, it is infact WAY longer and not possible due to the fact that the calculator is not subtracting the volume taken up by the port assembly itself. Sealed is your best and only option, sorry to say. Unless of course you are willing to sacrifice some space in the cab somehow.

Yes, I'm resigned to that. I was just trying to say it seems to me like in another less space-limited situation a sealed could be properly (mathematically) converted to ported. Maybe I should've used a 2 or 2.5 cu-ft box in my example.

Unless by sealed 0.9 sealed boxes sounds like d00-d00 I won't be trying it anytime soon.

Tks

dappa5
04-30-2009, 06:48 PM
where are you located?? i"ll take a crack @ it if you want

drpeeb
04-30-2009, 07:06 PM
where are you located?? i"ll take a crack @ it if you want

Well, I do appreciate that, but I've already spent lots o' time measuring to find the max box I can fit under the rear seat (one per side), regardless of shape, and it's basically 20Wx18.5Dx6.5H. I can squeeze an extra 0.18 cu-ft by adding a ~3.5Wx5H wedge shape along the back.

The only ways to add more are not really ways I wanna do:

- Put it on top of the rear seat(s).
- Keep it on the floor but put the rear seat(s) in the up position.
- Extended the box depth toward the driver, which would restrict the rearward seat's travel; I know, only occassionally, but still ... and the amp will be right there under the seat.

dappa5
04-30-2009, 07:09 PM
ok there is more space to be hade and amps mount on rear wall behind seat

dappa5
04-30-2009, 07:09 PM
but gl w that

drpeeb
04-30-2009, 07:15 PM
ok there is more space to be hade and amps mount on rear wall behind seat

Well cr@p you may be on to something!! Just went and looked. Behind the pass side rear seat there's a little rectangular spot that looks like it's made for an Alpine PDX-5!

Then I could extend at least the drvrs side sub box up under the drvrs seat. Still be shallow (~6.5") but should work.

Gotta do some more math ... !

Tks ...