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downfire questions

2551 Views 24 Replies 6 Participants Last post by  Jstaguy24
i think I've settled on going with a downfire sub box in my suburban for my 2-15's. I'm going round ports so i can change tuning if needed. but can't decide where to aim them.
1- aimed down with subs
2- out the back towards rear doors
3- out the sides towards each side panel

also should i carpet under the box? it will have deadener and probably insulation for road noise and vibration. but would carpet be of any benefit?
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I plan on 5" of clearance underneath
downfire boxes are slot loading, and add compression to the mix.

this adds group delay, and changes the tune of the porting, especially when using narrowed slot sizing.

5" of clearance brings the amount of compression down and gives a closer tuning to regular boxes, and gives enough space to downfire round ports too, but you may find there isn't enough room in the box to use a straight pipe to port with, to tune as low as you want.

If you drop the clearance to 3" and close off the front opening area, you may find a better response results, as the bass energy is directed towards the rear doors in phase.

Experimenting with clearance heights while leaving the ports the same length, is an easy and fun way to see how the sound changes without making time-consuming adjustments to box volume or port length.
Downfire ports will be more difficult due to length. So would you recommend rear Fire ports and 3" clearance at bottom? Can always raise it up from there
Of the choices, I'd say towards the rear doors.

Towards the sides may not allow for enough clearance for the ports and could choke them. Similar may be said of downward as well, though I have no idea what sort of clearance you're shooting for.

I'd vote for NO carpet, you want a solid surface for the subs to load off, not an adsorbent material. Place CLD Tiles in the floor of the truck to reenforce the surface more so, but I'd try without other materials for this location at this time.
I'm running a single Polk MM1540 in a sealed downward firing enclosure and at this point in time, I have 3.5" legs on the enclosure. However I will be testing out 3.75" and finally 4" in the spring.

Still, this is more so my best guess, as I've not dealt with many ported setups.
What vehicle are you running the polk in? I'm considering going with just 1-15. It sounded good with one ported. I Have only ran both sealed. The 1 ohm load is killing my electrical. Electrical upgrades are next
my single ported box was sub up, ports back.
here is the link to my PB account with pics of building process for 2 x 15" JBL W15 GTI DF box with AEROports facing back

SW BOX Photos by lbaudio_team | Photobucket
thats a nice box. mine wont be quite as fancy lol.
I just got my box assembled today finally. now i need carpet and get my wiring done. going to have to do the big 3 and possibly an alternator. my voltage drop is horrible when i push it.
i didn't take any pics. guess i would have set my photo bucket account. haven't used it do long
I haven't used photobucket in awhile. See if this works. front of box will be my amp rack. just behind the third row seat. Still need to drill holes and put ports out the back. box was a little big. left the top recessed if i need to throw some groceries or luggage bag in so it stays put. Mobile Uploads Photos by jstaguy24 | Photobucket
I honestly hadn't thought about all that. maybe I'll keep my amps under the back seat. make up an amp rack there. that's where amps are now, and was my original plan.
Thanks for the help everyone, I ended up mounting the amps where the spare tire goes. Cut out a round mdf panel about the size the tire would be. Got the box in today. Dang, it sounds good, hits hard. Sounded great on every type of music I played through it. Very happy with the subs. Now just have to get some bigger power on my front stage
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