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Discussion Starter · #1 ·
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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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.
 

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Seems another member, who's ID suggests they own a Yukon, recommends rear facing ports, so that suggests experience with such.

However, if I may, YukonXL04, have you ever used downward facing ports with a downward firing sub? I know JL Audio has slot ported enclosures designed with downward facing port and subs. Can't say I've ever heard one in such a position though as both I've heard were in trunks of cars that didn't have the clearance for such a position. Ended up with port and subs firing rearward.
 

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Discussion Starter · #6 ·
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
 

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Yes I have used down fire and both port and sub down. My current console is like that. I suggested rear fire port for ease of implementation. I would angle the floor baffle so it's flat on the bottom from the front of the box to the angled portion and mount the subs on the angle so it slopes like this / should help aim the bass to the rear doors to bounce back towards the front.
 

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Discussion Starter · #8 ·
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
 

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It's in my 99' Cavalier RS coupe. Not a large car, so it doesn't need much, besides, I'm not much of a bass head.

I've only had it in the car for a couple weeks now and I'm not feeding it much power. At this point in time, it's wired it to a Kicker ZR120, which i believe isn't able to produce much more than [email protected] ohms (it's rated at 120RMS). However, I set the gain for maximum clean power with a -3dB 50Hz test tone using a DSO Nano 201 with the master volume at 35 (loudest I listen to the stereo) and the sub volume at max level 10 (no boosts and flat EQ). Currently, I tend to listen to the system at level 30 and the sub volume is at -5 for break-in. I did crank it up to 35 and +10 after a few days for a matter of seconds just to see what it'd do. Was playing some Tech9Nine and it produced a fair amount of output (and this was with around 1/3 rated power). Not the most I've had, but ample for my taste. I feel 400RMS to it would be plenty for me.

Most I've had in terms of output would have been a Kicker F15c I ran very briefly in the early 2000's. Buddy built the box and set everything up as I didn't know **** and he was into the competition scene (He was running (4) 10" eclipse 500RMS subs in a sealed box on rated power in a 92' Cherokee. Claimed he hit 143.something when he took it to comp and got second). Think he built a 3.5cuft enclosure tuned to 32Hz, or at least that's what my memory keeps thinking. Gave it around 400RMS. Rattled my 88' Tempo like CRAZY. Sounded like **** with everything but Rap/Hip Hop, but even then, it rattled everything so bad it was just unbearable. After a week, the novelty wore off and I began missing my pair of JL 10W0s. Much cleaner sounding subs, just didn't hit hard at all and I thought I wanted to try and keep up with my high school buddies. Live and learn.

Never ran more than 800RMS setup and most have been between 400-600RMS, again, I'm by no means a bass head.
 

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It wasn't a Yukon, but in our suburban, there was a couple of tenth of a db better output sub up ports back verses subs down ports back.
 

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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.
Did you leave anything out? Lol. All good solid suggestions. Like a dumb ass I would have made six different boxes.......:D
 

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I'm running my second downward firing enclosure as of now, but the first was a generic one for a F-150. I have a 99' Cavalier as of now, so I built one that I'm experimenting with on height, or should I say I will be experimenting on height.

As of now, I have 3" clearance and I plan to go no lower. Sub has been used for roughly three weeks and should be broken in by now, so I'll soon begin changing out the legs to test the effects. Don't have a lot to measure sound at this time, pretty much just my ears and a relatively inexpensive Radio Shack SPL meter. Need to buy a decent mic and get software for my laptop to do a more thorough job with testing though, but...

Anyways, I'm running a Polk MM1540 and it's (temporarily) wired to a Kicker ZR120, which I set the gain with a cheap O-Scope for maximum clean output using a 0dB 60Hz test tone. Within the first week, I tried playing the sub at max levels and it seemed more than enough for me. Now, playing at master volume used when gain was set along with 0dB on the sub volume (HU goes from -10 to +10), any song that has any sort of respectable mount of bass rattles my car badly (REALLY need to deaden the car now). Tried playing at max volume and guess what, my rear window is no longer sealed. LOL

So, anyone got any idea what adhesive is used for holding the rear window in place? The damn thing now rattles all the time when driving. :mad:
 
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