[Huebie]

Last night I installed a new system in my 99 TJ. I put a Clarion DXZ535 head unit with Polk GXR46's 4 X 6 in the dash and Polk EX352 5-1/4's in the factory sound bar. I also piggy backed a set of Sony Xplod 6 X 9 's off of the sound bar speakers that are in seperate boxes behind the rear seat. I guess I was expecting more out of an aftermarket system as the factory unit with the 6 x 9's actually produced decent sound. I have an old Alpine amp that I am now going to hook up and try and find some 8 or 10 inch subs so I have at least a little bass.

My problem is this...

My Jeep is a daily driver and I sometimes haul my infant daughter and all her stuff around so space is an issue. I am invisioning a low profile, down firing sealed sub box that fits behind the rear seat. By low profile I mean no higher than 5". I don't care if it fills the entire floor area but I would like to still be able to haul stuff on top of the box without jeopardizing the sound.

Any input would be greatly appreciated.

[SirGCal]

Originally Posted by Huebie

Last night I installed a new system in my 99 TJ. I put a Clarion DXZ535 head unit with Polk GXR46's 4 X 6 in the dash and Polk EX352 5-1/4's in the factory sound bar. I also piggy backed a set of Sony Xplod 6 X 9 's off of the sound bar speakers that are in seperate boxes behind the rear seat. I guess I was expecting more out of an aftermarket system as the factory unit with the 6 x 9's actually produced decent sound. I have an old Alpine amp that I am now going to hook up and try and find some 8 or 10 inch subs so I have at least a little bass.

My problem is this...

My Jeep is a daily driver and I sometimes haul my infant daughter and all her stuff around so space is an issue. I am invisioning a low profile, down firing sealed sub box that fits behind the rear seat. By low profile I mean no higher than 5". I don't care if it fills the entire floor area but I would like to still be able to haul stuff on top of the box without jeopardizing the sound.

Any input would be greatly appreciated.

The reason your system isn't sounding up-to-par is because your overdriving your head unit's internal amp with the 6x9's being on the rear channel with the 5.25". That shows the head unit a 2 ohm load which it can't handle most likely.. Also each speaker is only getting about 15W or so, if that...

You'd get alot more sound simply running the 6x9's off an amp and the 5.25" back off the head unit.

However, if you wana sub it, I'd say dump the 6x9's inplace of some nice 8" subs. You could build a down-firing box in the rear but it would likely take up about 5.5-6.5" vertical height considering your going to need at least 1" in the front side of the box from the sub to the floor and .5-.75" in the rear. (so the sub is slightly tilted to the front for better sound escape and for the sub excursion room).

Add that to the mounting depth of most 8" subs (4") and the material (.625"-.75")x2 and you end up with about. (1" + 4" + .75"x2 = ) 6.5". To go as 'low' as possible you'd need 6" subs which could get you about 3.5" mounting depth and you could use .625" MDF and about 1" room benieth at the front = (.625"x2(1.5") + 3.5" + 1" = ) 6". That's about as thin as you can go with leaving room for the sub to move. Some even require some room behind the magnet for voice coil cooling... If you really tweak the box you could probably shave .25"-.5" off of those guestimates, but that's about it...

It may be easier to make a simple box that takes up just part of your insta-trunk (you could get one) instead of some shallow system. The only other item I could think of is something like I did with the seat. SirGCal's Stealth TJ

Good luck on what you choose to do...

[1BadTJ]

If I had a backseat I would do a sub install under the seat like SirGCals.

[Huebie]

If I had the patience to construct an under the seat box like yours I would in a second. I just thought if I could keep the height down below the latch systems on the tailgate I would eliminate making several cuts. After measuring the area I am looking at a box 35" across, 13" deep and 6" tall. What would be the best sub configuration for the box described?

Your expertice is greatly appreciated.

[SirGCal]

Originally Posted by Huebie

If I had the patience to construct an under the seat box like yours I would in a second. I just thought if I could keep the height down below the latch systems on the tailgate I would eliminate making several cuts. After measuring the area I am looking at a box 35" across, 13" deep and 6" tall. What would be the best sub configuration for the box described?

Your expertice is greatly appreciated.

Ahhh.. That's easy.. figure out the material size (3/4" for most, 5/8" for lighter subs..., we'll use 3/4" for this.

you know, at least where the sub is, that you need 1" in the front and .5" in the back for room. But you could go down to the floor on other areas (where the sub isn't).

For this example though I'll leave 1" and .5" room all the way across (accept for an extra leg or two for support. but those don't count against internal volume...)

Ok.. so we'll have a complex wedge design. The only other thing is the depth to the rear seat at the high and low positions... For this example, we'll asume 13" square but I don't think that's accurate...

35" - (3/4"x2) = 33.5" internal room.
13" - (3/4"x2) = 11.5" internal volume.
Height of 6" - 1" - (3/4"x2) = 3.5" internal height (WARNING... LOW LIMIT FOR SUBS... CHECK MOUNTING DEPTH... (3.5 + 3/4") 4.25" MAX MOUNTING DEPTH CLEARENCE WITH THIS DESIGN)

The internal square is 33.5" x 11.5" x 3.5" AND the little .5" wedge for tilting the face (Triangle of 11.5 x .5 x 33.5) = (.78 ft^3 + .056 ft^3) = .836 ft^3 total... That's alot of room!... You could EASILY fit a pair of 8" in there... It's even too big for many 10" models.. (though all models vary...) You could fit 4 6W0's in there... That would be trick... (get 8 ohm versions to show 2 ohms at the amp and an amp that runs 300W at 2 ohms mono if this idea sounds interesting.)

You could also shallow out the box in the areas where the subs aren't and use that room as amp storage or something... (A sunken 3" area in the center for example, or underneith...) Lots and lots of possibilities here... You might even be able to squeeze in a set of 10" subs if your creative. (a single would be easy as far as volume is concerned...)

[Huebie]

Originally Posted by SirGCal

Ahhh.. That's easy.. figure out the material size (3/4" for most, 5/8" for lighter subs..., we'll use 3/4" for this.

you know, at least where the sub is, that you need 1" in the front and .5" in the back for room. But you could go down to the floor on other areas (where the sub isn't).

For this example though I'll leave 1" and .5" room all the way across (accept for an extra leg or two for support. but those don't count against internal volume...)

Ok.. so we'll have a complex wedge design. The only other thing is the depth to the rear seat at the high and low positions... For this example, we'll asume 13" square but I don't think that's accurate...

35" - (3/4"x2) = 33.5" internal room.
13" - (3/4"x2) = 11.5" internal volume.
Height of 6" - 1" - (3/4"x2) = 3.5" internal height (WARNING... LOW LIMIT FOR SUBS... CHECK MOUNTING DEPTH... (3.5 + 3/4") 4.25" MAX MOUNTING DEPTH CLEARENCE WITH THIS DESIGN)

The internal square is 33.5" x 11.5" x 3.5" AND the little .5" wedge for tilting the face (Triangle of 11.5 x .5 x 33.5) = (.78 ft^3 + .056 ft^3) = .836 ft^3 total... That's alot of room!... You could EASILY fit a pair of 8" in there... It's even too big for many 10" models.. (though all models vary...) You could fit 4 6W0's in there... That would be trick... (get 8 ohm versions to show 2 ohms at the amp and an amp that runs 300W at 2 ohms mono if this idea sounds interesting.)

You could also shallow out the box in the areas where the subs aren't and use that room as amp storage or something... (A sunken 3" area in the center for example, or underneith...) Lots and lots of possibilities here... You might even be able to squeeze in a set of 10" subs if your creative. (a single would be easy as far as volume is concerned...)

SirG you truly are a plethora of audiofile information. I have some additional questions regarding my budget system for you. I have is an Alpine 3522 bridgeable amp that is rated at 35W X 2. On the side of the amp there is a switch for "stereo" or "L(mono)". If I am running the 6X9's I am guessing it should be in Stereo and a single sub should be in mono???? Also there is a Gain Control dial with a range of 2.0V - 0.1V....where should this be set??? I really do apprecaite your help. Also would this amp power a single 10" sub better in mono or stereo? If you are running a single sub off of an amp do you hook up both sets of speaker wires to it??? Sorry to ask such dumb questions but I just don't know the answers and really don't want to guess.

[SirGCal]

Originally Posted by Huebie

SirG you truly are a plethora of audiofile information. I have some additional questions regarding my budget system for you. I have is an Alpine 3522 bridgeable amp that is rated at 35W X 2. On the side of the amp there is a switch for "stereo" or "L(mono)". If I am running the 6X9's I am guessing it should be in Stereo and a single sub should be in mono???? Also there is a Gain Control dial with a range of 2.0V - 0.1V....where should this be set??? I really do apprecaite your help. Also would this amp power a single 10" sub better in mono or stereo? If you are running a single sub off of an amp do you hook up both sets of speaker wires to it??? Sorry to ask such dumb questions but I just don't know the answers and really don't want to guess.

Thanks! I appreciate the kind words offered by you and others very much.

Let's see here.. Alpine 3522:
2/1 Channel amp:
30W x 2 @ 4 ohms,
80W x 1 @ 4 ohms (bridged)

As for the input mode button; no. Good thinking but no... That button is for the following:

Run stereo mode to use both the right and left input or speaker input signals. Use mono mode to use just the left input or speaker mode.

This is useful on newer systems where the signal goes through a THX style signal filter and has only one sub output line OR if you are using one amp per speaker for a pair of stereo speakers.

So for you, using it for both 6x9's or a single sub, you'd want it in stereo mode.

As for the gain, that level of control show's the amp's age... Most gains now go from 4 or more V down to .5 or .1V. What you do is match the output voltage of your head unit with the input voltage of the amp. For example, if your new Clarion (for example) has 2V pre-amp outputs, then you would set the gain around the 2V area, and so on. Many modern heads have 4V outputs. Even with the amp set on minimum gain (2V), the signal will get distorted (clipped) before maximum potential volume is reached.

Many people think the gain is just a simple volume control on the amp, this is far from the truth. If the gain is too high, then the signal is getting too much amplification which can result in clipping of the signal, distortion, and hardware destruction.

Using the gain while using speaker-level inputs is another story and very difficult to set without the aid of a multi-meter or o-scope. Best thing here is to use the back-yard method of finding a secluded place to crank your radio, turn it up to 3/4 volume, and turn up the gain until you hear distortion (with all eq controls set to flat and no bass/loudness or other sonic changing features enabled). Then back it off a smidge and enjoy. Back it off more for balance if necessary. (3/4 volume is used here because most headunits start to run into self-distortion much beyond that anyhow...)

If your going to try to push an amp with this sub.. it should be a lower-end model (one designed for less power). Don't try to use it to run a big-dog sub...

To elaborate; your amp will supply 80W at 4 ohms into one output. (leave intput as stereo, but use only the white output lead as speaker output + and the gray w/ black stripe output lead as speaker output -. Do not use the gray or white w/ black stripe outputs when bridging.) So you want a sub that works best in the 75-100W range...

Some options include:
JL Audio 8W0 (8", 75W)
JL Audio 10W0 (10", 125W) (pushing it...)
Kicker Comp C8 (8", 100W)
Kicker Comp C104(10", 125W) (pusing it...)
Kicker KM10 (10", 125W, marine) (pushing it...)
MTX Thunder4500 T4508-04 (8", 100W)

The 8" models will work the best with such a small amplifier. Or running your 6x9s would work pretty well too probably.

[Huebie]

Originally Posted by SirGCal

Thanks! I appreciate the kind words offered by you and others very much.

Let's see here.. Alpine 3522:
2/1 Channel amp:
30W x 2 @ 4 ohms,
80W x 1 @ 4 ohms (bridged)

As for the input mode button; no. Good thinking but no... That button is for the following:

Run stereo mode to use both the right and left input or speaker input signals. Use mono mode to use just the left input or speaker mode.

This is useful on newer systems where the signal goes through a THX style signal filter and has only one sub output line OR if you are using one amp per speaker for a pair of stereo speakers.

So for you, using it for both 6x9's or a single sub, you'd want it in stereo mode.

As for the gain, that level of control show's the amp's age... Most gains now go from 4 or more V down to .5 or .1V. What you do is match the output voltage of your head unit with the input voltage of the amp. For example, if your new Clarion (for example) has 2V pre-amp outputs, then you would set the gain around the 2V area, and so on. Many modern heads have 4V outputs. Even with the amp set on minimum gain (2V), the signal will get distorted (clipped) before maximum potential volume is reached.

Many people think the gain is just a simple volume control on the amp, this is far from the truth. If the gain is too high, then the signal is getting too much amplification which can result in clipping of the signal, distortion, and hardware destruction.

Using the gain while using speaker-level inputs is another story and very difficult to set without the aid of a multi-meter or o-scope. Best thing here is to use the back-yard method of finding a secluded place to crank your radio, turn it up to 3/4 volume, and turn up the gain until you hear distortion (with all eq controls set to flat and no bass/loudness or other sonic changing features enabled). Then back it off a smidge and enjoy. Back it off more for balance if necessary. (3/4 volume is used here because most headunits start to run into self-distortion much beyond that anyhow...)

If your going to try to push an amp with this sub.. it should be a lower-end model (one designed for less power). Don't try to use it to run a big-dog sub...

To elaborate; your amp will supply 80W at 4 ohms into one output. (leave intput as stereo, but use only the white output lead as speaker output + and the gray w/ black stripe output lead as speaker output -. Do not use the gray or white w/ black stripe outputs when bridging.) So you want a sub that works best in the 75-100W range...

Some options include:
JL Audio 8W0 (8", 75W)
JL Audio 10W0 (10", 125W) (pushing it...)
Kicker Comp C8 (8", 100W)
Kicker Comp C104(10", 125W) (pusing it...)
Kicker KM10 (10", 125W, marine) (pushing it...)
MTX Thunder4500 T4508-04 (8", 100W)

The 8" models will work the best with such a small amplifier. Or running your 6x9s would work pretty well too probably.

Thanks for all of your advice and help with my project. I will post some pictures when I am done. By the way...do you do stereo's for a living?

[SirGCal]

Originally Posted by Huebie

Thanks for all of your advice and help with my project. I will post some pictures when I am done. By the way...do you do stereo's for a living?

I used to design and build cars for IASCA competition. Now I just do it for fun, friends and on request. I am a software engineer and system administrator now by trade. I write computer programs in a myriad of different programming languages and platforms. It pays alot better than custom audio designer. But, I could fall back on it if needed which is always nice.