The good bass, little space project

[Beej]

On a related note, I just finished a new bass cabinet yesterday. Well, the construction anyway, now it just needs some finishing. I bought a 1995 JBL GTx 12 woofer at a 2nd hand store for 5.99 CDN. It was in a box already but it was sealed and since I want a rolloff below 35Hz, I made a new, larger box with tuned ports.

I'm currently playing through a large mid-eighties 15", 8ohm 200w RMS cabinet, but my amplifier can deliver 400w at 4ohms. This new woofer is 4ohms and can handle up to 450w RMS. As long as I don't hammer it too hard, it should be okay.

I looked up the TS parameters for the speaker on the JBL site and fed them into a couple of box builder programs. I knew the box had to be at least 17" wide and 12" deep externally because that's the size of the amp that will sit on top. Since I needed at least 4350ci, I decided on external dimensions of 16 13/16 deep x 21.25 tall x 17.25 wide with three 2" diameter PVC ports at 7.7" long. This gives me an F3 of 32.58Hz. So even a five-string bass with a low B won't hit the resonant frequency.

I built it out of 3/4" MDF with screws and carpenter's mastic. The interior corners are braced with concave trim braces (to help eliminate standing waves) and caulked with acoustical sealant. The ports are glued into the baffle and caulked on the inside surface. The inside surfaces are all covered with 4" of acoustical filler, which is basically just Dacron polyfill. The wiring is soldered in place to an external 1/4 jack.

The first time I plugged it in, I realized why it was sold for 5.99. The polypropylene speaker surround had come unglued from the speaker frame. I peeled it up all the way around and used contact cement to reglue it in place. After securing the speaker onto the baffle board using T-nuts, I caulked the entire surround edge with black acoustical sealant.

The thing thumps really hard now, with no buzzes or whistles. Its considerably louder and reproduces lows more clearly than the factory 15" cabinet, although the 15" can still knock your breath out just due to its size. I'll post some pics a little later...

 

[OUG]

BeeJ,
The isobaric box hits crisper and produces lower tones better. Thanks again for the correction. I had to turn my bass level down a bit to keep the rest of the system balanced.

To all the other guys building a box, unless your looking for an overpowering bass level, don't mess with the 12's. Get a single 10 or dual 8's and you should be happy.

 

[CodyB]

Hey Beej, Would a 2x250W amp be too much for two Kicker 12" Comp Subwoofers?

http://www.circuitcity.com/ssm/Kicker-12-Comp-Subwoofer-05C124/sem/rpsm/oid/117479/catOid/-15481/rpem/ccd/productDetail.do

 

[Beej]

Hey Beej, Would a 2x250W amp be too much for two Kicker 12" Comp Subwoofers?

http://www.circuitcity.com/ssm/Kicker-12-Comp-Subwoofer-05C124/sem/rpsm/oid/117479/catOid/-15481/rpem/ccd/productDetail.do

Its going to depend on whether those amp specs represent peak power or RMS power. Those Kicker comp 12's are rated at 300w Peak and 150w RMS. If your 2x250 is referring to RMS, then I wouldn't run those Kickers with it, because if you really thump them you could blow them depending on the box they're in. If the amp is talking about peak power, then its RMS value is probably in the neighborhood of 2x100w and you should be good. Got more info on the amp?

 

[Krazors001]

http://www.naxja.org/forum/showthread.php?t=95990This is the box I made last fall. Works perfect for me and sound pretty damn good considering I didn't really take any measurements. I want to get a smaller amp so that I can mount it tucked underneath

 

[bknudtsen]

http://www.naxja.org/forum/showthread.php?t=95990This is the box I made last fall. Works perfect for me and sound pretty damn good considering I didn't really take any measurements. I want to get a smaller amp so that I can mount it tucked underneath

I made a very similar box and put a JL Audio W3 in it. It's sealed 3/4 MDF glued and screwed with poly fill. It fits very nicely and hits pretty well for a box that small. Of course now it just rattles the tuffy box.

 

[scoobyxj]

So I have grown out of the "piss your neighbors off" car stereo age and got rid of my subs, amps, and everything related to that when I bought my XJ about a month ago. After driving around for a month with just the Craptory radio and speakers, I decided that I still really enjoy sound quality and missed my last setup. So all the Craptory stuff went to the trash and new goodies went in, door speakers, head unit etc. I didn't want to sacrafice the whole hatch area for a sub enclosure and knowing that some of those pre-made "pods" sound like garbage I devised my own plan. Here are some pics of the enclosure in stages from start to finish, I hope this will encourage others to "think outside the pod"

The challenge:
http://i134.photobucket.com/albums/q81/jeffseim/100_0679.jpg

The template I made from cardboard to get the shape I wanted:
http://i134.photobucket.com/albums/q81/jeffseim/100_0680.jpg

The backboard of the enclosure 3/4" MDF cut like template
http://i134.photobucket.com/albums/q81/jeffseim/100_0681.jpg

Now here is where it gets fun, I lined the pocket with aluminum foil and held it together with blue painters tape so the fiberglass wouldn't stick to the pocket:
http://i134.photobucket.com/albums/q81/jeffseim/100_0682.jpg

Next I put the backboard back into place:
http://i134.photobucket.com/albums/q81/jeffseim/100_0683.jpg

Next I layed the fiberglass into the pocket, overlaping the backboard as I went around the pocket. I left the top of the pocket open because it kept falling down, so I let the glass set up a little removed the enclosure from the XJ and finished laying the glass for the top on the bench:
http://i134.photobucket.com/albums/q81/jeffseim/100_0684.jpg

Then I attached the front panel to the back panel. I came up with an external width of 5 1/2" which means 4" internal width:
http://i134.photobucket.com/albums/q81/jeffseim/100_0685.jpg

After that I needed to match the contour of the wheel well from the back board to the front panel, so I came up with the idea of using 1/8" X 1/2" aluminum bar stock for the bracing of the contour:
http://i134.photobucket.com/albums/q81/jeffseim/100_0696.jpg

Pic of the contour glassed:
http://i134.photobucket.com/albums/q81/jeffseim/100_0697.jpg

The finished product:
http://i134.photobucket.com/albums/q81/jeffseim/100_0698.jpg


The internal volume ended up being .88 and that was perfect for a 10" Kicker CompVR sub, the external dimensions are 25" X 16" an total cost of materials was around $40, cost of sub was around $60. the sealed enclosure sounds great with no rattles and hardly takes any space in my hatch.

None of these links work for me. Anyone else having problems?

 

[scoobyxj]

Here are the pictures of my isobaric box with 2 8" subs. Again the speakers are firing out of phase because of the one behind the other configuration.

http://i23.photobucket.com/albums/b368/OUG/IMG_0275.jpg

http://i23.photobucket.com/albums/b368/OUG/IMG_0276.jpg

http://i23.photobucket.com/albums/b368/OUG/IMG_0277.jpg

Not to be a smart ass, but you have your isobaric box loaded with front to back subs and as such, they should not be firing out of phase. Changing them to in phase will enhance the sound.

Isobaric loading of front to front and back to back configurations require out of phase alignment, but yours do not fire into one another. They work in the same direction, so they should be firing the same direction at the same time, hence in phase...

Now Beej you have me confused here. With his set up he is going to want phase set so when the front speaker fires in (toward the basket) the rear speaker fires out (away from the basket). Now wouldn't that require one speaker to be wired out of phase from the other one? Because if they both fired the same direction (in phase) at the same time they would cancel each other out. Unless of coarse the box is internally divided, and no air can transfer inside the box. Also that appears to just be a sealed box with a with a basic push pull set up. Correct me if I'm wrong but doesn't an isobaric box have two woofers dynamically connected by air inside a sealed box?

OR

 

[Beej]

Now Beej you have me confused here. With his set up he is going to want phase set so when the front speaker fires in (toward the basket) the rear speaker fires out (away from the basket). Now wouldn't that require one speaker to be wired out of phase from the other one? Because if they both fired the same direction (in phase) at the same time they would cancel each other out. Unless of coarse the box is internally divided, and no air can transfer inside the box. Also that appears to just be a sealed box with a with a basic push pull set up. Correct me if I'm wrong but doesn't an isobaric box have two woofers dynamically connected by air inside a sealed box?

OR

I think what you are first describing would require the speakers to be wired out of phase, but he has his speakers aligned like this:

This alignment requires in-phase wiring whereas this here below requires out-of-phase wiring:

A good rule of thumb is magnet to magnet or cone to cone: out of phase. Magnet to cone is in phase.

 

[CodyB]

Its going to depend on whether those amp specs represent peak power or RMS power. Those Kicker comp 12's are rated at 300w Peak and 150w RMS. If your 2x250 is referring to RMS, then I wouldn't run those Kickers with it, because if you really thump them you could blow them depending on the box they're in. If the amp is talking about peak power, then its RMS value is probably in the neighborhood of 2x100w and you should be good. Got more info on the amp?

The 2x250w is peak, but its an off brand I have never herd of so I don't really know much about it... Sound Storm Force F250.2

 

[camarors8992]

Just buy a kicker amp or at least a reputable brand. You'll be happier in the long run.

 

[scoobyxj]

I think what you are first describing would require the speakers to be wired out of phase, but he has his speakers aligned like this:

This alignment requires in-phase wiring whereas this here below requires out-of-phase wiring:

A good rule of thumb is magnet to magnet or cone to cone: out of phase. Magnet to cone is in phase.

I still don't understand why you're saying that.

In a box that is set up like this. (what that fella has as far as I can see) You are going to want the top woofer to move in toward the magnet while the bottom moves away. Witch would require them to be wired out of phase. If they both moved the same direction at the same time they would acoustically cancel each other out. Right? Now if you turned the bottom woofer around (so they where magnet to magnet) then they would get wired in phase. Right?

 

[Beej]

I still don't understand why you're saying that.

In a box that is set up like this. (what that fella has as far as I can see) You are going to want the top woofer to move in toward the magnet while the bottom moves away. Witch would require them to be wired out of phase. If they both moved the same direction at the same time they would acoustically cancel each other out. Right? Now if you turned the bottom woofer around (so they where magnet to magnet) then they would get wired in phase. Right?

Its actually the exact opposite. Its important to think about the air inside the sealed enclosure acting as a spring. When there is only one driver in the enclosure, that driver compresses the air inside the box with each movement of the voicecoil into the magnet. So hundreds of times per second, the air inside the enclosure is being compressed and allowed to expand. One of the reasons speakers can handle higher power in sealed enclosures is due to this expansion and compression of the air inside the box. In effect, the air functions like a spring, compressing with the in-stroke and springing back to help the driver move forward on the out-stroke. The spring effect exerts a pull on the cone when its at the height of its excursion and prevents it from going to far. Its like a safety net in a way. It allows the highest use of amplifier wattage without causing the cone to over-extrude blowing the voice-coil.

So keeping this in mind and looking at the isobaric enclosure: Let's say you have two speakers mounted in a single enclosure and they are set up magnet to magnet. Since they are sharing the same airspace and hence are each putting force into the "spring" of compressed/expanded air, they must move in unison in order to both utilize the spring effect. In the case of magnet to magnet, this unison must be out-of-phase, so that as driver 1 moves in compressing the air in the box, driver 2 must move outward allowing the air to expand. So even though the wiring is out-of-phase, the cones are not. They move in the same direction at the same time, one in, one out.

Take the enclosure we are talking about, where one driver fires into the box and the other fires out of it. They must move in unison as well in order to best utilize the air-spring inside the box. In this case, they must both be wired in-phase, as when the speaker driving inward fires in, the expanding air will want to drive the outward-facing speaker-cone outward. By wiring in phase, we can allow this to happen. If they were fired out-of-phase, they would be working against each other.

I hope this makes sense as I described it. If you google isobaric speakers, you'll find clearer explanations with better pictures...

 

[CodyB]

Its going to depend on whether those amp specs represent peak power or RMS power. Those Kicker comp 12's are rated at 300w Peak and 150w RMS. If your 2x250 is referring to RMS, then I wouldn't run those Kickers with it, because if you really thump them you could blow them depending on the box they're in. If the amp is talking about peak power, then its RMS value is probably in the neighborhood of 2x100w and you should be good. Got more info on the amp?

Well, I wound up with two Kicker Comp CVR's 400w RMS each, and only a 150wX2 Kicker amp(i believe peak) so I need to find a good 500w peak Kicker amp now...

 

[RaccoonJoe]

OK, good to see that this thread isn't completely dead =P

I've got a pair of 8"s sitting in a bandpass box (IIRC). It wouldn't be too much trouble to wire up the amp and such....I had held off so far because I didn't like the idea of the box sitting back there, inviting thieves and taking up valuable cargo space (not to mention sliding/bouncing around). If this box is going to be set up like I think it will...this should work out pretty well for me. I'm really just looking to help out the anemic stock system....it does pretty well, everywhere except for the low end.

 

[Beej]

A couple of 8's would add some nice background bass deepening. If you use quick release plugs and make sure there are some sort of cleats attached to the bottom so it doesn't slide around, then you could easily remove it if you need to and still have it for when you want it.

 

[RaccoonJoe]

Beej, you've got PM

 

[Sniggs]

Beej, you've got PMS

Fixed that for ya. :laugh3:

edit: Added the smilie fer da whinies.

 

[Beej]

I've had permanent PMS since my uterus was removed in 97...

:illegalflipoffsmilie: