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Discussion Starter #1
W12GTi MkII - JBL US

Above is a link for the T/S parameters for the pair of JBL subs I have...

I need to know what the ideal/optimal size and tune would be for a ported box, box is split in half, I will have anywhere from 3.5 CF to 4CF (PER SUB) once I modify the box. (yes, it's huge 48" x 18" x 24")

Goal is SQL in 3 or 4 way active.. Want to be able to run 2 modes.. 1) pure SQ, where everything is balanced and tuned w T/A.. 2) uncork subs and let them wake the dead

I need 30 to 60Hz, anything under 30 is a major bonus!!




I just picked up a very nicely made PA enclosure for 2-12s...

It's made of Birch Ply (close to 1" thick) has dual speakon connects, dual chambers..

I have almost 4 CF PER SUB!! Is that too much? Box is huge, but it fits nicely in the back of my minivan..

The plan is 3 way active for now, SQL, need a nice response curve from 30 to 60/80 hz.. Anything below 30 is a major bonus (FS is 18Hz on these subs)

So, is 3.5 to 4 CF per sub too large? What is optimal size for vented (per sub) and would a tune of 26hz be ideal for SQL?

I want to be able to run in pure SQ mode, where T/A tuning etc is all done to perfection, sound is balanced/reference quality..

I also want to be able to unleash all out fury when I uncork the sub section and wake the dead..

So, what to do? What would be ideal enclosure volume and tuning?

FWIW, I am temporarily running a Pioneer DEH-80PRS which seems to default to stereo on subs, also, the box is setup stereo (two inputs, two separate enclosures)

I also have a pair of JL 500/1 amps, 1 per sub, 500 watts RMS per side (plan on stepping up to 2k for subs, 1000 watts per side) will run in stereo for the simple fact that the Pioneer keeps defaulting to stereo when autotune is run)

Any help would be greatly appreciated!!
 

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I need to get on WinISD to do a plot but I can tell you that when it comes to ported boxes, it is very hard to build too big. If anything, you can build big and then tune very low in a "bass shelf" type config, and usually the results are amazing.

So I think you'll be very happy, we just need to figure out the proper port tune.

Edit: I'm wondering if you're better off making this box as one (like poke a hole between the two separate sections) just to even out any irregularities between the two, or not. May not make a big difference, but it may help. Again, best to get on WinISD or another box program, plot out response expected, and use it as a baseline. Tuning down to 26hz could be very nice though. A bunch of passive radiators may also be a nice option. It would be a bunch of them though.
 

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Discussion Starter #3 (Edited)
I need to get on WinISD to do a plot but I can tell you that when it comes to ported boxes, it is very hard to build too big. If anything, you can build big and then tune very low in a "bass shelf" type config, and usually the results are amazing.

So I think you'll be very happy, we just need to figure out the proper port tune.

Edit: I'm wondering if you're better off making this box as one (like poke a hole between the two separate sections) just to even out any irregularities between the two, or not. May not make a big difference, but it may help. Again, best to get on WinISD or another box program, plot out response expected, and use it as a baseline. Tuning down to 26hz could be very nice though. A bunch of passive radiators may also be a nice option. It would be a bunch of them though.
Thanks so much for the response! The current internal measurements per side are 22.75" x 16.50 x 17 deep.. I will be removing the face and existing ports, I could actually mount the face flush on top, effectively bumping from 17 to 20" (ish) depth.. subs are currently recessed approx 2" back from the front of the box..

I'm wondering if the shape of the box will hurt or negate the type of response I want.. It's very wide, but not very tall or deep.. All of the sub enclosures I see for SPL are very deep, usually much deeper than they are wide/tall..

My box is the polar opposite.. Thoughts?

While I'm in there, I could also remove the baffle/brace which divides the two chambers..

External dimensions of the box are 48.50 x 18.25 x 23 ish (going by memory) YES, BOX IS GINORMOUS!!!

The box fits snugly in the rear of the minivan, almost like it was purpose built for my application..

Again, I will be removing the face, all of the existing ports (4 per side) and all of the excess related to the ports..

I will have a 3/4 shell with which to finish any way I choose.. I definitely want OPTIMAL response!!

Those subs dig deep, I'm partial to heavy impacting bass.. I am aware of the fact that majority of music is 30hz and above, I still love the option of being able to play those EDM tracks which have the ludicrous low end thrown in to flex subs.. I don't have a lot of power on hand for true pavement splitting 22hz response, but this setup is temporary..

Once I have HO alternator and additional gelcaps in place, I'll probably end up swapping the pair of JL 500/1s for a single MMats D3500.1, which does a proven 2700 watts RMS @ 1 ohm.. which should give me right around 2200ish to both subs combined.. (If I go single slot ported in the center)

(Edit) I will be running 3 way active for now, will step up to 4 way soon.. I'll need these subs to perform from at least 26hz to 60hz.. I originally mentioned that anything below 30hz is a bonus.. Well, these subs are designed to dig, so let's let them dig.. Anything below 26 is a bonus!! I will allow midbass (4x8" with 400 rms per side) to deal with 60 and above..

(Edit 2) How about 22hz to 40hz, let my JBL 15s give me the rest of the impact to 80hz?

I had a pair of JBL 2226HPLs installed in a JBL 4648 subwoofer cabinet.. The low end was incredible.. I guess the minivans cabin gain bumped the sub 40hz response (box is tuned to 40, graph shows a pretty steep roll off below 40 hz.. Well, I had the subs firing against the back door, about 1.5' away from the door.. Perhaps this positioning bumped sub 40hz dramatically? Vehicle acoustics?

Regardless, I do regret pulling those 15s out.. With the Hertz ML165s in my doors, ML28 big chamber in pillars, music sounded absolutely incredible (considering the fact that I am using the Pioneer DEH-80PRS..

They gave a live club/concert venue type feel to drums and bass, but they did not impress with the infralows or pavement splitting lows.. which I do enjoy.. Still, when set to SQ mode, streaming from Tidal via phone, the sound was such that majority would be envious..

I am going to give these 12s a good run, let's see what they do.. If I don't get that impact club venue feel in the upper sub frequencies, I'd like to combine my 15s with these to make up my sub section (4 way active)

I have someone local who can help with tuning (specialized mic, laptop, O-scope, USB interface, tuning program etc)

(Edit 3) Vadrum, if anyone is familiar with Vadrum, the Italian drummer who plays with a full tilt orchestra. MIND BLOWN.. Orchestra sounded like it was in the van with me.. Drums sounded live, the clarity and detail absolutely insane (nothing nicer than a drum set tuned to perfection, recorded to perfection, played back through a nice system) imaging also quite nice (as good as it will get with an 80PRS)

Anyway, give Vadrum a listen on Tidal.. We're all here for the same reasons, we enjoy great music through a great sound system... Trust me on this, your ears will thank you for it..
 

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Discussion Starter #4
OMG too much caffeine!! (as per the norm with me) SMH..
 

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Lots of questions, my answers in bold in your quote

Thanks so much for the response! The current internal measurements per side are 22.75" x 16.50 x 17 deep.. I will be removing the face and existing ports, I could actually mount the face flush on top, effectively bumping from 17 to 20" (ish) depth.. subs are currently recessed approx 2" back from the front of the box..

I'm wondering if the shape of the box will hurt or negate the type of response I want.. It's very wide, but not very tall or deep.. All of the sub enclosures I see for SPL are very deep, usually much deeper than they are wide/tall..

My box is the polar opposite.. Thoughts?
Provided you have the airspace you want, the shape is largely irrelevant. Standing waves can occur in some shapes, but irregularities and strange shapes actually prevent this. Bonus!


While I'm in there, I could also remove the baffle/brace which divides the two chambers..
Not a bad idea but not a big deal either. But I like the idea of removing the brace, cutting it up to air can pass through unrestricted, and then re-installing. You probably still want the brace part of that, but the airspace can share. Mostly I'm thinking the share concept would help because you could then run a massive single port, or three ports, or whatever you want and they'll work together. It wouldn't need to be equal numbers then.

External dimensions of the box are 48.50 x 18.25 x 23 ish (going by memory) YES, BOX IS GINORMOUS!!!
Can't stress this enough, BRACE heavily, and often. If you can't install something big, just use lots of small things like clothes hanger rod or whatever works.

The box fits snugly in the rear of the minivan, almost like it was purpose built for my application..
Happy accidents and coincidences are great

Again, I will be removing the face, all of the existing ports (4 per side) and all of the excess related to the ports..

I will have a 3/4 shell with which to finish any way I choose.. I definitely want OPTIMAL response!!

Those subs dig deep, I'm partial to heavy impacting bass.. I am aware of the fact that majority of music is 30hz and above, I still love the option of being able to play those EDM tracks which have the ludicrous low end thrown in to flex subs.. I don't have a lot of power on hand for true pavement splitting 22hz response, but this setup is temporary..
That's right up my alley, and I love it. Matt Darey's shows, the amazing Moonbeam - Ticket to the Moon episodes, etc... all of them are ultra-high sound quality and dig super-deep. You'll love it or probably already do. Keep in mind, if you port with a low bass-shelf tune, you won't need much power at all. The subs will hardly be moving but they'll put out big time down there. Personally, I'm jealous. I never get to build to that level. It is always stealth and space savings for the builds I get asked to make. I have to compromise constantly.

Once I have HO alternator and additional gelcaps in place, I'll probably end up swapping the pair of JL 500/1s for a single MMats D3500.1, which does a proven 2700 watts RMS @ 1 ohm.. which should give me right around 2200ish to both subs combined.. (If I go single slot ported in the center)
The ports can be any number provided they are done right. Also, consider passive radiators, they can make even more use of this space, no port required.

(Edit) I will be running 3 way active for now, will step up to 4 way soon.. I'll need these subs to perform from at least 26hz to 60hz.. I originally mentioned that anything below 30hz is a bonus.. Well, these subs are designed to dig, so let's let them dig.. Anything below 26 is a bonus!! I will allow midbass (4x8" with 400 rms per side) to deal with 60 and above..

(Edit 2) How about 22hz to 40hz, let my JBL 15s give me the rest of the impact to 80hz.. I had a pair of JBL 2226HPLs installed in a JBL 4648 subwoofer cabinet.. The low end was incredible.. I guess the minivans cabin gain bumped the sub 40hz response (box is tuned to 40, graph shows a pretty steep roll off below 40 hz.. Well, I had the subs firing against the back door, about 1.5' away from the door.. Perhaps this positioning bumped sub 40hz dramatically? Vehicle acoustics?

Regardless, I do regret pulling those 15s out.. With the Hertz ML165s in my doors, ML28 big chamber in pillars, music sounded absolutely incredible (considering the fact that I am using the Pioneer DEH-80PRS..

They gave a live club/concert venue type feel to drums and bass, but they did not impress with the infralows or pavement splitting lows.. which I do enjoy.. Still, when set to SQ mode, streaming from Tidal via phone, the sound was such that majority would be envious..

I am going to give these 12s a good run, let's see what they do.. If I don't get that impact club venue feel in the upper sub frequencies, I'd like to combine my 15s with these to make up my sub section (4 way active)

I have someone local who can help with tuning (specialized mic, laptop, O-scope, USB interface, tuning program etc)
 

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and let me add, the "impact" feel in the upper sub range is usually associated with timing, not just with the actual speaker output. Therefore, T/A and tweaking it just right so the bass and midbass is not "late", is crucial.
 

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Discussion Starter #7
and let me add, the "impact" feel in the upper sub range is usually associated with timing, not just with the actual speaker output. Therefore, T/A and tweaking it just right so the bass and midbass is not "late", is crucial.
Thanks so much for taking the time to answer all my questions, you're a gentleman and scholar!

I will definitely use the central divider trimmed down for bracing, although there is plenty of bracing for corners and sides, only the one divider for central bracing for the length of the box..

Also, I picked up a nice piece of 3/4" 11 ply sheathing, I've had it cut down to size, will glue/clamp two pieces to make up face where subs will mount, effectively giving me a nice solid 1.50" surface for both subs...

I've never worked with slot ports, so I'm not sure how to calculate for correct tune..

I will say this.. I had a large box made of MDF which had taken water damage, so it wasn't 100%.. It was approx 6CF, 34 wide, x 14 tall, by seriously deep (I forget the depth of the box.. 1 large slot port in the center)

Not sure what it was tuned to, but I temporarily installed the pair of W12s in there, ran them off a single Punch 800A2 (3 ohms per channel which equals roughly 250 watts ish??)

In keeping with the comment you made about not much power being required, the OUTPUT WAS LUDICROUS!! Rear view mirror fell off within minutes, LOL.. I was totally unprepared for what these subs would do off that amp in that raggedy old box..
 

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Discussion Starter #8 (Edited)
and of the minimal wattage available, much of the energy of which was being lost to a sagging box which was coming apart at the seams, the output was still completely absurd..

In hindsight, with that thought in mind, I can't imagine what these subs will do with 500 per side in a properly prepped box..

Can't wait!

(EDIT) I almost regret pulling the pair of JBL Pro Audio 15s (2226HPL) I had playing through a JBL 4648 "fixed application" commercial sub enclosure.. Although the specs of this combo show a sharp rolloff below 40hz, I had them firing toward the rear door.. (cabin gain?)

with the Hertz ML165 IB in OEM door location, ML28 (big chamber) in pillars, I let the 80PRS autotune and MY WORD!! The impact and SQ was as good as it gets given the limitations of the HU and subs..

I didn't get that mirror breaking low end, but I did get well balanced live venue type response with very nice imaging, Vadrum sounded like he was setup in the van with his full on orchestral ensemble LOL..

I will def look for the music you mentioned, I've never heard of it.. Can't wait!
 

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I'm going to go model these up, brb

edit, done.

Any enclosure from 6 to 8 cubic feet, and tuned to 23-25hz, and you basically got it. Just make sure you with accurately plot the port once you have the box size properly calculated.
 

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(FS is 18Hz on these subs)
Where did you find this spec? It's not listed on the website you linked.


I'm wondering if the shape of the box will hurt or negate the type of response I want.. It's very wide, but not very tall or deep.. All of the sub enclosures I see for SPL are very deep, usually much deeper than they are wide/tall..

My box is the polar opposite.. Thoughts?
Won't make any difference at the frequencies you want to play.
 

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Discussion Starter #11
Where did you find this spec? It's not listed on the website you linked.




Won't make any difference at the frequencies you want to play.
18hz FS. You are correct, there's no spec for that..

When I posted that, I went by memory, I recalled reading 18hz, for some reason I recall that as the FS..

Turns out that's the low end of the frequency response, no real data for FS, just states an 18 to 1khz +/- 3dB response..

I should have double checked before I posted that. Thanks for clearing that up..
 

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Discussion Starter #12 (Edited)
I'm going to go model these up, brb

edit, done.

Any enclosure from 6 to 8 cubic feet, and tuned to 23-25hz, and you basically got it. Just make sure you with accurately plot the port once you have the box size properly calculated.
I am about to cut out the old face, remove old slats and ports, start clean with 3/4 of a box..

I have two pieces of ply I'll be gluing together, roughly 1.50" thick when done..

I went with round PVC for ports, I had an old holesaw collecting dust, 3.5/8" diameter, so I went with 3" PVC..

Now to calculate 24hz using 2 pieces of 3" PVC per side..

(round ports simplest way considering the limited tools I have available)

Now, with 3" PVC, I'm assuming that's the inner diameter? I have a 3-5/8" hole saw, outer edge of teeth match up with outer diameter of PVC, will be a snug fit once hole is cut out..

Man, it's been so long since I've done all of this, I recall using this holesaw once before, 3" PVC, used two ports per sub on an old install (10 years ago) I ended up having to tap the PVC in with a hammer, used glue and a thin finishing nail on each side to secure it..

With 4- 15" L-7 solobarics in a 12CF box tuned to 26hz, two Mmats D3500.1 amps, (1 per pair = approx 3K RMS per side) output was absolutely insane!

I had 2 pairs of the old school Boston Acoustics Pro 6.5" (3 way) used 4 midbass, 2 mid, 2 tweets, powered by a pair of MMats SQ4160 4 channels.. WOW.. Just... WOW... I'm not sure why I go through all the trouble, enjoy for a month or two, document nothing (via photos or portfolio) then tear it all down and sell everything.. ?? Still trying to figure me out..
 

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Um... 3" PVC...you are going to need a TON of ports to keep the velocity below scary numbers.

I would suggest returning 3" PVC asap. There's virtually nothing 3" can do with a bad ass sub like the JBL GTI. 3" ports may go well in an 8" sub config, that's about it.
 

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Discussion Starter #14
OK, so inner diameter 3" (3.5 outer) too small? got it.. I went with this without first modelling in Winisd because I have a 3-5/8 holesaw collecting dust, had great success with it years back.. I happened to be at Lowes shopping for router, saw a few shorter cut lengths of 3" on sale, grabbed it impulsively..

I'll check for myself on Winisd, what are we trying to avoid in terms of port velocity? Another thing I noticed, sometimes when you enter more than 1 port, the dimensions of the ports required become unmanageably long, often don't match dimensions of box..

Glad you pointed it out.. Although I would not have cut anything till I modelled on Winisd first, you just saved me multiple trips to Lowes.. I happened to be heading out there today, will check Winisd first, if this won't work, I'll return for appropriate size..

Slot porting is a bit out of my depth at the moment, I do not have appropriate tools.. I may not have the depth required either..

It's looking like I'll be spending approx $30 to $40 for a holesaw which will cut correct size for the larger PVC, which I think is 6".. (I should have kept all that thick cardboard tubing I had leftover from my cousins art gallery.. some of that material would have been perfect.. 6" 8" 10" diameter 1/2" thick heavy duty cardboard for shipping artwork.. tough as nails, looked like the same shit JBL uses in their cabs..

When plugging numbers into Winisd, the port diameter it asks you to enter, is it asking for inner diameter??
 

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Discussion Starter #15
Just plugged some numbers into Winisd.. I have the very basic version, nothing about port velocity..

What I came up with is this.. For 8 cf, 2 drivers, 4 ports 3" inner diamter, tuned to 22 hertz, I came up with 0dB @ 22, slight bump to .5dB from 25hz to 30hz, then beautifully flat along 0dB straight across the board..

I'm guessing port velocity is the speed at which the port propels the wave of the sub, I'm also guessing this leads to chuffing, will also skew waves?

Will it actually accelerate the wave? If so, your mention of "scary" I'm assuming it will behave beyond an acceptable margin of performance..

How does that work? Does it accelerate the speed at which the wave hits your ears, causing problems with phase cancellation or something like that?

Or does it simply have to do with chuffing or port noise?
 

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Discussion Starter #16
Also want to point out, when I plug in the standard 6" PVC, the port length Winisd suggests goes way beyond the depth of my box.. Do I have to add curved joints (u bends, or 90' angles) to achieve the length? How will I then calculate displacement?
 

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You will want to seek and download the WinISD Pro 0.7 version. It is still completely free. It will definitely serve you to find your port tune, and velocities and much more.

And yes, when the port length exceeds, consider bends. My best suggestion is to construct a port. A slot or square one. OR we can work out passive radiators.

edit:

Chuffing is an acoustic annoyance at low levels, and at higher velocities it becomes a hindrance to the performance, basically a restriction.

Air velocity is not congruent with air pressure waves
 

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Discussion Starter #18 (Edited)
You will want to seek and download the WinISD Pro 0.7 version. It is still completely free. It will definitely serve you to find your port tune, and velocities and much more.

And yes, when the port length exceeds, consider bends. My best suggestion is to construct a port. A slot or square one. OR we can work out passive radiators.

edit:

Chuffing is an acoustic annoyance at low levels, and at higher velocities it becomes a hindrance to the performance, basically a restriction.

Air velocity is not congruent with air pressure waves
I'm aware of chuffing, I'm still in the dark on the topic of port velocity, I'll do some reading..

I basically stripped the box down to 3/4 of a box, glued two pieces of 3/4 ply to make the face..

In the interest of maximizing internal volume, I can flush mount the new face to the outside of the old box, whereas the old face was recessed..

Not only does this give me the benefit of increased internal volume, it makes for a perfect guide for my router. No need for the inaccuracies of the cheap table saw I'm working with..

I can install internal bracing while it's open.. Once it's good and proper, I can simply lay the 1.50" face on top of the open end of old box, secure it, run my router across it to trim to perfection..


Anyway, I am finally going to post pics.. I have a good jigsaw now, so I can cut for slot porting.. I have no experience with this, do not know anything about calculating port size (do we work with inner or outer dimensions when inputting data in Winisd? )

I've attached some pics, also want to point out, 8.5 CF is bare bones internal volume with new face mounted atop old box.. That's before sub, bracing, port displacement..

I'm actually going to wait for instructions from you for proper bracing and port size.. (If you'd be so kind) Fire away!!
 
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