Box for jl 12W0v3-4

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fatpizza

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Joined 2016
#1
I'm trying to model a vented box for this driver, but I keep getting a hump at 45hz when I lower Vb. This graph is for a 3.8 cu. ft Vb which is already large.
An externally hosted image should be here but it was not working when we last tested it.
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I've got 3 choices
1 Make a huge box, although I'd rather not.
2 Use EQ.
3 Go for a sealed box

This is my first diy so go easy on me.
Edit. Ok, so I just realized I can't find any info on Le, how important is it for what I'm trying to achieve?
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#7
Hi Op, what do you expect from that driver...? It"s perfect for sealed. Some drivers are built for sealed speakers they don"t do the Bessel alignment you are looking for as GM already mention to you. Some drivers good for BR others for sealed in short. The sealed speaker 100 liter/3.5cf is very nice or 3.8cf you mention and closest thing to a Bessel, and plenty of sub LF info in the 20's Hz that a JBL can not get (look here at the famous driver JBL 128H). So if you are not happy after you build it you can always use the EQ/LT.
 
#8
Inductor said:
Hi Op, what do you expect from that driver...? It"s perfect for sealed. Some drivers are built for sealed speakers they don"t do the Bessel alignment you are looking for as GM already mention to you. Some drivers good for BR others for sealed in short. The sealed speaker 100 liter/3.5cf is very nice or 3.8cf you mention and closest thing to a Bessel, and plenty of sub LF info in the 20's Hz that a JBL can not get (look here at the famous driver JBL 128H). So if you are not happy after you build it you can always use the EQ/LT.
Click to expand...

100l is looking good right now, might go up to 160 and call it a day. The graphs above use an inductance of 0 as JL Audio seem to hate this parameter and do not mention for any drivers that I could find.
What would be an estimate Le for this driver?
 
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#10
fatpizza said:
It will be used in a medium sized room (about 1500 cu.ft) if that makes any difference.
Click to expand...

Assuming an 8 ft ceiling, a single 12" normally needs to be hard into a corner, but is often too far away from one channel to blend well unless XO'd very low, like with a 15 ft wall it would ideally need a ~1130/3/15 = ~25 Hz XO, though due to room and human hearing variables it can work well enough for some folks as high as 1130/15 = ~75 Hz.

Located along a wall at an odd harmonic [3rds, 5ths] where you lose ~3 dB of dynamic headroom, this equates to needing another sub+amp power to make up for it if need be or at least a bigger, more efficient single sub, which usually means some form of vented alignment.

Of course if it doesn't need to play loud, then EQing a small sealed sub will suffice.

Note that if the sub can be located very near the listening position [LP], it's like gaining one or more subs, so woofer 'coffee' or end table or even a platform or accent 'shelf table' behind the LP are common solutions with the latter two normally allowing sufficient room to build a fairly large tapped TL or horn to 'rock your world' ;). The ever popular, tall 'sonotube' sub like SVS markets allows a large cab with a small footprint too.

GM
 
#11
fatpizza said:
What would be an estimate Le for this driver?
Click to expand...

Assume it is high when it's not published, so probably as high as 4.0, but as Inductor noted it just 'plumps' up the mid-bass a bit and with digital XOs it's moot. For passives in LF though it's a big deal, requiring huge/expensive/power wasting inductors and one reason why they didn't use 'subs' before the digital revolution.

GM
 
#12
GM said:
Assuming an 8 ft ceiling, a single 12" normally needs to be hard into a corner, but is often too far away from one channel to blend well unless XO'd very low, like with a 15 ft wall it would ideally need a ~1130/3/15 = ~25 Hz XO, though due to room and human hearing variables it can work well enough for some folks as high as 1130/15 = ~75 Hz.

Located along a wall at an odd harmonic [3rds, 5ths] where you lose ~3 dB of dynamic headroom, this equates to needing another sub+amp power to make up for it if need be or at least a bigger, more efficient single sub, which usually means some form of vented alignment.

Of course if it doesn't need to play loud, then EQing a small sealed sub will suffice.

Note that if the sub can be located very near the listening position [LP], it's like gaining one or more subs, so woofer 'coffee' or end table or even a platform or accent 'shelf table' behind the LP are common solutions with the latter two normally allowing sufficient room to build a fairly large tapped TL or horn to 'rock your world' ;). The ever popular, tall 'sonotube' sub like SVS markets allows a large cab with a small footprint too.

GM
Click to expand...

Thank you for the feedback GM, the room is indeed 8 1/2 ft tall and I won't be needing this sub to rattle the room. Tapped horn would be cool but it would probably be too big.
This is the result for Vb =190l , Fb = 20hz, a Le=2 thrown in for good measure and medium fill

An externally hosted image should be here but it was not working when we last tested it.


It's as big as I'm willing to go, but I'd like a second opinion on it.
 
#13
You're welcome!

Looks like the TQWT I simmed, so should work fine and assuming a little room/boundary gain from being near/at a wall the 'drooping' low end will be boosted at least enough to flatten it out.

GM
 
#14
I've settled on a 7.5 cu. ft box, and I am now thinking about stuffing/lining the box.
Does lining or stuffing with foam/polyfill do anything for resonance in the 20-80hz region, or would I be better off using automotive bitumen sheets?
 
#15
No, high density fiberglass [acoustic] insulation will work down into the 200s IIRC [Google acoustic room construction], so LF requires lots of mass. I made some LF room dampers in the mid '70s and had to double up 3/4" 4x8 ft MDF panels to go low, so used ceramic and industrial rubberized floor tile when I started experimenting on speaker cabs to get Fs below its pass-band, ultimately staying with braced 3/4" or thicker no void plywood to push it above the pass-band where any resonances are weak enough to be easily damped with just lining the walls or using only light stuffing, not to mention to keep weight somewhat reasonable.

The bitumen used for cars is for damping fairly high frequencies, so tends to drop the metal's BW down where one ideally doesn't want it, so while it's bound to damp any material over some BW, it's not really suitable for anything thicker, denser than relatively thin metal panels unless a lot of it is used IME.

At 7.5 ft^3, braced > 3/4" no void plywood [BB, apple, some marine grades] where one of the braces also supports/mass loads the driver to the cab is the way to go IME, then lining one of each parallel walls with 1" acoustic fiberglass insulation [O-C 703 duct board] or = [light stuffed with polyfil is popular] is normally sufficient to quell the cab's eigenmodes if the cab's dimensions are an acoustically good room ratio or as a high aspect ratio tube with appropriate driver offset.

GM
 
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#16
I'm still a little confused about the role of lining, can it be replaced by bracing/dampening the panels or does it serve another purpose.

I'm not so keen on putting fiberglass in a vented box. Glass particles flying everywhere doesn't sound very safe so fiberglass wasn't on my list.
Polyfill I hear is pretty much useless so that leaves open cell foam (egg-shell crate).
 
#17
Basic damping is for reducing the amplitude of the cab's 'room' eigenmodes [you can use a room mode calculator to optimize a basic box shaped speaker cab], reflections back 'through' the driver, i.e. these modulate it, causing it to add tones not in the reproduction, 'coloring' it. These are what makes a cab sound 'hollow' when there's none, so neither bracing nor adding bitumen will help unless the latter is backless, exposing its goo to cab's air, which

Some myths never die. 🙁 I've been using FG for most of my nearly 63 yrs of off n' on speaker building with up to ~256"^2 open vents in really large cabs and never had it happen nor ever had to clean it off the inside of a speaker grill or driver backside nor seen it happen even in high power prosound apps, but I can appreciate the itch and powder that gets stirred up during installation 'damping' folk's enthusiasm for using it.

Then there's child, pet concerns, folks so allergic that just being in a house with it exposed can be too much, so recommend a sufficiently protective grill over it same as for the driver regardless of what's used. FWIW I usually use pet proof screen for screen doors. I've had big cats, dogs and hungry [one rabid] raccoons try to 'eat'/claw their way through the kitchen's glass sliding door screen with nary a single strand cut/torn loose. Impressive stuff! Did have to restretch it a few times though to get the sag out from all the hanging weight, pulling on it that ultimately bent the first frame too bad to straighten properly.

Note too that I normally use OC 703 duct board [see pic], which is designed for damping heat/AC ducts, so nothing like the loose stuff used in attics, walls, which is normally only used for stuffing a sealed cab, though have seen it in large consumer and prosound speakers built up through the mid '70s.

'60s era Altec Valencia [846A] shown with it: [http://classicaudio.ru/forum/uploads/monthly_08_2014/post-1619-0-29283900-1407423058.jpg

FWIW, I've never had much luck with any type of foam and as you noted it takes a lot of polyfil to do much good, though in recent years recycled shredded cotton jeans has become popular and from just listening seems to function over a similar BW as FG, so another option: UltraTouch 16 in. x 48 in. Denim Insulation Multi-Purpose Roll (6-Pack)-60306-16482 - The Home Depot

Another long time fave that's found in some upscale speakers of days gone by and still in use today for all I know is premium felt [not the foam and definitely not re-bond foam] carpet underlay: https://www.google.com/webhp?source...TF-8#q=premium felt cushion underlayment roll

GM
 
#19
Hmm, you do have central heat/AC systems, right? Scope out what the installers use to damp ducts and if you're lucky they may give you enough scraps for the project super cheap or free like in my general locale.

GM
 
#20
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