FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Jeff Babcock

Jeff Babcock

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Jan 11, 2011
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DUAL LAB12

Our friend Art Welter provides this plan.

The ''Dual Lab12'' is a compact dual 12'' front loaded subwoofer. It has very good low frequency extension for its size and fairly linear response.

PDF's of the design are attached.

The design uses 3/4'' ply (birch strongly recommended) and the Eminence Lab12 driver.

Processor settings recommended are:
HPF: 24db Butterworth at 30Hz
LPF: User to determine (response usable to approx 160Hz)
 

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Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

As with all speaker designs, compromises must be made according to priorities.

The largest priorities of this cabinet are a compact size and extended low frequency response.

Is this cabinet a good choice for your needs? As always, it depends.

Often added low frequency extension makes a sub sound larger than its SPL level might indicate. This sub is very strong in the 40-60Hz range (and usable lower), however it will have less output at higher frequencies than a similar design which sacrifices extension for output might have.

If these design goals work for you, then this is a very affordable, easy to build cabinet which should perform well.
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Does Art have a recommended Wattage also for these guys?? There's a local Open mic night that could use one of these to compliment their small system at this size. Just wondering if he went with what the lab sub was rated for or if someone else worked better.
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Adam Whetham wrote on Sat said:
Does Art have a recommended Wattage also for these guys?? There's a local Open mic night that could use one of these to compliment their small system at this size. Just wondering if he went with what the lab sub was rated for or if someone else worked better.
Click to expand...

You would be looking at 400 watts/driver or 800 continuous or 1600 program.

If you want to play the ''peak'' game then 3200 watts.

I would suggest an amp in the range of 100-1500 watts.

Now what the impedance is-That is another question. The drivers are rated for 6 ohms each. So it might be a 3 ohm cabinet.

But it would be good to have an actual impedance curve of the drivers int he cabinet to have a better idea of what real load is.
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Art is on these forums, hopefully he'll chip in.
I provided all of the info that was available.

It is a 3 ohm cab, but as noted by Ivan, that is a rough assumption and an impedance test would show a clearer picture.

Art ran distortion tests on it with 800W (49V at 3ohms)

It has very low distortion at low frequencies (ie 3% at 40Hz, etc)

Full distortion test specs are on PSW in a thread by Phil L.

http://srforums.prosoundweb.com/index.php/mv/msg/56314/0/80/0/
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Speaker cab design is something I know absolutely nothing about so please bear with me. Whilst maintaining the same internal volume and port characteristics, would it be kosher for me to morph these things into a trapezoid shape to make ''booster seats'' for SRX725s ?.

M
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Mike,

While maintaining the internal volume and port dimensions should yield a SIMILAR result, it will not necessarily be exactly the same. Changing the shape of the box will affect the internal resonance modes. You may want to consider this.

Also, are you certain that having your subs directly under the SRX boxes is going to give you the most even sub coverage for this venue (assuming other placement options are feasible)?
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Jeff Babcock wrote on Mon said:
Mike,

While maintaining the internal volume and port dimensions should yield a SIMILAR result, it will not necessarily be exactly the same. Changing the shape of the box will affect the internal resonance modes.

How much it will matter would at least require modeling this with your desired dimensions. You may want to consider this.

Also, are you certain that having your subs directly under the SRX boxes is going to give you the most even sub coverage for this venue (assuming other placement options are feasible)?
Click to expand...

Jeff,

Regarding conventional bass reflex designs: box volume is box volume is box volume. The speaker enclosure's shape (within reason) should not affect its tuning or output. The goal is to match the driver's electro-mechanical compliance to the internal air load's compliance and then tune THOSE mutually interactive factors to suit your performance objectives.

The reference to internal resonance modes brings to mind the contribution a carefully crafted violin body makes to tone, or the ringing of a glass filled with just this much water. If a PA box has internal resonance modes of any kind, it is probably better to repurpose that box as firewood. A contemporary, well-built PA box -- mid/high or sub -- should be as acoustically inert as possible. Mid/high boxes can benefit from asymmetrically-reflecting walls (trapezoidal), appropriate damping materials, and of course good construction. Sub boxes simply need to be airtight (except for the port, obviously) and really well braced. Art or Ivan could explain it better than I am able.

Or maybe I completely misunderstood you. It's been that kind of day today.

As far as stacking high boxes on subs is concerned, yes, a single block of subs will usually perform better than split sources, but from a practical point of view you sometimes just have to deploy the classic dual-stack high-box-high/low-box-low and just get on with it.

Thanks for getting this great new DIY resource up and running.
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Mike Smith wrote on Tue said:
Jeff Babcock wrote on Mon said:
Mike,

While maintaining the internal volume and port dimensions should yield a SIMILAR result, it will not necessarily be exactly the same. Changing the shape of the box will affect the internal resonance modes.

How much it will matter would at least require modeling this with your desired dimensions. You may want to consider this.

Also, are you certain that having your subs directly under the SRX boxes is going to give you the most even sub coverage for this venue (assuming other placement options are feasible)?
Click to expand...

Jeff,

Regarding conventional bass reflex designs: box volume is box volume is box volume. The speaker enclosure's shape (within reason) should not affect its tuning or output. The goal is to match the driver's electro-mechanical compliance to the internal air load's compliance and then tune THOSE mutually interactive factors to suit your performance objectives.

The reference to internal resonance modes brings to mind the contribution a carefully crafted violin body makes to tone, or the ringing of a glass filled with just this much water. If a PA box has internal resonance modes of any kind, it is probably better to repurpose that box as firewood. A contemporary, well-built PA box -- mid/high or sub -- should be as acoustically inert as possible. Mid/high boxes can benefit from asymmetrically-reflecting walls (trapezoidal), appropriate damping materials, and of course good construction. Sub boxes simply need to be airtight (except for the port, obviously) and really well braced. Art or Ivan could explain it better than I am able.

Or maybe I completely misunderstood you. It's been that kind of day today.

As far as stacking high boxes on subs is concerned, yes, a single block of subs will usually perform better than split sources, but from a practical point of view you sometimes just have to deploy the classic dual-stack high-box-high/low-box-low and just get on with it.

Thanks for getting this great new DIY resource up and running.
Click to expand...

Thanks Mike, I'm aware, perhaps I overstated the difference. ''Sure'' probably would have sufficed.

I did say it would be a similar result. How similar.... probably VERY similar. But not exactly identical. I've messed with this a bit personally and noticed measurable though not terribly significant differences. Agreed it is a greater issue as the frequency of interest rises and with the OP's rig and likely choice of a lower LPF it's probably of little consequence.

EDIT: Oops, realized I'm responding to a different Mike.

Cheers
Jeff
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Mike Diack wrote on Mon said:
Speaker cab design is something I know absolutely nothing about so please bear with me. Whilst maintaining the same internal volume and port characteristics, would it be kosher for me to morph these things into a trapezoid shape to make ''booster seats'' for SRX725s ?.

M
Click to expand...

Changing the shape is OK.

The shape was a result of conforming to some cabinets I already had, while still keeping some truck box integer dimensions.



A 30 x 30 x 15 inch size would work well for a larger base and less frontal area.
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Noticed a few mistakes on the Lab 2x 12+ design sheet, the design program evidently does not allow a few things we do in the real world.

Seth Hochberg did those sheets for me, I don't have the software to correct them, but here are the mistakes:

The internal dimension is 20 inches deep. The speakers are front mounted on the baffle, which is set back one inch from the cabinet front.

The more detailed plans show the correct dimensions.

This rough drawing may help some with the port detail:

attachment.php


I'd recommend recessing the speaker in the baffle to provide more grill clearance for those users that use amps rated more than about 1100 watts.

I'm using Crest CA 9 power amps, rated at 900 watts at 4 ohm, 1000 at 2 ohms for the 2 x12s. When the clip lights flash pretty bright, the cones just start moving the grill. With those amps, with stiff AC power, a pair of cones are probably getting close to 1500 watts peak, which pushes the cones right around their Xmax of 13mm.

The Lab 12 cones are pretty tough, but I wouldn't recommend more than about 1600 ''real'' watts, unless using a peak limiter capable of limiting below 30 Hz and the 45 -50 Hz range.

The Lab 12s are so clean that it would be easy to tear them up with too much power, they just won't give much audible sign of distress before they smoke or tear.

Art Welter
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Helge A. Bentsen wrote on Tue said:
I like this concept :)~:-)~:smile:

Art: Could you provide us with some detailed pictures of your subs? I'm curious about some construction details.
Click to expand...

Message 3338 and the two plan drawings should answer construction details, but if not, I'll try to answer any specific questions.

Just recently got to compare the ported Lab 2x12'' to a JBL SRX 728, using pink noise, BW filters set at 25 and 125 Hz, same drive level to each cabinet, measured at 2 meters, unused cabinet shorted out:

attachment.php


I have moved the charts below up and down to conform with one watt one meter half space measurement, the EAW SB1000 is the left chart, JBL SRX 728 is center, the EV QRX right. Use the center chart lines for spl comparisons.

attachment.php


These popular dual 18''s all have a large upper sensitivity advantage compared to the Lab 2x12''.

All the cabinets still adhere to Hoffman's Iron Law, their sensitivity in the 30 to 40 Hz range is very similar.

Below 40 the difference between the dual 18s and the 2x12'' is only about 3 dB, so a pair of the 2x12'', which take up less space than a single dual 18, would have about equal sensitivity down low.

However, the 728 can not take close to full power down low without exceeding Xmax, while the Lab 12s can. Four Lab 12 can take the same power as two of the JBL 18'', and will have less distortion down low.

From previous listening experience, I'd reckon the JBL to be cleaner than the other two dual 18s when pushed hard.

The Lab 12 design, having very flat response, does not require out of band EQ, so it ''plays well'' with with any top cabinets that have flat response at the crossover point.

Makes getting things to sound ''real'' a lot easier, especially if setting crossover points ''by ear'', or using crossovers that don't have delay, EQ, or the ability to have different crossover frequencies between low and mid.

Art Welter
 
Re: FREE SUB PLAN: Dual Lab12 (Front Loaded) by Welter Systems

Chris Gruber wrote on Wed said:
Is there a picture of one that is real?
Click to expand...

attachment.php


The 2x12'' subs are the two cabinets on the bottom of the stack.
The photo was taken while doing some measurements to determine how big of a plinth the stack needed to be stable in high winds.

Turns out the bathroom scale when center loaded did not read as high of a weight as it should :roll: .

A 45 x 45'' plinth was adequate to make the stack stable in higher winds than a pair of stacked EAW KF 850, or a pair of stacked Clair Brother's S4 cabinets.
 


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