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[Moby (Mike Diack)]

When I built my pair of Labsubs, due to an organisational error, I ended up buying two sets of Lab12 drivers. Whilst it's always nice to have spares, the infrequency of gigs I do means that the 4 spare drivers are liable to be sitting on the shelf for a long time. What to do with them in the meanwhile? (The obvious thing is build another pair of Labsubs but storage and van space preclude it). My weddings/funerals/barmitzvahs/birthdays system consists of EV QRX115/75s or modified EVOs (the modification being removing the disasterous amps and externally powering them) on sticks, and I'd kind like to beef up the bottom end without adding too much to the cubic footage. Running the numbers in WinISD suggests that the Lab12 driver would do qiute nicely on a 100 litre ported box, but numbers don't always equate to reality, so I'm asking : has anyone tried this, and how did it sound ?.
M

[Antone Atmarama Bajor]

Yes I've built a pair of subs using a pair of Lab 12's each.

~6cu' per box.
   
    The perform quite well.  I think max output at 30Hz is about 124dB for The pair (all 4 drivers).  They are clean down to 20Hz ~115dB, should be able to do 118dB @ 20Hz but the vent velocity gets a little high.

I have the .dwg's or jpgs if your interested.











THD 2nd and 3rd Harmonic



I also built these sealed subs with the Lab 12's

This one is designed to be used with the 1kw Parts express plate amp.





And this one I power with a pair of ICE amps



Good times.

[Art Welter]

Moby,

I went from horn loaded to ported with my Lab 12s.
I found that 2) Lab 12 in a 7.76 cubic foot enclosure tuned to 36 HZ was the best compromise to be able to still get good response to 30 HZ and not run out of excursion up higher.

Antone's boxes go lower, but will run out of excursion in the 45-55 HZ range at a lower drive level. Everything is a compromise.

I tested many sizes and tunings before coming up with this alignment. Lots of sawdust and listening and testing, no predictive programs.

I like the sound quite well. I was kind of surprised that the difference between the horn and the ported cabinet was not as noticeable as I would have thought.

Art Welter

[Antone Atmarama Bajor]

    My models and predictions, don't exceed xmax until rated power, the closest I come to exceeding xmax is arround 30Hz, before port tuning reduces excursion.

   My cabs are also ~1.6cu' smaller per pair internally (Not counting port).

    I can confirm that Excursion gets quite high at 30Hz, but stays reasonable!

[Art Welter]

Antone,

I should have looked at my test results before that last post, I did several different box tests in 2008 and did not remember them correctly.
Your larger box tuned lower should give less (not more) excursion in the 45-55 HZ range than my smaller (per cone) box.

However, the sensitivity in the smaller box went up almost 3 dB in the 35-60 HZ range, I decided the extra sensitivity was an advantage that offset the excursion disadvantage, and I did not have space for the larger box anyway.

My actual measured excursion results using about 24 volt sine wave input (around 100 watts per cone) with 2)Lab 12 in one 7.76 cubic foot box tuned to 36 HZ were 13 mm peak to peak at 30 HZ, 5 at 35, 8 at 40, 12 at 45 and 50, tapering off to less than 2 mm above 110 HZ.

Using a single Lab 12 in a 6.5 cubic foot box with a 27 HZ tuning, the results with the same drive were 19 mm peak to peak at 25 HZ, 12 at 30, 11 at 35, 13 at 40, 6 at 45, 5 at 50-60, and down to less than 2 above 90 HZ.

I’d expect your box to be similar to those excursion levels, which would definitely be over the rated 13 mm Xmax at 400 watts.  
I would be curious how the actual measured (with a ruler) results compare with the box predictive model. If you do try the real test, be advised that 49 volts (400 watts at 6 ohm) will make the speakers stink within a very short period of time, I’d suggest only using 24 volts and just do the theoretical doubling of excursion.

Also wondering if you have noticed a difference in distortion between the push pull arrangement and both cones firing the same direction?

Art Welter

[Antone Atmarama Bajor]

I have 2 drivers in a 6 cu' enclosure (port excluded).  I'm not sure if you're calling it larger because of the space wasted by the push pull, or does your 7.6cu' factor in port for your cab?

    I've also done a box tuned to 30Hz that has a much more linear response to 30Hz  I forget the cab volume.

    The distortion is quite low on any configuration I've done with the lab sub, sealed ported, and push pull.  I haven't been able to do a head to head on the Lab 12 ported, push pull vs. standard, but I think the push pull is a little more transparent when pushed hard.

    I used Harris-tech Bass Box pro (same as eminence speaker design software).  It predicts my box to have ~13mm excursion at 30Hz and 20Hz @ 800 Watts 2 drivers 6cu' tuned to 21Hz.

That's why I built the box.  I wanted a sub that was able to perform across its intended RMS power bandwidth, without crapping out.

    The cone certainly moves more at 30Hz than it does at 25Hz, my impedance graphs also seem in line with whats predicted, but I've only really visually inspected the cone motion.

    They seem to do great with ~1kW per cab.

Antone-

[Art Welter]

Antone,

I misread, I thought yours were 6 cubes per cone.
I should have snapped to the fact that the box is not very deep.
I think you will find your actual excursion to be  more than the Harris-tech Bass Box pro prediction. Easy to test with a sine wave signal, amp, a ruler and a white dot on the cone.

Although I measured near Xmax with only 100 watts per cone, I have found the cones are not moving near that far with normal program with 500 watts per cone.

[Antone Atmarama Bajor]

    Yah 500 Watts music is normally a little less Sine heavy.

    I guess I should try the dot and the ruller sometime.  I've heard of people using a piece of solder wire held a distance from the surround or cone.

[Art Welter]

The dot and ruler method is very easy to read, and you can quickly go through the frequencies without re setting a piece of solder.

Have seen my Lab 12s doing 26 mm peak to peak, with no clacking, even though the Xlim is only rated 22 mm. No noticeable distortion either (other than wind noise!), easy to see why people blow them up without hearing a problem.

Does the Parts Express plate amp seem to put out a “real” 1000 watts?
Have you compared it to any  “pro” amps?

[Antone Atmarama Bajor]

     I have not done any real tests with it.

It is a Class G amplifier.  The one thing I really dislike about it is that it Highpasses right around 20Hz so its ~-3dB @ 20.

    I got it for free and built the Dual Sealed Sub for my friend.