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[Harry Sookraj]

not to say this would be a great idea, but for some reason my labs get a significantly higher spl, when i don't cover the side panels....but i cant stack them if i do leave them uncovered....i thought of making a port from the rear chamber that would come to the front of the box with pvc...(disclamer: i am not a pro, and  this is my first post, so take it easy on me )

[Brian Dill]

Interesting..... Tell us more....??? I hAve not heard of anyone doing that before..
I would love to hear Mr. Danely's opinion.

[Harry Sookraj]

well it's like this

my brother raj brought a pair of modified labs (referred to as the FrankenLab in this forum, sorry to bring this up again raj) to a sub shootout in NYC in 2007....many people were puzzled:? by the fact that he did not cover up the sides and left the rear chamber open...in addition, at the time we had a dodge caravan we used to transport them, but to make it fit in the van we ended up cutting off the last 5" of the horn opening...the insides are all the same as the original lab, but the box is now 45" high X 22.5" wide, 40" deep...

for some strange reason when the side panels are off they sound WAY louder...but we are unable to stack them side by side, or on top each other on their sides...we've been spacing them 10in apart...i don't have an original lab to compare it to...so I don't know what the differences in sound are...but we get non stop compliments at every gig we do and the 4 we've been using sound great:d...we blow away all the cerwin vega and scoop trucks/floats in every carnival we do...

I thought of using a pvc pipe from the rear chamber to the front of the box so I could close up the sides thus being able to stack them the right way and get that sound I like...

I am aware:

-the labs may blow out sooner
-the sound will be different from the original lab
-this version is not a LabSub

but I am interested in knowing what you think is causing this phenomenon in my FrankenLabs

here's a pic of the back of our truck

http://viewmorepics.myspace.com/index.cfm?fuseaction=viewIma ge&friendID=241528912&albumID=663877&imageID=324 3781

[Art Welter]

Harry,

You don’t mention at what frequency your Labs have a significantly higher SPL with the chambers open.

Or what frequency you cross them.

Or what type of signal sounds louder.

I suspect by leaving off the compression chamber covers, Raj has  created something similar to a scoop, a horn loaded port. It probably pounds out a lot of sound over a limited range.

Paint a white dot on a cone. Run a sine wave generator into an amp and through the speaker. Put the frequency to about 100 HZ, turn up the level until you see about 1/4” of movement.
Sweep the frequency down, and watch what happens to the excursion. Turn down the level if you approach one inch of movement peak to peak.

I expect you will find the cone travel gets to a minimum at some point around 50 HZ or so, then goes up rapidly below that.

The minimum excursion point will be the FB of your ported box. That could be quite a bit louder than the normal Lab at that frequency, especially if it happens in the dip range the normal Labs have between 35 to 60 HZ.

Your cabinets probably have a port frequency that works with the type of music you like. At the tuning frequency you can hit the cabinet  with a ton of power, and the cone will hardly move. Frequencies much above or below the tuning frequency will cause the cone to move much more than with the sealed chamber, with less output.
As long as you HP 5-10 HZ below the tuning frequency, and keep an eye on excursion above the tuning frequency, you should be OK.

As far as duplicating the effect you have with ducts, I don’t see any way you could with the layout of the Lab horn.

Art Welter

[Tim McCulloch]

I was at the shootout, and we expected some seriously compromised performance but did not hear what we thought we would.

Right now I can't recall for sure if we did a TEF sweep on Raj's "FrankenLabs" but I think we did.  Ivan?  Mike?

Have fun, good luck.

Tim Mc

[Ivan Beaver]

This is with 2.83V input @1m

[Antone Atmarama Bajor]

Looks almost as good as having a CV Sub only with a Lower SPL Shelve out  to 40Hz.

  I imagine the Distortion must be quite high with the covers off.

[Ivan Beaver]

Antone Atmarama Bajor wrote on Sun, 08 March 2009 01:27

Looks almost as good as having a CV Sub only with a Lower SPL Shelve out  to 40Hz.   I imagine the Distortion must be quite high with the covers off.

Actually no.  The below graph is with 28V input.

The big thing I noticed about the response graph is the very  low sensitivity.  The real lab sub has something like 6db greater sensitivity.

[Harry Sookraj]

ok....i normally have them on the x-over at 100hz and high pass filter them at 30hz...

as for the shoot out's response, raj told me that the boxes were wired in series 12ohm, if that makes a difference in the spl...

also i used hornresp and made changes to the "horn segment mouth area" to reflect the new mouth opening, changes to the horn "segment exponential flare axial length" to reflect the 5in off the end of the horn, finally "Vrc" and "Lrc" to zeros to reflect as infinite, since they are open, and this is what came up....please tell me if i need to make any additional changes to get a more accurate reading...but as far as i can see from this graph i am just moving the dip over aprox. 10 hertz

if anyone in south florida has a couple of originals i can give a side by side test please PM me. thanks again guys...

as far as music, we mainly play soca, calypso, reggae, dancehall, chutney, and indian...slower reggae and calypso baselines get pretty deep, but all the other genres listed are more punchy

hey, any shootouts coming up?? how about one in Florda?!

[The Guy]

I haven't heard Raj's subs, but I have heard reports, and they were that the subs did not perform well at all.

I do know this; in my LAB subs, even a TINY air leak in the rear chamber will almost immediately result in driver death.  The floppy suspension of the Lab 12 driver requires a tightly sealed rear chamber, otherwise you will reach excursion quite quickly.

-J