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Author Topic: labsub modification  (Read 7935 times)

Harry Sookraj

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labsub modification
« on: March 05, 2009, 12:29:37 pm »

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 Rolling Eyes )
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Harry Sookraj
Bubbler Sound System
"talk is cheap, bass is everything"

Brian Dill

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Re: labsub modification
« Reply #1 on: March 05, 2009, 12:49:15 pm »

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

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Re: labsub modification
« Reply #2 on: March 05, 2009, 04:19:39 pm »

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
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Harry Sookraj
Bubbler Sound System
"talk is cheap, bass is everything"

Art Welter

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Re: labsub modification
« Reply #3 on: March 05, 2009, 05:36:17 pm »

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
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Tim McCulloch

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Re: labsub modification
« Reply #4 on: March 05, 2009, 06:22:31 pm »

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
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Ivan Beaver

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Re: labsub modification
« Reply #5 on: March 06, 2009, 05:08:40 pm »

This is with 2.83V input @1m

index.php/fa/21399/0/
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Antone Atmarama Bajor

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Re: labsub modification
« Reply #6 on: March 08, 2009, 01:27:20 am »

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.
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Ivan Beaver

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Re: labsub modification
« Reply #7 on: March 08, 2009, 10:39:59 am »

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.
index.php/fa/21426/0/

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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

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Danley Sound Labs

Harry Sookraj

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Re: labsub modification
« Reply #8 on: March 08, 2009, 02:55:12 pm »

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 hertzindex.php/fa/21427/0/

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?! Very Happy
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Harry Sookraj
Bubbler Sound System
"talk is cheap, bass is everything"

The Guy

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Re: labsub modification
« Reply #9 on: March 08, 2009, 08:52:02 pm »

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

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Art Welter

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Re: labsub modification
« Reply #10 on: March 09, 2009, 04:39:26 pm »

Harry,

Having the drivers in series rather than parallel would reduce the level by 6 dB assuming the amp’s output voltage was the same.

Have you tried the test I suggested yet?

Art Welter
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Art Welter

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Re: labsub modification
« Reply #11 on: March 09, 2009, 04:46:12 pm »

Jim,

The “floppy suspension of the Lab 12 driver” works fine in a ported cabinet as well as the sealed LAB design.

Many of us are using the Lab 12s in designs other than what you are using, and not having excursion related problems.

Art Welter
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Harry Sookraj

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Re: labsub modification
« Reply #12 on: March 16, 2009, 10:04:54 am »

Art Welter wrote on Mon, 09 March 2009 16:39

Harry,

Having the drivers in series rather than parallel would reduce the level by 6 dB assuming the amp’s output voltage was the same.

Have you tried the test I suggested yet?

Art Welter


Hello again,

I tried the experiment, and if I read your directions correctly, the cone has the least amount of excursion right b/t 47hz - 50hz. As I was listening, I did notice the cone reaching max excursion at about 35hz.

I have burnt out at least 6 lab12 drivers, but never ripping any part of the cone or suspension. As a matter of fact, still looking for a supplier to sell me some recone kits. Sad
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Harry Sookraj
Bubbler Sound System
"talk is cheap, bass is everything"

Art Welter

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Re: labsub modification
« Reply #13 on: March 16, 2009, 05:34:21 pm »

Harry,

So I guessed within two HZ your FB, the gray computer between my ears still works.
My bet is the Frankenlab is quite loud at 50 HZ also, right in the middle of where the normal LAB 12 design has a dip.

Since your open chamber Lab sub FB is about 48 HZ, you would  be best HP at 40 HZ, no need to put much power into the box below what it will produce well, and it is dropping about 24 dB per octave below FB.

Are the Lab 12 driver coils burnt, or just open?

There was a defect in some early Lab12 that Eminence would fix under warranty, I had three of four fail at random intervals. That defect (a bad crimp where the voice coil wire crosses behind the former, IIRC) occurred without any discoloration. If you have burnt the coils they are not covered, of course.

Art Welter
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Ivan Beaver

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Re: labsub modification
« Reply #14 on: March 18, 2009, 07:57:58 am »

Art Welter wrote on Mon, 16 March 2009 17:34


There was a defect in some early Lab12 that Eminence would fix under warranty, I had three of four fail at random intervals. That defect (a bad crimp where the voice coil wire crosses behind the former, IIRC) occurred without any discoloration. If you have burnt the coils they are not covered, of course.

Art Welter

There was another problem they had for a little while in which the curing process wasn't working properly and the coils would fall off.

That has since been fixed.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs

Gareth James

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Re: labsub modification
« Reply #15 on: March 19, 2009, 01:42:01 pm »

Harry, from looking at the graph you posted and my own sim it would seem you might be able to smooth off the power distribution over the entire band by leaving one cover off and one sealed. You won't get either peak but a smoother more even response from 35hz on up. Of course this is the theory, would love it if someone could perform a test sweep to confirm this  Very Happy  Ideally on a standard LAB sub for the sake of easy comparison.
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Raj Sookraj

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Re: labsub modification
« Reply #16 on: March 19, 2009, 08:29:55 pm »

In the 2007 NYC shootout the speakers were next to each other which changes the response.  However, we leave space on both sides of every cabinet.  Here's the response overlayed with the TH-115.  Keep in mind my speaker were wired in series so each cabinet is about 12-16 ohms.  The last 5 inches at the horn mouth was eliminated which lowered the response about 3db if I recall correctly. Also, notice how similar the response and phase curve is.
index.php/fa/21697/0/
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Art Welter

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Re: labsub modification
« Reply #17 on: March 20, 2009, 08:26:39 pm »

Raj,

The horn being shortened by only 5 inches should have a negligible effect on a horn as long as the Lab.

The fact your cab was about double the impedance of the TH 115 would mean you can raise your cab by  about 3 dB (or lower the other 3 dB) to be apples to apples.

Having another cabinet on either side, if that was the case,  seems to have turned the cabinet, which seem to be operating like a scoop type enclosure, into a tapped horn, and lowered the FB  a few HZ.

Do you know how close the other cabs were to the side of yours when it was measured?

Art Welter
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Ivan Beaver

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Re: labsub modification
« Reply #18 on: March 20, 2009, 09:38:33 pm »

The cabinets were not measured in pairs-just singles.

The pairs came into play when listening.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
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Danley Sound Labs

Art Welter

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Re: labsub modification
« Reply #19 on: March 21, 2009, 01:37:52 pm »

Ivan,

Raj said:
“In the 2007 NYC shootout the speakers were next to each other which changes the response.”

Were there cabinets adjacent to Raj’s cab in the “ TH-115 and labish at 28V.jpg” response chart?

Art
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Ivan Beaver

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Re: labsub modification
« Reply #20 on: March 21, 2009, 02:57:50 pm »

When the measurements were taken, all the other cabinets (except the installed ones in the club) were moved about as far away as we could practically get them-generally the closest ones were about 30' away.

The place was small-especially for subs.
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For every complicated question-there is a simple- easy to understand WRONG answer.

Can I have some more talent in the monitors--PLEASE?

Ivan Beaver
dB Audio & Video Inc.
Danley Sound Labs

Harry Sookraj

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Re: labsub modification
« Reply #21 on: March 21, 2009, 04:01:55 pm »

Gareth James wrote on Thu, 19 March 2009 13:42

Harry, from looking at the graph you posted and my own sim it would seem you might be able to smooth off the power distribution over the entire band by leaving one cover off and one sealed. You won't get either peak but a smoother more even response from 35hz on up. Of course this is the theory, would love it if someone could perform a test sweep to confirm this  Very Happy  Ideally on a standard LAB sub for the sake of easy comparison.


i'll give it a shot, never thought of that....of course the results will be by ear...no fancy equipment for testing
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Harry Sookraj
Bubbler Sound System
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Gareth James

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Re: labsub modification
« Reply #22 on: March 23, 2009, 07:34:41 am »

Cool, let me know how you get on! Smile
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