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Vented box suggestion Eminence Lab 12C
Vented box suggestion Eminence Lab 12C
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Old 13th September 2017, 03:01 PM   #1
RedMan is offline RedMan  Ireland
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Default Vented box suggestion Eminence Lab 12C

Hi all

Recently picked up two Eminence Lab 12C's for a very reasonable price and am looking for cabinet suggestions, needs to be vented and tuned as low as possible with no larger than 3.5 cubic feet used for the cabinet.

I currently run a single slot ported 15'' but really want to try out a stereo subwoofer setup, I understand I will loose some overall slam and authority moving to two 12's. I also to be honest just want another project to get my teeth into. The 12C seems to be very close to the original Lab 12, slightly lower QTS and the extra 100W on paper.

I have a simple design in mind, essentially a well braced box roughly 3.3 - 3.5 cubic feet with hopefully a 4'' port depending on port speed tuned to an F3 as close to 20hz as I can get (I am open to lower F3 if possible and willing to sacrifice some db for lower extension). I understand that to many this is a tiny box for porting and indeed they will be a smaller box than my present single subwoofer, however space it at a premium and I simply can't go bigger than 3.5 cubic feet. I only wish I had the space for some of the Horn designs I have seen produced with these but I don't.

So, just thought I would throw it out there as I know these were an extensively used subwoofer in the past so there may be some glaringly obvious designs in or around my requirements that I don't know about.

Thanks everyone
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Old 14th September 2017, 01:11 AM   #2
Brian Steele is offline Brian Steele  Grenada
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Have a look at the DSL CS30 for inspiration. That can be modelled in Hornresp. I think venting @20 Hz might be pushing it a bit too low however. What are the t/s parameters for the Lab 12C?
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Old 14th September 2017, 01:59 AM   #3
Dave R is offline Dave R  United States
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Here's a link to the Eminence spec sheet for the Lab 12C.
http://www.eminence.com/pdf/LAB_12C.pdf

There are box recommendations in the R/H column under Mounting Information. Quite a wide range of possibilities.

One possibility:
A vented box about 55 liters (with just one 12C), and tuned to 28 Hz gives a fairly smooth response. (f3 ~ 26, and f10 ~ 20.5) A 4 inch diameter port would be a bit over 19 inches long, so maybe a shelf port or a passive radiator would work better. Sorry, my program doesn't calculate port velocity.

Maybe someone else could chime in with other possibilities.
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Old 14th September 2017, 03:10 AM   #4
Brian Steele is offline Brian Steele  Grenada
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Quote:
Originally Posted by Dave R View Post
Here's a link to the Eminence spec sheet for the Lab 12C.
http://www.eminence.com/pdf/LAB_12C.pdf

There are box recommendations in the R/H column under Mounting Information. Quite a wide range of possibilities.

One possibility:
A vented box about 55 liters (with just one 12C), and tuned to 28 Hz gives a fairly smooth response. (f3 ~ 26, and f10 ~ 20.5) A 4 inch diameter port would be a bit over 19 inches long, so maybe a shelf port or a passive radiator would work better. Sorry, my program doesn't calculate port velocity.

Maybe someone else could chime in with other possibilities.
An interesting question. I like to start with the CSA of the vent to be at least 1/3rd Sd for subwoofer duty, so for the LAB 12C, that would be 507/3 = 169 cm^2. That's a lot higher than the CSA of a 4" vent, 81 cm^2. But shoe-horning a long enough vent with a 169 cm^2 CSA into a box that small to achieve a 28Hz F3 might be a bit of a challenge.

I spent a few minutes tonight having a look at what might be possible with a larger box, in this case 77 l net, 110 l gross. Fb should be around 30 Hz once the box is lightly stuffed in the large section behind the driver, and the vent has a CSA of 170 cm^2, which meets the 1/3rd Sd requirement. The aspect ratio of the vent is a bit high though at 8:1. If I have some time tomorrow, I'm going to mod the spreadsheet to include a bifurcated vent option to see if that improves things a bit.
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File Type: png 2017-09-13 (6).png (21.4 KB, 83 views)
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Old 14th September 2017, 03:24 AM   #5
Dave R is offline Dave R  United States
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Quote:
Originally Posted by Brian Steele View Post
An interesting question. I like to start with the CSA of the vent to be at least 1/3rd Sd for subwoofer duty, so for the LAB 12C, that would be 507/3 = 169 cm^2. That's a lot higher than the CSA of a 4" vent, 81 cm^2. But shoe-horning a long enough vent with a 169 cm^2 CSA into a box that small to achieve a 28Hz F3 might be a bit of a challenge.
Thanks for mentioning that. I failed to point out that the 55 liter box would probably perform better with a 6" or 8" diam vent, but the length would be much less manageable. Of course, the tradeoff is that the 4" may be limited by how much (little) power it takes to reach an objectionable port velocity.

Also, I have seen shelf ports that form an "L" along the bottom and back of the cabinet.
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Old 14th September 2017, 04:07 PM   #6
GM is offline GM  United States
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Quote:
Originally Posted by Brian Steele View Post
I like to start with the CSA of the vent to be at least 1/3rd Sd for subwoofer duty
And why I prefer to use a TQWT for long vent alignments as it allows a 0.25*Sd.

GM
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Old 15th September 2017, 12:11 AM   #7
Brian Steele is offline Brian Steele  Grenada
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And why I prefer to use a TQWT for long vent alignments as it allows a 0.25*Sd.

GM
No doubt - that's one of the advantages of gravitating towards any of the QW resonant types of alignments.

The "problem" I've run into with the TQWT alignment though is that the driver has to be a certain distance along the line to get the smoothest passband, and when it comes time to fold the thing in half to make a rectangular box, it sometimes becomes difficult to put the driver at that distance, because it ends up being around the bend rather than on one of the flat faces of the box, LOL, and the vent invariably ends up on a different external panel than the one holding the driver, which means that the build would not be a close match to the sim. I do also have concerns about the "vent" geometry perhaps leading to increased distortion (especially with TWQTs where S1>>S3), but I've never tested that hypothesis with an actual build and measurements.

In any case, I've gravitated towards MLTL type layouts because they offer a bit more flexibility and you can actually fold them up into a box and have the driver mounted at the distance you want it down the path without much difficulty, and you can get the driver and vent on the same panel. There's still a bit of vent geometry mismatch, but not as much as the TQWT.

I've attached an idea that I'm playing around with at the moment that is both MLTL and attempts to deal even further with the vent geometry mismatch issue by using a "nozzle vent" that has a symmetrical entrance and exit. Is it going to make a difference, and is that difference going to make a difference? I guess there's only one way to find out...
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Old 15th September 2017, 06:37 AM   #8
GM is offline GM  United States
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True, but then I never had to fold one up more than twice, so not a big deal plus normally I was primarily interested in max acoustic efficiency, so driver, vent were at extreme ends.

To me, for descriptive purposes, a MLTL is a vented constant taper [pipe] TL whereas yours is a modified ML-TQWT since it has an inverse taper and expanding [horn] vent. This type vent historically was designed as/called a 1/8 WL horn.

Better overall IME to make the initial inverse expansion shorter and the vent/horn longer, though if all you're primarily interested in lowering vent mach, then never mind.

GM
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Old 15th September 2017, 10:31 AM   #9
RedMan is offline RedMan  Ireland
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Thanks for the response everyone. I had seen the Eminence spec sheet and this other one: http://www.eminence.com/pdf/LAB_12C_cab.pdf

However the designs laid out in that PDF will not suit me.

The T/S Parameters are indeed in the PDF posted by Brian Steele, thanks.

IF I am being honest a lot of what you guys have mentioned has gone so far over my head that I can't even see it... I have seen plenty of TQWT designs but they look scary to me, I have used WINISD before but that's about it, will look into Hornsrep.

My primary aim with this project is low end extension with these drivers within the size constraints I have to deal with. I had planned to build a cabinet that is relatively tall, around 650mm or so with a downward firing round port so this should help with a long port. I really just wanted to run this driver past everyone to see if there was any glaringly obvious tried and tested designs that would be easily usable for this driver within my size requirements.

Would I be wasting my time trying to work out some form of horn design within size constraints that will reach an F3 in the low 20's or lower?

Thanks again all, have lots of research to do
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Old 16th September 2017, 12:32 AM   #10
GM is offline GM  United States
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You're welcome!

Yeah, this is what happens when posting on an advanced tech forum, especially when not all the app's details/limitations have been included.

Hmm, 65 cm [o.d.] high is way too short to be any sort of TL unless folded horizontally, making for a deep cab, so a down-firing vent seems to be your only option unless there's no height restriction to allow a much taller cab, i.e. 60"/152.4 cm o.d. is my default MLTL to keep vents short, vent mach low.

Horns typically require at least driver Vas [ ~124 L + driver, baffles] and often considerably more to just match a BR's output. Running a few sims, a tapped TQWT [TTQWT] is smallest at ~134 L + driver, baffles and a tapped horn [TH] is 184 L, etc.. Note that the BR with a large enough vent for a < 5 % mach is ~194 L, yet has the least output, though don't know how much floor loading might allow some vent size reduction.

Don't know if these can be folded into whatever form factor you're stuck with, but guessing probably not unless you can go high to keep them a single fold.

Vent mach based on the vent only 'feeling' 150 W peaks, except the TH can handle 250 W, so the peak SPL 'winner' by a few dB.

Note too that these will be limited to ~80 Hz XO.

GM
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