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Old 1st September 2009, 07:34 PM   #1
sangram is offline sangram  India
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Default Eminence Lab12, ported box

Hi there, first post in subwoofers

http://www.diyaudio.com/forums/showp...96&postcount=3

I'm looking at building two smallish efficient subs for home use, mainly music. I'm not a basshead, but I think the L18 boxes I'm building will not be able to take too much juice and was thinking of crossing them over at the low end. The Lab12 is locally available unlike the Dayton woofers (those cost over $350 after adding shipping and customs ), as are some of the JBL pro sub drivers.

I don't have very much power (LM4780 BPA, ~150-180 watts max) so I need efficiency over extension/xmax, though I'd like to hit about 25-30Hz in-room. I don't need it to be very loud either, just enough to take the load off the L18 woofers at the very bottom (<60Hz).

My boxes came out a bit different from sreten's calculations in the linked post - 3.5cuft (not small but not too big) with a single 4x3 port, tuned to 26Hz, -3dB at 26 Hz, 111 dB SPL with 180 watts and well within the driver's excursion limits. Room is 22x18x12 ft, and two of these will be used in a stereo configuration (budgets permitting).

Does this look good to go or am I missing something? I've never built a sub before, or even needed one so I'm not sure if this is the right way to go.

TIA for your help
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Old 1st September 2009, 08:00 PM   #2
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You could try the design as is from Eminence's site.
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Old 5th September 2009, 01:27 PM   #3
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Looks very good, congrats on that.

You could (if you wish) tune lower, and get a f3 of 23Hz, by tuning in the 22-23Hz region.

There are many designs on the Eminence site, the small version looks quite nice - small box, f3 of 40Hz.

Alternatively, a small, sealed box and a Linkwitz Transform circuit may do better, as a sealed box protects the driver from over-excursion below port tuning, and yu can choose how low you want it to go. I did that for my first sub, turned out well. Advice on that: don't try to make it go below 30Hz, the excursion will be huge, and not much music goes down there, but when it does, you'll get alot of nasty distortion...

Another idea - buy 2 of those drivers, make a small sealed box and use iso-brarik loading.

Whatever you go for, good luck with it.

Chris
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Old 5th September 2009, 01:31 PM   #4
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i have 2 lab12's in a 4th order bandpass. very small, very low & loud, very inefficient. 89.X dB is very inefficient.. but once driven with enough power the sound is incredible.

the lab12's are pretty unique. originally designed for a HUGE horn (LABhorn) with enormous SPL in low-end, but also perfect for cabinets not much bigger then the speaker itself.

if you want efficiency, i'm afraid you need to seek other speakers..
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Old 5th September 2009, 01:42 PM   #5
sangram is offline sangram  India
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@chris, I was thinking of two drivers for sure. Somehow I'm losing SPL when I load the drivers with an isobaric enclosure. Any idea what's up with that?

@powerflux, I don't have many options in this country, unfortunately. The alternatives if shipped in from USA or Europe, will end up at $400 each. There are a few JBL pro drivers I can get my hands on, so if there are any recommendations in the $150 range (per driver) I'd be glad to take a look. I have only about 150 watts of power on tap though, so I'll need something more efficient than a 87dB Dayton.

As a guide, my main rig is a pair of 85dB/w spakers and an 80 watt amp, and I usually turn deaf after about 30 watts. I am assuming the 110 dB output per sub (with these drivers and amps) should be enough given this situation.
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Old 6th September 2009, 08:47 PM   #6
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Quote:
Originally Posted by powerflux View Post
i have 2 lab12's in a 4th order bandpass. very small, very low & loud, very inefficient. 89.X dB is very inefficient.. but once driven with enough power the sound is incredible.

the lab12's are pretty unique. originally designed for a HUGE horn (LABhorn) with enormous SPL in low-end, but also perfect for cabinets not much bigger then the speaker itself.

if you want efficiency, i'm afraid you need to seek other speakers..
Can you please share your design? I'd be interested to have a go. I have 2 of these drivers and would like to cover the low end to go with Fostex 168 Sigmas; enormous amp power is not a problem for me. Thanks.
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Old 6th September 2009, 09:04 PM   #7
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Originally Posted by Samuel Jayaraj View Post
Can you please share your design? I'd be interested to have a go. I have 2 of these drivers and would like to cover the low end to go with Fostex 168 Sigmas; enormous amp power is not a problem for me. Thanks.
let me search, it's on a scrap paper somewhere the design was for PA, with the absolute minimum size possible in mind. this makes the cabinet very instable (0.5 litre too much in one chamber is disastrous). there are better designs (labhorn), but not smaller with the same response!

this is the pre-final design:
-3dB points: 38Hz, 117Hz.
the response is near-flat between 50Hz-90Hz with 2dB gain wich gives 118dB SPL @ ~750W according to winisd - no problem for the drivers. i measured 116dB @ 300W, never had the chance to measure full-power but i expect 118 is possible.
the response is as you can tell absolutely PA.

and now the chambers: front 18L, rear 21L. pipe: 10CM dia, 20CM lenght.. so: very very very small. use good stuffing/padding or else the higher harmonics will ruin the sound.

the final design is somewhere on scrap paper, but it doesn't differ much from this one. i believe the rear chamber is a tad bigger.

i can't say the sub is musical, but the bass is very tight and controlled. did some open-air cinema last summer. if you want to go lower; a TL or horn is the way to go i think. but i don't know if that's a good match for the lab12.

to test the drivers i'd build one of the cabinets from the spec-sheet from eminence. they can't be bad if you add extra bracing

Last edited by powerflux; 6th September 2009 at 09:12 PM.
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Old 7th September 2009, 04:49 AM   #8
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powerflux, thanks for the details. I was however looking for a sub that goes down to 20Hz and not necessarily above 100Hz.
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Old 7th September 2009, 01:09 PM   #9
ahegyes is offline ahegyes  Romania
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Lab12 realy does go down to 20hz.
in 100L enclosure tuned to 23hz has a f3 of 24hz in a 2pi enviorement, that mens that in a real world room it goes flat down to 20hz (if properly set up).
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Old 7th September 2009, 09:50 PM   #10
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Quote:
chris, I was thinking of two drivers for sure. Somehow I'm losing SPL when I load the drivers with an isobaric enclosure. Any idea what's up with that?
That's the catch with isobaric, using 2 drivers to create a new single driver with halve the Vas, thus losing 3 dB efficiency compared to a single driver in a cabinet twice the size. You're also missing the coupling of using two drivers, in seperate enclosures. So using 2 drivers in a cabinet 4 times the size of the single isobaric enclosure means 6 dB higher sensitivity in the bass range.

Best regards Johan
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