Sunn Model 3 cabs - want to convert to bass cabs

lerret · #1 08-01-2011, 12:18 PM

I have an old pair of Sunn Model 3 PA cabinets that I want to convert for use with a GK Backline 600. I want to gut the cabinets and drop in some decent 12" bass speakers.

To get an 8 ohm cab, would I use 2 x 16 ohm in parallel, or 2 x 4 ohm in series? Does it matter?

Any advice on a good 12" speaker that won't break the bank?

BassmanPaul · #2 08-01-2011, 01:39 PM

Typically the cabinets used for an old PA rig will be too small to be suitable as bass cabinets. Getting good results isn't simply about putting drivers into any old box.

lerret · #3 08-01-2011, 01:43 PM

The cabinets are not small by any means - I can't find online specs, but will measure when I get home.

Is it all about internal cabinet volume?

T-Bird · #4 08-01-2011, 01:52 PM

Hi.

What Paul said.

Being Sunns, those cabs are probably worth something?
If the Sunn vintagey PA look isn't Your goal, selling the cabs and finding a bass specific cab, Sunn for example, would probably be better choice.

The cabs internal volume pretty much dictates what will work in there and what won't.

Downloading WinISD or similar and playing with drivers and porting will eventually give an estimate how a particular driver will work in that enclosure.

As for the wiring, doesn't matter much with SS like Your GK, but with tube amps parallel is always safer.

Regards
Sam

lerret · #5 08-01-2011, 02:33 PM

Thank you for the helpful comments.

I kind of like the way the cabs look, and that's part of the reason I'd like to use them.

will33 · #6 08-01-2011, 03:33 PM

It is about internal volume and port tuning as far as being suitable for bass cabs so start there. If for example they're 115 pa cabs that are really too small for good bass response because they were designed with vocals in mind, better results may be had by building in the baffles to convert them to 112's. Don't know yet until you get them measured and see what there is to work with. Can take the HF horn out of one of them and just have one in the top cab for bass as well...or go tweeterless alltogether to gain some internal volume.

lerret · #7 08-01-2011, 06:28 PM

Each cabinet is 17.5"w x 35.5"h x 11"d

At the top of the cabinet, there are two 3" diameter ports, each 3.5" in length. There is also a 3" tweeter between the two ports.

The cabinet was designed by Sunn with 2 x 12", but I understand that a bass cab has different needs than a PA cab.

I did download and install WinISD, but I honestly don't know what I'm looking at. I've got the help file open, so at least I'm trying...

Here is a link to the Sunn catalog page from 1979 showing their PA gear. The Model 3 is at the top, right

http://sunn.ampage.org/site/catalogs/1979/1979catp9.jpg

lerret · #8 08-02-2011, 11:46 AM

The volume of the Model 3 (based on exterior dimensions) is 6834 cubic inches

These other 2x12s are a little bigger, but not much:

Ampeg PB12H = 7246 ci (17"W x 27-1/2"H x 15-1/2")
Gallien-Krueger 212MBE = 7694 ci (19-1/2"W x 26-3/4"H x 14-3/4"D )
Ashdown VS-212 = 7142 ci (28" x 19.25" x 13.25")

will33 · #9 08-02-2011, 12:29 PM

Are your dimensions internal or external measurements? Internal is what counts. If they are thats about 3.95 cu.ft. gross and there are 12's that will work for bass. If they are ext. dims., figuring 3/4" walls and a 1" baffle recess I'd guess 16x34x8-1/2? That's about 2.68 which is too small. Could then consider modifying it into a 210, adding on/building it deeper, or just leaving it alone if they're worth some $ as is.

will33 · #10 08-02-2011, 12:32 PM

Duh, you said external there. One other option would be to look for 12's that'll work in a sealed cab and plug the ports. Likely aren't too many of those out there.

lerret · #11 08-03-2011, 10:36 AM

Thanks, Will. You are spot-on with the internal dimensions. I finished gutting and cleaning the cabs last night.

If I wanted to go with 10" drivers, I see that some folks offer a pre-cut adapter for doing it, as opposed to replacing the whole baffle. Not sure how good the finished product would look, though. And at $25 each, I've just added $100 to the project.

What happens when the enclosure is undersized? Is the resulting sound simply less than optimal, or could it be awful? It seems that this is *almost* big enough - I'm just trying to understand what might happen.

BTW, reselling the cabs is not really an option; I would need to put more into them then I would ever get out. The only salvageable parts are the boxes.

staindbass · #12 08-03-2011, 11:26 AM

my speakers (in my avatar,18's and horns) were just put in the box, no measuring, no specs, no t/s parameters. pure magic. totally happy. dont assume because people say you wont get good results from just putting speakers in a box that you wont. i dont think instrument speakers should be treated like reproduction (hifi, or stereo) speakers. you want a reproduction speaker to be flat so it transcribes the original electrical signal as closely as possible, and adds nothing of its own. with an instrument speaker, you want character that pleases your ear and lets you hear what you enjoy. i like crispy metallic treble, so instead of boosting it on my amp and using up amplifier headroom, i made the speakers sound the way i wanted them to with the eq flat by changing the crossover slope and level of the horns. dont be afraid to experiment. at worst, you might have to build a new cab if it isnt large enough. from my experiences with building car sub cabs with the same speaker, too large a cabinet and the speaker makes lower bass but handles less power (less air pressure in the cab so it can vibrate more easily) and if too small the bass gets less but the powerhandling goes up. ( not the voicecoil powerhandling, but the wattage at which the coil smacks the backplate of the magnet).

staindbass · #13 08-03-2011, 11:30 AM

you could use 2 x 4 ohms in series, but if one speaker blows the other wont work either. maybe its safer with 2 x 16 .

joshwilkesbooth · #14 08-03-2011, 11:33 AM

I threw two 10" Eminence something or others into my Sunn Model 2 enclosure, and didn't have a single problem. Sounded just fine.

You won't know until you try...

will33 · #15 08-03-2011, 12:17 PM

Putting too big a driver in too small a box results in a loss of response in the lows and a hump in response im the midbass aroind 100-120hz. A little of that hump can make it sound louder/fuller.... too much makes a bunch of boom, loss of clarity/articulation.....a whole lot can get so boomy you can lose sense of pitch between notes that are close together like a G and a G#. Another thing to consider is the mid response of the driver up to where it crosses to the HF horn. Another is the amp being used.....how much power is available.

lerret · #16 08-03-2011, 09:03 PM

@ staindbass: That's an interesting observation. I'm ok with it sounding a little 'colored' - what I don't want is some horrible chuffing, farting or inconsistencies in output. I built a 2x15 vented box as a woodworking project in high school. Made up the measurements, dropped in a pair of Black Widows, and it was awesome!

@ joshwilkesbooth: Could you please tell me what the dimensions of the Model 2s are? They only have the 2 x 10 and no horn, correct?

@ will33: thanks for your detailed and patient responses. I haven't even thought about the horn yet. The tweeters in the cabs were not original and were just crappy little speakers. I would want a horn, maybe even with a volume control, to sit between the two ports.

lerret · #17 08-10-2011, 07:52 AM

I've decided to go ahead with restoring the cabs to see what they sound like. Worst case, if it sounds like crap I'll just build or buy a new enclosure for the speakers.

Is there anything I can do to improve my chances of getting a good sound? The cab did not have any insulation inside - is that ok, or would adding some be an improvement?

The two ports are 3" diameter, 3.5" in length. Should I make any changes, or just leave it as-is?

will33 · #18 08-10-2011, 08:36 AM

Line them with matress pad foam or quilt batting, 5 panels, don't need to line the baffles. That'll be enough port area to prevent chuffing with common 10's or 12's. A long excursion 12 like the kappalite, or any decent 15 would need a pair of 4" pipes. You should be fine there. Making them longer lowers box tuning, shorter raises it. Can leave them as is for now, at least until you select drivers.