Cab Project

[slayer63636]

i want to build a cusom cab that houses 2x12s and a single 15inch speaker. after doing some reseach ive found that its gonna be bigger than normal 4x12 cabs. my question is about the 15 inch speaker. dose anyone know where i can get one. on ebay all they have are old ones and on Avatar all they have is the big ben. i would get it but under the APPLICATIONS it says that they are for open back APPLICATIONs . the thing is i do not want an open back cab, i want a closed back. dose anyone know where i can get a 15inch speaker?

[lovekraft]

What are you trying to do, in terms of results? Do you want more (or deeper) bass response, or do you just like the idea of mixing speaker types? Is there some particular characteristic that you're looking for?

[slayer63636]

i am trying to creat my own "sound", i once played thru one of those blue voodoo cabs that have 2x15 and i really liked the low end i got out of it. the only problem was when i used ONLY that cab there was a lack of the high end i want. the guy had a normal 4x12 on top and the mix of both those cabs sounded really good in my book. so after some research i thought if i were to put the 2x12s and the 15 it would make a very good balcance and that way i could still have the 1/2 stack since i dont have the room or need for a full stack at the time.

to sum it all up i like the idea of having the bottom end when im playing muted riffs but at the same time having the high end for solos.

[lovekraft]

OK, here's the problem - it's gonna take a large ported box to really take advantage of the extra low end from the 15, and if you throw two 12s into that same box, they're not going to have that tight response that they have in a sealed 4-12. I guess you could make two cabs, one for the 15 and one for the two 12s, but that's still gonna be bigger than a half stack.

[slayer63636]

i see what you mean. at first i recondered the 12s and thought about 10s but then decieded to just build the 4x12. the can would of at lease needed to be 30 inches and about and extra 5 with wheels. if i were to build another one and with the hight of the head i would be looking at over 6 and 1/2 feet with a stack. im only 5'6. so for now im just gonna do some research on the 4x12 cab. later on i might build a 2x15 can just like the crate i played thru. thanks for ur help, i could of made a mistake i would of regret.

[silvertonessuckbutigotone]

sorry if this is thread jacking, but is there a reason why stacks are always stacked on top of eachother, could you 2 cabs from across the room? I know it would take up less floor space but for a guy whos 5'6" it would probably be worth it to take up more floor space than height. i think if your playing alone, 2 cabs apart from eachother is fun, ive used two amps locked together before across the room from eachother it sounded pretty sweet.

[slayer63636]

ive never thought of it that way and it dose sound like a good idea. i guess it would give me a surround sound type feel i have on on each end. ive concidered stacking just the cabs and building a table like stand for the head so i can have a good hight level.

what type of metairal would be best for a cab? what are the high end companys using?

[Paul Marossy]

what type of metairal would be best for a cab? what are the high end companys using?

I have seen finger-jointed pine and birch. I have also heard of maple and walnut being used as well. Most people say that you should avoid MDF and particle board, but OTOH, I have heard speaker cabs made out of those materials that sounded good to my ears.

The thing I wonder about is to stuff the cab or not stuff the cab. I have heard arguments for both cases...

Edited October 13, 2005 by Paul Marossy

[slayer63636]

i read a review on a basson cab in the guitar world magazine and it said that it was made out of MDF. i have my eye on that since its not to spendy. i can get a full sheet for 20 bucks at a local hardwear store. in the review it said that its ..."a highly resonant material that most high end audio manufactures use..." last would it matter if i mix speakers? i have 2 8ohm celestions and i can get some eminence 8 ohm speakers really cheap. would there be any problem here?

[frank falbo]

Mixing is okay, so long as the ohms match. In my "glory days" I had two stacks, each consisting of a 1x15, a 2x12, and a 2x10. They weren't stereo L/R, they were stereo with L=15's and 10's, R=12's. That way I could also adjust the balance between cabs per program to focus on the fat vintage 12's mids, or the more hi-fi 10/15 combination. I still use that setup in the studio. It's fantastic if you're wise to your phase relationships.

I know you've decided what to do already, but for the sake of future searches, I'd recommend a seperate single 15" cab under a 2x12. If you want the hugest sound possible, use a passive crossover network to cut below 150hz on the 12's and above 4-5Khz on the 15. You'll be blown away. I do that stuff all the time with my combinations. For a vintage sound I usually run them all full range with most of the emphasis on the 12's. But man when you need it, that 15 can just pound away like no 4x12 can.

There are many grades to MDF. I don't know if there's an "official rating" or anything, but hardware store MDF for home projects is likely very different from cabinet grade MDF. And I have no idea what would make a good sounding cab. I would reinforce your corners and edge joints with MDF. Once structural integrity is breached with MDF, it pretty much turns to powder.

[lovekraft]

MDF has some very attractive properties, but it's heavy, and it doesn't work and play well with moisture - for me, those are deal-breakers! Maybe for a permanent installation, but not for a gig rig.

[thegarehanman]

I have a 2x12. It used to be a randall rg300 combo amp, but the amp bit the dust. It had 2 perfectly fine electrovoice 12's, so I removed the amp, chopped/lowered the top, and recarpeted the whole thing. It's now a 2x12 cab for my carvin. The whole thing is made of plywood w/ an open back. It's lighter than an mdf 2x12 and sounds great. By the way lovekraft, I cleaned up the contacts on the tubes like you said and it made a very noticable improvement on the lead channel. Thanks.

peace,

russ

[slayer63636]

thanks for all the help. im gonna look into other woods befor i get the MDF. im also concidering looking for solid wood like poplar for it. honestly when you think about its like playing a guitar, you wouldnt want one made out of particle board or plywood.

[Mattia]

I don't think you're looking for quite the same resonance in a speaker cab as you are in a guitar, quite honestly. You want a resonant cavity, not one that'll vibrate all funky-like when you're trying to reproduce the tones cleanly. Quality birch ply seems to be a popular choice for guitar cabs, often with MDF baffles (non-resonant) although I've got a home-built (not by me) all MDF cab here that does the job perfectly.

[Paul Marossy]

If you go sealed cab style, the dimensions are somewhat important. The two most commonly used proportions are 1.0x1.6x0.60 and 1.0x1.25x0.80 - which means you could have a speaker cab that measures 30"x18"x9" or 23"x18"x14.5" for example. The dimensions of an open back cab aren't really that critical in comparison.

I built a pair of 18"x18"x10" sealed and stuffed speaker cabs for my stereo rig a while ago, but now I am not so sure that those are the best dimensions to have used. I am thinking of porting the cabs, but I really haven't used them enough to have gotten a good feel for what improvements could be made. It just seems as though the bass could be tighter (which is why I am considering porting the cabs).

[lovekraft]

IMHO, the Golden Ratio cab dimensions have some very strong physics behind them, and generally sound very nice! However, in practice, they're a wee bit awkward to implement, and some of the best sounding classic commercial cabs aren't even close - the Ampeg SVT810 (48”x26”x16”) stretches the vertical significantly, and the Marshall 1960B and Fender Bassman 4-10 are very nearly square, yet they all sound incredible! If you're designing a cab for full range ( 20Hz-20KHz), I'd say stick pretty close to 1.618x1x.618, to avoid standing waves, but that's going to require drivers that generally aren't used in guitar cabs (or bass cabs, for that matter) - otherwise, especially in a ported cab, ease of construction and transportability should probably take precedence over getting the ratio right. To quote Jens Moller:

...the sizing factors used to create some of these classic guitar/bass cabinets were not based on complex formulas or extensive modeling and testing, they were often done by estimating how much space was required to house the particular speakers that were planned; a few samples were built to see how they worked and adjustments were made from there. Sometimes a variety of common speakers were used, occasionally special modifications were made to the speakers to deal with any sonic issues. The sonic qualities were measured by the builders using just their ears. The goal was to conform to a specific sound and feel, along with a business need to reduce waste material from the lumber used to build them. The frequency response of a guitar or bass cabinet is highly restricted and often can be fairly uneven; this relates to what it is being used for. Guitars don't put out many frequencies above 6,000 Hz, and those that are above 6,000 Hz tend to be harmonics, not the fundamental notes. These sonic restrictions, which are optimal for a guitar or bass, are usually sub-optimal for vocals, keyboards or recorded music playback.

But again, these are simply my ideas, based on what I've read, and a couple dozen cabinets built over the last 20 or so years, so if Jim Demeter (or Mike Soldano, or the spirit of Leo Fender, or even Randall Smith) tells you something different, he's probably the guy you should listen to.

[slayer63636]

so far here are the demensions: 30Wx30Hx13D. i got those from looking at many cabs such as a few marshalls, a few crates , a mesa and a huges and kettner. i also did some mesurments and reserached head sizes and most of them will fit with a 30" cab. my brother told me to port the box and its something im concidering.

[lovekraft]

If you port that box, it'll be a totally different beast! The whole Marshall cabinet sound is about speakers working against the air trapped in a sealed cabinet! Porting may improve bass response and efficiency in the low end (if done correctly - you can't just cut a random hole in the cab and throw a plastic pipe in it), but it won't sound like that classic 4-12 cab anymore.

[slayer63636]

this can only mean one thing.. MORE RESEARCH!!!!

ive been reading a lot from here http://www.colomar.com/Shavano/construction.html

its a good thing i havent spent a dime so far

[Paul Marossy]

Thanks for the info lk. I guess those dimensions really are more for full range speaker type scenarios as opposed to a guitar speaker cabinet. It probably matters a lot more for a bass speaker cab.

So, any opinions about porting the cabinet?

[lovekraft]

Paul, honestly, I can't do the math myself (I'm clever, but not that clever), so I use a freeware program, WinISD, from linearteam.dk - it lets you enter the driver's T/S parameters, and you can specify cab interior volume, resonant frequency, number and shape of ports, and it'll generate frequency, phase and SPL plots for each design. FWIW, it defaults to the Golden ratio dimensions for the cabinet design, but simply using the correct interior volume and port dimensions has yielded us really good results for bass cabs, from a 2-10 cab (about 24"X15"X18") to a hulking Eminence Kilomax 18 cab. What 18s are you using? The porting is all about adjusting the cab resonance to get what you want from a specific driver.

[Paul Marossy]

What 18s are you using? The porting is all about adjusting the cab resonance to get what you want from a specific driver.

Actually, it's a 12" Celestion G12S-50 speaker in an 18"x18"x10" speaker cab. I have a program also, but I haven't been able to obtain all of the specs for the speaker. But, this is what I have so far:

Mechanical specs:

Nominal diameter: 12"

Magnet diameter: 120mm/4.7"

Magnet weight: 27 oz.

Voice coil diameter: 38mm/1.5"

Coil winding length: 10mm/.39"

Magnet gap depth: 8mm/.31"

Unit overall depth: 130mm/5.11"

Unit weight: 2.9kg/6.6lbs.

electro-acoustical specs:

Frequency range: 85Hz-5kHz

Sensitivity (dB, 1w @ 1m): 97

Power handling: 50 watts

Nominal impedence: 8 ohm

Resonance fs: 85Hz

Magent[sic] gap flux density, B (T): 1.3

I'm not sure that you can design an "optimum" speaker cab with just these specs, though...

EDIT: Actually, I'm just after the best possible bass response in a cab with those dimensions.

Edited October 16, 2005 by Paul Marossy

[lovekraft]

I'd try a 3" length of 4" ID PVC pipe with the inside edges rounded smooth with sandpaper ( or one of those pretty trim-to-length ABS cab ports, if you've got access to it). So long as it doesn't whistle when you crank the bass, that's probably about as good as you're gonna get. That's tuning the box to approximately 55Hz, which should definitely bump up the bottom over a sealed cab. Unfortunately, that Celestion doesn't really have much of anything below 65Hz, but the port might improve it significantly above that. I always use silicon RTV to mount the pipe in the baffle - just mount it flush with the outside surface (tighter is better), glue it up so it doesn't vibrate, and spray paint the whole thing flat black! If you decide to go for it, let me know how well it works!

[Paul Marossy]

I'd try a 3" length of 4" ID PVC pipe with the inside edges rounded smooth with sandpaper ( or one of those pretty trim-to-length ABS cab ports, if you've got access to it). So long as it doesn't whistle when you crank the bass, that's probably about as good as you're gonna get. That's tuning the box to approximately 55Hz, which should definitely bump up the bottom over a sealed cab. Unfortunately, that Celestion doesn't really have much of anything below 65Hz, but the port might improve it significantly above that.

Now that sounds pretty good to me. I know those cabs can get a deeper bass still. One problem, though, don't have room for a 4" dia. port unless it's a rear port affair. It looks like I would need four 2" dia. ones to get the same cross sectional area in a front ported arrangement...

[lovekraft]

The port's location isn't critical, so long as there's some free air space in front of it - while it's probably not practical, you could even put it in the cab's top, pointing upwards at the ceiling. If the back is convenient, and it's not flush up against the wall, no reason not to use it. Ditto for side panels.