A little OT but speaker design?

[Chuck]

I heard that there is a black art to making a speaker cabinet.
But dang, it doesn't look that hard.

If anyone has some good links to closed cabinet designs, could you please post em?
I'm specifically looking for a 2x12 closed cabinet.

Thanks all

[Meanderthal]

 With a closed cabinet, not much engineering is necessary. It's when ya get into ported cabinets that everything gets tricky. Just build a closed cab 'about the right size' and it'll sound fine. 

[Chuck]

Is it worth the investment in good plywood?
Like a good birch or oak ply?

[mars_bringer_of_war]

Is it worth the investment in good plywood?
Like a good birch or oak ply?

Depends where you get it. Often so-called "birch" or "oak" ply is junk wood (low rate pine or fir, though sometimes louann (sp?) mahogany), with a hardwood face.
why not be different and use solid wood for your cab? Even solid pine can sound good, imho better than plywood.

[Meanderthal]

 

Is it worth the investment in good plywood?

Absolutely! Cheap plywood has voids in it, rattles and resonates, and even falls apart. Good birch(Cabinet grade) is the way to go. Oak is heavy and hard to work with.
Some will disagree, but I've found that dense, thick particleboard(furniture grade) sounds pretty good too, but it burns up saw blades and is also heavy.
Ya want to be able to pound on the side or back of the cab and NOT have it go 'boom', resonance will screw up the sound. So, ya want it nice and thick(5/8"), and screw, glue, and reinforce the corners. I also like to line them with carpet padding. If the back is resonant, try screwing and gluing in 2 by 4s in a + pattern, that should dampen it down and sturdy it up.

[John Lyons]

I make my own cabinets but it's sure hard to beat an Avatar cabinet at $200 ish for a tolexed 2x12 that is ready to go and sounds great.
You can't really make one for that!
Look em up...

John

[petemoore]

  Yea...good wood, no voids etc.
  Antique pine's really cool, [needed planing] I have 3 cabs made of this stuff, takes dents easy enough, but certainly does sound 'woody' and is otherwise strong/lightweight, I really like the look, sound, and lightweight aspects...also the way it 'works'...plywood will tell you if a blade hit a nail before by splitting out 'n stuff like that, I found the pine easy to work with and plenty strong.
  1/2'' may not be thick enough plywood, 5/8'' minimum I'd say for baffle board.
  Thinner pieces might not 'warble' too much on the sides.
  I've been going to just almost thick enough, 1/2'', then.. adding thickness/stiffness by adding 'tuning' boards, if the top and bottom for instance are over-resonating, I'll simply put 'span length ribs' in. Having ribs substantially increases the span stiffness per weight, the same way I beams do.
  Basically I used to test for warble, by pushing a back or side until it changed the tone, then stiffen that area, now I know just use 5/8''s or..1/2'' w/some damping/stiffening.
  A little bigger volume is just right for me, I like the bass sound of slightly 'oversized' enclosure [fender made a cab type for 2x12'' or 4x12'' speakers..the only difference in # of drivers and baffle board], they sound great depth with 2x12''s cranking, *cranking 4x12''s sounded louder/different..'cramped' in our comparison, whatever that's worth.
  you will need some shop tools to make a really good cabinet easily, though I've done it with a straight edge, hammer, clamps and a radial handsaw...
  Dado joinery is what I like to use, the baffle fit into the surrounding boards, that means table saw, router comes in handy also [I use it for cutting the speaker holes and quarter-rounding everything], as does the air hammer pin nailer for assembly. the nailer makes the wood 'suck it up' to tight glue-joints, but it doesn't hurt to have many long clamps around during assembly and glue time, a number of other little things.

[trevize]

I recently completed my madamp m15 + an 1x10 cab with jenen p10r speaker with finger joints.

I used spruce from valdi fiemme in italy. It is relatively cheap here and it's used for musical intruments.
http://www.ciresafiemme.it/benvenuti-e.htm

You would not believe the difference in volume, clarity and bass response of a solid wood cab till you
don't try it.

ps: talking about speaker design I would try open back for the first time. Closed back can be complicate and unpredictable.

[MartyMart]

I think that "Session" make cabs too, 2 x 12 for about £160 , you can;t beat that !!
Got good report in UK guitarist mag last year.
MM

[Iron Code Monkey]

Plans for a basic stereo speaker cabinet:
http://colomar.com/Shavano/stereocab.html

And all parts and tools you need to build one:
http://www.parts-express.com/index.cfm?&raid=1&rak=parts-express

[Meanderthal]

Closed back can be complicate and unpredictable.

It sure can, if you try a Diy ported cab. I tried that once a long time ago- a DIY cab for bass guitar- 2 15" and 2 12". It wound up putting out less bottom end than a single sealed 15" cab, yet it was still muddy and flabby sounding, in fact it was just awful.    I had thought- build it big, let it breathe... I was wrong. Ports and cab dimentions and speakers(and their specs) have a complex relationship that I knew nothing about. The complexity is all about tuning the port to get the most out of the speakers...

Close the front, sides, and back(eliminate the port) and it's pretty hard to screw up. Granted, a closed cab dosen't give ya max efficiency(volume wise), but it's easy, relatively foolproof, and winds up sounding pretty good. (provided ya use good speakers and wood, and eliminate any resonance)

[Chuck]

Ah, so we want to keep the resonance low.  Solid wood seems like a better option.

With a 2x12 cabinet, I wonder how deep it needs tobe.  Solid wod around here is about 10-12 inches wide max.  So if it needs to be deeper, then putting two board together will need to be done.

Solid wood with ribs routed in would definately stiffen the sides.  Can it be too stiff or too non-resonant?

Whats odd is some people say closed cab is tricky, others say its hard to screw up.

The Marshall 1960a cabinet I have seems to be about 12 inches deep (subtracting the rim).

[R.G.]

There is no black art to speaker design.

There is a black art to good speaker design - wide range, smooth response, good dispersion, and as good a bass response as the speaker is capable of.

Guitar speaker cabs sidestep some of the hardest issues by having a limited range (70Hz to 7khz is fine) and by being music production devices not REproduction devices.

Guitar speakers all by themselves usually have sufficient bass response because of the high (by hifi standards) lowest notes to be reproduced. All they need is some way to keep the back wave away from the front wave for a while. Hence open back cabinets work OK, as you're listening to the speaker, not the speaker and cab.

Open back cabs do not damp the speaker motion at the low end. Hence many guitar speakers have quite stiff cone suspensions, and so they do not suffer (too much) from excessive cone motion. The cone just won't move far enough to bang into things at their rated power.

Closed back cabs effectively put a damped resonant chamber behind the speaker. The tuning of this chamber is designed to interact with the speaker's own low end resonance and extend the speaker's bass output lower than the speaker could normally do, while at the same time damping the speaker's own resonance to keep it from being pushed too far in or out. This is more complicated in terms of calculation than an open back, although as the volume of the cab gets bigger, the cab has less and less effect. If it's big enough, an open back cab is no design work at all. Making a closed back cab small and good sounding at the same time is harder.

Ported cabinets are the tricky ones. In a ported cabinet, you are noting the speaker's low end resonance, and tuning the resonance of the cabinet to extend its bass response, while simultaneously applying just the right amount of acoustic damping by the venting action of the port. You must simultaneously fit the unchangeable speaker's resonance to the resonance of the box and the damping and resonance of the port itself. While this is not rocket science, rocket design was pretty well known in the 1960's. A prescriptive theory of how to tune ported cabinets was not know until the late 1970's, so understanding of ported enclosures came later than rocket science, and not for lack of trying. Ported cabinet design DOES affect the speaker's "voice".

Materials:
The less flexible, less resonant, the better. Hifi nuts have been very happy with speaker cabs made of concrete. That's kinda hard to haul into the local bar, though. Solid wood, usually pine, is OK if you want the coloration of your sound by the imperfections of the wood. Note that this is not predictable, and each cabinet will sound different, like each spruce-top-guitar sounds slightly different.  In this case you're matching the colorations of the wood parts of the cab to your ear. The speaker projects its own sound, interacts with the cabinet volume, and excites the vibrations of the cab at the same time. This is not in general predictable, but may be a result you like. It's a lot like trying out many guitars.

Well damped is good. Metal cabinets are out because they ring too much, as well as being impractically heavy. Solid wood is OK. particle board is well damped; MDF is very well damped. Many-plied, void free hardwood plywood is modestly damped.

For speaker cabs only, MDF is a good choice if you put them in one place and leave them - hifi, that is. It's not durable enough for speakers hauled to gigs. Gigging speakers had better be tough. The material of choice is 9 to 13-ply Baltic birch plywood. This stuff comes from the countries around the Baltic sea, especially Russia. Chinese 9-ply birch plywood is a second choice based on price, and US hardwood plywood is a second choice based on availability and performance. All of these can make excellent speakers. Do not use pine plywood. It's not flat, can't be made flat, won't fit, isn't dry, has voids and rattles, and is very difficult to work to precision.

Thickness:
For solid wood "voice" cabinets, 1/2" is the thinnest to consider, 5/8" is OK, 3/4" is sturdy. Notice that wood that is sold as 1" thick is actually 3/4" or a bit less in actual dimensions.
For big speaker cabs, use hardwood ply or better, in 3/4" thickness. The plywood guys have been at the nominal versus actual game, and "3/4" ply is actually 23/32 or 18mm if you get metric. Measure the actual plywood you get.

Joints:
Fit airtight, glue and screw.
Finger joints are the industrially prefered method. Home makers can get by with rabbeted joints. Butt joints are OK-ish if you glue and screw them to a reinforcing block inside the joint.

Sizes:
All of the evidence points to the Marshall 4x12 being the smallest size that Marshall could make a box that would hold four 12"  speakers.  There was little or no acoustic design. It's colored. We have come to expect speakers to sound that way.

For a 2x12, pick your poison. You can make it literally half of a 4x12, or make your own design. It's going to sound how it sounds. I heavily suggest knocking together a throwaway cabinet of the same internal dimensions as you intend to build. Make this airtight, but don't expend a lot of care making it tough or pretty. Listen. If it sounds good, Go build a good one. Or two. I like two 2x12's.

Reinforcing:
Unless you're after the "colored wood sound", make it stiff. Reinforce the front-to-back at least. It helps if you put a stiffening rib on each panel. Make the rib run at an asymmetrical slant across the sheet. You want to have non-reinforcing resonances. Make it tough. For big, high powered cabinets, it can't be too stiff or too dead.

Go read the construction section at Shavano music.

[Meanderthal]

 Thanks for the info R.G.!

It appears I've only been lucky with closed cabs(I thought I knew what I was doin')... I didn't know any 'tuning' was possible... let alone necessary 

Maybe approximating the dimentions of existing cab designs explains my good results... if ya wanna stack speakers, it helps to have em 'about that size'...

[runmikeyrun]

I haven't looked in a long time but last time i did i thought that there were places online where you could plug in your speaker's specs and it would tell you what size to build (or at least internal cu. ft.) and, if you want them, port size and length.  I play bass so my advice from her e on out is based on my experience w/ bass speakers. 

Closed boxes are pretty easy to guess and sound good, make sure it's at least 3" larger on each side of the size of the woofer (12" woofer would get 18" size face) and at least as deep.  If you look at cabs w/ good low end response vs. not so good the depth makes the difference.  Compare a marshall 1960 to a crate 4x12 and you'll see what i mean.  Stuff with fiberglas and you'll get even more perceived depth (or a good way to fool the speaker it's in a bigger enclosure if you can't make it that deep).   Open back will be thinner since you will get some phase cancellation from sound waves from the front coming around to the back and cancelling, cutting low end.

For bassm I like the sound of sealed cabs, i don't like ports they always seem to overemphasize certain frequencies and when you crank them those certain frequencies can really overpower the rest of the range, making some notes way louder than other ones and your playing sounds inconsistent.  I have a ported 12" box in my car stereo that i need to close off.  All my bass cabs are sealed.

Speaking of speakers, the specs... usually you need a bunch of numbers with weird abbreviations if you use a speaker box calculator.  If you decide to wing it and just buy a speaker and build a box, make sure you at least know the impedance, RMS watts (NEVER rely on peak watts) voice coil diameter, and possibly the most important, xmax.  xmax is the distance the speaker can travel.  Anything less than 3 will probably bottom out and create a terrible noise, especially if you slap/pop. 

Shoot for voice coil diameter of at least 3" and 4" is best.  Smaller speakers (10") can do with smaller voice coils.  Get too small a coil and it could overheat. 

Magnet weight should be substantial depending on the size of sub.  For a 15" speaker i always shoot for 80 oz or above.  for an 18" 100 oz or more.   

I always get more RMS watts than i plan to use because you never know what you might do later down the road.  I like to have my bass cabs rated at 600w or more.  Don't forget that speaker wattage ratings are combined for multiple speaker setups, 2x15 @ 300 w each = 600 w rated cab.

I like to build 4 ohm cabs.  If you only use one cab you get the best power transfer vs 8 ohm.  If you decide to use two cabs later you can connect them in series to get 8 ohm since most amps don't like 2 ohm loads (two 4 ohm cabs in parallel).

[petemoore]

  I like to build 4 ohm cabs.  If you only use one cab you get the best power transfer vs 8 ohm.  If you decide to use two cabs later you can connect them in series to get 8 ohm
  I've done this but it required bringing the speaker connections outside the box and the use of outside junctioning..extra stuff/wires/connections...+ looks messy [could be done with 'unconventional' wiring of amp jacks].
 

[runmikeyrun]

Ah, not so!  I thought the same thing and then i realized i would lose (or forget at a club) anything not connected to the cab.  I had one Randall 2x15 cab that i found outside of a chinese restaurant that someone had bought and was cleaning out (and wedged into the back seat of my wife's brand new Taurus given to her from work) and it had two holes for jacks.  I wired the two 15s to 4 ohms in parallel.  Then i connected the + from the speakers to the sleeve of #1 speaker jack.  I ran a wire from the tip of that jack to the tip of jack #2.  I connected the - from the speakers to the sleeve of jack #2.  I then took a right angle 1/4" mono plug and wired the tip to the sleeve internally, then attached it with a short wire (~2") to the cab right next to jack #1.

So, here's how it works:

The 1/4" mono plug is a shunt (dead short).  For normal, one cab operation plug the shunt into jack #1.  This shorts the ground to tip, which connects the + side of the speakers from the sleeve through the shunt to the tip, and over to the tip of jack #2.  - from the speakers connects to jack #2.  Plug your cable from the amp into jack #2.  You now have a internal complete 4 ohm circuit wired properly with regards to - and +.

for 8 ohm two cab operation you plug your amp into your modified cab's jack #2 like normal, then run a regular 1/4" mono speaker cable to your other cab.  This sends your amp's + juice through jack #2's tip, over to jack #1's tip, through cab #2's + side of the speaker, back through the - side of cab #2's sleeve, then back to jack #1 sleeve, through to the + side of cab #1's speakers, and finally back to jack #2 sleeve and to the amp's - speaker cable for a total of 8 ohms.  It sounds complicated but i will draw out a pic when i get home to explain it. 

The shunt plug is one of the old style flat right angle ones so it is low profile and doesn't break off when plugged in (you can keep it plugged in all the time like i do so i don't forget it and fry my OT) and is attached so you can't forget it at home and not be able to use your speakers when you get to the gig without it.  The only thing you have to remember is to change your ohms setting on your amp between one and two cabs, and if you have SS head you don't even need to do that.  The only important part of the whole thing is to use a NON CONDUCTIVE plate to mount the two speaker jacks to on the cab that has the shunt.  Otherwise the + and - short together when the shunt is in place and bang goes your amp.  I used a piece of hard plastic that still has a little give so it doesn't crack.  You can get lexan at most home stores that would work well too, it's virtually unbreakable.  My jack plate is also recessed about 1/2" so the shunt stays in there and no chance of it getting ripped off when being slid around.  I also clearly labelled the plate with which jack is which and how to connect it because the guy who gets it after I die should know how to use it.  It's been like this since 2001 and i've used 100w tube heads and 800w power amps through one and two cab setups and never had a problem.

[Chuck]

I did run into several brands of speaker design software.
Ranging from $25 to %300.

I tried one shareware one called boxplot.  But either it wasn't working right or I wasn't using it right.
Maybe I simply didn't understand the inputs enough.

There should be something in this world where you select the brand/model speaker and it tells you the optimum box.
I'd think the speaker manufactures would do that.  Eminence seems to be close since they give Thiele and Small Parameters.
Celestion doesn't and I wouldn't even know where to start getting parameters for their speakers.

I guess in the end it doesn't matter.  Make the cab as dead as possible and pump huge watts into it.

[Rob Strand]

> There should be something in this world where you select the brand/model speaker and it tells you the optimum box.

There's no such thing as an optimum box because the meaning of  "optimum" varies!!

A common choice for hi-fi is the maximum-flat also called the Butterworth alignment - think of alignment as 'tuning'.   This is optimum in the sense that is gives the the lowest possible -3dB point with a sealed box that doesn't use EQ.   Another choice for hi-fi is the Bessel alignment which gives maximally flat group delay.   Both of these are optimum in the sense they are defined.

There are also constraints on what you can achieve with a given speaker.   Many speakers have high Qts specifications.  If your speaker has a Qtc greater than 0.707 you simply cannot design an un Eq'd  box which will give you a Butterworth alignment.  If the speaker has a Qts close to, but smaller than, 0.707 then you can get a Butterworth alignment but the box is impractically larger.   The question here is can you actually hear the difference between the ridiculously large box and a somewhat smaller practical size - it depends, but often the difference is small.

There is software about which will pick "optimum" boxes and have databases for the loudspeakers.  One problem with these is they rarely contain guitar speakers and guitar speaker manufacturers don't always release the Thiele-Small parameters (eg. Celestion).  There's a couple of good free programs.

The above is for hi-fi (and to some extent bass guitar) speakers.  What is actually optimum for a guitar?   I don't think there is one.   Many people use Marshall quads a a reference speaker.  The Marshall quad design was simple pick a 12" drive and shove it in the smaller cabinet possible!  Whatever resulted seems to work  but at the other end of the scale you have the open back Fenders which sound quite different.

Despite all the Thiele Small modelling stuff, in reality, the panel width also has an effect on the response because the enclosure itself introduces baffle edge diffraction.  And then there's how close you place it to the wall, floor etc.  This is where is gets complicated.

With the amplifier fixed and the speaker driver fixed you have to do some playing around to get the optimum box (for you).

[Meanderthal]

 Well, I guess ya gotta decide if ya want the ultimate engineered guitar cab, or a box with speakers in it like what comes with an amp... I'm not sure you'd be thrilled with extended hi-fi frequency response... it's a guitar cab, not a stereo speaker.

Having tried(and abandoned) several speaker design softwares I came to the same conclusion as you- it's hard to get ALL the specs to input, unless ya find a speaker whos specs are documented to the tiniest detail... easier said than done.

I also wish there was a thing you could input- 2 greenbacks, output - the ideal cab...  or even a good general 2 12, 4 12, 1 15, 1 10, etc... no such animal, but for a GENERAL design there are examples everywhere- existing cabs. For instance- most 4 by 12 cabs are about the same dimensions as a Marshall cab, regardless of what speakers are loaded. Gee, I wonder why... But, I figured if copying dimensions is good enough for large manufacturers with a budget to pay for research and development, then it's good enough for me.