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Bubonic Chronic 10-13-2004 12:33 PM

Cabinet Tutorial
 
As a budget-conscious musician, I realized that a Marshall full-stack was out of my price range, and that everyone and their Sheep dog has one anyway.

So I went speaker-hunting.

Choosing Speakers

When choosing speakers, figure out what you want to do.

12"s work very well for guitar, and Celestion is the most talked-about speaker of this type. It's the Coca-Cola of speakers. You know it's good, everyone likes it, etc.

Consider others, though. Sometimes the most common solution is also the most ordinary.

I settled on the Peavey Black Widow 15". Why? Because it can double as a bass speaker when it needs to.

So my cabinet, dubbed the "Bass Monster," has one BW 15" and a pair of 10" Scorpions (also Peavey) that I can opt for if I want more attack. When mixing, you often want to leave out some parts of your tone to make room for other instruments. If I plug a bass and a guitar into this cabinet together, I achieve a nice tone for both which is easy to mix.

Cabinet Design

When you buy a set of speakers from the stereo store - particularly high-end speakers for audiophiles, there is often some fancy wood used. This wood selectivity is not that important for guitar or bass. Pine and plywood work just fine.

The next consideration is size. Don't over-size your cabinet for two reasons; first, you want to be able to move it. Second, consider the acoustics. How can you make your cabinet work right acoustically? Odd-numbered dimensions!

Go for 13" by 17" by 23", or 25" by 17" by 49", something like that. Common sense says "design the cabinet to be 2 feet by 3 feet by 4 feet," but you may introduce modes, which are big, honking, unwanted bass noise that you don't want.

It's not that hard to overcome modes. Just pick ODD numbers that suit the size of you want the thing to be. Instead of making it 2.5 feet tall (30 inches), how about 2.3 feet? 2.7? Not a lot of difference, but it can go a long way.

Now think about speaker placement. Where to put the 15"? For most efficiency, I suggest putting the 15" at the bottom. This will cause the power of the speaker to nearly DOUBLE because the sound will reflect off of the hard floor and compliment itself (hard to explain, but it works.) That means more power, less electricity.

As for guitar, it doesn't matter a whole heck of a lot. Guitar cabs are easier to build than bass cabs because they don't put out all that low sound. Just make sure to build it solid.

STRUCTURE - The best thing to do is to build it like a house, out of "studs" or 2 x 4's. Build a frame out of 2 x 4's first, then add plywood second. I suggest putting the 2" side of the studs around the front and back of the cabinet, and using the 4" sides around the sides of the cabinet. This saves space, makes the cabinet smaller, and allows room for your speakers.

Run a 2x4 along the top and bottom of where you intend to put each speaker. Don't worry about the sides. If your cabinet is taller than 2 feet, use an extra stud to support the middle of the cabinet, about halfway up on each side.

Finally, plywood. 1/2" ply is fine for the front, and should work all the way around. If weight is a concern, use 1/4" ply for the back and top.

Venting/Breathing

As the speakers move, they will "ask" for air on the way out and will "push" on the air on the way in. You need to allow air to move freely in and out of the cabinet. If it's a guitar cab, just cut a slit in the back of the cabinet, or drill a large hole.

For bass, it's a bit tougher, because a hole in the wrong place will KILL your bass response. You can use a passive radiator or a port or both. For a radiator, you just need a speaker - preferably a blown one - that will move in the opposite direction of the others. To save weight, cut off the magnet and most of the metal behind the cone. You only need the cone itself.

Porting can get pretty complicated, but it doesn't need to be. Cut a hole in the FRONT of the cab, and put in some kind of cylinder that is AIR TIGHT, that extends all the way to the back of the cabinet. Just leave room back there for air to move (a cm or two.)

With mine, I used both methods.

Wiring

Last, but certainly not least, is wiring. Again, you can pay $10 a foot for special wire that is solid 24K gold or cryogenically treated. Don't. While this cable does improve the flow of electricity to your speakers, it DOES NOT work any better than plain old thick cable.

Thick cable is the best way to go for two reasons; you get extra energy flow, the exact same that fancy cable will give you, and you get the added benefit of greater power handling. Amps put out a lot of juice, and thin wire can get so hot that it will melt and break. Thick wire is also safer.

Wheels

Wheels, otherwise known as casters, will provide you with two advantages - mobility and acoustic isolation. If your cab sits directly on a wooden floor, the vibrations can travel through the floor, and rattle something else in the room. I've hunted around for hours trying to find what's buzzing in my jam space, only to discover it's Sharpie I set on the desk, or a picture hanging from the wall. Wheels will help out a lot with this.

dave_c2k2 10-13-2004 06:17 PM

Very interesting. You should submit this as a proper article or get it put in the archives or something....or a sticky!!!

The1963Riffer 10-13-2004 06:23 PM

Im motivated to build my own now.....:P I think it would be great to have a 2 x 12 extension cab for my fender princetions....

pooch0072 10-13-2004 06:26 PM

could you include pictures, especially for porting and the stud frame. great job man :cheers:

Bubonic Chronic 10-13-2004 08:16 PM

I'll work on pics, for now I'd suggest just looking at a set of speakers you've got as a model. Some people have used plain poster board to port the speakers, and this just requires about a 3 or 4-inch diameter hole cut in the speaker, usually at the bottom corner(s). Roll the poster board up into a cylinder (cutting off excess you don't need) and taping it so it stays the right size. Once its the right size, a few cm shorter than the front-to-back length of the cabinet, feed it into the hole and secure it with staples or small tacks/nails. Hot glue around it and you're set.

p00n 10-14-2004 04:37 AM

this may sound like an ignorant question, but i don't find your rationale for the odd lengths.. how would the odd sides alter this 'modes' etc? acoustics do not really conform to that regular a pattern..

Bubonic Chronic 10-14-2004 11:03 AM

Quote:
Originally posted by p00n
this may sound like an ignorant question, but i don't find your rationale for the odd lengths.. how would the odd sides alter this 'modes' etc? acoustics do not really conform to that regular a pattern..
An excellent question, but one I'm afraid may be a bit too technical for general "I want to build my own cab" info...here goes:

Modes result from sound waves building on each other. Think of waves in the ocean, not crashing waves for surfing, but the ones farther out, the nice round ones. Well, if you put a concrete wall out the, the "up" part of the wave will bounce off the wall and move in the opposite direction. Sometimes, if the waves bounce between two walls lets say, the "up" can exactly counter the "down" as it arrives, so the two waves - the original wave and its reflection, will cancel and you get nothing.

The opposite happens with modes. If a wave (a sound wave now) is 2 feet long, that's one up and one down, each one foot apart. So a cabinet designed with a dimension of exactly two feet will cause the wave to encounter the "up" of its reflection while the wave is also "up," so the resulting wave is twice the size of the original. This keeps happening, so that the "up" parts of the waves keep building, and you get higher and higher waves that don't move - a standing wave. A mode, and I'm sure you've heard on at some point, is a standing wave in a room (and a cabinet is basically a small room.)

..told you this was complicated. :(

Anyway, by choosing odd numbered dimensions, you cut down on - not eliminate - standing waves. It's an easy and cheap solution for cabinet (and room) design. In reality, professionals use computer modeling, sophisticated gear, etc. to specifically "tune" a cabinet, but we don't have that. The best we can do is make it, say, 3.1 feet by 2.7 feet by 1.3 feet. Just good practice in general. If a wave bounces off the top, then bounces off the sides, there is less likelyhood of mode formation when you've got uneven numbers - especially prime numbers like 11, 13, 29, etc. It saves us from spending all the time to build this then and then have, let's say Bb, obnoxiously honking out of your box.

...phew. Haven't even thought about this since college.

Bubonic Chronic 10-14-2004 11:19 AM

Picture of frame
 
1 Attachment(s)
Notice in the picture how the wide side of the studs face the top, bottom and sides. The narrow sides (the 2" sides) face the front and back. This makes the cabinet smaller and allows more room for speakers.

Also note the use of butt joints in the construction - how I've got 2x4's just nailed directly to one another. Since we are using 1/2" plywood, and adding extra studs to support the speakers this is not a problem. It will be plenty sturdy when we are finished.

wahappen 10-14-2004 11:34 AM

Re: Cabinet Tutorial
 
Quote:
Originally posted by Bubonic Chronic
For bass, it's a bit tougher, because a hole in the wrong place will KILL your bass response. You can use a passive radiator or a port or both. For a radiator, you just need a speaker - preferably a blown one - that will move in the opposite direction of the others. To save weight, cut off the magnet and most of the metal behind the cone. You only need the cone itself.

Porting can get pretty complicated, but it doesn't need to be. Cut a hole in the FRONT of the cab, and put in some kind of cylinder that is AIR TIGHT, that extends all the way to the back of the cabinet. Just leave room back there for air to move (a cm or two.)



Great thread :cheers: IMO, port diameter and length can be critical depending on the size of the cabinet. I'll see if I can pull up some charts showing related frequency responses that reflect the box size/ port size.

Anyone ever hear of compound loaded drivers in bass cabs ? I know the ergonomics aren't the best when considering space, but the frequency response is real tight in a sealed chamber. I just don't know if this has ever been tried in bass cabinets.

Bubonic Chronic 10-14-2004 11:44 AM

A quick note on Ohms
 
You've probably noticed that speakers have Ohms as well as Watts. Generally, guitar and bass speakers come in either 4 or 8 ohm varieties, and are designed to be used alone, in pairs, or in fours (multiple of two.)

Here goes:

Usually, you want the cabinet itself to be 8 Ohms. It's the safest way to go. 4 Ohms is louder, but you can blow up your amp more easily this way, so I recommend going for 8.

Single speaker design -

One 8 Ohm speaker wired like so...

+___X___-


..simple.


A speaker pair -

in this case you have two 4 Ohm speakers...

+___X___X___-

..this is an example of series wiring. Think of taking two AA batteries and putting them end to end. If they are Duracells, the gold top will touch the black end of the other battery. This is series wiring at its simplest: a flashlight.

A guitar jack has two leads, a positive and a negative. Start by connecting the negative lead of the guitar jack (the tip) to the negative lead of one speaker. Now run a wire from the positive lead of that speaker to the negative lead of the next. Now run a wire from the remaining lead, the positive lead of speaker #2, to the positive lead of the guitar jack. Done.


A quadruple speaker set-up (like a 4 cone Marshall or similar cabinet) -

In this case, we will use a series/parallel wiring scheme. We'll start with the parallel, since that's new.

In this case, we will be using 4 8-Ohm speaker cones!! - very important.

Since there are 4 speakers (cones), we will have 2 PAIRS of cones, each wired in parallel. Start by wiring each PAIR of speakes as follows...

+
/
X=X
/
-

..not the greatest diagram, I know. Here it is in steps:

Step 1) Run a wire connecting the negative leads of each speaker together. Now run a wire connecting the positive leads together. This should look like a loop, or an "=" sign, as in the diagram.

When we do this, the system of speakers we have connected becomes a single 4 Ohm circuit.

..do step one for each PAIR of speakers, which will result in 2 4-Ohm circuits (essentially 2 4-Ohm speakers made up of two cones apiece.)

Step 2) This is the easy part. Just as with the 2-speaker system above, connect the two circuits together in series. This will double the resistance, giving us a single 8-Ohm circuit.

-___X=X___+|-____X=X____+

..again, think of a simple flashlight with two Duracell's in it. Gold top to black butt.

This leaves us with a single negative lead and a single positive lead. Connect the negative lead to the tip of the guitar jack, the positive to the sleeve.

Done.


...other configurations are possible, but a higher level of expertise is required. My cabinet contains 2 jacks, each representing a 4-Ohm system. The 15" is a 4-Ohm single-speaker circuit, and the pair of 10's, each 8-Ohm's, is a double-speaker, 4-Ohm circuit. A bit riskier, but then I've done this before.

If you are nervous about this, or want to deviate from these plans, I strongly suggest experimenting with a small electronics kit, available for a few dollars from Radio Shack or similar. Try different circuits out with resistors, etc. Does it blow up? No big deal, that's what the kit is for. Find out if it will blow up first, THEN apply it to your expensive speakers once you know it works.

Cmogi10 10-14-2004 05:43 PM

Congrats!

Awsome thread, it earns a sticky ;)

cant wait to see pics

pooch0072 10-14-2004 06:53 PM

What about covering? Waht did you use, did you use any? And did you put some kind of grill or mesh in front of the cab to protect the cones? And in the end, how much does your cab weigh?

ebashnitzil 10-14-2004 08:20 PM

i am thinking of making a cabinet - but i would use carvin speakers ( www.carvin.com ), maybe 4x12

Bubonic Chronic 10-15-2004 10:28 AM

Quote:
Originally posted by pooch0072
What about covering? Waht did you use, did you use any? And did you put some kind of grill or mesh in front of the cab to protect the cones? And in the end, how much does your cab weigh?
I actually made a lot of mistakes in mine, lol.

There is no mesh most of the time, because I use it in the studio, and sometimes I'll stick a mic like .01 cm away from the cones. Depends, though. Generally I don't really move that one around, so no, no mesh. I did build a cheap protection thing out of screen for, like, a screen door, but that's when I was hauling that thing to gigs, which I don't do anymore because I just bring my acoustic/electric for gigs. Plug right into the board with that.

:cheers:

In all, it weighs probably 80 or 90 lbs. Too heavy in my opinion, but it's nostalgic, you know? My cab has been with me for the better part of a decade now, but when I built it I wasn't thinking too much about it being too heavy or, like, the size of a fridge or anything.

:bonk:

I covered the sides with basically astro-turf, but not the green stuff you're thinking. It's like outdoor or industrial type black nylon carpet (rubberized on the bottom) they sell for $2-$3 a yard at Menard's. I swear by that stuff now. More recent work, like my studio rack, has really turned out sharp. You'd think I spent a thousand bucks, but it only cost me about $10.

The cab itself is all black around the sides, but the face is bright orange. That blown twelve I used as a passive radiator I painted as an eyeball, all bloodshot with a blue Iris.

Like I said, I would do it completely differently today because I know a lot more of what I'm doing, but I always liked the looks of that thing - big and orange, just staring at you from the corner like "I'm a ****ing big amp, mother****er!!" Like I said, nostalgia.

If those fairies from H&G TV came to redecorate my house, they'd try to toss that out in a heartbeat. I'd just stand and watch them try to pick it up, drink a beer and laugh at them.

Pansies.

TGM 10-15-2004 09:17 PM

What about the baffle construction? It's a pretty important part of your cab.

Bubonic Chronic 10-18-2004 03:50 PM

Baffles
 
http://dictionary.reference.com/search?q=baffle

Baffle: "A partition that prevents interference between sound waves in a loudspeaker."

Depending on how you design it, you should be able to avoid interference. I've never actually used baffles before, perhaps you can enlighten us.

TGM 10-20-2004 02:32 AM

The baffle is the board that you mount the speakers onto, I was wondering how you made yours, and why.

The baffle does spot you from losing low end through phase cancellation, but depending on how thick it is and how you mount it it can change your tone for the better. (IMHO)

http://www.tone-lizard.com/lesson4.htm

Towards the bottom that article has information on baffles.

I guess that you used something solid, you wouldn't wan't it to flap out with a bass. I just found it kind of wierd that you didn't say anything about it,

Bubonic Chronic 10-20-2004 10:08 AM

^^ I guess I never knew the official name for it, but sort of inadvertently designed one anyway in that I support the speakers essentially with 2x4's on the top and bottom, so they are not held in place with the plywood at all. This also provides added rigidity, preventing almost any (except high frequency) vibration in the studs, and by default the ply, which is fastened tightly to the studs.

I also use 1/2" ply for the "face" of the cabinet, plenty sturdy to resist most vibration.

Edit: Some background on frequency and wavelength.

Frequency is short for "cycles per second", or #of waves/time elapsed.

Western music (yes, rock 'n roll and metal and punk and funk and pretty much everything else) is based around the "A" note, which is 440 Hertz, 440 cycles per second.

Octaves are multiples of the notes: 220, 110, 55 are all octaves of "A".

A guitar puts out a 160 Hertz "E," and a standard rock bass puts out an octave below this, 80 Hertz.

A wavelength is how far a wave will travel in a given amount of time. If you clap your hands in a large room, you can measure its size.

Say you stand in front of a distant wall and clap. If the clap takes 2 seconds to return to you...

CLAP..........clap

..then the "clap" has gone to the wall and back, and thus took one second to get to the wall. Sound travels 344 meters per second, so the wall is 344 meters away.


More important would be wave cancellation through the air by way of energy traveling around the cabinet, into the back, and impinging upon the back of the speaker. Cancellation will occur where a half-wavelength travels to the back of the speaker, resulting in a rarefaction that meets the compression caused by the speaker. Desnser air + less dense air = something in between, in this case something very close to average air pressure, or what we might call "silence."

In other words, you don't hear sh*t.

The wavelength has to be calculated as follows: (in metric)

(lambda) = v/f = (344 m/s)/160 = 2.15m

(in English - feet)

(lambda) = v/f = (344 m/s)*(3.281 ft)/160 = 7.05 ft.

...but you're not concerned about lambda, you are concerned with lambda/2, that's where you get cancellation.

7.05/2 = 3.503 feet

If the distance from the front of your cone, around your cabinet and into the back of your cabinet is > 3.5 feet, you're ok to just put a big-assed hole in the back of your guitar cab.

In general, though, you'll find that cabinets are usually enclosed. That means a sealed box, but if you think about it, a sealed box will resist changes in pressure, "wanting" to be the same pressure as the outside air. Thus you will "rob" your speakers of efficiency - a lot of power will go into fighting the air pressure differential, which doesn't give you any sound.

So you have to port. A simple porting method is to create a series of holes in the back of the cabinet, and then place another "box" in front of the back panel of the cab, then a third "box" in front of the previous one.

What I mean is, allow air to come in at two or three points in the back:

|
|

|
|

|
|

..something like that. Remember, this is the ghetto "I don't want to bother with math or anything" method. It does work, though. I chose this method because I wanted the cabinet to serve multiple purposes, even keyboards occasionally, so I wasn't sure about which frequencies I wanted to "tune" the cabinet for. If it's specifically for bass guitar, 40 Hz is a good ballpark, but keyboards can go lower, and guitars start much higher, so for a multipurpose cab like this, go for a semi-random porting technique that is not really "friendly" to any frequency by using a series (three is good) panels, each having holes of different diameters cut different distances apart. Keep in mind, though, that the total area of the holes in each successive panel should be about equal, and most importantly sufficient enough to allow enough air for the speakers to work efficiently.

Once holes are cut in the back, make a small frame out of cheap wood, 1/2" to 3/4" thick around the area where the holes are cut. This should be a square or rectangle that looks somewhat like a backyard garden frame. Solid base, rectangular surround, open top.

Now make holes in the second panel, this time using a different extreme of dimensions - either cut tiny holes at random locations throughout the panel, or place two or three very large (but not too large) holes in it. Whatever you did for the holes in the back (a lot of small holes is good for the back), do the opposite with this panel. So in my case, smale holes | large holes.

The reason for poking small holes in the back is just structural, you want the back to be strong. Big holes would mean you could reach inside the cabinet, or that you might wind up with a weak spot in the back. Not good.

Also important: space the holes so that they are far away from the holes in the previous panel. This way, air (and sound) must travel the greatest distance before entering the next stage of the port. This lowers the interference frequency, and gives the sound more material to travel through, which attenuates the sound and makes any interference less severe.

Slap the panel onto the frame and repeat.

I did Small | Large | Small, and by large, I mean about an inch diameter, not 5 inches. Small is like a pencil-width.

In all, three panels should do it: the back of the cab having several pencil-sized holes drilled in it, the next panel having three or four inch-or-so sized holes, then the third panel having pencil-sized holes again.

Any given hole will let in certain frequencies, and by using different sized holes, you reduce the number of frequencies that can get through. Ideally, only air will come through.

Another factor to consider is sound coming in from the sides. This is why I again use 1/2" ply attached to studs. Low frequencies do NOT like this construction, so only very high frequencies (which don't matter anyway) will easily rattle that cage.

Shoestick 11-03-2004 02:06 AM

:confused: :bonk: :confused:

Maybe its the sleep deprivation talking, but could you possibly upload some photos/diagrams to go with these things? My head is spinning. Plus I just want to see a huge orange homemade cabinet.:D

EDIT: Forgot to applaud you on your knowledge and willingness to share it with the UG community. :cheers:

Bubonic Chronic 11-03-2004 01:43 PM

^^ Of course.

The photo will take a bit of time, though, as I'm working with a disposable camera and a scanner. Usually turns out better than digi anyway, though.


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