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Old 11-03-2004, 02:15 PM   #21
Bubonic Chronic
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Here is the basic port design. I'm neglecting a lot in doing it this way, but it's the easiest and cheapest way to go. If you line these panels up, back to back, the cabinet can breathe, but less sound will get through.

Basically, you are building two small chambers, each about one and a half feet on side, and seperated by 1/2" or 3/4" of wood. Think of it as a sandwich:

Wood|Air|Wood|Air|Wood

It's crucial, though, that these chambers be otherwise airtight, meaning no air (sound) can escape except through the holes you've made. Also, use relatively small holes (between Sharpie-width and pencil lead width) so that sound really can't get through. You shouldn't need more than about ten Sharpie sized holes in a 2 foot by 2 foot panel for air to get through.

You're playing a balance game here. Too few holes will not allow enough air through, and too many will make the panels "acoustically transparent," meaning you've wasted your time, and basically opened up a big acoustic hole in the back, which defeats the purpose of building a cabinet.

I added a passive radiator (the blown 12" detached from its magnet) so I would have to put less holes in the cab. Each approach has its inherent weaknesses, but by using a bit of both, I compromise less of my sound overall.

Adding a passive radiator is easy, just put in a dead speaker that moves freely. If you don't have one laying around, check a resale store for a cheap set of stereo speakers. Anything over 10" will do.
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Old 11-03-2004, 03:11 PM   #22
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Wiring Scheme diagram

Here is a diagram of the most complex wiring scheme for a guitar cabinet, the series-parallel scheme. All others can be derived from this.
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Old 11-06-2004, 06:19 PM   #23
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Bass Enclosures

When designing a bass enclosure whether it is for Bass guitar or the bottom of a PA rig you have many options to consider. The first option is which type and make of loudspeaker to use. Budget loudspeakers offer the best value for money and with todays developement in technology you can get a very good loudspeaker at a very reasonable price, for my money Eminence speakers take a lot of beating, Once you have chosen your configeration ie 10s 12s 15s + horn (my favourite being 15" + 10" + Horn) you must then design your enclosure. A cab with one particular brand of speaker will sound totaly different with another brand in it, this where the Thiele Small parameters play a vital part. Next you must choose the materials, for a bass enclosure 18mm (3/4") plywood all round is best, it is lighter and stronger than MDF or chipboard, Finnish Birch Ply is the ultimate followed by Marine Ply. Finnish Birch has a very tough exterior and therefore can be painted the others need some form of covering. The tuning ports in a Bass Reflex cab require precise tuning for the required resonance frequency of the cab, 4" plastic drain pipe is the handiest material. To tune a cab properly you need a frequency counter and a signal generator as well as being a mathematical genius (the easiest way is to purchase one of the design programmes available), but you will still need a counter & generator. If your cab is tall (15+10+Horn) a front to rear brace near the centre of the cab is essenrial. If you design your cab and work out a cutting list any decent timber merchant will be able to cut a sheet to you measurements you will have to pay for each cut but it saves a lot of time. a hole cutter will cut out your tuning port holes I make a simple compass using two woodscrews through a scrap piece of wood to mark out the speaker holes most manufacturers supply dimensions. if a 10" speaker is in the same cab then unless it is of the enclosed chassis type it will need its own airtight section otherwise the 15" will affect it, you will also need a three way crossover if using this configeration a two way if you are using a 15" + horn.
When constructing the cab all joints must be screwed and glued, handles and socket panels must be secure and airtight. The two most popular ways of protecting the speaker cone is either a round grille held in with clamps or one of the various pattern metal messhes, I prefer to fasten in the speakers using 'T' nuts and bolts. For covering the cab I use Flight case type edging and corners with Vynil covering on the panels>
My own personal rig consists of an Ashdown preamp, a 5 band parametric EQ, a 400watt 4 ohm 15" sub bass cab with its own 450 watt amplifier module bult in and a 400 watt 4 ohm 15" + Horn full range cab once again with a 450 watt built in amplifier.
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My guitars are a Musicman Stingray 5 and an G&L L2500 tribute Bass.
I live in England, I have built my own many other musicians/artistes enclosures for a good number years now, I object to paying the very high prices that most manufacturers charge.

All The Best Bassman
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Old 11-07-2004, 10:42 AM   #24
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^^ Thanks, I'm glad that there are other contributors to this thread with some know-how and experience behind them.

I just approached mine from the standpoint of killing all modes (resonance) thus the cabinet doesn't resonate at all. I kind of started with just a box, then made modifications as I went, like a front-to-back brace (just a pair of studs) and the kind of port I described.

Yours is certainly more conventional, I wouldn't mind knowing how to pick a resonant frequency and tune a cab, etc. on my next projects.

Got any photos/diagrams?
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Old 11-11-2004, 09:55 PM   #25
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i do believe they are nodes ot modes
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Old 11-12-2004, 11:32 AM   #26
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No, they are modes. Nodes are the zero crossings of a wave, the point at which the air pressure is equal to the average pressure.

Modes are resonant frequencies within an enclosed chamber. Nodes are related, though. Your primary mode frequency between two rigid surfaces will be the distance between a node and an antinode, the point at which the pressure differential between your sampling point and the surrounding air is a maximum.
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Old 11-13-2004, 01:39 PM   #27
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Congrats

Hi Bibonic Chronic its nice to see someone prepared to spend a great deal of time as you have helping others.
If people had helped me as much when I was less experienced I would have saved a lot of time and money.

I hope you don't mind me adding a few tips.

Things to remember :- replacing a loudspeaker with a much more expensive one can just as easily make the cabinet sound worse and not better, cabinets if properly designed are tailored for the intended speaker.

Resonance can be reduced by using adhesive panels (the type used in automobiles for deadning sound)

A Bass loudspeaker likes to receive a good quality signal, therefore the amplifier must be up to the job, very often when people think that their speaker is flapping (farting) it is actualy reproducing the results of a clipped signal. Clipped signals on bass damage a speaker more than overloading it. I always use more amplifier watts than the rating of the speaker, as speaker technology has advanced so much in recent years it is within reason ok to do this.

More so on bass than any other band instrument will you find different venues effect your sound that is why I also us a 5 band parametric EQ this lets you fine tune your sound better than a 31 band graphic EQ. A parametric EQ lets you control the level and bandwidth of a frequency without filtering it out as in a graphic EQ

Hope that this is of help

Keep up the good work Bubonic

Regards Bassman
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Old 11-13-2004, 05:51 PM   #28
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^^ absolutely.

Glad to have you on board.
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Old 11-20-2004, 04:06 AM   #29
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Bubonic, you are the next powerfreak, but for cabinets. Why? I don't understand a single thing you're saying, good job!

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Old 11-20-2004, 07:17 AM   #30
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Cool thread can't wait to see the pictures.

For the modes if anyone is wondering how you see if your going to get modes with your cab the way you calculate it is. In metres you do the Length times 2 then 340 divided by your answer and do the same for the Width and Height. Then on some paper draw three coloums and write your answer for the Length in one , Width in another and Height in the last. You should then have something thats like:example 30Hz -Width, 50Hz - Length, 20Hz- Height to work out the resonant frequencies for the say the Width add your original answer to your answer you just got so it will be something like this: 30Hz, 60Hz, 90Hz, 120Hz, 150Hz, 180Hz, 210Hz, 240Hz,270Hz,300Hz. The gap inbetween the numbers is 30 which was the original answer so the Length would be 50Hz,150Hz, 200Hz, 250Hz, 300Hz. The modes are when you have the same resonant frequencie in another coloum so in my example I have modes at 60Hz, 120Hz, 150Hz, 180Hz, 200Hz, 240Hz, 300Hz I actually picked a really bad shape for my cab. You don't want these modes so you have to design your cab shape around them to avoid getting any. You don't measure modes over 300hz as it's only the bass and some of the low mids you have to worry about.

Hz = Hertz

I hope this helps as I didn't see it explained anywhere and I hope the thread starter dosen't mind either, as I know working out modes can be confusing.
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Old 11-21-2004, 10:04 AM   #31
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Sheet of Plywood

Reply to :- Kirk_Krobain

Hi Kirk
One of the problems with cab manufacturers is that often their main concern is getting the optimum number of cuts out of an sheet 8 Foot by 4 Foot (2440mm x 1220mm) sheet of wood. this often compromises the effidiency of the cabinets.

Unfortunately most musicians who try to construct their own cabs possess very little knowledge regarding woodworking requirements (tools methods etc), also, very few posses the equipment required to set up and tune a bass enclosure properly.

As each individual loudspeaker has its own characteristics it will always be a compromise when building your own cab if you don?t posses this knowledge and equipment.

As I said in an earlier reply there is cabinet design software available if anyone is serious about designing their own bass cabs.

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Old 11-23-2004, 01:48 PM   #32
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Using prime dimensions goes a long way towards fighting modes. 17cm long, 31 cm tall, 63cm wide...something like that. Also, shy away from square shapes. Tilt the face a bit, at a small angle upwards. Angled surfaces are less prone to modes.

And bassman is right, building bass enclosures is really involved. Guitar cabs are relatively easy as most of the energy is > 300 Hz. At that point, you're just dealing with building a rigid enclosure, something that won't fall apart. Also, attaching the speakers to a face constructed of studs facing width-wise (the short side to the speaker) will reduce vibrations (which suck up energy) considerably.
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Old 11-23-2004, 02:09 PM   #33
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Quote:
Originally posted by Bubonic Chronic
And bassman is right, building bass enclosures is really involved. Guitar cabs are relatively easy as most of the energy is > 300 Hz. At that point, you're just dealing with building a rigid enclosure, something that won't fall apart. Also, attaching the speakers to a face constructed of studs facing width-wise (the short side to the speaker) will reduce vibrations (which suck up energy) considerably.

To carry on the point the most famous guitar cabinet in history (the Marshall 4 x 12) was to designed to be the smallest possible size that the 4 speakers can fit in!

This is a really interesting thread, I have never really got into speaker cabinet design before I am normally more concerned about the amplifier! Which I guess is best considering my wood working skills aren't great!

With the next Hifi collective order I might pickup a cabinet design book, it sounds like fun.

I can't wait until I can get back to making my amp and writing some more articles and stuff but I have been so busy lately, why does school always prevent me from doing anything.

Congrats on the cab man

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Old 11-24-2004, 05:18 PM   #34
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Hi power freak
In the 60s when Jim Marshall began building amps and cabs for people like the "Who" etc he first built an 8 x 12" but it was to big hence 2 x 4 x 12"s.
The main reason for the mutiple speaker loading was that in the sixties very few 12" speakers were rated ar anything over 25 Watts. I believe that the blue speakers in the Vox AC30 were only rated at 15 watts each, on bass it was terrible, I know, I had an AC30 for bass.
Anybody could build a high wattage amplifier, but nobody, in those days, had the technology to produce a speaker to handle the power hence 4 x 12"s and 2 x 15"s 18"s etc.
With speakers now being more effecient and able to handle more power you don't see the massive rigs at concerts these days that you used to do, where banks of massive JBL 4560 & 4520 bass bins were stacked up.

You can buy the best bass amp in the world, but, without a first rate cab you'r wasting your money.

Regards Bassman
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Old 11-25-2004, 02:04 AM   #35
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You only get a 3dB increase for a doubling of the power. That means 2X12 is only barely louder than 1X12. 2X4X12 is just a touch louder than 4X12...

That's why it's a good idea to buy good speakers in the first place.
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Old 11-25-2004, 04:40 AM   #36
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Loudness v Volume

Good reply Bubonic
I don?t think that many people realise that to double your acoustic power you have to have ten times the wattage i.e.: - a 300 watt amplifier will be needed to deliver twice the acoustic power (twice as loud) of a 30 watt amplifier.
The real benefit of the multi speaker cabs is the actual volume of sound that they provide.
It is much easier on the ears to hear the same Dbs from a 4 x 12? than a 1 x 12?; this is called volume of sound and should not be used in the same context as loudness, which basically means more Dbs not fullness of sound as provided by volume.


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Old 11-27-2004, 10:38 PM   #37
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How much did the cabinet cost all together?
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Old 11-29-2004, 01:30 PM   #38
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^^ About $300, but that's because the single 15" cost me about $150 from the factory. I spent a lot on speakers.

Actually, the cabinet I built has a lot of flaws, and I've considered rebuilding it. Instead, though, I'm thinking of just keeping it around and building a new one now that I know more. I learned a bunch from building that first one, and the rest I picked up from books and stuff.

It does have a great sound for my fretless Jazz bass. The two have always gone well together.

Your cab will cost about as much as the speakers, because wood is cheap. Also, industrial carpeting is, like, $2 a yard and the paint is dirt cheap, too, because you don't have to buy much (if you paint it.) A can of spray paint will do fine, that's about $1.50 to $5.00, depending.
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Old 11-29-2004, 07:27 PM   #39
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so if i were to buy 4 celestions and make a cab outta that...then i bought an ADA MP-1....would that be it....because that would be only like 400 some odd dollars...thats nuts.....would it be good quality?
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Old 11-29-2004, 07:35 PM   #40
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As mentioned above, a 4X12 Marshall cab was originally designed to be as small as possible (thereby saving money on wood.)

So yes, it would be (roughly) the same quality as a Marshall cab. The thing is, guitar cabs are much simpler to design than bass cabs because wattages are much lower and frequencies are much higher, so you are only concerned with the structure and the wiring. As long as the face and sides are air-tight, you can even leave the back open.
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