stevie

[This is a completely modified post.] I originally laid out the crossover the old fashioned way with pencil and paper, but to make the circuits clearer, I have now drawn everything out in Paint. It works, but it's not great for making corrections. The square on the top left for the inputs and outputs is tag strip, which looks like this: The dots are holes in the board for the components' leads. The straight lines in red between the dots are the connections between the components on the underside of the board. The two 22 ohm resistors connected in parallel result in a value of 11 ohms as shown in the circuit diagram.

I've now attached Marco's excellent CAD drawings to Post #1. Crossover layout and cutting list to follow soon.

It's true that you're more likely to punch the surround with a slotted screwdriver. The secret, however, is to make a habit of putting your thumb in between the screw and the surround when tightening or undoing the screws. I do it automatically now and have done for years.

The Beyma goes lower than most. Here's a simulated comparison of the Beyma in our 50 litre cab with the Kappalite in a larger (60-litre) cab tuned lower (45Hz). The Eminence has the edge at 40Hz, but the Beyma is a couple of dBs louder above 100Hz. There's not a great deal in it really. The excursion of the two drivers is comparable. The Eminence scores on power handling, as it has a 3" coil and it is also 1kg lighter. On the other hand, it costs more than twice as much and needs a midrange driver. Blue = Beyma Orange = Eminence

Well thanks for that, Luke.

Well it's nice to see at least a flicker of interest in the higher end version . I wasn't going to bother, but I'll post the details and the measurements and crossover circuit diagram later in the week. We still have a few details to clarify about the tweeter version.

I gave up trying to make the Jazz bass pickup on my P/J sound less like a guitar and fitted a Duncan Musicman humbucker in its place. It did require routing but it gives me a useable alternative sound, which none of the Jazz bass pickups I tried did. The memory is fading a bit now, but I had to wire it in series (I think) because its output was too low in parallel to keep up with the P-bass pickup. I've never looked back. At the flick of a switch, I now have a P-bass or a Musicman sound, or a mixture of both.

The crossover type doesn't really matter. I'd treat the MkII cab as a standalone solution, as it should be loud enough for just about any semi-pro gig and it is flat response when placed on the floor. If you put another one underneath it, it will be bass heavy. Plus, unless you use a crossover on the bottom one, you will get destructive interference at higher frequencies because there will be phase problems due to the distance between the bass/mid drivers. I'm not sure that commercial manufacturers really think about this. Most of them just want to shift boxes, which is fair enough. All of the small bass cabs I have heard have been very "middy" and bass light. However, adding a second one gives you 3dB of lift where the two drivers are 1/4 or less wavelengths apart, i.e. at the bass end. This makes the overall sound "fatter" and is, I suspect, why some people say that two cabs are better than one (and also why a lot of cabs sound better with the mids pulled back on the amp). The manufacturers are happy with this situation because they get to sell two cabs. If you really need a 212 box, it should be designed as a 212, IMO. Think of it like this. You have an expensive pair of monitors in your recording studio, a pair of ATCs, let's say - a three-way design, carefully engineered and built to be one of the world's most accurate monitors. Do you think that adding another box containing a second bass driver is a good idea? And if by some strange magic you were to improve the sound of that ATC simply by doing this, what would that tell you about the ATC monitor? I wasn't going to post anything controversial on this thread, as I didn't want to distract too much from the DIY content. But you did ask!

[quote name='Beer of the Bass' timestamp='1488541755' post='3249793'] That's a pleasingly clear set of drawings, and it looks like you should be able to get a pair of them out of a standard sized sheet of ply too. Is there a typo in the side panel size though? It looks like it says 510mm while the baffle and back are 540mm, or is it a combination of the image resolution and me not having my glasses on? [/quote] I've double checked and the side panels should be 540mm. Well spotted!

[quote name='Gottastopbuyinggear' timestamp='1488808346' post='3251910'] Presumably it's things like that which many manufacturers are skipping? What's with the other resistors - just attenuation? [/quote] From those commercial speakers that I've seen, there are virtually no manufacturers fitting a proper crossover at all - with one or two notable exceptions, I must add. The usual practice, as with the TC Electronics cab we looked at yesterday, is just to fit a simple filter to roll the tweeter off so that it doesn't blow up. I'm convinced this is why so many players don't believe in tweeters and switch them off most of the time. There's no doubt in my mind that a properly implemented HF unit makes a huge difference to the definition of the bass both for the player and the audience, even if - like me - you play a P Bass with flats.

It is actually a Linkwitz-Riley 4th order crossover, although you can't tell from the circuit. The components roll the drivers off at the crossover point, adjust the phase of each driver and also change their frequency response outside the crossover area. The zobel on the tweeter that you noticed is there to modify the tweeter's frequency response rather than its impedance, although it does both. The resistors in this circuit have a dual function: attenuation and either damping of peaks or modifying the slope of the frequency curve. It might look simple, but it isn't. Oh, and Chienmortbb is quite right: if you change one or more of the drivers you need a new crossover. [Edit: something Phil just brought up reminds me that the 24dB L/R is just on the LF section of the crossover. The HF is 18dB Butterworth. If you want to know more about this stuff, The Loudspeaker Cookbook is a good place to start.]

I'm finding it a bit difficult to follow what you have done, but I can help with the hole in the driver surround. No need for a recone - that's an easy repair. You'll need to get some of this glue: http://www.homebase.co.uk/en/homebaseuk/unibond-repair-extreme-power-glue---transparent---20g-692332 You could probably get away with just pushing the surround back into place and gluing it, but if you can get hold of some old black tights from your wife or girlfriend (or if you wear tights yourself - don't want to be sexist, do we) , cut two small rectangular pieces and glue one to the front and one to the back of the hole. Push into position so that it sticks closely to the contours of the surround. I've used this technique to repair much worse damage than a small hole.

A system with the Faital Pro PR300 and P-Audio PHT-407N (both neo drivers) would reduce the weight of the cab noticably. I've not worked with the Faital Pro driver, but I would expect it to sound a bit more refined than the Beyma in the upper mids. However, it won't go as loud as the Beyma because its excursion is not as great. That's could be why a lot of people use two Bergantino CN112s. The internal volume of this cab is approx. 50 litres. So reducing it to 46 is not going to reduce the weight much. As long as you maintain the baffle dimensions, you can reduce the depth if you want a smaller, lighter cab. The port would have to be recalculated, of course, and I wouldn't recommend going under 40 litres. A 4-ohm PR300 is a special order - so it's not really a goer for that reason alone. If there's enough interest in a lightweight system with this combination of (8-ohm) drivers, I don't mind designing the crossover as long as somebody lends me the drivers. You can fit a Beta 12a or virtually any other "full-range" bass guitar speaker to this cabinet without any problem. They will all work. What you can't do is use the tweeter without first redesigning the crossover.

Agreed. I think it's fair to say that the goal of the MkI was to provide a cab that was compact, easy to build, produced good bass and didn't cost a fortune. And I believe it succeeded in doing that. The MkII is really a completely different design - the only common factor being the bass driver and the cabinet volume. This time, the goal is to offer a DIY project at a relatively low cost that performs as well as or better than most commercial offerings out there, and offers the satisfaction - which to some of us is priceless - of having "rolled your own". By the way, fftc, both cabs use the same bass driver.

What I don't know, I have to say, is whether the spec of the P. Audio horn has changed over the years, as mine is a few years old. To save me buying another one, it would be good if someone could send me theirs for a couple of days so that I can check.

Yes, you can used your existing drivers. Beyma just changed the way they presented the specification. I measured the T/S parameters of Phil's original driver, which is probably older than yours, and Chienmortbb's driver, which is quite recent. The parameters were comparable - so I'm quite sure the driver hasn't changed at any time during its production.

Yes, the idea was to get two out of one sheet of plywood. John (Chienmortbb) is going to produce a cutting list next week that anyone should be able to take along to their local wood supplier to get the panels cut to size. You're right about the 540mm. Sorry about that. I'll check all the dimensions against the prototype cab this afternoon - that's the beauty of building a prototype . We'll fix any discrepancies in the PDF - and if anyone else sees anything that's not quite right, please say.

[quote name='Chienmortbb' timestamp='1488534306' post='3249690'] I would recommend building the MK2 but it is more complex You could put the new port into the MK1 but the baffle is smaller and so there will be np room for upgrading later. I suggest you what until Ghost-bass and Stevie have finalised the drawings and then decide. As far as I know they ar a few days away. I will do a MK1 v Mk2 comparison later if it helps. [/quote] If you look take a closer look at the drawings, this box isn't really that hard to build because the baffle, back and all the braces are the same width. That should help to line everything up neatly. The only difficult bit is cutting the 5" hole for the port. If anyone would like to borrow my 5" hole cutter (and has a drill and an arbor) they are quite welcome. Just post it back to me when you've finished, or perhaps post it on the the next builder.

Here are the drawings. A very big thank-you to Marco (Ghost_Bass) for doing these. I’m attaching the higher resolution PDF to Post no. 1 in this thread (when I figure out how to do it) and will update that with any future amendments. Please note that the braces G, I, H and J do not have to be cut out of a sheet. They can just as easily be made from 12 or 15mm x 32mm batten.

If you want to build the MkII cab without the tweeter, just leave the tweeter out. You then have the option of adding the tweeter any time you like. The tweeter and crossover will only cost about £25 total, but they do represent a useful upgrade in sound quality. I'm going to do a crossover layout so that you can see how to assemble it and Ghost_Bass has kindly offered to do some proper drawings of it.

Bracing is vital to the performance of this box - it's not an afterthought. I have the MkI and the MkII cabs in my workshop, and I can say without a shadow of a doubt that there is no comparison between them as far as panel stiffness is concerned. The 1 to 1.5kg that went into reinforcing the butt joints in the MkI is now doing a much more useful job stiffening the whole of the MkII cabinet. Siegfried Linkwitz has this to say on the subject. "Conventional box loudspeakers very often suffer from spurious sound radiation, which is caused by the mechanical vibration energy of the drivers being transmitted into the cabinet and exciting the cabinet walls to vibrate at certain panel resonance modes. Furthermore, the high sound pressure levels inside the cabinet can excite panel modes. Since the cabinet's radiating surface areas are usually much larger than the driver cone area [i]even relatively small panel excursions can lead to significant spurious acoustic output.[/i] Depending upon the cabinet construction [i]the output might even be larger at certain frequencies than the desired output from the driver[/i]. Knocking with your knuckle on a panel can give you a rough idea of the dominant mode frequency, though it might not necessarily get excited by the driver. This test can also tell you how stiff the panel is, when the pitch is high, or how well the panel is damped because it hurts to make it respond. There are several ways to reduce modal panel vibrations. Because the vibration energy from the driver decreases rapidly with increasing frequency it is advantageous to push the panel vibration modes up in frequency where the excitation energy is small. [i]This is best accomplished by increasing the panel stiffness[/i], but often goes together with increasing the mechanical Q of resonance. As my rule of thumb, no un-braced box panel area should be larger than 4 inch squared for 3/4 inch thick wood panels. That is a lot of bracing, but it pushes modes into the low kHz range." Just to clarify - for those that get a headache reading technical stuff - when you play your bass through a conventional wooden cabinet, the cabinet itself can produce more output than the driver on certain notes. Because the radiating area of the cabinet is much larger than the radiating area of the driver, the cabinet doesn't have to move very much to do this. The bracing is not there to stop the cabinet rattling; it's there to stiffen the cabinet and stop it "playing along" with the driver. You only realise how much mush the cabinet contributes to your overall sound when you compare it with a cabinet that has been properly treated. A cabinet designed for acoustic performance (rather than ease of manufacture) is demonstrably cleaner, tighter, more natural and has more punch.

Chienmort and I will both be building one of these cabs from poplar ply in a few weeks' time and we'll be able to provide a more definitive answer on weight, as well as providing a step-by-step build guide. As the cabinet volume of the MkII box is identical to the MkI, the weight should be the same, but calculate 1kg for the tweeter. Putting the port on the back is fine. Position it 2/3 up in between the braces. You will probably have to space the braces out a bit more, but that's OK. The Eminence 2012LF is a pure woofer and needs to be crossed over no higher than 1kHz to a midrange unit. Alternative bass drivers are possible but would mean a crossover redesign. Now that Bergantino has discontinued its CN112, an interesting lightweight possibility would be the neodymium Faital Pro PR300 with the neo version of the P. Audio tweeter.

If you have the skills, use whatever fancy jointing method you like. The rest of us will use normal butt joints, which are perfectly fine and used by everyone and his dog for this kind of cabinet. Remember, we are not building furniture. Here is a video showing how to screw a box together. It's not difficult. Fast forward to about 3 minutes 20. https://www.youtube.com/watch?v=L5tkfhXjSTk Here's another guide on how to assemble a speaker cabinet: http://www.speakerplans.com/index.php?id=guide Once the glue has dried, remove any screws close to where you intend to round over and fill the holes with car body filler (not wood filler). You can leave the other screws where they are and just fill over them. Marco, also known as Ghost_Bass, has been working on the cab drawings. When they are up, they should answer a number of the questions that have been raised.

Unfortunately, you're not going to escape the 4x10 cancellation phenomemon whatever you do; you can only make the best of what you've got. If you pay a visit to Bass Gear Magazine and look at some of the measurements (issue 10 has a couple), you'll see that cabinets with multiple full-range drivers have a power response that looks like the Swiss Alps. It's partly combing and partly beaming, although beaming is the main culprit, and it starts about 250Hz (you said you wanted a figure). You only get proper mutual coupling up to 1/4 of the centre-to-centre wavelength frequency - above that you should really be crossing over to a smaller driver. I'm surprised that they work as well as they do - and clearly plenty of bassists love 'em. But they have about as much "throw" as a mouse tossing a caber. It does, of course, depend on the size of the rooms you're playing in.