stevie

I know everyone on the other thread is recommending Copydex, but this stuff is a bit more 21st century. I can also confirm that it does a great job on fabric surrounds.

I doff my hat to you. Really nice work!

This is an odd one. If the noise stops when you lift the amp up from the cabinet that would indicate that the cab is vibrating and passing the vibrations through to the amp. What is odd is that it gets better when you reduce the output from the horn, because a tweeter should not really be able to drive the cabinet panels into vibration. If the ceramic insulators are vibrating, they are vibrating, and there's no reason to suspect microphony. You should be able to locate the problem frequencies by playing sine test tones through your system. There are plenty of free ones available on the internet. That should help you locate the cause of the problem and fix it.

I take your point about the parallel resistors, 6v6. From a circuit standpoint, 2 parallel resistors are seen as a single component with half the resistance and twice the power handling. But I can see that it could cause confusion. When I get a minute, I'll change the diagram to show the two components.

I've now tarted up the first part of the crossover drawings and will do the second one as soon as I can.

Actually, John, posting your build on here would not be a bad idea, as it's certainly on topic and it would help anyone considering building this cab. I'm summarising the most important information and placing in Post #1 for easy reference, but the vast majority of the posts in the thread so far contain useful comments. I've just posted a PDF of your cutting list.

Yup, you're right. The first change I made was incorrect; I should have moved the output wire from the inductor. I'm now working on this in Microsoft Paint, and will post a revised version.

Yes, you're absolutely right. There should be no connection between A and B on the LF board. I'll correct it and repost. Done.

I usually build my one-off crossovers on 6mm plywood, but stripboard would be perfect for this build. I'm compiling a Word file with a list of parts and suppliers and I'll include information like this. You could also use the plywood offcuts from the wood you make the cab from.

[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.