stevie

We're a bit under time pressure here, what with the SW bass bash looming. I've wound the coils for John's cab and he will be picking them up tomorrow. All very skin-of-your-teeth. So here is the LF section of the crossover with the board layout. Please shout if you see any silly mistakes. There will be a PDF pinned to message # 1 in due course.

Supporting the section between the port and the horn is a good idea. A simple strut on the baffle would suffice, but a triangular piece is even better. I like the grille too. It's a lot tougher than your usual fabric but a lot lighter than perforated steel. Let's hope we can iron out the assembly snags. Another thing..... I've found that you can apply Tuff Cab to other finishes all right. I think that the distributors are perhaps being a bit over-cautious with their advice. Of course, there's always a first time.

[quote name='sk8' timestamp='1490741199' post='3267658'] Maybe I've spent too much time on TB.......... [/quote]

They fit an MP520.

These are the components that John will be fitting to his cab. A P Audio PH-170: and a Celestion CDX1-1455 compression driver: My prototype version looks something like this: It is worth mentioning that 1" exit compression drivers come in different voice coil sizes. The most expensive versions have 1.75" coils. This one has a 1.4" coil, which offers a good compromise between performance and price as long as you don't try to use it too low. But it works well down to 2kHz. I have always found that compression drivers with 1" coils sound really tizzy and are only useful as supertweeters. Some bass cabs manufacturers use them, however, because to most people a compression driver is a compression driver. Because we are unable to take advantage of the natural rolloffs of the drivers this time, the crossover is more complex. Also, this is a constant directivity horn, which by its very nature requires a more complicated crossover circuit. The design is finished, and I'll post the details of the crossover, the crossover layout, frequency resonse and impedance measurements as soon as I can. Despite the fact that the horn and driver only cost around £50 together, this is probably the most advanced HF unit on any bass cabinet on the market.

Yes, well I noticed. But would you say it to your friends down the pub, or is this an internet thing? I'm not being critical - I am genuinely curious.

My printer packed up leaving me with about 20 cartridges, a few originals but mostly not. They fit the following Canon printers: IP3300, 3500, 4200, 4300,4500,5200, mp500, 510, 530, 600, 610, 800, 810, 960. They are CLI-8s and PG-5BK. They're all brand new, sealed and boxed. I'd prefer pickup from Dorchester at the moment. If there are no locals who can use them, I'd be happy to pack them if you can arrange for them to be collected.

I'm just idly wondering whether people actually say "pull the trigger".

Not really a purchase, as BC member Alyctes generously gave me a Behringer BX4500H head; I just needed to replace the internal fan to get it working properly. Anyway, I took it to a two-hour rehearsal recently and kept switching over from my normal Tonehammer 500 to the Behringer - both set flat into a very transparent cab. I listened very carefully. There was *[i]no discernable difference[/i]*. How is that possible when the TH500 is considered to be the cream of the current amplifier crop and costs about £800 while the Behringer originally cost about £180 and can now be picked up for peanuts? This was a bit of a reality check. Definitely recommended for anyone on a budget.

The speaker used in the F112 certainly woofs very well indeed. Interestingly though, the Beyma SM212 we used in the BC 1x12 DIY cab goes just as low. I have both here and have measured them in the same cab. If I didn't roll my own, Greenboy's creations would definitely be at the top of my wish list.

I believe the Matrix guitar amp has the damping factor artificially lowered to give a "looser" type of sound preferred by guitarists.

This is why I spent the time sorting out the bracing. With a birch cab, a circular brace above the driver, one behind the driver and one on the top panel would be more than enough. If weight isn't an issue, that would be my first choice for performance. 7kg sounds good though.

[quote name='The Shrek' timestamp='1489696507' post='3259092'] Hey guys, I can't stress enough about sourcing good plywood. [/quote] Totally agree with this. If you are going to spend your valuable time building a cab like this, don't dry to save pennies on the wood. You can make this cab from just 1/2 sheet - so it's not that much more to get the good stuff. Cheap plywood will just not do the job properly. If you're going to use normal ply, get Finnish or Russian birch plywood. If you're going to use poplar ply, get the Italian stuff. Unless you're a wood expert, avoid anything from China.

I quite like the idea of using round holes for this. I imagine it would be a lot quicker.

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.