stevie

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.

Chocolate teapot?

I don't get all this advice to buy monitors, headphones, in-ears, wireless etc. Am I missing something? If you can't hear yourself in your small practice room, the problem is with your backline. Stick your 2 x 10 on end on top of your combo so that one of the tens is as close to your ears as possible. It also sounds like you'd benefit from a more powerful 2 x 10 - or a complete rethink on your speakers.

It could be lots of things: something loose, something leaking, something worn, something rattling. You can't really troubleshoot this kind of thing from a distance, but test tones can help pinpoint the problem. Download the 30, 40 and 50Hz tones from here - http://www.testsounds.com - and play them through the cab. You should quickly be able to locate where the problem is coming from.

https://www.google.co.uk/search?q=1U+class+bass+amplifier&ie=UTF-8&gws_rd=cr&ei=Ny6oWIaKLcbHgAbO9JHYBA#q=1U+class+d+bass+amplifier

Just make sure you use a proven design or get some advice before you cut the wood. This thread - and I think the OP will agree - is a good example of how not to DIY.

I'd hardly compare those Eminence drivers with a Ferrari.

To use a single 100mm port, make it about 70mm long. [EDIT] Just double checked this. Anything between 70 and 110mm would be OK.

Two 75mm ports, 100mm long will tune the box.

Here is the crossover circuit (it's not very clear, but the first inductor is .6mH and not 6mH): [url="https://postimg.org/image/nfy4sbfz1/"][/url] Film caps throughout. 1mm wire on LF coil, .7mm on HF coil. 17W resistors on HF. 30W minimum on LF (2 x 17W/15 ohm resistors would be OK). If you need a layout, I can do one, but it's quite a simple circuit. Here are also a few measurements I took of the finished system. They are anechoic measurements without any smoothing. The curves that look a bit rougher than others were taken further away and are not 100% anechoic, as they contain some reflections. Ignore the droop to the far left of some of the measurements – it’s an artefact. Showing the tweeter response. Crossover point is 3kHz. [url="https://postimg.org/image/yp4m6xw9b/"][/url] Impedance. This is a very easy amplifier load. [url="https://postimg.org/image/4c8vjwbyp/"][/url][url="https://postimage.org/"]imgurl[/url] Response 30 degrees off axis (top curve is on axis). You can see that the frequency response collapses between 2 and 3kHz because the bass driver is beaming too much here. [url="https://postimg.org/image/7ezc5xd6b/"][/url][url="https://postimage.org/"]uploadimage[/url] This is what you can expect if you are of average/above average height standing 1 metre in front of the cab (upper curve is directly in front of the cab). The response of any 12” driver starts to collapse at 1kHz off axis, and you can see that happening here. However, the output from the tweeter helps compensate for this drop from around 2kHz, which will help the player to hear what he is playing. [url="https://postimg.org/image/x963q3yk7/"][/url][url="https://postimage.org/"]upload pics[/url] I would stress that this is not your usual boom/tizz tweeter solution. Here, the tweeter really helps to define the sound of the bass. Once you have played a system like this, you are unlikely to go back to a single driver design. I’m trying to get drawings sorted now so that anyone can build one of these. I’ll post as soon as they are available - hoping for end of the week. I have also finished the design of a 12 + compression driver and horn system that Chienmort intends to build. It uses exactly the same cab and bass driver but has a Celestion compression driver and a CD horn, which will obviously cost a bit more than this tweetered version. The crossover is a lot more complex because of the CD horn and lower crossover point. If there is any interest, I'll post details of that here too. Finally, it would be really helpful if anyone who owns a top-end 12” bass cab and is not too far from Dorchester could arrange to pop in to see me for half an hour so that we can compare that cab with the Basschat 12 I have here, and also take some measurements – whether for publication or not. Just message me and we’ll get something sorted.

This is what the inside of the cabinet looks like now. [url="https://postimg.org/image/t91t3ld7t/"][/url] I’ve been using felt on a lot of my boxes recently (a wool/cotton mix) and I’ve found it works exceptionally well. I did try foam and BAF wadding in the cab, but they weren’t as effective. As usual, the material is inexpensive and readily available from eBay. £6.99 (delivered) gets you a square metre, which is enough for two cabs. I’ll list information on where to get all of the bits and pieces when we're finished. Use one layer all round except for near the port, with two layers on the bottom 25% of the back panel. This arrangement was arrived at by systematic measurement and is not just a best guess. The felt needs to be glued to the cabinet panels, with a few staples to keep the second layer in place. Contact adhesive is best (just apply to one side). I found this spray can of contact adhesive in Poundland, which makes the job easier. It contains enough for one cab: Not much more to say about this, except that if you are thinking of putting damping into your current cabinet, this is a good way of doing it. Now that we have a sorted cabinet, we can start designing the crossover. I’ve put a handle on the side and this is what the cab looks like with the drivers in: If you’d prefer a black port, it can easily be painted black with something like Holts bumper paint. The two raw drivers we'll be working with measure something like this: [url="https://postimg.org/image/pik463nxt/"][/url]

You've looked at the specs of the RCFs?

I couldn't have put it better, Phil.

Yes, one big port, Luke. The idea is to minimise friction and turbulence within the port; the less friction, the less chuffing and compression. It's not so critical with large cabs, or general purpose PA cabs for voice, but with small, high powered bass cabs like this one, optimising the porting makes a *huge* difference to the output produced by the port - and reduces distortion audibly. A single round port is simply the best solution for minimising friction. They're called flared ports, MoonBass. I have a selection of them here, including some very nice Precision Ports 4" ones. Unfortunately, availability is a bit of a problem in the UK, but they do work really well. I considered using the Precisions, but their external diameter is about 18cm and there wasn't enough room on the baffle. Also, a single flared 4" port wasn't going to be long enough to tune the cab to the target frequency. The performance of the 5" we are using is equivalent to a flared 4" port. The ideal would be a 5" flared port on the back of the cab, but nobody makes one. If somebody could use a 3D printer to make some flared port ends cheaply, that would make me very happy. It seems like an ideal job for a 3D printer.

This is the port that eventually worked best and which generates very little port noise even at fairly high levels. [url="https://postimg.org/image/km8htctt5/"][/url] It’s a 120mm Manrose pipe (125mm external), available from Screwfix (and lots of DIY and plumbing stores). You can cut two ports from it and it costs £2.69. I tried various sizes and types of commercial port, but this was definitely the one. In the process, I cut and filled so many holes, my baffle ended up looking look like this: [url="https://postimg.org/image/x8756ba9r/"][/url] This is the hole cutter I used, which produced a really snug fit in one go. [url="https://postimg.org/image/3wg83i137/"][/url] If you don’t have one (which is admittedly very likely), you will need to use some kind of hole cutter or router to cut the hole. Unfortunately, there is no commercially available port in this size with a lip to hide dodgy woodwork. I am now making a start on the internal damping. [url="https://postimg.org/image/6q42ragcd/"][/url]

A bit too much chuffing for my liking, John. Sorting the porting out has taken a while and lots of hole cutting and gluing with glass fibre and filler. However, I do believe I now have the solution, which I will post later today. David, PU glue is great when you don't have accurate joints and need to fill gaps, but these braces really do need to be pressed very tightly to the cabinet panels for optimal effect. If there is a slight gap because the brace (or shelf) hasn't been cut correctly or fixed down tightly, it won't work properly. While the gap-filling properties of polyurethene will prevent vibration if the joint isn't perfect, you really don't want any gaps at all. The damping effect of attaching bracing comes more from stiffening the panels than any properties of the glue. In fact, you can hear the effect of the brace just by pressing it tightly on the panel without gluing - which is how I arrived at the positioning of the bracing for this box.

Yes, I would also expect plywood to be stiffer than the softwood I’m using, JPJ. The softwood is actually quite stiff on edge, but the big advantage for me is that I can pick it up from the local wood merchant and simply cut it to length. I’ve now carried out sine wave testing on the fully braced cab and this proved quite interesting. Without boring everyone with all the figures, I found that the spurious vibrations at the fundamental frequencies of the bass (40 to 100Hz) had virtually disappeared and that the level of vibration at all other frequencies was much lower than before. This will have a positive effect on the sound of the system. It will also ensure that amplifiers placed on top of the cab will not dance about or fall off – perish the thought! Now that the cabinet is so much quieter, the sine wave tests showed that some more work needs to be done on the porting. Test tones are very good at revealing problems that you’d miss just using a bass as a sound source. So the next job is to take a closer look at the porting arrangement to make sure it’s optimum.

I found that the best way to brace the end panels was across the longest dimension. When the glue dries the bracing will be finished. I needed two lengths of 2.4m batten to effectively brace this particular cab. I forgot to weigh the batten before I started cutting it up, but I calculate that it adds around 1.2kg to the overall weight of the cabinet. Using poplar ply strips or shelves might reduce this a little. I’ve carried out this exercise on plenty of cabinets before. It is a particularly good way of “fixing” an inexpensive shop-bought cabinet, as these are hardly ever braced adequately.