stevie

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.

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]