stevie

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.

I haven't quite finished the bracing, but the cabinet walls are already impressively quiet. I've been using lengths of 12mm x 32mm softwood (as mentioned by JPH) , which are readily available from local wood merchants and the usual DIY stores. The advantage of using these is that they are cut perfectly square, which makes it easy to get a tight glued connection between the brace and the cabinet panels. The secret of getting the brace clamped tightly to the panel is to use wood screws and to pre-drill through the brace into the panel (not right through it, obviously). Use plenty of PVA and make sure it oozes out from both sides right along the length of the brace. The most important brace is a figure-8 brace just above the driver, as this cuts down vibration on the baffle and stiffens the cab close to its centre point. There is another semi-figure-8 below directly behind the driver with sufficient space to allow for the driver and magnet. With a birch ply box, that is probably all you would need. The remaining two braces are glued to the back and side walls in a "U" shape. One set positioned near the top of the cabinet, and one set near the bottom. The figure-8 configuration cross brace is not needed here because the top and bottom panels provide sufficient stiffness. I ended up with four circular or semi-circular braces fairly evenly spaced along the length of the cabinet. By the way, this bracing arrangement was arrived at systematically using the sine wave test tones from my Alan Parsons test CD. I still have to brace the bottom and top panels. Then I’ll report on the final results. [PLEASE NOTE: THIS WAS A PROTOTYPE. THE FINAL BRACING DESIGN APPEAR LATER IN THE THREAD.]

Feeling for vibrations with your fingertips works really well. Even with an accelerometer custom designed for this type of work, you have to set up and calibrate your measuring gear, glue the device to various areas of each cabinet panel, and save or print off your results. With your fingers, you can check the different areas of the cab in seconds. The only drawback is that it is subjective, but once you've done it a few times, it's very effective. I'm now sorting out the bracing for the box, which will take a few days. Has anyone tried the test tone MP3s yet?

Before we can even think about working with the drivers, we need to take a closer look at the cabinet to make sure it’s fit for purpose. So let’s install and connect the bass unit. I’m going to carry out some tests on the box, which you can easily replicate on your own cabinet at home if you wish. The standard material for wooden cabinets in the world of sound reinforcement is, and has always been, 18mm birch ply. Because they are stiff, cabinets made from birch need relatively little bracing (I say relatively....). The lighter stuff is different, however: here, bracing is mandatory. The lightweight spruce plywood that our test box is made of is unlikely to be as stiff or well damped as the poplar ply we will ultimately be using, and it is certainly nowhere near as stiff as birch. Bracing is therefore a necessary exercise and we should be able to transfer the lessons learned to the final version. The test CD I’m going to be using contains test tones at the usual frequencies. Playing them through any cabinet starting at 40Hz quickly reveals resonances and problems, if there are any, with the cabinet’s structure. You could say it’s a bit of a torture test. If you’d like to try your hand at this on your own cab, download some of these MP3s and give it a go: http://www.testsounds.com. It’s a sad fact that many expensive bass cabinets suffer from cabinet resonances, by which I don’t necessarily mean rattles. It’s often a commercial necessity to build cheaply in order to remain competitive. After all, who checks a bass cabinet for resonances before buying, or even looks inside it to see if it has been properly braced and damped? The problem is that a vibrating cabinet will colour your sound and detract from its perceived sound quality. Panel vibrations simultaneously add to and subtract from the sound of your bass, continually altering and masking its tonal colour – so it’s important to try to keep them under control. To make matters worse, the bigger the cabinet you have, the more difficult resonances are to control. Fortunately, the DIY builder is not constrained too much by the extra cost of building a well-behaved cabinet. Test results Not great. Not unexpectedly, the cabinet as it stands rings like a bell. The worst vibrations were on the baffle – so that will be the first area to deal with. This test is normally carried out using an accelerometer, which is a type of vibration detector. Since I don’t have one, I simply felt the vibrations on each of the panels with my fingertips, rated them subjectively for level, and entered them on a sheet of paper in tabular form. Rather than reproduce the entire table, which is a bit difficult on here, I can summarise the results as follows: Baffle Resonances starting at 40Hz and going through to 400Hz. The worst frequencies were 63 and 80, but 50 and 100 were also excessive. Sides Resonances starting at 100Hz through to 250Hz. Then a single resonance at 630Hz. Top Resonances at 80 and 100Hz. Then at frequencies between 250 and 400. Back panel Resonances from 40 through to 315 Hz, with particularly bad resonances at 80 and 200Hz.

That can't be right. My maths is rubbish! [Edited for a grocer's apostrophe]

It would be a bit lonely if nobody commented. So all comments and suggestions are, of course, welcome. One of the problems I've encountered over the years of playing on small stages and in typical pub settings is the inability to hear what you're playing when you're directly in front of your cab. The usual solution is to raise the cab or to use a second one closer to ear height. It should be possible, however, to design a speaker with dispersion characteristics that allow you to hear your bass even when you're right in front of the cab. That is one of the design objectives of this speaker.

The cab is the same internal volume as the one from the first thread ([url="http://basschat.co.uk/topic/227904-1x12-cab-design-diary/"]http://basschat.co.u...b-design-diary/[/url]), but the height has been increased to allow for an HF unit. It has also been sized to accommodate a half-inch picture frame for a cloth (or similar) grille, which should be easier, cheaper and lighter than a punched metal one. We discussed, and decided against the use of a slot port, as it would make the box too tall and ungainly. The porting arrangement has been taken over from the first design, although the ports have been repositioned. So let’s get cutting! Here is my 70mm hole cutter, which makes a perfect hole for 63mm (internal) drainpipe. Four holes cut in next to no time. I love hole cutters! And here are four ports that I cut earlier. Now installed. Just grabbing my 80mm hole cutter to cut the hole for the tweeter. The first HF unit we will be working with is the P. Audio PHT-407, available in the UK from Blue Aran for a very reasonable £13. Don’t be put off by the price; it’s a quality unit. Install drivers, connect up, and we are ready to carry on.

That design was basically Phil's baby, and I know he has some assembly instructions and photos nearly ready to post. I think life got in the way a bit. I'm sure he'll be along shortly to confirm. It's true, however, that there is enough information contained in that thread to build a working cab.

Replied to 3below in pm.

At the moment, the project is for a two-way cab, 3below. We're going to start with a reasonably priced but high quality tweeter and then move on to a compression driver and horn. The Faital looks very impressive. I'm not quite sure how they get that kind of efficiency out of a 5" driver. If I were doing a three-way, it would probably be at the top of my list to audition. What are your plans for them?

Although it's been a while since there was any visible activity on the Basschat 12” cabinet diary, we have recently been discussing it again in pm. I have started this new thread because we have decided to take the project in a new direction. Phil’s original design objectives for the cabinet were these: Capable of keeping up with an unamplified drum kit (120dB across most of the frequency range) Compact (60l or less) Neutral /clean sounding Easy to handle Good low frequency power handling Readily available components, and easy to build Value for money. The end result was a 50-litre cab containing a Beyma 12” driver – the SM212, which a few of you have built and which Phil has been gigging for a while now. But we didn’t want to leave it there: this box has a lot more potential that we would like to bring out. A thread that Luke started a few years ago piqued my interest and got me messing around with bass guitar cabs based on PA/stage monitor design principles. I’ve knocked up a few cabinets since then, using some pretty tasty drive units picked up cheaply from eBay, and am convinced that this is the way forward. It also seems to be the direction that a few of the boutique builders are going in – so that’s a good sign. I therefore persuaded Phil that a flat-response, PA-type design would be a good avenue to pursue, although I have to say that Phil remains convinced that non-flat cab also have their benefits. Unfortunately, it has been necessary to alter the size of the baffle from the original design to make room for additional drivers. If I remember rightly, Phil built the original box in response to requests for a cabinet 19” wide. We are now going to jettison that requirement (sorry!) and adhere to the principle of form follows function – not a problem for everyone with a modern compact amp, but anything else will overhang. If that disturbs you, you need read no further.:-) At about the same time as we were discussing this, John, who is Chienmortbb and lives not far away from me in another less salubrious part of Dorset, offered to build a suitable cab using some spruce ply panels he had in his garage. As the plan was to try for a lightweight, poplar ply cabinet this time round, it seemed like an excellent opportunity to develop a prototype. The cab is here and I’ve marked it up for cutting. Game on! The parts list is for the latest version of this cab. It will be updated at regular intervals to reflect changes in the market. basschat-112-v3.pdf PartsList.docx

Funny you should say that......

If you don't have a soldering iron, you could get away with cutting and stripping the wires and connecting them with a terminal (aka chocolate) block. Not quite as elegant though.

That's very sensible. Two tweeters in two cabs will tend to produce cancellation - the dreaded 'comb filtering'. It's best just to have one active.

That looks like it might be a properly designed x-over. Why not give it a try before disconnecting it? If you do this, you need to bypass the crossover completely. You need to disconnect the wires that go from the input panel to the crossover from the crossover, and connect them directly to the bass unit. There's no need to disconnect the tweeter at all. From what I can see, that means unsoldering two of the red and black wires and connecting them together (solder and shrink wrap, or terminal blocks). I'm not sure what the third red and black wire is from the photo (second bass unit?) - so just make sure the input is connected directly to the bass driver(s) - and not the crossover - and you'll be good to go.

I didn't say anything about UK sales figures. I based my statement on what is shown in the For Sale section of this site and it is perfectly valid within the context of the recent discussion. Not only that, but anyone can check it out for themselves and dispute the figures if they want: there are ten times as many used Bareface cabs being sold on this forum than Bergantinos. This shows that molan's claim is not unreasonable. On the other hand, if you're going to claim that more Barefaced cabs have been sold than Bergs, you really need to produce the figures, otherwise you run the risk of looking like a real tit.

[quote name='Kev' timestamp='1484244525' post='3213960'] Bergantino - probably the most common 'boutique' cabinet in the for sales sections on this site. Somewhat at contrast to a couple of posts in this thread! There always seems to be one for sale. [/quote] In the interests of fair play, I've just trawled through the For Sale section on here. There are about ten Barefaced boxes for every one Bergantino. I have to admit, I stopped at about the second Bergantino - but you get the idea. It certainly backs up molan's statement. Not that this surprises me, as molan is one of the few knowledgeable contributors to this part of the forum.

You're looking for a resistance reading of anything between 3 and 10 ohms, depending on the tweeter. A blown tweeter normally won't give you any resistance reading at all. Disconnect the wires from the tweeter first and measure across the connections.