stevie

I think I pointed out the main weaknesses of the RCF 745 as I see them, Cameron, but I don't want to run it down. While it's not perfect, it's a great product and excellent value overall.

My next job is obviously to do a proper circuit board layout. For the time being, however, here is a measurement of the finished system. I'll post off axis and impedance curves another time - I did do them, I just didn't save them.

OK - next up is the crossover. I do the initial work in CAD, but that is followed by hours of plugging and unplugging components and listening. This is my little crossover corner after a hard session. The first crossover I did looked like this: I built it on a fibreglass PCB board I happened to have to hand. This is the crossover that John Chienmortbb and Phil heard when they came over for an afternoon's auditioning. However, I thought that I should try to simplify it a bit, and ended up with this one: The good news is that not only is that crossover simpler, it sounds noticeably better. It has just eight components, which is excellent when you consider that it is a fourth order crossover with CD horn correction.

I'm in two minds about this FRFR thing. The upside is that the systems are relatively uncoloured, which in my opinion is what you want from a bass guitar cab. Plenty of people disagree with that, but if I want colour I can always add it. If it's in the cab it's there all the time. The acoustic design of these boxes is also about 20/30 years ahead of what you get in a bass guitar cab. The other great thing about all of these active PA cabs is that you get such a lot for your money. Their pricing puts them in the same area of the market as boutiqe bass guitar cabs, but because they are mass market products (unlike boutique bass cabs), they offer you a much bigger bang for your buck. The other side of the coin is that they are jack-of-all-trades speakers. Although a lot of them handle bass, the cheaper ones are very limited, and even the expensive ones I've looked at aren't wonderful. For example, the RCF 745, which is considered by many (including me) to be a superb cab, comes in a plastic box. There is a video on YouTube in which a music dealer takes one apart and examines the components and build quality. He bangs on the plastic box and convinces himself how solid it is, but is sounds like a plastic bucket to me. And while the compression driver and horn are impeccable , the 15" driver has a pressed steel chassis, and if you look at RCF's driver specs, an xmax of less than 3mm. Finally (although I could go on), there is too much wall area in the porting arrangement and with bass guitar those ports will start compressing well before the system gets anywhere close to its limits. Just a few thoughts.....

Thanks for your contributions, guys. The reason I did the grille this way was because of the weight. An expanded metal grille is lighter than a punched metal grille. Because it is thinner, you need to support it all the way round to stiffen it up. I also put a small piece of foam on the top of the bass driver (you can probably see it if you look carefully) to support it in the centre as well. Ashdown used this grille material for some years and it doesn't rattle as long as you support it properly. The downside is that fitting it was quite time consuming. Not only do you have to obtain and cut the grille support battens, you also have to glue them to the cab and then paint them. Plus you have to apply special thin foam to the grille support frame. I had a problem sourcing thin foam strip – so I removed the foam from the old Ashdown 2x10" cab and reused it. If you use normal thickness foam, it pokes through the holes and looks really amateurish. With a metal grille from Speakergrilles, you simply put it in place and secure it with four screws. Done. But your cab will weigh about half a kg more. The last time I fitted a box pan-type grille was on carpet-covered speakers. So the carpet gripped the grille all round and rattling wasn't a problem. I'm not sure about painted cabinets, but Gottastop will know.

The crossover's done, Richard - I just haven't got around to drawing it yet. I should be able to do it tomorrow. Don't worry about the components. I can wind the coils and have stocks of all the other components. So you won't have to order from different suppliers and wait ages for delivery.

Exactly. The retail price of that compression driver alone is £225.

Not enough to matter. The top handle is one of the problems I came across when gigging this cab, and I suspect this is what you're referring to. The feet on your average 500W compact amp aren't tall enough to raise the amp high enough to clear the handle. I've been using a piece of sponge under my amp to deal with this, but it's not ideal. We could move the handle to the side to avoid this, but I find it easier to pick up and carry with a top handle - so I'm not too keen on that. Builders can, of course, do this if they like; that's one of the benefits of building your own. The alternative is to use a different handle, and funnily enough, I have three of these Adam Hall handles on another cabinet in my garage that I was going to use on a larger design. <http://www.bluearan.co.uk/index.php?id=ADH34062&amp;browsemode=category#> When I mentioned this to John (Chienmortbb), he decided to get hold of one and fit it to his cab. The round handle not only gives you the amp clearance you need, but according to John, it makes the cab easier to manoeuvre. I hope this image is big enough. If not, have a look at the Eich cabs on the Thomann site. The flat pack cabs will be cut for this round handle but the drawings we are publishing on here will leave the choice of handle to the builder.

Interesting point about the horn, Richard. Yes, it's the P.Audio PH-170. Time for a quick lesson on compression driver specs. The most common type of horn/compression driver combination is the 1". That figure refers to the exit of the compression driver and the aperture at the beginning of the horn. There are also 1.4" and 2" exit compression drivers, which are less common and more expensive. The other figure you see in connection with compression drivers is the voice coil diameter , which is normally (but not always) the same diameter as the diaphragm. The traditional voice coil/diaphragm diameter of a 1" exit compression driver is 1.7 inches. The best examples of these can be used down as low as 1.2kHz. There are two other, smaller diaphragm sizes in use with the 1" exit: the 1.4" and the 1". These are cheaper and don't go as low. Depending on the design, a 1.4" diaphragm is useable down to about 2kHz and a 1" diaphragm to about 2.5kHz. Making the diaphragm smaller allows the manufacturer to reduce the size of the magnet and associated components and to reduce the cost of the product. So you have to be clear what the figure is describing. There is a big difference between a 1.4" compression driver and a 1" compression driver with a 1.4" diaphragm. (1.4" exit compression drivers have diaphragms between 2.5- and 4-inches in diameter). It's not uncommon for manufacturers to (erroneously) refer to their 1" exit / 1.4" diaphragm compression driver as a 1.4" compression driver.

I'd say those costings are about right, Richard, although I'd mention that the £75 for the plywood in our case covered the cost of cutting two cabs accurately to size. If and when we have flat packs in place, I'll try to sort out some special prices for the components. As far as cost is concerned, I'd like to say two things. Firstly, the DIY concept behind these Mk II designs is not to save money. If you want to do that, buy a second-hand cab. However, if you compare the cost of a new Bergantino CN112 or a Vanderkley 112EXT, the Basschat cabinet is substantially cheaper, although admittedly you're never going to match the excellent finish of the Bergantino. More importantly, however, and this is my second point, it's technically a much more advanced design than either of those two. So, build one of these if you want a compact high-end cab and enjoy the satisfaction of making it yourself.

I didn't really set out to make something close to the Barefaced. We've equalled the weight of the Barefaced but have got there by a slightly different route. This design is a development of the first one in this thread but the design objective this time was high performance and light weight. The performance is similar to the system with the Beyma 12 and ceramic Celestion 1" compression driver, but it's much lighter - and obviously costs more. In answer to your question, I believe the Barefaced BB2 uses a Faital Pro HF102 compression driver. Both the ceramic and neo version of the Basschat design use compression drivers with a 1.4" diaphragm - twice as much diaphragm area as the Faital. They are much better compression drivers for our purpose, but the neo Celestion we're using costs twice as much as the Faital in the Barefaced.

Thanks Luke! A fair bit has happened since I posted regularly on this thread. So it's not the Beyma, fleabag. It's the Faital Pro PR320. I think I mentioned it earlier in the thread. It's a more advanced (much greater xmax) version of the driver used by Bergantino in their CN cabs. So it has quite a good pedigree. Its power handling to weight ratio is outstanding.

Before I go into the internals, the crossover and measurements, this is what I came up with for the inputs at the back. The two holes are two inches or so in diameter. They are bevelled just using sandpaper. In fact, I used a sander and some hand sanding to soften the edges all round the cabinet itself. Because poplar ply isn't as hard as birch, it's actually quite easy to do. You certainly don't need to bother with a router. Anyway, I just cut a piece of scrap poplar to size and glued it inside the cabinet to cover the holes Then drilled two holes for the Speakons - and Bob's your uncle. Anyone building the cab can, of course, use a normal metal input panel - but this looks good, costs less, and more importantly perhaps, weighs less. Unless you absolutely need two inputs, I'd advise builders using this arrangement just to fit one, as linking the two Speakons can be quite tricky whether your crimping your connections or soldering them.

Pea Turgh did ask for lots of piccies....... I think you'll all agree, this does not look like a homemade cab. The Ashdown badge probably helps here, but you can buy all kinds of badges on eBay for a few pounds (plenty of Trace Elliot, for example). So if you feel like putting a name on your cab there's nothing to stop you.

The hole for the other horn proved to be slightly too big, but some fibreglass filler came to the rescue. In the drawings, which Ghostbass is very kindly reworking for us as we speak, the horn is located more centrally on the baffle, as that is acoustically the best place for it. I also decided to position it vertically to improve the dispersion to the player's ears when standing up close to the cab. So - the handle is fitted and I've foamed the grille support. This is what is looks like with the grille. Although perhaps I should say, that's what it looks like under flash. So I took the cab outside and took some more pictures.

Since I last posted on this thread, there has been a change of plan on the drivers. I struggled to get the cab sounding right with the original horn and decided to revert to the P. Audio horn I'd used previously. I haven't given up on the asymmetric horn and may revisit it later. However, as the design objective of this particular version of the cab is light weight, I thought that the combination of the P. Audio horn and a Celestion CDX-1415 compression driver would be a good choice. The total weight of the 12" bass driver, the Celestion compression driver and the P. Audio horn is just 3kg. Amazing! So even though we've used 15mm ply for the cab, a proper crossover, and a metal grille, the total weight of the finished product is 13kg. I'd call that a result. It was difficult to get a decent photo of the compression driver with my cheap camera and flash, but it really is dinky - weighing in at just 250 grammes. It's not cheap, but it does have a 1.4" voice coil, and not a 1" coil like cheaper compression drivers.

We resume our little story after the cab has had two coats of Tuffcab paint. Time to sort the grille out. I was fortunate enough to obtain an Ashdown 2x10 cabinet with blown drivers, whose grille proved to be an ideal fit. But first I cut some 15 x 12mm pine strip to make a grille support. A coat of matt black paint, and I had this: The observant among you will have noticed that the port is no longer grey. The grey port looks quite good in actual fact - it's distinctive - but I thought I'd paint it black anyway, as I had paint in my garage that was unlikely to be used for anything else. It worked fine, as you can see. I did have to cut the grille to size with my ancient, trusty metal-cutting shears. .

Altering the compressor setting on my RM500 head also alters the overall volume. I wish it didn't but I just set it to 12 o'clock and leave it.

Wow - that's excellent!

I guess you have to be German to play Bach then.

Yes, I appreciate that, Paul. Sorry for the thread derail but I was asking the question for my own information.

This will sound daft, but what if I just want to record from a microphone into the laptop? I don't need a DAW and don't need to equalise, have separate tracks or anything like that. Just a straightforward recording. Like plugging a mic into a tape recorder and pressing the red button. I have a high quality mic and a USB soundcard with a built-in mic preamp. What software should I use? Does Windows 7 Sound Recorder work?

Just bought a strap from Pete. Excellent service and the item was exactly as described. Thanks Pete!

Sounds good. Shame you can't fit a 100mm port in there, but you should find the 75mm one an improvement on what you have. I wouldn't recommend you keep the small port, but you can always experiment and it's your choice. To get the tuning frequency for the port arrangement you have now, I split the difference between your original port tuning and what a 75mm hole would give you. I wouldn't bet my life on it though.

A bit of patience isn't a bad idea when you have a saw in your hand, Doug.😀 Anyway, I'll try to explain what's going on, although none of this is 100% reliable as I don't have the cabinet here and I'm relying on the accuracy of your 37 litres measurement. When I checked the tuning of your cab with the 50mm port, it worked out at around 42Hz. That's normally too low, and I expect the port wasn't doing very much at all - even ignoring the fact that it would be compressing very early. By cutting an 80mm hole, you have tuned the cabinet higher, to just over 60Hz by my rough reckoning. That would normally be too high, as it would seriously reduce power handling at the lowest frequencies, but the combination of greater port area allowing the ports to do their job more efficiently and the higher tuning frequency means that the ports will now actually be producing useable sound. So you should be hearing a difference, as you clearly have done. When your plastic port arrives and before you seal up the55mm hole - and make sure it's sealed solid - you could compare the cab with the 55mm port and with the 75mm port by blocking each one in turn with a t-shirt or similar, and having a listen. You should then be able to hear the difference between the old and the modified cab. I had the impression originally that there wasn't much free space on the baffle. So my question now is - would there be room on the baffle for a 100mm port in place of the 75mm one? But please don't go sawing any more holes until we measure what you have now. For that we need a frequency sweep generator and some rice. Although maybe you've now had enough DIY.....