stevie

For those who like to roll their own, here's a layout for the crossover. Read together with the circuit diagram I posted earlier. I think that building a crossover might have been a step too far for a lot of people last time. So.....this time, I'm prepared to build and test a quantity of crossovers to get the ball rolling. All you'll have to do is screw the board down inside the cab and connect the wires. The six connections you can see on the bottom of the board are screw connectors for the wires. I'll precut the wires to size and crimp the connectors so that you won't have to solder anything. I'll even include a Speakon. As long as you cover the cost of the components, I'm happy. I'll do this for the first ten. Then you're on your own. If the flat packs work out, I'll be using a local CNC company. So I'll be able to collect and send a flat pack and a finished crossover out together to those wishing to build them, which will save on carriage. Building a crossover on a plywood board is a bit of a time consuming exercise. So if we have anyone out there who can produce fibreglass PCBs in small quantities (milled would be OK), please make yourself known.

It's nice to see some community input. Thanks, Richard. However, it looks as if I may have cracked the flat pack issue. I don't want to speak too soon, but will post more details when I have firm details.

That got me really excited this morning, Luke. I researched it and it looks like the 18mm version of that ply would have a similar stiffness to the 15mm poplar we're using at the moment. Although there's a cost penalty, it would cut the weight of our cab by 3 KG. That's a lot! So I phoned them up. The material is made by a Swiss company and, according to the UK supplier you mentioned, they have decided not to export to the UK in the future. They weren't sure why. Once the UK company has sold off its existing stocks, you won't be able to get hold of it any more. Interestingly, they said they were trialling an alternative plywood. That one is actually a bit stiffer than poplar, but would still cut the weight of our cab by about 1.5kg. I'm going to keep my eye on that, but I'd rather not take the risk of using an unkown type of plywood for the time being. All good information though.

Well the Barefaced does have the advantage that it has been designed specifically for bass, but if I were buying a powered cab for bass and could afford that kind of money, I wouldn't think twice: I'd go for the RCF. What about you?

I'll make some more measurements and post them tomorrow to give you all a better picture of how the cab performs. On the matter of flat pack cabs, I know that some of you are keen to get hold of some, but despite spending a lot of time on it, I'm struggling to find a competent cab builder. The ones I've been talking to either don't seem to know what they're doing (one was unable to source poplar ply!), or are so slow in responding to messages that they give the impression of being very inefficient. There are still a few possibles left on my list, but I'd prefer to deal with a company that's not half way across the country. The other option that's open to us is to have the CNC plans prepared so that any competent woodworking company with a CNC machine can work with them. Phil tells me that there are some Basschatters who produce those files for a living. If so, I'd appreciate if you would help us out. Marco (Ghostbass) is busy preparing technical drawings of the cab and I can supplement this with drawings of all the components, hole sizes, etc. that you would need. Can anyone help?

Here's the circuit for the crossover:

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 refer to their 1" exit / 1.4" diaphragm compression driver as a 1.4" compression driver.