nekomatic Posted May 19, 2021 Share Posted May 19, 2021 I have a 1x12 cabinet that my dad and I (well mostly my dad) built together many (many) years ago. It's made of 18 mm ply with all internal edges battened and all joints screwed and glued. That makes it pretty sturdy but there's no internal bracing and currently no damping except for some bituminised felt stuck to the back panel, for some obscure historical reason. Allowing for the speaker the volume is about 50 L and it has a slot port that tunes it to about 70 Hz. It was always intended for bass but for some further obscure reason ended up with a Fane guitar speaker which is very loud but doesn't sound great. Driving it with a signal generator sine wave it feels like the back panel resonates a little bit at 55 and 110 Hz and it sounds like there's another slight resonance at about 300 Hz. One final bad choice is that I sprayed it with grey Hammerite without adequate priming, so it really needs properly refinishing too. It's time to sort all this out and because the volume is close to the Basschat 12" design, and I reckon the full-range 'hi-fi' approach works for me, my current plan is to: block the slot port by gluing in an 18x18mm softwood strip and fit a 125mm tube port instead as per the Basschat design sand it back to the wood and paint it with Tuff Cab replace the existing handle with inset handles top and bottom, so it can easily be placed upright or sideways line the inside with acoustic wadding replace the Fane driver with either a Beyma SM212 or a Faital Pro 12PR320 probably, fit a P Audio PH-170 horn, Celestion compression driver and crossover as per the Basschat design depending on cost, get a grille made to cover the whole front face. Have I missed anything? Is it likely to be worthwhile trying to add any bracing and if so where? The back panel is glued, so the only access to the inside is through the driver hole... Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted May 19, 2021 Share Posted May 19, 2021 If you want an SM 212you'll have to find a used one, they stopped making them. The good news is that you can use a Beyma 12CMV2 and they are cheaper. You should be able to copy the bracing of the Basschat design by cutting strips and glueing them in place. Fiddly but achievable. Quote Link to comment Share on other sites More sharing options...
stevie Posted May 20, 2021 Share Posted May 20, 2021 Inset handles are a good idea, as that existing handle makes it awkward to put an amp on top. I don't understand why you'd want one on the bottom though. You can indeed fit bracing retrospectively as Phil suggests, although you'll probably not need quite as much as in the Basschat design because you're working with heavier and thicker material. A central figure 8 brace is always a good idea to start with. Then it's suck it and see. I suspect you'll need a vertical brace on the back panel behind the driver and a vertical brace between the horn and the port on the baffle. Quote Link to comment Share on other sites More sharing options...
nekomatic Posted May 20, 2021 Author Share Posted May 20, 2021 Thanks both! I'd forgotten about the new lower-cost Beyma. Would that need a crossover redesign compared to the SM212 though, assuming the SM212/CDX1-1445 crossover circuit turns up? Blue Aran claim to still have two SM212s left in stock... My thinking for what it's worth is two handles on opposite ends would make it easier to lift the thing in and out of a car boot, for example, or to position it on its side (compared to the photo). A vertical brace on the rear panel sounds sensible and should be straightforward to fit - I'm pretty sure I can get a full height piece in through the driver hole. By 'central figure 8 brace' do you mean something like brace K from the Basschat cab diagram? Would you advise cutting it from ply as in that design, or can I assemble it from battens in situ? Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted May 20, 2021 Share Posted May 20, 2021 You won't get the figure of eight brace through a 12"cutout. I've used strips of ply in the past to do this but use what you have. I'd use the SM212 if you can get hold of one and are happy to pay the extra. Everything was designed around it and it is a better speaker than the 12CMV. Quote Link to comment Share on other sites More sharing options...
nekomatic Posted May 24, 2021 Author Share Posted May 24, 2021 Thanks to Phil I have a line on an SM212 and have identified where to get everything else I need… except for the PH-170 horn flare. Blue Aran have confirmed they won't be getting more stock until September(!) and the only place I can find who stock it and will ship to the UK is in Germany. Is there a suitable alternative to the PH-170, or is the match between driver and horn critical enough that I should obtain one at any cost? Quote Link to comment Share on other sites More sharing options...
stevie Posted May 25, 2021 Share Posted May 25, 2021 I have a spare you can have for the cost of postage. I could get it off to you at the weekend. 1 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted May 25, 2021 Author Share Posted May 25, 2021 That would be amazing thanks! I'll send a PM. Quote Link to comment Share on other sites More sharing options...
nekomatic Posted June 17, 2021 Author Share Posted June 17, 2021 Right… My first task has been to scrape, dissolve and sand off enough of the bituminised felt gunk from the rear panel to bare wood so that I can glue a couple of braces there. If I get my hands on the idiot who read somewhere to use that stuff and thought it was a good idea… oh. Meanwhile I've got all the bits now, and looking at where they'll go on the front panel it's going to be pretty tight for the horn: I don't want to fit it and then find that I've got a problem with how to fix a grille on the front - I'm thinking I may even need to cut the front of the horn down a bit along the two sides parallel to the long axis of the ellipse. So I'm going to get a grille made before I start cutting any holes. Unfortunately the front recess isn't deep enough to use a flat grille like the Basschat design, so instead Mark at speakergrills.co.uk has quoted me to make one with folded edges (in powder coated steel - he doesn't powder coat to order for small quantities any more, due to cost, but says he's got a pre-coated offcut he can use and will touch up any cracks along the folds) which is not super cheap but I think it's the right solution to both protect the speaker and look decent. I'm thinking I'll add 'ears' to the cab at each corner to effectively extend the recess and protect the grille corners, and I've got some oversize plastic corner protectors which I'm hoping will make the thing look reasonably professional. So next stop is to await the grille, make final decisions about positions and then (gulp) get sawing… 1 Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted June 17, 2021 Share Posted June 17, 2021 It looks like your baffle is just screwed on and could come off easily. You've also got to fill the slot port from the looks of it. I would be tempted to cut a new baffle and place the speaker further down to make space for the horn if the baffle is detachable. It might work out quicker than having to do a lot of fiddling around. Another option would be to fit the port on the rear panel, sound wise it would work just as well there. 2 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted June 17, 2021 Author Share Posted June 17, 2021 The baffle is definitely glued. I’m going to glue in the bracing and a strip to block the slot port after I’ve cut the various holes and sanded the existing paint off, because there’s no point sanding the bits that I’m going to cut out anyway! Good point about rear porting - space for the port on the baffle isn’t an issue but it would mean I could stop worrying about whether to try and paint the port tube. I guess it would also improve the rigidity of the baffle? It wouldn’t have the grille to keep lost objects and mice out though. Quote Link to comment Share on other sites More sharing options...
JohnDaBass Posted June 18, 2021 Share Posted June 18, 2021 (edited) 11 hours ago, nekomatic said: Good point about rear porting A forward facing port is generally considered the most optimum but there are many cab designs with rear ports as the low frequencies are omnidirectional. One of the draw backs of rear ports is positioning close to walls on small performing spaces. I would recommend considering a side mounted port, I was really surprised how my BF One10 sounded when laid on it's side with it's bottom facing port pointing sideways. It was on a stand not on the floor and having tried both positions the side fireing sounded best to my ears. Edited June 18, 2021 by JohnDaBass 1 Quote Link to comment Share on other sites More sharing options...
Muzz Posted June 18, 2021 Share Posted June 18, 2021 IIRC, someone who knows much more about these things told me a while ago on here that the wall thing would only be an issue if you were verrry close (like, inches) from the wall - down to the wavelength of the lower notes... Quote Link to comment Share on other sites More sharing options...
nekomatic Posted June 18, 2021 Author Share Posted June 18, 2021 57 minutes ago, Muzz said: down to the wavelength of the lower notes... The low notes on a bass have a wavelength of over a metre though - even for their second harmonics. Quote Link to comment Share on other sites More sharing options...
Muzz Posted June 18, 2021 Share Posted June 18, 2021 Maybe not that (80hz having a wavelength of 14ft, so it's not that), I forget the precise details and I can't find the exact post, but it was Bill Fitzmaurice who mentioned it; a few inches from a wall is all that's needed to negate any effect, ports being omnidirectional and all that... 1 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted June 18, 2021 Author Share Posted June 18, 2021 If Bill Fitzmaurice said it, I believe it. I think I’m probably leaning towards the front port though, if only for the benefit of the grille protecting it. 1 Quote Link to comment Share on other sites More sharing options...
Muzz Posted June 18, 2021 Share Posted June 18, 2021 Yeah, despite all that, I've always favoured front ports...probably cognitive bias...mind you, I've never been that squeezed up against a back wall... 😐🙂 Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted June 19, 2021 Share Posted June 19, 2021 (edited) 20 hours ago, Muzz said: IIRC, someone who knows much more about these things told me a while ago on here that the wall thing would only be an issue if you were verrry close (like, inches) from the wall - down to the wavelength of the lower notes... What you remember is correct. the problem isn't one of directionality, sounds at those frequencies are omnidirectional and also not a problem of phase cancellation. If you ram the port hard against the wall it would block it. Slightly further out it could create some back pressure on the port but further out even by a few cm the effect will disappear. For downward facing ports there's normally a small adjustment to the port calculations to allow for that configuration and using one side facing would change the tuning away from the designers target, as would changing the length of the feet but probably not by much. you really don't need to worry about this but if anyone is interested airflow around the port ends is affected by the termination. The internal end of the port is assumed to be in free air and the external one flush with the baffle and only radiating into 180o Design software like WinISD makes allowances for this in it's calculations but this is usually only a fraction of a cm. That might only change the tuning by a few Hz and this is of a similar magnitude to the sorts of manufacturing spread of speakers or the inaccuracy of some of the published specifications of speakers. So yes it's there but not usally significant. Even the output impedance of the amp and the resistance of your speaker leads can alter tuning. By and large these are not huge issues in practice but with the Basschat designs we check and sometimes adjust the tuning of the ports when we build the prototypes and those are what we publish. As a rule of thumb I'd say that if you can slide your hand down the back of the speaker to pug in a lead you are comfortably far enough away from the wall. Edited June 19, 2021 by Phil Starr 1 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted July 9, 2021 Author Share Posted July 9, 2021 (edited) Progress on this has been delayed by Various Things. Apologies to anyone who was on the edge of their seat. Anyway, the grille arrived and unbelievably, I had transcribed the dimensions wrong and it was five centimetres too long for the cabinet. Measure twice, cut once, kids. Even more unbelievably though, using only the Dremel, the cheapo workmate thingy and two bits of wood, I managed to correct it such that I honestly believe only I will ever know it was wrong. Well, and now you lot will, obvs. Anyway I am hoping this was the obligatory screw-up of the project and everything else will now go smoothly 😄 and also half thinking that I could have saved a few quid by just buying the perforated steel flat and doing all the cutting and folding myself. Next time… I am assuming that the grille needs to be at least Xdamage in front of the rest position of the speaker cone plus a bit for safety. The datasheet quotes Xdamage as '27 mm peak-to-peak' so I assume that's 13.5 mm from rest. Here it is on the mounting blocks in approximate position: When it comes to mounting this properly, would people fix the blocks permanently to the baffle then screw the grille on to that, or screw the blocks to the grille then screw that assembly to the baffle? In the next instalment I plan to have cut some cutouts… Edited July 9, 2021 by nekomatic removed extra image file Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted July 9, 2021 Share Posted July 9, 2021 Yep 13.5mm should be fine. I'd probably make up a 'frame' of battens all the way round the circumference of the baffle, fixed in and then screw the grille to that but anything that will hold the grille firmly enough to prevent rattles is good enough. 1 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted July 9, 2021 Author Share Posted July 9, 2021 I’m pretty sure the space I need for the horn prohibits running a batten all the way around the baffle, but I’ll have another look at the options before I commit to anything. Quote Link to comment Share on other sites More sharing options...
Phil Starr Posted July 10, 2021 Share Posted July 10, 2021 10 hours ago, nekomatic said: I’m pretty sure the space I need for the horn prohibits running a batten all the way around the baffle, but I’ll have another look at the options before I commit to anything. The advantage of a DIY cab is that you don't 'have' to do anything so if wht you've done works in holding the grille secure and no rattles then it's fine. It looks from your pictures as if you opted for the folded grille. that will give it more rigidity which will help. Quote Link to comment Share on other sites More sharing options...
nekomatic Posted July 16, 2021 Author Share Posted July 16, 2021 I cut the apertures for the handles, using a hole saw to start off two opposite corners (as I didn't have a drill that makes a big enough hole for the saw blade) then cutting 'freehand' with the cordless saw - I didn't know if this would work but tried it out first in the middle of one of the bits I was about to cut out and it was fine. Next, the fittings for the speaker. The original speaker took larger bolts than the Beyma, and on a slightly larger pitch circle diameter, and the aperture itself is a bit larger than the Beyma needs, so I decided it would be a bit marginal trying to put new T-nuts into the back of the baffle itself, apart from the issue of whether I could hammer them in properly when the baffle doesn't come off. So I cut short lengths of batten and fitted the M5 T-nuts to those, then glued the battens to the back of the baffle. To get them in the right places, not wanting to get wood glue anywhere near the speaker, I used a sheet of A3 foamboard I happened to have to make a template from the speaker mounting holes: I then marked up the positions on the baffle using the template, and drilled four of the holes using the Big Gator drilling aid thing - I can't remember if this was recommended on here or elsewhere, and it does seem expensive for a lump of metal with a few holes in it, but it did do the job of enabling me to drill exactly vertical holes very close to the edge of the aperture without problems. The four previous mounting holes overlapped where the new ones needed to go, so for those I just had to cut notches out of the aperture. Here's the inside view, also showing a handle cutout: Glue dry, template removed, deep breath, try mounting up the speaker… and it fits! Phew! Next up, fitting a brace across the baffle just below the speaker, and then making the holes for the horn, port and connector… 3 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted July 29, 2021 Author Share Posted July 29, 2021 I MADE HOLES IN IT Horn aperture is four holes with the hole saw, joined up with the power saw. Port aperture is cut with the 127mm hole saw (I've got this set which I don't think could possibly be any cheaper, but it has worked.) This was a bit necky as my mains drill has no speed control, so it's flat out or nothing! Space on the baffle was even tighter than I expected, so the port aperture has ended up taking a tiny bit out of the transverse brace, and I couldn't cut the right-hand edge of the port aperture so just sanded down the pointy bit with the Dremel. It looks terrible, but the horn covers up my shoddy handiwork nicely… I may need to drill new fixing holes in it though, as the lower two existing ones end up right on the edge of the baffle, where the join with the batten to block the slot port will be. Port aperture is slightly too small for the tube so will need some sanding (as if there isn't enough to do already) but I guess better that than too big… Last of all, one on the back for the connector plate. I put it in the corner so it looks OK with the cab in either horizontal or vertical orientation, and I made it round because that was easiest, but actually I think it looks kind of cute: 3 Quote Link to comment Share on other sites More sharing options...
nekomatic Posted August 1, 2021 Author Share Posted August 1, 2021 Some bracing - I'm going to stop there for now and see how it performs, I can add more if it seems like anything's vibrating and the slot port blocked: 1 Quote Link to comment Share on other sites More sharing options...
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