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Post by karatestu on Dec 17, 2019 15:22:25 GMT
The area of this resistive "hole" should be about 10 sq. in. per cubic ft. of enclosure volume. So for a 86 litre cabinet ( approx 3 cubic ft) at 10 sq. in (65 sq. cm) per cubic foot i need a hole (don't like the word "vent" ) of approx 190 sq.cm. It is currently 135cm and so not big enough and probably over damped (not porous enough ). Some tweaking required
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Post by MartinT on Dec 17, 2019 15:42:47 GMT
Try also Yello - The Expert and Billie Eilish - Bad Guy for more stonkingly good bass.
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Post by karatestu on Dec 17, 2019 16:00:12 GMT
Thanks Martin. I don't have those albums No streaming here so i will have to purchase them after having a listen on youtube .
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Post by karatestu on Dec 19, 2019 14:31:03 GMT
Pictures or it never happened Here is a pic of the aperiodic vent with foam in that moulds itself to the 130 mm circular hole i cut. I'm sold on this concept. As the 24" x 24" x 2" pressed concrete slab worked so well under the speakers i decided to go one better and add another one...............................on top of the bass cab. Smaller cuboid sits on top of all that . I couldn't keep the bass cab up firing and put the concrete slab on top so it had to go back to front firing for the moment. Well here we go again. This is the best bass reproduction i have heard , period. It's so god damn tight, in fact as tight as a duck's arse in water. Sat here listening with a huge smile on my face it's ridiculous. The use of concrete seems like a real winner for bass cabs - push the cabinet's resonance in to the mid range where it won't do any harm. I don't even have a full concrete cab just two slabs, one under and one on top of my chipboard cubes. I can't help imagining what the effect would be of constructing the whole cab from some of these 2" thick slabs. Could i move it ? It's hard enough just lifting a single 24" x 24" x 2" slab. At least i don't think any bracing will be required Now getting somewhere near the end of the experiments with these particular cabs. Almost time for a prototype of the final design.
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Post by karatestu on Dec 19, 2019 16:42:51 GMT
The few problem tracks that i had as regards bass are good now, really good. So all along the problem was the cabinet vibrating along with the bass. The flattening of the resonant frequency impedance peak (aperiodic vent) has probably helped as well. Makes me feel like i have been chasing my tail a bit . Next bass driver cabinets for the isobaric 12 inchers are gonna be built like a brick shit house. I will build a separate cab out of wood for the 5 inchers and tweeters to keep the overall weight down. I am going to use the design sketched a while back with up firing bass,up and down firing 5" and tweeter firing forward, up and to both sides. Might try a rear firing tweeter as well. Cutting one 12" hole in a 2" thick concrete baffle won't be too bad. I don't want to have to go through that with the top cab and all the holes for 5" and tweeters. Plus having a wooden top cabinet (for it's low resonant frequency) will be better for the mid range and high frequency. That will also keep the centre of gravity down and if both cabs can be moved separately then that will be a lot easier on the old back. 5 inchers will have an enclosure volume far too big (much bigger than the Vas for two drivers) to keep low frequency output as low as i can which i hope will improve the quality of the mid range. Just needs grille cloth across the open areas in the middle to hide the drivers and any screws / nuts & bolts. I think the whole thing will be about 90cm tall which will be just enough to get the tweeters at ear height when slobbed on the sofa. From an aesthetic point of view i dislike the domed mesh grilles that are found protecting drivers (yes i am starting to think about how the things are going to look) If i mount the up firing 5" driver from the inside of the cabinet then a grille will be much easier to do - just a flat circle of grille mesh or cloth flush with the baffle. It is not so easy with dome tweeters as the face plate needs to be flush with the baffle to avoid diffraction. I could use wave guides (Visaton make one for the G25ffl) and so a flat circle of mesh could be used. Only thing is a wave guide increases the tweeters output at the bottom end of it's frequency range and makes it more directional. Might be a problem or might not. I won't know unless i try. Onward
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Post by MartinT on Dec 19, 2019 17:08:34 GMT
Your ideas are coming together, Stu. Any ideas on type of wood, cabinet joints etc.? With the concrete, will you abandon the use of tyres?
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Post by karatestu on Dec 19, 2019 19:00:30 GMT
Hi Martin, thanks for your interest.
There are three ideas i have that are going to have to be separate ongoing projects, using the same drivers though. They are the tyre idea (don't have any tyres at present), the boffle with the whole back panel being a resistive aperiodic vent and the infinite baffle idea with bass manifold under the floor and the rest of the drivers in an enclosure "up top".
For Joining the concrete panels was going to just glue along with rawl plugs and screws. I had an idea to remove some of the central area of each concrete panel just to lower the weight a little but not sure about that yet. For the wooden cabinet i might mitre the joints and glue or do a basic 90 deg joint with dowels and glue. Will probably use baltic birch for the top enclosure.
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Post by speedysteve on Dec 20, 2019 19:23:15 GMT
Try also Yello - The Expert and Billie Eilish - Bad Guy for more stonkingly good bass. Better still bury a friend
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Post by MartinT on Dec 20, 2019 20:38:19 GMT
Oh yes, that's POTENT in capitals!
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Post by karatestu on Dec 21, 2019 9:21:02 GMT
I will have to try that track. Need testing bass to try and highlight any problems with the speakers. How to finish concrete ? The slabs i will be using (recycled of course) are quite rough to the touch. Apparently wood veneer will not take to concrete . That would have been my first choice. I don't want to make the enclosures any bigger than they are so it would have to be thin. I thought about car body filler but that gets expensive. How about a thin mortar rendering ? Will that sand smooth ?
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Post by ChrisB on Dec 21, 2019 9:46:44 GMT
Plaster!
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Post by John on Dec 21, 2019 9:58:20 GMT
This is the track I use to test out bass You want to also hear the piano and drums clearly in the mix. There a lot of detail and the bass can take over if you do not have the right balance
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Post by karatestu on Dec 21, 2019 10:53:07 GMT
Plaster, of course that would work and be suitable for sanding. Thanks Chris. Would need painting then or maybe i could wallpaper them Others i have thought of are fabrics (felt maybe ?), leather, very thin black perspex (will give it a look of NVA), very thin sheet metal (anyone for polished copper ? ).
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Post by MartinT on Dec 21, 2019 11:11:09 GMT
Plaster will give you an even surface for any finish you like.
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Post by ChrisB on Dec 21, 2019 11:13:48 GMT
Paint the plaster, then give them a coat of polyurethane varnish for a shiny and tough finish.
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Post by karatestu on Dec 21, 2019 15:54:25 GMT
Thanks for steering me on the right path. Plater, paint and protective coat it is then. I can cover any cracks between the panels with plaster. Should come out looking good i think. Bought two more 5.25" mid bass drivers today for the upper enclosure. Only £22 inc delivery . I have bisonkit and plastidip already to dope them.
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Post by karatestu on Jan 28, 2020 9:10:07 GMT
A few things have happened in speaker land no i haven't melted them. Built an upper enclosure out of fluted softwood decking boards and the usual scraps of recycled chipboard. Put some bracing in made out of old garden tool shafts - nice hardwood. There are cut out for down and up firing 5.25" mid bass and up, front, in & out firing tweeters. Had to buy two new 5" drivers at £10 a pop - ludicrously cheap. Masked them up for spraying. A couple of coats of plastidip to start off with.
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Post by MartinT on Jan 28, 2020 9:21:32 GMT
You're certainly brave with driver treatment - mind you, at that price it's worth experimenting.
I've gone as far as surround replacement (very successful with the Gale 401s) but not doping the cones.
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Post by karatestu on Jan 28, 2020 9:45:17 GMT
Hi Martin. Brave ? Yes probably. When i first started doping cones it was rather daunting but after a while the fear lifted and as you say at £10 each then nothing lost. Being from the RD school of hi fi design then i try lots of wacky ideas some of which i think he never even tried. It is possible to ruin a driver by putting too much on and it is very hard to reverse (not impossible). Best to do in small stages and then listen. Add a bit extra if required. I have even sprayed the metal dome of a mordaunt short tweeter with plastidip. It sounded better after believe it or not . Not all have been success stories though. Tried doping a continuous aluminum mid bass cone (no dust cap) with bison kit contact adhesive (as used by RD on his cube designs). I couldn't get it to sound right and kept adding more and more until i realised it was a lost cause. I later found out metal cones are impossible to dope successfully when not using any electrical crossover filters (inductors). Having no dust cap made the situation even worse. Luckily when i soaked the dope with white spirits for a couple of weeks, it all came off and the driver was usable again.
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Post by karatestu on Jan 28, 2020 10:50:54 GMT
I used what ever tweeters i had. A visaton G25ffl (the original tweeter) along with a 1" metal dome from my B&W P4 speakers, a 1" metal dome (doped) from some MS902S speakers and a cone full ranger pulled from a broken portable cd player. I wired them all in series with two 3.3 uf Russian K75 paper in oil capacitors in series to give 1.65uf. Isobaric bass is up firing and the two 5 " mid bass are up firing and down firing. I listened and listened and listened. The only doping on the new up firing 5" is two coats of plastidip. I was overjoyed with the result but there were a few wrinkles to iron out.
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