| mulletdude |
Dont know if this really goes here but.
I am planning on boilding a huge subwoofer i have most of the materials but the one thing i am wondering about is isthere a formula or something for figuring out voice coil windings anr dimensions as well as layers any help would be appreciated . also i was wondering what gauge of wire to use because i most likely will be firing a couple of thousands of watts through it. any feed back as to how to figure out a box size would be appreciated as well |
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| MJL21193 |
Hmm, that's interesting. I had a similar idea. I guess it's a case of great minds thinking alike! :)
What would you use for the magnet and pole piece? How big of a woofer were you thinking?
Voice coil winding would depend on the diameter of the former, whether you were going overhung or underhung and the Re.
For example: It would take approx. 30 turns of 28 gauge wire around a 6" former to equal a 3.5 ohm Re. This winding would be ~10mm high in a single layer.
BUT for 24 gauge, it would be three times as much - nearly 90 turns and about 46mm high in one layer. The power handling difference would be 2.5 times better for the 24 gauge. |
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| Mikey p |
any feed back as to how to figure out a box size would be appreciated as well
Box size is determined by the parameters of the subwoofer. |
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| kelticwizard |
| quote: | | I am planning on boilding a huge subwoofer i have most of the materials but the one thing i am wondering about is isthere a formula or something for figuring out voice coil windings anr dimensions as well as layers..... |
There seems to be a contradiction here.
On the one hand, you seem to be saying that you are prepared to build your own subwoofer driver-the thing which has the cone, basket, voice coil, magnet, etc. Those are generally manufactured in factories, not made by hand. I'm not sure that building one of those by hand is possible. But if it is, it would be by a very, very advanced audio person.
On the other hand, you seem to not know how to build an enclosure to suit the driver, whether there are formulas, etc. There are formulas, and we would be glad to show you how to use them. People buy subwoofer drivers all the time and build the proper sized enclosure to suit it, and we help them here on the forum. But if you are just getting started doing this, how is it you are in a position to build the driver itself? That is very, very advanced audio work. |
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| mulletdude |
| i can't find the links right now and the e-bay auction is over but ive seen a couple of giant subwoofers built by the average joe like you or me and ive also seen one built by MIT. and its really not that complex because all you need is a cone which i can make in like 5 minutes. a voice coil all i need to do is buy some wire and make a former. and you also need a magnet i have several that would suit this perfectly. as well as a speaker surround not very hard to cut up an old tractor tire tube now is it? and a box which shouldnt be to hard to figure out good sizing. now the only reason i am asking for advise on this is because i am not some empoyee at behringer or pioneer audio and i do not derserve criticism as i am a very ambitious 16 year old bass junky. and since subs deal with lower frequency's they tend to be quite forgiving with minute imperfections. and i will probably make it overhung with the magnet centered in the former, speaking of which what would be best to make the former out of? tin or steel or the like. my magnet is likely about 4 to 5 inches in diameter i scabbed one from one of my two ten inch subs i blew up. but thanks for the input so fat. keep em coming. |
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| djk |
Let's take a poll:
Troll ?
0r
Candidate for the Darwin Award ?
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| paulspencer |
| If you want the novelty of actually making a driver, sure go for it. It could be fun. Are you expecting it to be more than that? If so, count on needing something more than tractor tires! You would be better looking for actual parts designed for subs like you want to build. Spiders, surrounds and so on. |
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| Moondog55 |
Check-out "MythBusters" for the use of a truck tube as a surround, but seriously Perhaps you need a slightly bigger magnet, as the driver cone area gets bigger it gets much heavier REAL FAST and the cost of big magnets is quite high.
There is a 'Bespoke' speaker builder i:e driver not boxes here in Reservoir who says its no problem up to 36inches and how many thousands of dollars are you wanting to spend.
Attila recomends a 4inch voice coil minimum preferably 6 and has some idea of how to build from scratch.
Cheaper to buy but a really good way to learn, ignore the critics and have a go |
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| moray james |
| why don't you make this easy and build yourself a full wall size electrostatic sub woofer? You will only need one high voltage supply and a bunch of transformers to drive the panels. You can use one mil mylar film diaphragm material (cheap and easy to find) and 35% open perforated 1/8 inch hardboard for the stator panels. Use contact cenment to apply tinfoil on the outsides of the perf board(to make the stator conductive (don't touch these when the speaker is playing). Build them in floor to ceiling strips that will fit across your studs and space them off of the wall a foot or so (on a sub frame) install fiberglass behind. A diaphragm this large moving forward just 1/16" at the speed of lightning will blow you out of your chair and put the Maxell commercial to shame. You tube here you come. Peter Walker of Quad did this in the fifties or at least he wrote about it in a technical article. You could never build a dynamic woofer to equal this and it is all very low tech to impliment. Rock on. Be aware this will probably cause structural damage to your house. No magnets no machine work no box and it breaks down to easily transport when you move into your college dorm. That might come sooner than you had planned. |
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| kelticwizard |
Believe it or not, I was not trying to criticize you, just wanted to make sure you knew what you were getting into. For instance, this business of using a tin can as a former. In commercially produced woofers, the clearance between the voice coil wire and the slot it must travel in is about five thousandths of inch, I believe. So if you are going to use a ready-made magnet, the chances of you finding a tin can exactly the right size is not good. If you make the slot larger to give you more clearance, you lose efficiency very quickly.
My suggestion is to take an already existing driver, (say 12 inches), leave the voice coil and magnet system intact, figure out how to expand the basket to a 30 inch circumference, cut away the existing cone and replace it with a 30 inch cone attached to the same voice coil the 12 inch cone used to be attached to.
I have an idea on how to make an inexpensive 30 inch surround, if you go that route.
I think you would have a better chance of success that way.
Good luck. |
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| kelticwizard |
PS: Here is a link for a fellow producing a field coild loudspeaker by hand. A field coild loudspeaker differs from a regular speaker in that instead of a permanent magnet, it uses an electromagnet instead. But the page might give you some idea about what is involved in starting from scratch with such a project.
http://home5.inet.tele.dk/f-hammer/index.htm |
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| just a guy |
| quote: | | ...why don't you make this easy and build yourself a full wall size electrostatic sub woofer? |
Hi Moray. Easy? I don't think so. Interesting? OH YEAH!!! But the chances of making an actual functional electrostat (not to mention a wall sized version) on your first try are little to none.
Back in college I built an electrostat panel for a school project. (Fully documented report included ~ 12 pages or so on electrostat history, theory and a breakdown of the build with pics and such AND A WORKING (albeit somewhat melted) FUNCTIONAL MODEL. I got an A, but so did the guy that wrote 2 handwritten double spaced pages on why he liked electric cars, along with a handdrawn pic of him driving an imaginary electric car. (Apparently profs have better things to do than READ assignments before grading them)
ANYWAY... it was about 150 sq inches and was made from...
- perforated metal (as used inside grain dryer bins) for the outside panels (called stators IIRC?)
- saran wrap diaphragm, lightly coated with dishsoap to make it conductive (used intentionally instead of proper conductive plastic to illustrate that this could be done for essentially $0)
- plastic strips for spacers to space the diaphragm a safe distance from the outside panels (calculated by voltage vs excursion)
- an signal generator, whose output was channeled through an old console tube amp output transformer (backwards) to bump the output signal voltage up to ~ 600V (IIRC)
- the high voltage output from an old black and white 19 inch tv provided the constant current to charge the diaphragm (this was controlled by using a variac to fine tune the high voltage charge from 0 - 15000V (IIRC)
It was an incredible pain in the *** to assemble.
During testing, we started with low voltage to the diaphragm and turned it up steadily to increase sensitivity. By the time it got loud enough to hear reasonably well, the high voltage started arcing between the stators and the diaphragm, making large holes in the diaphragm (but it still works until you burn a large percentage of the diaphragm).
OK, so even a tiny panel was hard to make, and did not perform well, even in the target frequency range (1000 hz IIRC) based on panel size and spacing between diaphragm and stators.
Now, to extrapolate this to subwoofer size, the panels individual sizes have to be very large to make low frequencies efficiently (making it harder to assemble and meaning that the stators will have to be stronger than perforated wood) and the stator/diaphragm spacing has to be large(ish - compared to the small full/wide bw models you see for sale) to allow for low frequency excursion. The larger you make the stator/diaphragm spacing, the more voltage you must apply to overcome this spacing distance. The more voltage you apply, the more risk there is in high voltage arcing between the stator/diaphragm. The "xmax"/high voltage compromise is a particularly interesting challenge.
Everything has to be PERFECT (in size and construction) in order to get decent efficiency within the desired bandwidth without melting the diaphragm.
And even if everything is perfectly designed and constructed, displacement still rules. No matter what you do, you can't make the diaphragm move more than a few mm, so even a full wall panel won't have much more excursion than a handful of super xmax conventional drivers in IB.
Believe me, I've thought about making electrostat subs, and for the diy'er of average abilities (like me) it's not worth the time, money or frustration.
OTOH, if done properly, you are correct that it would be MINDBLOWING. But keep in mind that it would have to be truly IB, in that your electrostat panel wall would have to be wall to wall, floor to ceiling with NO spaces in between, and would probably require some massive framework to hold it all in place.
Also, keep in mind that it is INCREDIBLY DANGEROUS to have massive high voltage panels exposed in your listening room. I believe the commercial electrostats all have some type of protective high voltage coating on them, something that I did not get far enough to investigate. BUT... if you have trouble with a male cat spraying your house and marking his territory, I GUARANTEE this will never happen more than once if he sprays your electrostat wall (which is essentially a sandwich of several hundred volts on the outside and several thousand volts inside).
Fun, but not practical. (Unless you have the time/money/desire to design and build a cost no object ultimate IB that will probably catch fire at least a couple times during inital prototype testing)
BTW, please link to the Quad tech article you mentioned, as this is fascinating to me, if not feasible.
Also BTW, I have thought up a way to make large panel (sub)woofers with high sensitivity and without all the nasty high voltages. PM or email if interested, since it's not conventional and I don't like being laughed at publicly. |
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| moray james |
cause it's bigger than yours and it would so work! You could use aluminum bug screen instead of tinfoil. That would save you having to poke out (the foil) at each hole on the stator panels and then clean out the hole of any foil and it would have the added benefit of keeping any bugs out of the inside of the speaker. You could insulate the screen (or foil) with a paint roller and a half dozen coats of latex paint (you are on your own to keep the screen over the holes open You are the one who wanted the insulation so that part is up to you). That ought to make it fairly safe but this will not be a set of Martin Logans. Sorry but you are wrong about this it can be done.
This method of construction has been done and published in Audio in the early sixties. Peter Walker's article was in the Seventies in three parts in Electronics and Wireless World magazine (UK). This is not a set of plans for Jr. it is the suggestion of an idea that is a lot more practical than what he had in mind to begin with, some assembly required some thinking will be necessary. Operator must be awake while running dangerous equipment. Doh! These could be bone crushers!!! Even if he has a drillpress in the basement and a grinder in the garage this "I am going to build the worlds biggest Hartley" is not going to fly. Take a drafting class and draw a plan first. See if you can pass a drafting class first.
You do make a very good point though to which I whole heartedly agree. Build a small one first. figure out all the things that you may not have considered or that arise for unforeseen reasons. When you can build a little one then you can plan on a trial run of a big one. I built a mars lander when I was a kid but the box got rained on in the back yard one night or maybe it was the sprinkler I don't know. Hey the kid can drive a tractor so who knows what the heck he is capable of doing? Dennis can't you help me here was I wrong to try and help? Man that moon lander would have been great I was only a day away from lunch. oooo i feel dizzy they won't ever let me fly, once you throw up they won't let you fly....... |
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| just a guy |
FWIW I did use several coats of thermal paint on the outside of my stators, but have no idea how well it worked as electrical insulation since there is no way I was going to touch it while juiced up.
Anyway, I LOVE the idea in theory. But it's really tricky in practice. For example, it's really hard to get the diaphragm stretched to the correct tension, and it must be absolutely uniform across it's surface area. The diaphragm has to be mounted COMPLETELY flat, which sounds obvious, but is not as easy as you might think, with tiny deviations ultimately leading to less potential voltage and less sensitivity. YES it is possible, but NO it is not easy at all.
There is a reason you don't see any commercial units that even try to make any bass. The reason is that the individual panels that make up the whole panel are sized based on the desired frequency bw. The lower you want to go the larger the individual panels must be, which means that there is more diaphragm surface area with less spacers. I don't remember the math now, but even a 30 hz panel (not even really low enough to call a subwoofer) would be rather large and have spacers spread wide apart. Due to the wide spacing between the supporting spacers I still maintain that hardboard is not nearly strong enough for the stator material. Can it be done with wood? Yes. Will the wood flex? You better believe it. The lower you need to go, the further the supporting spacers will be spaced, the weaker the finished panel becomes. The far superior choice is perforated metal, and it's not THAT expensive, considering it's structural superiority.
Anyway, like I mentioned, there are much easier (and safer and cheaper) ways to make a radiating panel speaker (or subwoofer).
Having said all that, I'd love to give it a go if you'd care to fund the experiment... |
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| myyykmeister |
Hey, here's an idea I want to try sometime for about $3.5k. It would only work if you had a smaller room bordering a larger "listening" room which had one side essentially open (like several (not glass) doors or maybe a porch). Try to make sure there are no windows in the rooms, so that they aren't removed later. You'll have an easier time if the rooms have concrete walls. People have probably already tried similar ideas:
Buy a whole mess of the cheap (like $60.00 Pyramid or whatever) 15" car subs, same model, and put like 32 of them in a wall IB-style, but make the back space of such size so that each sub "sees" maybe 15ft^3 (.4245m^3, or 425 l) of air volume. If you use more than 32 drivers, you'll need to adjust the following dimensions accordingly. This would be a room (that you didn't need anymore) about 8 x 8 x 8 feet (2.44 x 2.44 x 2.44 m). If not reinforced concrete, then reinforce this room very well first on all walls/doors and between walls and floor/ceiling, using up 1/15 of the room's volume with overlapped double 3/4" MDF and wall-to-wall / floor-to-ceiling studs every 18 inches! Screw all the studs together where they cross, as well as to the wall paneling at each end.
But It won't really be IB, since the volume per driver is comparatively small, definitely not infinite. Also you are going to port this smaller room to the larger, open room by putting two 30" x 8" long sonotube ports/room entrances in amidst the woofers. Center these on the wall with about 2' between them and surround them with drivers. Still, the drivers (which won't come with t/s specs, btw) might not like such a large volume. You won't want to measure the specs for that many woofers, nor bother to separate the reinforced room into 30 separate subenclosures. But that's OK, since you will significantly derate the driver's actual power handling of 150 W continuous program per driver, let alone their greatly exaggerated claimed rating of 1 kW per driver. This derating will reduce distortion as well.
Try using 50 W per driver, for a total of 1.6 kW. Wire them in identically balanced series/parallel combinations to properly load an appropriate pro amp(s) of your choice that you have purchased broken on eBay and subsequently repaired, beefing up the filter capacitors in the process. Be sure not to get any driver's polarity reversed, or that driver will be destroyed. Nor should you allow one amp channel to put out more voltage than the other. Oh, you might possibly need a bit of parametric eq to smooth/shape response a bit, and definitely a subsonic filter below 12 Hz. Also hook up a high-powered set of floor speakers or possibly some powered PA speakers that you happen to have on hand for the rest of the frequency range, Set them for optimal stereo imaging before you turn on the bass, because you won't be able to do it after. :wave2s: :hot: Turn you cellphone to silent so it won't disturb your listening experience. Now play some good pipe organ music that goes down to C0. Start at low levels while watching how things go, including the woofers in your mains and your body. If you can, gradually crank it up to full power. I'm not going to try to explain what this setup will do to your relations with your neighbors.
Extensions:
After this system was proven, I would probably be comfortable going up to maybe 100 W per driver, assuming no displacement overload.
If you have many more tens of thousands of dollars floating around unused, you could always install high-end drivers of your choice and bigger/more amplifiers. Buy more drivers than you need. If you match the drivers carefully to each other and to the air volume, you could probably run them much closer to their ratings, still without having to give each driver its own subenclosure and port. Maybe a handful of subenclosures would be enough to adequately isolate the several general ranges of driver parameters you identified. If you use subenclosures of more than one driver, make sure only one amp channel is feeding all the drivers in that subenclosure if possible, or balance the channels very well.
You could go up to 18s, using proportionately bigger air volume room and ports.
If you're having trouble with response flatness, you could create some higher-bass cabinets within the room to make sure those higher frequencies around 25 to 35 Hz are adequately represented. At this point you'll want a more sophisticated crossover.
If you have limited space (i.e. you're packed in amongst neighbors you don't like) you could use a tad over half the room size and cause each driver to become an isobaric pair. This would also have the benefit of further reducing distortion. Be sure to lengthen the ports accordingly.
That's all I've got. :shy: |
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| moray james |
you can go to the scrap yard with a razor knife and slit open every fridge and freezer door and remove the plastiform magnets (same stuff magnepain use) get a sheet of perf steel glue down the magnets and some spacers for the diaphragm and then glue down wires or copper tape. Now you have a magnapain. Build it same size as the ESL version floor to ceiling wall to wall. done like dinner. Check out this project. No joke.
http://infraplanar.free.fr/infraplanar-english.htm
Regarding the multiple speaker idea. That idea was discribed in Audio magazine in the 50's. A guy bought a load of discounted 8 inch 32 ohm VC drivers for less than a buck each and covered the ceiling in his attic listening room. When he played a test record of thunder his neighbour stopped mowing his lawn and stared at the sky to see where the storm was. Good idea, but this guy wants to build a driver. |
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| MJL21193 |
| quote: | Originally posted by mulletdude
. and its really not that complex because all you need is a cone which i can make in like 5 minutes. a voice coil all i need to do is buy some wire and make a former. and you also need a magnet i have several that would suit this perfectly. as well as a speaker surround not very hard to cut up an old tractor tire tube now is it? |
Hi mullet,
You can't downplay the complexity. It would be a rather difficult project to do well. Lots of people could possibly build a driver, but the results would be not worth the effort. If you want to do this, you need to put some effort into it.
The motor is the critical part. For a large driver, you need a large voice coil. The large voice coil means a large magnet and pole piece assembly. There are several ways to do this, but they have this in common: there is nothing trivial about this relatively complex metal work. Tolerances and cleanliness of the gap are crucial.
The basket needs to be STRONG. I would use steel flat bar stock and steel plate, welded at the junctions. This metal work is not easy either. It is possible to use wood in it's place, but it would be twice as massive and need to be extremely well made, to resist the forces developed by such a beast.
What would the cone be made of? It needs to be strong yet light.
The inner tube for a surround is not a bad one. How you glue it to the cone is tricky. You could use contact cement, but I'm not sure how well this would hold up.
The spider is more important than the surround. It keeps the voice coil centered in the gap, throughout it's excursion. This seems like an easy task, but not so.
I'm not trying to discourage, but to point out a few of the harder aspects of building a driver. It can be done, of course and it could be done cheaply, certainly cheaper than a production woofer of very large size would cost.
You need to weigh the time it would take to build (without guaranties of success, or quality) against the other alternatives: multiple smaller production drivers to equal the cone area of one bigger one. |
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| moray james |
| you can buy excellent drivers for cheap and build a horn sub if you want huge or a Tap If you want bass in a small box. But if you are expecting me to believe that any one in a shop no matter how well equipped is going to replicate much less better a current sota drive for cheap ie under a thousand dollars you and mister mullet head are sniffing the same glue. Buy one that works and get a warranty and listen to tunes. This is a waste of time do you really think??? How about a lightning driven plasma woofer? A giant shilo fan with motor controlled veins or just put a tactile transducer under the couch. I don't get the impression this guy could install one of those much less even build one. Good night Gracey. |
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| MJL21193 |
| quote: | Originally posted by moray james
you can buy excellent drivers for cheap and build a horn sub if you want huge or a Tap If you want bass in a small box. But if you are expecting me to believe that any one in a shop no matter how well equipped is going to replicate much less better a current sota drive for cheap ie under a thousand dollars you and mister mullet head are sniffing the same glue. Buy one that works and get a warranty and listen to tunes. This is a waste of time do you really think??? How about a lightning driven plasma woofer? A giant shilo fan with motor controlled veins or just put a tactile transducer under the couch. I don't get the impression this guy could install one of those much less even build one. Good night Gracey. |
Hi,
I never did figure out when I crossed you, but it's getting old.
This is a DIY site? Do It Yourself? Am I missing something?
Yes, there are high quality drivers for less (I have quite a few). There are also plenty of ready made speakers out there, some are very good for "cheap". Ditto for amps. Why bother going to the trouble of building any of these things when places like Future Shop and Best Buy are filled to the rafters with them?
What have you built lately Moray, besides a linked website where the only content is point and click ads? :up:
I don't sniff glue. I have the technical know how and mechanical aptitude to construct a large sub, if I choose to focus my energies upon the task. Whether I deem it viable, of worthwhile to do for bragging rights alone remains to be seen. Budget, for me, is immaterial, but I don't think it would cost as much as the amp to drive it - DIY or not.
The lightning driven woofer was YOUR idea above, no? Electrostatic deathtrap.:dead: |
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| chainenoble |
| hi mullet,can you give us more details of what you want to build and achieve.size,cone material,basket, frequency, spl,etc. |
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| moray james |
| knock yourself out sunshine. You and your friend with the pipe wrench and the tractor tire innertube can build away. I would say you were being made fun of. You don't have to defend your decissions to me or anyone. I don't have to work any miracles for you today either. I am going to look for the DIY funny bone making forum I'm not funny anymore neither are you. |
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| MJL21193 |
| quote: | Originally posted by moray james
knock yourself out sunshine. |
Thanks for your help moray.
No hard feelings? I know you were just having some fun at our expense, and that's ok by me.
When I get mine done, you're welcome to come over for a listen. I'll BBQ some strip loin and wings , a few beers and I'm sure you'll like it!
:) |
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| tt398 |
If you are looking for prodigious infra-bass why not try to make a DIY clone of Tom Danley's ServoDrive subwoofer? They use a servo motor to drive the woofer diaphragms -- no voice coils in this one. I've heard the commercial ServoDrive subs and they are impressive.
Good luck on your project... |
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| opcom |
| an old-time giant size computer disk drive linear motor and a reinforced but lightweight closet door? probably a ridiculous idea.. but for the lowest octave only, to 16Hz., 1812 overture, organ music.. |
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| MJL21193 |
How about a Speed Queen wringer washer, 265 feet of copper tubing, 4 rubber bands and a roll of duct tape?
:joker: |
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| EWorkshop1708 |
I always wanted to build a large subwoofer too!
I'm not sniffing glue, but I sure might be smoking something green ;)
Anyway, when I was a teen, I drew plans, and wanted to build a 60 inch woofer (5 feet) and use thick black tar paper or similar, and lots of glue to hold the paper together for the massive cone, and thin aluminum strips to hold the cone's shape.
For the voice coil, I'd use 16 awg magnet wire and the coil would be 8.5 inches in diameter, using aluminum sheet made into a tube as the former.
The magnet, would be an electromagnet wound with 12awg magnet wire around a 10 inch diameter plastic former to hold the coils. The Pole piece is a section of 8-inch diameter steel pipe. The 8.5-inch voice coil fits inside the 10 inch electromagnet former, and over the 8-inch pole piece. The Magnet would be run directly from a 12V car battery for a smooth DC source. The top and bottom steel part of the magnet would be steel plates.
The basket would be thicker aluminum strips bolted together. The surround would also be tire tube. The spider would be made of 3-5 layers of spandex for the flex and support needed for the moving voice coil. There would be no dustcap, but it would use window screening to cover the open coil, and allow heat to escape and keep stuff from getting in the coil cap. |
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| myyykmeister |
Sounds like a possible solution, of course time consuming, but all large-scale projects are. Remember to make the spacing in the gap as small as possible. The pipe might not be enough cross sectional area for magnetic conduction. Schedule 160 would be better, Grade A better than B, since lower carbon. Solid bar better still, though extremely heavy. How about making both coils similar, and driving them out-of-polarity with two amplifier channels? No wasted DC power, and no field strength limitations! Xmax would probably be limited though, wouldn't it, due to the fact that magnetic coupling would go down rapidly as the coils moved apart with relation to each other- how would you keep each in the other's field at all times? And how would you core that?
How about taking the high-frequency output from a switching amplifier directly? At 300 kHz or whatever, the coils may exhibit good enough coupling through the air to not need any core. Then the mass of the cone would demodulate the signal and you'd get bass!! No pole piece to worry about! 300 kHz would probably be too low to get much efficiency out of air core, tho... too bad.
In a previous post:
Silo fan with motor-controllable vanes? Sounds like the Rotary Woofer. http://www.rotarywoofer.com/
You'll want to cross it over at 20 Hz. LPF that is. LPF at 20 Hz. Hee, hee, hee!!!! :devilr:
Response down to DC. That's right, they will pass a DC signal. Anyone got a DC coupled amplifier? This thing will play it! But that's not very impressive, since that's just a fan blowing. Try this:
"Specifications
Specifications: Amplifier Requirement: 200 watts @ 8 ohms Impedance: 8 ohms 0Hz - 40Hz Frequency Response: 1Hz – 30Hz +/- 4dB Suggested Crossover: 20Hz @ 18dB/octave Sensitivity 94dB 1 watt 1 meter @10Hz Maximum Acoustic Output: >115dB between 1 and 20Hz. Distortion: Typically 3% or less between 1 and 30Hz @90dB Warranty – 3 years parts and labor Patent Pending"
It's not cheap, but I want one anyway. :bigeyes: |
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| mulletdude |
| Ok so i dont have all the specs figured out yet for this so i'll calculate out what i want as i am typing this. cone area should be approx. 2400Sq inches. cone would be made out of reinforced tin so it is very large yet quite light a circle of 30 inches would be dificult to make witht the tin i have so i'd cut out 4 triangles out of the tin and rivet them together so it is a square(also more practical for the space i have availiable) now for the fromer i would probably use a peice of tin wrapped around something that is very little bigger than the outside diameter of the magnet i will use ( around 6 inches). the magnet will not use a pole peice instead the former will move around the outside of the magnet so centering will be very very important.i will post a design later. the surround would be as i said a tractor tire tube cut out so that it is about 1.5 feet wide and stretch it and rivet it or secure it some other way to the cone. i'd probably use 20 awg wire so that it will stand a couple thousand volts of course solid wire though. the box will have to be sealed so it can be size reduced while still having a flat response and good volume. i would like it to have a response of about 100 db. and i would like it to accurately reproduce frfequencys down to about 10 hz if not lower would be nice though to get it all the way down to 1 hz accurately. and i would also like to limit it with a very simple crossover to about 30 hz tops. any more help would be appreciated because i am almost confident to try and start building a prototype thanks. |
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| MJL21193 |
| quote: | Originally posted by mulletdude
for the fromer i would probably use a peice of tin wrapped around something that is very little bigger than the outside diameter of the magnet i will use ( around 6 inches). the magnet will not use a pole peice instead the former will move around the outside of the magnet so centering will be very very important. |
Hi mullet,
The method you propose will not have enough motor strength to drive such a massive cone. There is a reason why the magnet assembly on a speaker is designed the way it is.
Do this simple experiment: take an old, cheap or burned out speaker and take the cone, spider and voice coil out. Drop some iron filings on it and notice where most of them go - in or around the gap. This is the concentration of magnetic flux. This is where the voice coil needs to be.
Unless you do this, you will end up with a speaker that will need 2000 watts to produce 50db of sound. :down:
It goes back to what I said about either doing it right, or not at all. |
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| MJL21193 |
| quote: | Originally posted by myyykmeister
It's not cheap, but I want one anyway. :bigeyes: |
Hi,
$13,000.00 is not cheap, for sure.
There was a (short lived) thread on here where the contributors were discussing the ways and means of a DIY version. Funny, I haven't seen any of the working prototypes yet. :) |
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| just a guy |
Actually I made one of those too but stopped just short of completion for a number of reasons. I had some parts professionally machined. All I had left to do was bolt the motor and driver together, epoxy the swashplate adapter to the vc and add blades (which were to ride inside the basket rim rather than cut the whole basket off as the commercial unit does).
I didn't bother to finish because:
1. I was exasperated when none of the parts I had on hand would work (4 different ac motors, etc) and I didn't want to buy these things new
2. I realized rather late in the process that this unit would actually NOT be maintenance free and that was mostly what killed my motivation
3. I could not bring myself to cut the cone out of this driver.
4. Conventional driver displacement is so cheap now it's not really worth it anymore.
I might still finish it one day, but only as a novelty, not for regular use. |
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| just a guy |
| BTW, the third and last pics are a good example of how tight the former has to fit inside the magnet. (Look, I'm finally on topic!) You'd be hard pressed to get a business card to fit in between them. |
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| Don Bunce |
mulletdude,
A cone made of tin is not going to work very well...it will be too heavy,and any flexing will make an incredible racket.
Electrovoice made a 30" woofer some years back.It used a cast styrofoam cone. A sheet of foam from your local home improvement store would probably be a good place to start.
Good Luck! |
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| mulletdude |
| OK so then what would be the best way to do this with as littl money used as possible would the idea of two electromagnets with a 180 degree phase change from eac other be at all practical? i really look forward to your input. |
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| MJL21193 |
| quote: | Originally posted by just a guy
Actually I made one of those too but stopped just short of completion for a number of reasons. I had some parts professionally machined. All I had left to do was bolt the motor and driver together, epoxy the swashplate adapter to the vc and add blades (which were to ride inside the basket rim rather than cut the whole basket off as the commercial unit does).
I didn't bother to finish because:
1. I was exasperated when none of the parts I had on hand would work (4 different ac motors, etc) and I didn't want to buy these things new
2. I realized rather late in the process that this unit would actually NOT be maintenance free and that was mostly what killed my motivation
3. I could not bring myself to cut the cone out of this driver.
4. Conventional driver displacement is so cheap now it's not really worth it anymore.
I might still finish it one day, but only as a novelty, not for regular use. |
Hi,
I like your mechanism to vary the blade pitch. Very nicely done. Does it operate freely?
The motor. Is that a normal induction motor? One from a furnace blower or the like? If so, it would turn too fast (induction motors turn 1725 or 3450 rpm, depending on the winding). This would create a lot of wind noise and would also cause the blades to act as a propeller, thrusting it backwards. This would easily overwhelm the piston action of the voice coil, forcing it back in the gap. The motor would need to turn fairly slowly, maybe 50 rpm, to reduce noise and thrust. |
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| MJL21193 |
| quote: | Originally posted by Don Bunce
A cone made of tin is not going to work very well...it will be too heavy,and any flexing will make an incredible racket.
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Yes, heavy.
I would build a form from styrofoam and do the cone in paper mache. Let dry and dope this with water based urethane coating to make it stiff and moisture resistant.
| quote: | Originally posted by mulletdude
OK so then what would be the best way to do this with as littl money used as possible would the idea of two electromagnets with a 180 degree phase change from eac other be at all practical? i really look forward to your input. |
You need to do some machining. You can use the permanent magnet on the inside, but you need to create the gap. With the magnet on the inside, the motor strength would be reduced, but it would still be usable.
Iron ring on top of the magnet, bigger iron ring under the magnet and one to go around the outside. If you are willing to do this much work, you should consider ditching the big magnet you have and using rare earth disk magnets to ring the outside. |
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| just a guy |
The mechanism to vary the blade pitch is a $99 main rotorhead from a remote control helicopter. Actually this is the part that I was quite unsatisfied with, as it was not nearly as precision-made as I would have liked (although it's probably quite good enough). The control rods with the ball link ends are made of plastic and that is the part that will wear with time, making this NOT maintenance free. I have no idea what you mean when you say "Does it operate freely?".
The part I had machined is the adapter to lengthen and replace the stock rotorhead shaft. Radial runout was 2 microns IIRC, so pretty precise.
The motor is a single phase ac motor. The one in the picture is 1/3 hp, but I noticed upon testing that it gets VERY hot very fast so it is not really suitable for anything but the dump. 3 other motors I had onhand had similar stupid problems, squeaky bearings, etc. The ruined the mood, as this was supposed to be an extremely cheap build.
The commercial unit uses a 3 phase 1/3 hp motor (to ensure continuous rotational speed under heavy load), but I saw no need to rewire my house to accomodate 3 phase since I don't think you'd notice it much in it's intended bw, and 1/3 hp is plenty strong to keep it fairly consistant anyway.
The commericial unit uses a motor speed controller to manually adjust speed for max output vs out of band fan related noise, and is usually set to about 800 - 850 rpm. I did some pretty extensive calculations (considering that I'm a math idiot) and ultimately determined that due to the fact that my blades are significantly shorter than the commercial models (theirs is an 17 inch blade span while mine is only 13 inches), the relative blade speed (measured at the far end of the blade tips while rotating) would be quite similar if my motor was spinning considerably faster, justifying the use of a 1725 rpm motor with no speed control. Still slightly too fast, but I planned on aleviating any extranious blade noise with careful blade shape design as well as a heavily padded "high frequency tunnel trap" with several well padded bends, which the commercial unit uses anyway. 50 rpm would be WAY too slow and sensitivity would then be a HUGE issue. The commercial unit produces a huge amount of force at 800 rpm, but obviously noise is easily managed, otherwise no one would want one. (It should be noted that if I was indeed to buy a new motor, I would probably buy a 700 rpm blower motor and not have to worry about noise at all, although it probably would not be fast enough to realize this thing's full potential).
The most common question is whether the rc heli rotorhead is strong enough to withstand these incredible forces (it's main shaft is only 5 mil thick), in fact I was a firm disbeliever at first. But then I watched a few youtube videos of kids piloting these things, and it's really amazing. These heli's are not particularly lightweight, but they can snap back and forth like a dragonfly with lightning speed and precision, so you KNOW these can throw around a LOT of air. Maximum thrust is what it's all about. |
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| MJL21193 |
| quote: | Originally posted by just a guy
I have no idea what you mean when you say "Does it operate freely?".
The commericial unit uses a motor speed controller to manually adjust speed for max output vs out of band fan related noise, and is usually set to about 800 - 850 rpm.
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I meant "as in does it move without binding". I didn't recognize it as a helicopter prop, not into that.
I was a bit off in the rotational speed. My thinking was more about the thrust. As the blades pitch forward, the air load increases, wanting to push the blade backwards against the voice coils forward thrust. Less rotational speed makes for less thrust, but does mean less production, as you say.
I still think that 1725 rpm would be way too fast, even for smaller blades. |
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| just a guy |
It moves very fluidly, although it's got a mechanical stop to prevent overexcursion which I'd like to modify to allow more travel.
If you look at pics of the commercial model and pics of mine (you can check the driver specs too, for mine at least) you will see that my driver is WAY stronger than the one used by the commercial unit so I'm not worried in the least that it would be strong enough to withstand the pressures placed upon it, especially considering the fact that my unit would only move about 2/3 as much air as the commercial unit (even at 1725 rpm).
WRT relative blade speed, you can do the calculations, as I did, to figure out how many feet per second the blade tips move on the commercial unit (17 inch bladespan spinning at 800 rpm) vs mine (13 inch blade span spinning at 1725 rpm). There is a bit of difference, but not so much as you might think. (As you move outwards down the length of the spinning blade, the speed of rotation/feet per second increases exponentially.)
| quote: | I didn't recognize it as a helicopter prop, not into that.
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I guess I'm not either, as it turns out. Although a couple of small mods to this device (which I'm too lazy to bother with) would actually make it maintenance free, at which point I kinda would be into it again. |
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| MJL21193 |
| quote: | Originally posted by just a guy
WRT relative blade speed, you can do the calculations, as I did, to figure out how many feet per second the blade tips move on the commercial unit (17 inch bladespan spinning at 800 rpm) vs mine (13 inch blade span spinning at 1725 rpm). There is a bit of difference, but not so much as you might think.
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The calculations:
13 inch blade - ((1.083 x 3.14) 1725)/60 = 97.8 fps
17 inch blade - ((1.416 x 3.14) 800)/60 = 59.3 fps
40% less blade tip speed for the 17 inch fan at 800 rpm. |
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| just a guy |
| Ok so you're smarter than me, and really really fast too. That doesn't come as any great surprise to me, although in my defense (although it doesn't count for much) I did mention that if I actually finished it I'd buy a 700 rpm blower motor. |
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| mulletdude |
| ok so this got really off topic man. i would like to say something right now but i would probably offend someone so i wont. nut anyway, come on guys stick to one topic sheesh. oh somethign else i should mention is that this whole thing should be relatively to strip down to nothing pack inside its own box and move it because i am moving not too long in the future . any further input would be appreciated . and please no more getting off topic i beg of you. |
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| just a guy |
Yes it did get off topic, and if you count word for word I'm probably the worst offender here.
But if you read between the lines people with the appropriate knowledge are helping you, suggesting possible alternatives, and in the case of my own personal stories there is a moral as well, which happens to be unless you are making a novelty, it's probably not worth it to try. 2 ambitious projects and 2 resounding failures for me.
You don't want to accept that, that's fine, I wouldn't either when I was 16. But it seems that you have a very clearly defined end goal and absolutely no idea how to get there. I fully admit that I'm not the smartest dude around these parts, but I do know enough to realize that this project is not going to end well unless you do a bit more research. There is a LOT more to driver design than putting together a collection of parts that ultimately physically resemble a driver (if you actually want to use it for audio reproduction).
These are some of the questions you need to answer, or continuing this conversation on topic is pretty much pointless.
Do you know how to measure and mix and match parts to come up with usable ts parameters? I sure don't. If not, do you at least know how to measure it's parameters when completed? It's going to be impossible to guess and I'm thinking vas is going to end up being so large that you'd need a box a lot larger than you might think to compliment it.
What are you planning to make the basket from and how are you going to fabricate it? This is super critical and if it's not super strong and "straight" everything that gets attached to it will be misaligned. This might not seem like a big deal, but when you think about the tolerances involved in the vc gap, slight misalignment = instant failure.
What are you planning to make the spider out of, and are you planning on a conventional spider, dual spider or some other form?
Before you try making the driver motor part of the design, why not start out with trying to make the passive radiator part first, and if that goes well, add the vc and magnet?
Sorry dude, but you were the one that wanted to get on topic, and these issues have to be addressed before this can even be taken seriously.
What equipment do you have available in your shop?
Unfortuately I don't know nearly enough to even answer some of the questions I have posed here, but I do know that there is no chance of success if these issues are not accounted for.
Having said all that, good luck, and I'll leave you to it. |
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| MJL21193 |
| quote: | Originally posted by just a guy
Ok so you're smarter than me, and really really fast too. That doesn't come as any great surprise to me, although in my defense (although it doesn't count for much) I did mention that if I actually finished it I'd buy a 700 rpm blower motor. |
I'm no genius, that's for sure. Not especially good at math either.
| quote: | Originally posted by mulletdude
ok so this got really off topic man. i would like to say something right now but i would probably offend someone so i wont. nut anyway, come on guys stick to one topic sheesh. oh somethign else i should mention is that this whole thing should be relatively to strip down to nothing pack inside its own box and move it because i am moving not too long in the future . any further input would be appreciated . and please no more getting off topic i beg of you. |
You have been getting good advice, positive and negative. You are not really making much of a contribution yourself. You refuse to discuss the specific details, focusing on big picture instead.
Once again, if you are serious about this, you need to learn a few things. I, for one, have been giving you good stuff, details and aspects you need to work out. These are not as simple as you assume.
Making it so you can take it apart to move it is not a good idea. It will needlessly complicate the design. How big do you want this to be?
Just a guy echos my point about the basket. It needs to be very rigid and strong. Well aligned to keep everything in place under extreme stress (only if you actually get it working). Propose a few of your thoughts and be prepared for some honest critical comments - your skin seems to be thick enough to withstand the flames. :) |
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| chainenoble |
you said you want the cone area to be 2400sqin.is that not something like almost 5ft in dia.that would require a pretty big box,which would make "stripping it down" and transporting it
alot of work.a properly reinforced box for such a driver would be quite heavy,or did i misunderstand something? |
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| mulletdude |
| ok so a couple of things 2400sqin. is about 3 feet in dia with 10 inches from the front to back of he cone according to my rudimentary math and i found the link to MIT's huge sub here . http://neurosis.mit.edu/mjolnir/ now this is kinda what i want to make almost the same as the MIT students made but bigger. instead of 23 inches i want more like 36 or so. and if you guys wnat more fine details of my plans you shoudl probably ask more direct questions abot hem and the main reason i am not inputing much myself is whenever i get to typing up a reply i end up getting sidetracked by someone distracting me. all the rest of the input will be appreciated. |
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| ppcblaster |
| quote: | Originally posted by mulletdude
Dont know if this really goes here but.
I am planning on boilding a huge subwoofer i have most of the materials but the one thing i am wondering about is isthere a formula or something for figuring out voice coil windings anr dimensions as well as layers any help would be appreciated . also i was wondering what gauge of wire to use because i most likely will be firing a couple of thousands of watts through it. any feed back as to how to figure out a box size would be appreciated as well |
http://www.recone.com/
http://www.diysubwoofers.org/
http://www.humblehomemadehifi.com/Serious-Sub.html |
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| just a guy |
That info is a bit misleading. They might have paid under $100 for those parts, but I'm not so sure you could get them anywhere near that. The box itself contains over $100 in mdf. (It is probably also smaller than it should be, although with the power of those magnets qts might be surprisingly low. It should include extensive bracing, but that is not the point).
I cannot really see how it works from the picture, but the motor is made of unobtanium (from a dishwasher sized hard drive), so the driving force of those magnets will be vastly superior to anything you can put together for any reasonable amount of money. Also (and I am not sure on this so do not quote me) I do not think that thing even uses a voice coil at all, I think they have rigged up the hard drive mechanism to directly provide the driving force for the cone. (Which also would mean that they do not have to make sure it is as precisely aligned as you would with a conventional driver motor).
I applaud them for making a working model, but I deeply question how well it works. I am quite sure it can get very loud but I wonder what kind of response it exhibits. Maybe I would be very pleasantly surprised.
Either way, I would not recommend trying to recreate that one, do you have a link for the other models you mentioned earlier |
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| MJL21193 |
| quote: | Originally posted by mulletdude
ok so a couple of things 2400sqin. is about 3 feet in dia with 10 inches from the front to back of he cone according to my rudimentary math and i found the link to MIT's huge sub here . http://neurosis.mit.edu/mjolnir/ now this is kinda what i want to make almost the same as the MIT students made but bigger. |
That MIT one is an example of the waste of time variety. It looks like junk and that box will resonate stronger than the driver:eek:
Your cone area calcs are a smidge off. 2400 would be ~ 55 inch diameter cone, not a 36". 36 would be ~1030 square inches. |
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| mulletdude |
| im sorry about my calcs i must have accidentally used the wrong formula will consult my math teacher tommorow. and the other model i metioned earlier was in an ebay auction the guy said he wound his coil and everything. and the main reason i wanted to use the magnet inside the coil was this link here which works quite well http://www.josepino.com/circuits/in...wto-speaker.jpc this is the thing that sparked my interest in the first place(warning th guy put up like a million pics so it may take a bit to load). other than that i dont think i said anything about any other ones. |
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| opcom |
well don't disrespect the linear motor from the ancient hard disk. These are very powerful and can take hundreds of watts. The moving parts usually ride on ball bearings. Some downsides are:
1.) The deign was for a long stroke of 3" or so, not along the lines of the typical large woofer.
2.) The mass of the moving portion is high and so it does not like to travel far on short notice. Check the seek time for the disk, 50 mS maybe on a good day, so the top end of that beast would be 20hz?
In the 1980's, I put one from a DEC RA60? drive on the workbench and fed it 60Hz at 10A from a variac and it moved only about 1/8". |
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| EWorkshop1708 |
| quote: | Originally posted by opcom
well don't disrespect the linear motor from the ancient hard disk. These are very powerful and can take hundreds of watts. The moving parts usually ride on ball bearings. Some downsides are:
1.) The deign was for a long stroke of 3" or so, not along the lines of the typical large woofer.
2.) The mass of the moving portion is high and so it does not like to travel far on short notice. Check the seek time for the disk, 50 mS maybe on a good day, so the top end of that beast would be 20hz?
In the 1980's, I put one from a DEC RA60? drive on the workbench and fed it 60Hz at 10A from a variac and it moved only about 1/8". |
On Youtube people are playing open hard-drives at full range |
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| mulletdude |
| now earlier on i was browsing the subwoofer topics and i found a thing called the klien horn would this be a better alt to building a huge sub just building one of these horns then put a smaller sub in it with the increased eficiency. |
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| MJL21193 |
Low frequency horns need to be BIG! Huge even.
You should look into a Linkwitz Transform driven sub. This will give great bass performance from a small package. The trade-off is the amp needs to be very powerful.
Here's a look at my sub. It has two 18" drivers in a sealed 100 litre box. The amp that drives it is quite powerful though, as shown here in this thread. |
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| DigitalJunkie |
| quote: | | On Youtube people are playing open hard-drives at full range |
I once built up a small chip-amp,and was looking for a small test speaker,but couldn't find one in the mess..So i looked at the gutted HDD on the bench,and said to myself "Hey,it is called a 'voice coil',right?"
Yea,it worked well..Sounded better than I expected too! :clown: |
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| moray james |
| I once heard about a bat so big it flew away with a cow. I saw it on youtube so it must be true. Come on dude this is a contribution to the audio world? Read a book. |
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| opcom |
| quote: | Originally posted by moray james
I once heard about a bat so big it flew away with a cow. I saw it on youtube so it must be true. Come on dude this is a contribution to the audio world? Read a book. |
Sir, surely you jest, to think it was anything but humor. :)
Attached is a pic. of one of my rooms with books. It's the cats' room also, but they are not into reading. There are about 1500 or so in here (shelved two deep) and yes to anticipate any questions I've read and understood every one of them and I freely admit to being a little weak in the higher mathematics.
The subject matter in this room is 90% engineering and technology, and the topics are concentric about the physical sciences of electrical, electromagnetics, electronics, communications; steam and nuclear power; acoustics, laser including gasdynamic, other nonlinear optics; audio system, amplifier, studio, and speaker design; chemistry; interaction of radiation with matter; radar; optical, nuclear, and nuclear magnetic resonance spectoscopy, and there are more but I've probably bored everyone many words ago. I also hold patent # 6,313,878 for those that are counting.
So, I am serious about technology, and as far as this board is concerned, audio. I do enjoy a silly joke once in a while. I think you misunderstood the intent of my post.
Patrick J. |
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| Cal Weldon |
| Where do you sleep? ;) |
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| opcom |
| sleep? just an adjacent room as free of the annoyances of the times as possible. |
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| M50SNIPER |
| Yea its pretty easy to make your own subwoofer. Well first put the magnet behind the cone, then put paper about 3 inches tall wrapped around the magnet. Then wrap 30-35 AWG wire around the paper with the magnet inside. Wrap at least 50 times. Then permanantly attach wire where it is. (I use hot glue but that's the cheap way. After that just pull the magnet and paper out. Then put the magnet behind the voice coil like this. O|< O=Magnet |=Wire Coil <=Cone. And permanantly attach it there. BAM YA GOT A SUBWOOFER! I found something like this on www.instructables.com and this is where the idea came from. |
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| Pikefish |
I too am embarking on a ground-up subwoofer build (among others).
I bought a boxed pair of "Big Funky 15" 70's speakers" off a local auction site for $10, picked up. I had the intention of either using them driven, or as passives (after some doping & damping the paper and maybe a surround that isn't painted with glue) for my XLS10's.
It turned out, these were infact 18" speakers, made in England by Goodmans, the "AUDIOM 18-P 100W", and have a very stylish four-narrow-reinforced-spoke cast aluminum basket. Xmax of 1.5mm. One point five. Xmech looks about 10, if it wouldn't catch fire before fighting that far.
One was pretty much destroyed when someone slashed most of the spider with a knife to find and reattach the vc to braid, and it had a big tear full of hot glue, so I carefully extracted diaphragm, and have decided 1.5mm won't be enough gap for my voice coil, so magnet assembly is going to be machined, if not replaced with a larger diammeter one.
Moral (and on topic) of the story is, I've got a platform to start from, and that makes it immeasurably easier to decide specifications and target parameters.
You want to build something bigger than usual, so my recommendation would be to source a Truck Wheel, alloy being the more stylish and expensive, and say that will be the basket.
Your polepiece-housed magnet has potential aslong as there is an overhanging plate directing it across the gap. Letting the top pole of the magnet find its way through the air to the steel guide I think I recall seeing in one of your posts will result in a highly asymmetrical BL vs excursion. Field strength will also be decreasing away from the magnet in the middle as you move towards the gap because of the increasing radius, and this might be why your approach isn't widely used, you probably couldn't make the iron at the gap magnetically saturated, which I hear so doing creates lower distortion. I'd recommend magnets at the outside of the vc and keeping that area open for a superbly vented polepiece, lessen the strain on your dust cap (assuming there is one). |
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