Attention all structural/mechanical engineers/ anyone who has a say in DIY

[Jay481985]

A simple thing dawned on me yesterday while thinking of a DIY

subwoofer. Everyone makes braces etc etc to make the box stiffer. What

if I were to make the enclosure thinner but supported internally with

wire? Kinda like having eye socket screws inside the subwoofer and then

adding tension on the wire to keep the box stable. I know the tension

cannot exceed the box's structural strength but instead of having an

enclosure with volume eating braces how about a socket eye screw with

wire stretched internally parallel to the other side? I know my

engineering skills are very limited but usually we want to lessen the

vibrations of the subwoofer enclosure. What if we were to wire an

intricate system from corner to corner, side to side and so forth to

internally dampen the enclosure?

[TheEAR]

Wiring the box in a matrix pattern inside woudl lessen vibrations,sure thing.Now the complexity of such an undertaking makes it not so worthy. You would have to have to use stiff panels to be able to apply the tension to lessen the vibrations.And you would have to use bolts all around with some kind of very strong(steel or other material)wire.

Better use the classic method,or use pieces of round sticks cut to size like you would find in brooms for example,these when again used in a matrix configuration would stiffen the box much more than cables.And the work for you would be a much simpler task.

[]

[michael hurd]

You could tie parallel walls together with a simple hardwood dowel, drill 2 holes slightly smaller, apply glue, assemble, and clamp overnight.

With very heavy drivers, you may want to double up on the front panel thickness, for extra structural integrity. Doubling the thickness = 8x the stiffness.

[Jay481985]

I was thinking more in lines with a stiff material say polycarbonate

(aka Lexan or bullet proof glass) It might be more economical instead

of bracing to use cables to reduce vibrations. As polycarbonate is

about 20 dollars a square foot? Michael Hurd or TheEar, did you ever

see how a tennis racket is strung, something to that degree where the

shape can hold itself (unstrung tennis racket) but essentially becomes

stiffer by the string (tennis players are highly religious with psi)

the higher psi usually have more control (less give) but the lower psi

have more power (the ball touches the strings longer so more armswing

is diverted into the ball). But does everyone see my point in using

steel cables or something to use as bracing to have more internal space?

I was thinking something in the exotic catergory, maybe polycarbonate

as that is similiar to wilson X material. But I cannot justify the cost

of the braces/ new tools (polycarbonate is rough on the tools) to see

it through. Though it would be awesome to have a clear subwoofer.

Also on another tangeant I was thinking of a tube subwoofer like svs ss

which recently was taken out of the lineup. I wanted to and brought up

in past post about the use of paper tubes as opposed to sonotube as

they are rather thin. I found a website that does any size paper rolls

up to 1/2 inch thick. I remmeber my father's remaining paper rolls from

his photo lab and am pretty sure they could withstand a gunshot without

penetration. I was thinking 16 inch od, 5 foot high, 1/2 thick sides.

And I believe Michael said something that it would be tough to cut. I

was thinking a dremel or so forth. Router? Extra large pipe cutter?

[michael hurd]

Many years ago I built a subwoofer with a clear Acrylite 1/2" thick sheet for the motorboard, after experimenting it wasn't too bad to cut on the tablesaw, but I used a general purpose (combo) blade. I found that a jointer really cleans up the edge nice, just have to sand a bit and then flame polish the edge.

The driver cut-out was a royal PITA, a jigsaw was near useless, the sheet melted back together from the friction of the blade! I ended up drilling a lot of 3/16 diameter holes all the way around inside the cutout, then cutting through the left-overs with the jigsaw.

The driver was a Radioshack 8" subwoofer with 4 ohm coil, and I had a 7.5 uf coil in series with the driver, that one of my brothers gave to me as a hand-me down. I think that it started to roll off at about 80 hz or so, and didn't go much below 35 hz. The gross internal volume was .8 cubic feet, the rest of the enclosure was 3/4" particle board, salvaged from a shelf unit. I applied rockgard to the interior and exterior, and painted it with a lacquer spray-bomb, a black metallic.

Not bad for a first attempt, this was about 12-13 years ago when I was still in high school. SInce then, I gave the radioshack driver to a buddy, but I still have the enclosure. I cut up the motorboard to make something else out of the rest of the acrylite.

[michael hurd]

Jay, if you really want maximum rigidity in a tube design, you could always take two sizes of normal sonotube, like 16 and 18", and pour an expanding foam mix between them. You would have to router a groove for the inner one to sit in, and make the outer tube flush. Glue both, mix up a two-part foam, and pour it into the cavity.

Endcaps can benefit from tensioning with threaded rod running from top to bottom.

[Jay481985]

I was hoping the rigidy (1/2 inch and circular) would be quite dampened

by itself. I believe the cardboard paper they use would dampen most of

the resonance. But your idea of the foam is a new and unique one. I was

thinking sand, thought that would weight a ton. The foam idea intrigues

me but would it stand the test of time? would the foam actually stick

to the sonotube after a couple years or would it vibrate off an cause

an unwanted event or not do what it was supposed to do in the first

place? Also I wanted it no bigget than 16 inches as I think 18 is

strecthing the acceptance factor, yes even guys have acceptance

factors. I was thinking a good 12 inch sub av12 anyone? or maybe a 15

inch if it would fit... totally depends. But I wanted a 6 inch flared

port, lol gotta have some big things! I heard of random different ideas

being spread around. Being that I just moved from a house that had an

unfinished attic to a house that has no space for woodworking I am

trying to build a subwoofer within limited means. Meaning as much

preassembled as possible. Hence the paper tube that will already be cut

to size. I wanted to have a maple veneer to make it look nice, I

believe a speaker looks are an important issue, though the driver and

tune is much more important.

The bracing idea intrigued me one night before I fell asleep and I

thought instead of making braces that usually involve more time than

the actual sides, why not try a different approach plus it increases

volume. I want to thank you Michael for answering many of my questions.

If you ever saw my subwoofer that I am still making, basically done all

it needs to be is glued and painted, you will notice that my internal

bracing was quite intricate and time consuming. I am all about

experimentation and trying new evolutionary techniques. Sorry but there

really is no revolutionary in the audio world.

[michael hurd]

I have seen the cabinet that you have started, it is very nice, but it is likely overkill. Then again, there is no such thing, lol! I would think that veneering over a paper sonotube would be troublesome, but I have never attempted it. The only reason I mentioned it was because of the seam where the layers overlaps, the exterior is far from flat.

You would have to bondo the entire outside of the tube ( not a nice process ) and sand it smooth, in order to get a smooth substrate over which you could veneer. This in itself will be a headache, requiring time and effort.

I would think that veneering over PVC pipe would simplify things, it is smooth already.

FWIW, Hsu and Svs both used sonotube for enclosures. If it is good enough for them, good enough for me. The only drawback is that it must be covered with something like a knit sock to look good.

[DrWho]

The only problem I see with your cable/hook technique is that it only works against a positive pressure inside the cabinet....in other words, with a negative pressure (the woofer moving out) the cable is going to help the wall flex even more.

I have always liked the idea of doubling up layers. It's only a few inches bigger in all dimensions, but greatly improves the strength. Make sure you rough up the areas being glued together and use a lot of glue. Wood glue bonds stronger than the wood itself which means a good thick layer will dramtically improve the strength too.

Btw, you don't have to go crazy insane with the damping either...and really it shouldn't look like webwork on the inside. Just add bracing to the middle of large surfaces and try to brace to another surface that will ideally be moving the opposite direction. Then when a strong mechanical connection is made, they will cancel each other out.

So what kind of subwoofer are you looking to build? One of my favorite designs involves using a triangle, somewhat tucked into a corner with a front-firing active and two "side" firing passives. Since triangles are strong and almost every face is covered with a driver there isn't much need for too much excessive bracing. In fact, the only real thing to worry about is the entre sub itself jumping around [] (but that should be minimized cuz no two drivers are facing the same direction...they all cancel each other out).

[Jay481985]

As to Michael Hurd's response I was going to use a wood filler to fill

the seams of the paper. I would think that it might be easier to try

the method of using wood glue to bond veneer over the cardboard tube as

both surfaces are porous. I think titebond sells it.

As to DrWho yes that is a problem I thought since there is nothing to hold it back. the sub itself.

Also as with the glue yes I know wood glue is usually stronger than the

wood itself. Also I brought the gallon of titebond III woodglue for $27

dollars at Lowes. It supposedly is even stronger than the polyurethane

glues like gorilla glue. Also I brought it for economical reasons as I

needed to bond the two 3/4 inch sheets of mdf together to make my 1.5

inch thick siding.

I remember once reading an article in the Robb Report yeah I know I

dunno where I read it but the person I belive it was a wilson audio

representative boasted that you can put a cup of water and the water

will not vibrate on the speaker. That was how well dampened the speaker

was. That is sorta my train of thought too.... If your going to DIY why

cheap out when its already better than many pre made systems out there.

Right now I am in the works of a 20 X 20 X 30 inch 4.5 cubic feet

sealed dual tumult enclosure that I been procrastinating because adire

has not released the new tumults yet. Its been about a year since I

started. And I am in college now and really have no motivation to

finish unless there is a freaking driver..... Also I modeled a system

in winisd with the same dual tumults. the 15d2. The enclosure a huge

one 24 by 24 by 60 with 6 stryke 18 inch passive radiators, sorta like

the acoustic-vision everest but modified bigger and more passive

radiators. It comes out using 3/4 inch mdf to 16.7 cubic feet? or with

1.5 inch thick sides 15. But respectively the 16.7 is flat +- 3 db from

16 to 120 and the 15 cubic footer is +- 3 db 20 to 120. And it would

seem that both max out at 120 db from whatever respective range,

anechoic of course, no roomgain [] That would be my master subwoofer.

Thinking dual of that to have a stereo sub effect.... My god... and

imagine if they were aluminum instead of mdf......

But anyways the triangle idea passed my mind but.... The problem is

area of a pyramid is 1/3 the respected square.... So its losing 1/3 of

the volume... not my cup of tea as it would have to be a big pyramid in

the corner though I do like the idea as there are no parallel sides,

the passive radiators on two sides, I doubt it would bounce??? as the

pyramid should push the sub down.... but maybe it would but I'm

guessing with some lead shots in there to add some weight.

Well I always try to think of new and creative ideas for speaker

designs and so fourth but its hard being that all the good ideas are

already spoken for!!!... But right now I feel rather depressed as most

of the DIY subwoofer companies are remodeling to release their new

speakers anytime NOW!!! Since Ascent Audio does not want to pay

royalties to xbl (adire) and Stryke is still waiting and Adire

grrrrrr....... I

feel soo depressed and non motivated to do anything. I been looking

around at other subwoofers like the McCaughly and Aura but there just

too expensive and honestly I could get the same quality for cheaper

from compies written prior. Also 18 inch subs cause quite a stir for

the size of the box and the sub itself. There is a thing too me called

too freaking big that is showing off style. I prefer my high excursion

12 and 15 inch subs anyday over 18s for some reason

[007]

I think the main problem here is wires stretch out, its only a matter of time. <?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

[ygmn]

What exact shape are you trying to accomplish?

If you want stiff sides....but more volume...use different material for enclosure.... something Stiffer with less modulus of elasticity....

Steel, aluminum, Composites...etc etc...they are stiffer then wood...but in some cases heavier....Higher strength might be required if the material gets thin enough that stress levels get high but I highly doubt it...

for some comparisons...Modulus of Elasticity of various materials:

Steel = 29,000,000 psi....

Timber = 1,200,000 psi

Aluminum alloys = 10,000,000

What does all that mean? It means for the same amount of stress....the aluminum deforms about 3 times as much as the steel and the wood deforms about 24 times as much as the steel.

So if the structural shape was the same.....say for your sub....and the wood deflects 0.0625 inches...then if made from Aluminum it would deflect about .0075" and if fr0m steel it would deflect about .0026"

but if same shape the steel would weigh about 12.3 times as much

if aluminum would weigh about 4.25 times as much....

So for steel versus wood...you could make it from steel for roughly the same weight less say...and it would deflect about 1/2 as much as wood....(shape really matters here..)

So....what is it you want this structural shape to do?

PS

I am an Mechanical engineer who did structural work....hehehe

[ygmn]

PSS

If you want maximum volume in the smallest surface area then think Sphere....

How about a sphere sub...?? with one flat side to sit on floor or maybe legs??

Then flat area for woofer... hmmmmmmmm

[Jay481985]

I think the main problem here is wires stretch out, its only a matter of time.

not necessarily... Steel wiring tends to hold.

[Jay481985]

PSS

If you want maximum volume in the smallest surface area then think Sphere....

How about a sphere sub...?? with one flat side to sit on floor or maybe legs??

Then flat area for woofer... hmmmmmmmm

I thought that a cube is the maximum volume per given space? eh wait

you said smallest surface area.... I thought of a sphere shape sub but

without massive amounts of expensive machinery to cast or forge it I

highly doubt I can make that. It would be cool if a woodcompany,

(georgia pacific etc) would make hallowed out mdf spheres. !!!

And a sphere is the strongest shape.... supposedly

[DrWho]

no no no, not a pyramid....a "triangular prism." A 5 sided cabinet. The bottom and top look like equilateral triangles and then each side face is a rectangle. The drivers are still normal front firing (no funky angles). In fact, a PR must fire horizontally. This makes the only "free" panels the top and bottom, so bracing would only need a vertical pole in the center.

And I'm not sure why the heck you would need so many PR's for a dual tumult setup. Two 18's per driver is all you need. Also, you might want to look into building an active peaking 2nd order highpass filter to go in front of your amplifier...it will limit cone excursion, while also increasing SPL AND decreasing the necessary cabinet volume. I've got a design here somewhere I can show you...it basically makes the sub indestructible.

Btw, since you've got two drivers you might want to consider going with a stereo subwoofer setup (or at the very least a mono setup with a driver in each corner). It really helps balance the sound out and you most certainly don't have to worry about maxSPL with a tumult []

[DrWho]

...Modulus of Elasticity of various materials:

Steel = 29,000,000 psi....

Timber = 1,200,000 psi

Aluminum alloys = 10,000,000

You get your numbers screwed up, cuz timber looks to be the lowest of the three? []

[Jay481985]

A five sided prism hmmm that now seems like a challenge. But where to

put the amp or have an external amp? Do Pr need to be exactly verticle?

you know what I mean being placed verticle, I know over time they will

sag if they are on the bottom but will pr angled make much of a

difference?

Oh for the PR on the dual tumult setup it actually evens the response

down further, with four pr the bottom end suffers a -3 at about 20

hertz instead of 16 hertz. The thing is the 4 pr are a bit louder spl

wise lower end but who needs that when its again 120 db anechoic! at 16

hertz?

[CECAA850]

PSS

If you want maximum volume in the smallest surface area then think Sphere....

How about a sphere sub...?? with one flat side to sit on floor or maybe legs??

Then flat area for woofer... hmmmmmmmm

How about a "Death Star" sub?

http://www.objectreality.co.uk/DeathStarPlans/

[michael hurd]

Jay funny you say that about a wood company making a hollowed out sphere with mdf. I have seen something similar, roto-moulded with glue and kraft fiber. Was a little more like a square on two faces, the bottom and the baffle, and the other surfaces were a continuous curve like a sphere. This was a few years ago at Bay city sound and vision, they were considering carrying these enclosures, but decided against it, because of the high cost.

They were definately heavy, that is for sure.