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

[Jay481985]

I sw the death star but am not impressed on how they made it... Seems to air leak prone

Also Michael I would bet that it was heavy as hell, how large was it? rough estimate?

[michael hurd]

The rep brought in a 12" as a sample, the baffle was about 14" x14" on the outside, maybe a little more than 14" long. They were available in 10", 12", and 15" models, as well as dual 10", dual 12", and dual 15".

I can't recall what company produced them, but they were definately different.

They were similar to this picture, except the baffle was at 90 degrees, and all of the other surfaces were curved. IE: compound curve.

[DrWho]

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?

The amp could go on the top facing up...though for such a sub I would be far more inclined to go with an external amp. All but one of the plate amps on the market have filters that roll off the power around 20Hz (making that 16Hz extension useless). The one that doesn't is a BASH amp design putting out a measly 400 watts.

PR's MUST be vertical. They have a very very loose suspension and will sag like 1/2" when mounted facing up. This totally ruins the tuning of the PR and also you run the risk of shooting the PR out of the cabinet. I've never done it, but I know people that have tried down-firing PR's and it just doesn't work.

Btw, you will run out of excursion on the tumult before two 18" PR's will...I think you might be modelling a lighter version of the 18" PR's. Go with the PR18 - 2500:

http://yellow.mynethost.com/~bv126368/shop/catalog/index.php?cPath=24&osCsid=1007d5e062fc1986c76a96425f9aa46f

If you still want a lower tuning point, then add weight to the PR's. They come with a threaded rod extending through the back (where the voice coil normally goes) and there are weights that you can screw on. If you need a higher tuning point then go with the PR18 - 1600 (and then add weight as needed).

Btw, be careful of tuning the sub too low....I know it yields a flatter, deeper response, but it also hurt the transient response. Also, a slightly smaller cabinet tuned a bit higher rolls off slower, which sounds more natural when you've got frequencies around the "corner" (aka, try to make the corner as round as a circle....not a rounded square corner and not a flat oval). If you spend a lot of time optimizing the cone excursion you'll see what I'm talking about.

Have you considered using the AES AV15? (available from that same link). You can get the same frequency response as the tumult and only sacrifice 6dB in overall output...but will require far less power from the amp (300W versus 1000W). You can get similar results with the Dayton Titanic 15" driver with the right filters.

[007]

Ok problem #2, metal and wood have different MOE's so if you plan on building it a cool environment, then using it in a hot one, it will loosen up.

problem #3, resonance of the strings may color the sound.

[Jay481985]

in response to drwho. Oh there finally out I haven't checked that

website for months since they have not updated it in months. Also I was

modelling it using the 2500 gram not 2000.

That new sub is interesting project for the winter break.... maybe the tube sub is a go?

for the tube that I was thinking before, the 16 inch outer diameter,

1/2 inch wall thickness, so 15 inch internal, and 60 inches tall...

also that parts express is selling that bash amp that will deliver 500

watts matches the pe max of the driver.... Though I believe that an amp

with higher than sepcified rating of the sub is better to reduce

clipping. Hey just remember not to go past 9/10 of the amp then for

sustained time. Plus usually amps distort near limits to unacceptable

limits.

Hmmmm 180 for the av 15

150 for the bash amp

100 for veneer, baffle

50 for a 6 inch flared port if they still sell it

around 500 plus minus for a very capable sub hmmm!!!!

I like the av 15 but I think the av 12 will be better suited. Also I want to tune to port to about 20 hertz.....

I admit it I'm a deep bass lover not a boomy bass lover.....

I have one love, its called 20 hertz frequency lol

[Jay481985]

Ok

problem #2, metal and wood have different MOE's so if you plan on

building it a cool environment, then using it in a hot one, it will

loosen up.

problem #3, resonance of the strings may color the sound.

ummm #2 would mean that everything in the world that is made of wood

and uses screws would loosen up sure they do but within tolerable

limits. Yes everything loosens up over time but do suspension bridges

sag to an unacceptable limit, no they already account for the slack.

BTW most people don't like their house 32 degrees or 100 degrees, I

have air condition and heating.... The normal temperature flux should

be around 68-74?

Problem #3 we are not plucking the string like guitars or string

instrumentsI think your trying to get. Yes violin strings resonate but

at a much higher frequency then a sub hits. And the wire I would use

would be around Violin gauge thickness. I doubt that it will color the

sound at all since one it is in a box, two it is a much lower

frequency, three no plucking its a equal pressure. Unlike string

instruments that have a direction to cause vibrations or guitars that

pluck the string, this is a sub that moves in and out way to fast to

make a difference. I would say the is no directional pressure inside

the box unless you place it near a port tube or so forth.

[formica]

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 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.

If you are limiting yourself to 15" there are some pretty good DIY options.

In the mid excursion range, you've got the O-Audio TC2, the

SoundSplinter RL-P15, the AcousticElegance AV15, and whatever Parts

Express is pimping. Note that Ascendant's offerings also fell

into this general range.

Although the Tumult isn't available, in the high excursion range you do

have the SoundSplinter RL-S15. OTOH, Adire's Tumult and

Acoustic Elegance HE15 (Deon's baby) still seem a while

away. None of these are cheap though....

ROb

[ygmn]

...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? []

Nope....

Right out of strengths of materials textbook....

the lower the number the less stress is required to deform....

[ygmn]

Ok problem #2, metal and wood have different MOE's so if you plan on building it a cool environment, then using it in a hot one, it will loosen up.

problem #3, resonance of the strings may color the sound.

Modulus of Elasticity is not used for change in temps....

That is called Thermal expansion co-efficient... complete different...and for home use...not that big a deal as the temp only varies about 20 degrees for most peeps... 60F - 80F....

any colder and it is cold...and hotter and it is hot.... wood expands more per change in Degree F then steel....

[ygmn]

after thinking about it...the steel tension members would not be a good idea nor would you gain much...volume...

they would have to be prestretched which means...thousands of pounds ...which nmeans anchor points would have to be reinforced....

If you want to reinforce MDF ...use aluminum or steel instead...and material can be much much less thinner and less cross sectional area which means less volume lost....

[wstrickland1]

if you were able to stress the tendons within the enclosure material, as in a post tension slab, to say, 10,000 psi you may be on to something. Hmm, how about a concrete box?

[Jay481985]

Well I was thinking not so much a socket screw and tension. What about more of a hurricane nut

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=081-1080

that instead of the chance of the mdf really tearing out as it is prone

to do but brace it with a soft edge. Like have that and than tension

the string somehow from there maybe like a bridge, I live near one of

the largest arch bridges in the world and saw it many times I believe

they use a method of having the wire, stretching to proper tension,

then adding like a wedge with teeth that bite into the wire and wedge

itself into a hole. Obviously the wedge is bigger than the hole thus

the tension alone keeps it in place. Using a hurricane nut limits the

tearing effect of say a screw. So tension can be set much higher.

[Jay481985]

Michael I see that basic idea of the shape but wonder its more tube

like with a rounded end? Hmm I wonder how much it would be to custom

make a mdf sphere. I remember that someone had the idea to cut 1 inch

thick rings of various size and than glue them together to make a lego

sphere I guess the closest thing to come to my idea and than lathe it

smooth. Though the inside would loose some volume as to not being

smooth inside. Also what about the idea of instead of wood but using a

epoxy based enclosure, I know expensive!!! but epoxy is very strong and

light. I believe you can possibly make a sphere of say plaster, paint

the epoxy with a mesh shape like fiberglass or say a fiber of some

sorts to renforce the epoxy. Or hell has anyone made a carbon fiber

subwoofer enclosure? Carbon fiber is getting cheaper, around I believe

10 dollars a square foot as opposed to 100 dollars ten years ago.

relatively it is easy to make, make the sphere say out of steel or I

others ways I know of another way but am not sure if I can say it. But

then you basically paint the sphere with the resin and then heat it in

a huge furnace. Now who has a large argon furnace, hell they have ones

that can fit fighter jet planes in them (F22 carbon fiber shell)

[michael hurd]

If you can make an MDF driver mounting ring, and a basic skeleton, you can stretch fleece over, staple it tight, and fibreglass right over that. 2 coats of resin on the fleece, and it will set up nice and hard. Grind it slightly afterwards with a 36 grit grinding disc, then add additional resin and chopped mat sections.

You can build it any shape you want really, the techniques are used by a lot of car stereo installers in making custom components and consoles.

[Jay481985]

what exactly is a MDF driver mounting ring Michael?

[Jay481985]

Heck I worked at Stevens Institute of Technology in Hoboken New Jersey

in the materials lab of the engineering department as an internship

during my high school summers. I worked with a material called SiAlON

Silicon Aluminum Oxy-Nitride which has a hardness of 9.5 is very

similar to SiN Silicon Nitride which is a moisonette (man made diamond

that is brighter than a diamond) and is stronger than carbide.

Basically it can withstand 1800 degrees celsius before it starts to

burn and can be formed into most intricate shapes as it is a powder

that binds when heated to 1700 degrees c for 2 hours. I thought and is

thought to be used in the aerospace and nasa, especially since

Columbia. The fact that you make a cast and than paste it on and heat

it to form a solid item is unique. They want to use it in jet turbines,

lightweight, as strong as a diamond, etc etc... Also a key point

for nasa, it can withstand the temperature of reentry without the

problem prone heat tiles that keep falling and hitting the damn

vunerable carbonfiber and alloys that cannot withstand the heat without

fatigue and catastrophic failure.

[michael hurd]

This is a view of two MDF driver mounting rings, secured to a mold made from the interior of a vehicle. You would staple to these with the fleece, and then paint on resin mixed with the appropriate amount of hardener.

http://chris.pfharlock.com/glass/mountrings.htm

[Jay481985]

duh silly me I was thinking along the lines of that was needed to make mdf..... Its late like 2:45 and I had a rough week....

Why not use aluminum or so rings? I guess mdf is easier to work with,

though tapping metal is not really hard you just have to be careful,

know what your doing, and go slow.

[Jay481985]

oh btw a shameless post to add more posts to my name but

I want to thank you for your quick responses Michael as it would seem you are glued to the computer as well.... []

but also thank you to everyone else who responded. Hopefully this

sparks new thought and bring to the table some ideas that people had

but never expressed them. I think this thread is quite interesting. I

like the triangular prism idea with the dual pr, I now know what sub I

am going to get thank you Stryke for finally making the new av's. And

thanks Michael as you know your stuff. BTW If I were to try and veneer

a maple veneer, probably nothing special no paper back or so fourth,

maybe a mottle maple if the price is cheap enough, but how would I go

about gluing it to a cardboard tube like previous? since its not really

wood I am not too sure that the cardboard paper may be more absorbant

of the glue? and what type of method would you choose: titebond,

contact cement, etc?

Also Happy Holidays and Happy New Years to all!

[michael hurd]

It would be hard to say, but I think that I would chose contact cement, having experience in applying vinyl to simple panels before. No messing with irons, etc. Be aware that the substrate has got to be perfectly smooth, otherwise the thin veneer will conform to the undulations below.

Also, AE is out of stock of some of the parts to assemble AV-15 subwoofers for the moment, they are trying to get a bunch of parts plated, and build up a few magnetic assemblies. However they are shooting to get a bunch built up by april or so. After the woofers are assembled, the magnetic assembly has to be "charged", and they do not have that capability in house. They will build up a batch, then take them to a facility that can charge them.