Idea for a cheap sub...

[DrWho]

I'm the new workshop director for the AES chapter at the University of

Illinois and I'm looking to get a head start on some workshop ideas for

the fall....one of which will be a suwboofer workshop. Since it's

college town, low price is a big plus, but we also don't want to skimp

on the performance (otherwise it'd be a waste of time).

So here's what I'm thinking and was wondering what you guys thought of the idea:

Ascendant Audio Assasin 12" driver ($75):

http://www.ascendantaudio.com/assassin12specs.html

PartsExpress 250W Sub Amp w/Bass Boost ($120):

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=300-796

The enclosure will be 5 cubic feet tuned to 20Hz and will be using one

of the 4" flared precision ports cut down to 14 inches ($13):

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=268-352

The cabinets will be precut by another member's dad off campus so we'll

pretty much only have to drill the thing together. I'd figure about $30

per cabinet unfinished.

The subamp will be rewired for 3dB of boost at 25Hz (so I'll have to figure out some new values that aren't in the table).

Overall the system should have an F3 around 19Hz and put out 110dB. The

following plot shows the behavior of the driver with and without system

nonlinearities - this is a very reassuring plot as most drivers look

way nastier than this. Total cost should be under $250....with student discounts we might be able to swing $200 [H]

[TheEAR]

Looks like a serious copntender for best "student" sub under $300.

A dorm shaker and war starter. []

[Jay481985]

that seems like a feasible project. Hmm I might want to model the sub in autocad if you want and give me directions. Right now im too err buzzed.....

[Spkrdctr]

When are you going to start selling them?[] It will be fun to see how this works out. Great project and looks to be a lot of fun.

[DrWho]

Probably sometime in the fall semester of 2006...I posted the idea here

in hopes that someone might be interested in building one themself.

I never thought of selling anything though...that could make for an awesome fundraiser...

[CECAA850]

Those Ascendand drivers are pretty impressive for the price. I bought 2 of the Arsenals when they could be had at the preorder price. My son and I built a box for them and stuck them in his van. They totally blow away some of his friends "name brand" subs. Ascendant conservatively rates their drivers so don't be afraid to give them their fair share of current.

[DrWho]

The problem isn't the current so much as it is the cone excursion...the

further the voice coil moves, the less B-Field it sees and thus less

power in the motor.

Attached are some more nonlinear projections - the input power for all

the plots were adjusted for excursion limits (besides the yellow one).

Light Blue = linear behavior, excursion limited (150W)

Dark Blue = voice coil temperature taken into account (95W)

Purple = VC temp and 50% drop in B-field (250W)

Green = VC temp, B-field, and slightly lower tuning due to port compression (200W)

Orange = VC temp, B-field, port compression, and reduction in effective driver diameter (100W)

Yellow = ignore everything, throw in full power (350W)

As you can see, things quickly turn to crap when you really start

pushing the system. But you could still claim +-3dB from 20Hz to 80Hz

[] Though it's not apparent, I would anticipate needing the entire

250W from the amp in order to achieve 110dB...which means the system is

exhibiting quite a bit of power compression. Fairly linear low

distortion behavior will probably end around 104dB. But ya, these are

merely projections of what I hope to be the worst case scenario and I'm

not sure what other non-linearities can be accounted for, but there has

gotta be more.

[CECAA850]

Still looks awesome for the ching. What kind of pre-assembled units do you think it will be comperable to?

[DrWho]

It would be comparable in output to a KSW-12, but dig lower.

Two of them would cost the same as a sub-12, same output but would dig lower - the downside is it'd take up twice as much space.

It would beat the KSW-10 and the sub-10...and definetly any of the promedias subs.

[bhendrix]

What are your plans for cabinet dimensions and material? Will both driver and port be front firing?

[DrWho]

If it were a cube it would have dimensions of 22" on each side with

.75" wood...front firing driver with a front firing port: 4" flared

port, 14" long.

We were also throwing around the idea of sonotube, but don't want to go

to a down-firing woofer as it would reduce maxSPL and cause more

nonlinearities. So if it's more cost effective we would go with a front

firing driver and a rear firing port with an amp somewhere in the

middle. (picture SVS on its side).

And finally a triangle design like the RT-12d would be 24" along the

sides (34" face) and would be 35" tall. It may seem big, but when

tucked into the corner it's a big space saver.

Those are the ideas floating around right now...I'll probably build

something that is 18x18x33 as it would fit nicely beside my desk.

[Jay481985]

the triangle design causes more complications as it takes longer to build those pieces.

I asked a tube company how much a 16 inch inner diameter tube is, 12 feet at 3/16 an inch costs 99 dollars free cutting. To think of just cutting the baffle and such would be a cost cutter by a long shot as compared to the triangular sub

[Xover]

The triangle sounds like a good option to me. A couple less parallel sides and plenty of room for a passive radiator if you so desired. The face and top could be nice hardwood veneer the other three sides won't show so MDF would be fine. And corner placement usually doesn't offend the decor or mama.

Duh-O forgot about amp placement on the corner option......

[Jay481985]

wood veneer hahhahahahhaahahha in a college seting hahahha!

btw amp on top

[Xover]

Ok let's make that optional and spend some money on a protective cover for the woof.

[DrWho]

Since it's a workshop, whatever wood cutting needed is going to be done

ahead of time in one of our member's dad's woodshop. You could argue

the triangle takes less time to cut because there's less pieces and

setting angles isn't that big of a deal. It definetly is the least

invasive on the room and has the added benefit of no parallel vertical

sides.

The problem with sonotube is mounting the amp. With a driver on one

side and port on the other the amp would need to be flushmounted in

some way...and that'd be a lot of work to make airtight. A 6 foot

section with I believe a 15" diameter was running $20 at the Lowes in

town...talk about a steal. But since we would want it to lay on its

side without rolling, I think we could house the amp in a box that has

rounds holes in two of the sides through which the sonotube goes...and

then you just need a small hole in the sonotube for the amp wires to go

through. I'm not too sure what the effects of heat will be on the amp

in such a tight space though...

A cube would be the easiest, but the problem is it takes up the most usable floorspace.

The workshop is actually going to be spread out over a few meetings

too...the first couple will be me discussing some of the theory and

design considerations involved. Perhaps we might be able to get someone

like Tom Danley or Tom Nousaine to come down and talk too...the more

"educational" we make these workshops, the more money we get from the

school to help bring the costs down.

All that to say...I'm thinking we will present a few possible designs

and then vote on 2 or 3 of them during the first meeting. The whole

point of DIY is the ability to customize so perhaps we'll present a few

coffee table, lamp stands, end table options...

[DrWho]

Oh, I almost forgot....this is one of a few speaker building

workshops. All of the designs will be raw wood and it'll be up to the

end owner to finish them however they want. Everyone has different

tastes and budget constraints - and I kinda like the raw wood look []

[Jay481985]

maybe because you're a raw kinda person []

eh setting up angles is not as easy as you think

[keepinitcool]

That is a pretty cool idea. Some extensions of it could be to built a passive sub and allow the use of external amps (which people might already have), and then build a crossover as an extension of the project.

[colterphoto1]

can you go for a more space-saving design, say a bit more tower look? 22" cube is almost a LS bass bin- that's pretty darned big!

If you want- you can do final assembly over here! Maybe I'll have the fibreglass thing figured out by then and we can 'dorm-proof' them!

This Saturday at BS and Woo's should be fun, are you getting off Fri night or coming in way late so's I gotta pour you into the car early Sat am.? We want to get there early in the day so we can spend some time blowing up their stuff!

M