Idea for a cheap sub...

[Daddy Dee]

I think that idea has alot of merit and offers an exciting option. Having the cabs precut is a huge convenience. I suspect that there are lots of folks who consider DIY projects, but when it comes to building the cab, it's a deal breaker for many, I think. This is so such a user friendly alternative, it's a winner.

Way to go DR WHO.

[DrWho]

I just discovered two awesome new programs: Picasa and SketchUp, both

of which were written by the dudes over at google (which means it's

definetly awesome)...and they're free:

http://www.google.com/intl/en/options/

(over in the "Communicate, show & share" section on the right)

So to learn the program I thought I'd mess around with this subwoofer

project and figured I might as well share what I was

thinking...pictures are always a ton more helpful. For what it's worth,

all these designs are 3 cubic feet.

[DrWho]

And here's showing the internals...the port is a bit close to the side

walls, but alas it'll have to be an accepted tradeoff. I'm anticipating

the port tuning to get lowered a bit due to the boundaries, so cutting

the port a bit short will be something to consider after it's built.

[DrWho]

And here's a pic of the rear where the amp will be mounted.

[DrWho]

And for those that wanna stack stuff on top, an optional board to be mounted on top:

[DrWho]

Or how bout a down-firing design to work like a lampstand? There is 3"

of clearance between the plates on both sides. The side with the amp on

it will have recessed holes or something so that it can be easily

removed for dialing in the sub (or maybe 3" of clearance is enough). On

its side with the two plates, the unit stands 2'6" tall.

[DrWho]

And then some internals just because they look cool []

[ancientdude]

Very Original!

...no where have i seen something like that before []

[DrWho]

I would like to go even smaller, but shrinking the volume requires the

port to be longer for the same tuning and the 18" baffle is the

smallest that fits both a driver with port on one side and amp on the

other side. Tis a very tight fit and the port running so close to the

one side is already a compromise that will increase air velocity (port

chuffing) and probably lower the tuning a bit. The 3" expansion for the

vertical mounting is yet another compromise and should also lower the

tuning a bit. But this is all "good" in that it's relatively easy to

cut the port to be shorter - thus raising the tuning back to where it

should be. Still going on about the port...the velocity is rather high

at maximum output: 40m/s when it should be under 20m/s. But this

corresponds to about 120dB after room gain...at more sane levels (below

110dB) the port velocity is acceptable. But the way I see it, the air

rushing through the port will be a "wow factor" despite how "bad" it is

for the sound.

I'll attach a few more pics of the anticipated response curves. Blue is

the ported cabinet with room gain typical of a rather large room

(starting at 35Hz). Green is the same everything, but sealed (no port)

and is showing room gain typical of a rather large car (starting at

65Hz).

So, the first graph....the anechoic response when playing in a field. It's -9dB at 20Hz.

[DrWho]

Very Original!

...no where have i seen something like that before []

lol, carpet coated cylinders have been used by the car audio crowds long before SVS ever came into existence []

Speaking of being 9dB down at 20Hz, here's the what the response looks like after typical room gain (+10dB at 20Hz):

[DrWho]

The next thing we should look at is cone-excursion:

Note how the cone becomes unloaded below the tuning point, but that's

why we have the EQ on the amplifier which will drop its output (and we

drop it only just enough to match the peak excursion above the tuning

point). Also, the cone doesn't move much at all at the tuning point

either - another thing the EQ is doing is 3dB of gain there because

there's free excursion available:

[Jay481985]

sonotube based (cheaper) or papertube based (expensiver)???

sonotubes are cheap but thin while the papertube based I hunted some people at the factory to give me an estimate at 90 dollars per 18 inch wide 3/8 inch thick 12 feet tall tubes.

Also some companies allow up to 50/s port velocity and say "it adds to the bass" but most stick tops around 40m/s at max volume which should be fine. 20m/s is really overengineering and optimizing the box.....

[DrWho]

Speaking of the fancy EQ, better be sure the power capabilities of the

amp aren't exceeded. It's rated for 250W into 4ohms, and with a 150W

nominal input we see a peak just under 250W right at the tuning

frequency (where we are implementing 3dB of gain).

[DrWho]

Very related to the power handling is the impedance of the system.

Characteristic of all ported system we see two impedance peaks and then

only one impedance peak with the sealed cabinet. The higher impedance

peaks are the resonant frequency of the system so you will find those

notes hanging on a bit longer than they should. Combine that with the

natural resonance of the port and you'll find yourself a little extra

boom in those last octaves - though not a very big deal, most musical

music happens above 40Hz and anything below that should be obnoxious

loud anyway []

[DrWho]

And then here we have the port velocity:

[DrWho]

I think I'll stop there...there's a few more things to look at, but

this covers all the "basics". One thing that's fun to do is to go

further and look at the non-linear behavior for every one of these

graphs. I already did that at the beginning of this thread so won't do

it again, but if you're not careful you could end up with some real

nasty effects.

I hope y'all don't mine me posting all this crap...this is the kinda

stuff we'll be discussing during the seminar and I was figuring I could

make this thread a reference that way nobody needs to take hardcore

notes.

[darkside]

Just a quick question(s) Doc, how do you get sketch up to calculate the

volume of those figures you drew if it does at all? Also, how do

you know that the dimensions of your figs are what they need to be in

sketch up. I do not recall seeing measurments anywhere in the program,

unless i missed something...

[DrWho]

Well you calculate the needed volume and dimensions ahead of time using WinISD or some other similar program. And then when building each piece in sketchup there is a window in the bottom right that shows the dimensions of the piece you're building. And then there is also a tapemeasure to measure stuff after the fact.

[darkside]

Okay, thanks Doc.

Now, off topic, I punched in the T/S parameters for an Ascendant Audio

Arsenal 15 into WinISD and it calculated a ported box to be 17.1cu

ft[] with a 4in long port with a 4in diameter and tuned to

17hz, For a sealed box I got a 9.1 cu ft box, does that sound

right? This is the first time I used WinISD and am not sure

whether or not I did something wrong...

[DrWho]

The arsenal 15 subs stink for the money []

Try checking out the assasin lineup or look at the Dayton drivers from PE (either the Titanic or the DVC subs) and then check out TC Sounds - they've got some killer offerings right now.

Probably better off making a new thread if you're serious about building a sub of your own (so it catches more attention from others that might comment on it).