Too Much Air Space??

jakelm

Built a new enclosure this weekend for my SVS 12.1 w/ Rythmik amp.

Something didnt sound right. The dems are 17"W X 18.5"D X 44.5"H, using 5/8" MDF board. 4" port 19" long.

I dont have the SVS parameters so I cant use winisd.

I thought I had too much air space, so I added poly fill. Still doesnt sound right.

Not sure if its the amp or sub or box or all of the above.

My guess, after all the poly fill is, its ~6cuft. Might still be too much for the SVS? I dont want to start cutting w/out other opinions.

I wish SVS would release parameters for thier drivers.

Or I might just replace it with a Titanic III 15".

I will try to get some pics up.

Thoughts?


Jake

ShinAce

You don't really need specs. The box volume and tuning frequency have been stated.

Assuming you gave the external dimensions, your box has 6.8 cubic feet of space, minus driver displacement and 0.14 cubic feet for the port.

As a ballpark guess, you are tuned around 20 Hz. I'm at work, so I can't tell you for sure what the tuning is, but I figure you know very well.

Polyfill will not do much for the airspace of a vented box, it primarily will absorb midrange frequencies.

You can always try stuffing the box with solid objects to reduce the airspace. Bottles full of water might do the trick, if you have enough of them.

Best of luck.

jakelm

Thanks Shin. A second measuring did a pretty good job at what I'm working with.. I posted a graph in the other REW thread I have started..

Deadof_knight

OK its depth times width times length divided by 1728 and then minus any other ports or speaker displacement 6.8 is just a tad big is it not ?

ShinAce

Not neccesarily.

Adire Audio released some subs a while back that used boxes ranging from 5-7.5 cubic feet tuned to 20 Hz. The cerwin vega stroker wants a box that big to shine.

For HT, 2-3 cubic feet for a 12" is the norm, but 6 is not unheard of.

Jake, if you really wanted to, you could measure the specs. The easiest way is to take an impedance plot and send it to me. You will need an additional test to find Vas.

You would need to remove the driver, preferably hand it up in the air, and run a signal generator through your amp. You could use tones, but you will need tones from 10 Hz to 100 Hz at every 2 Hz minimum. The setup is just the speaker connected to the amp with a 10 ohm resistor in series. You measure the voltage across the woofer and then the voltage across the resistor and jot it down. Change frequency, lather, rinse, repeat. You'll want to use a low voltage for the test, roughly 50 mV across the resistor. The speaker doesn't even need to be audible.

It's a fair amount of effort with the possiblity of me coming back at you with "yep, 6 cubic feet is fine for the driver". Trust your ears on whether this is something you want to try.

jakelm

Measurement taken here. Looks pretty good and sounds good, so I think I'm ok, for cuft. I probably could chop it down and re/tune it, but then it wouldnt look so massive..:p:p

BIZILL

i used my old svs 12 for a truck sub box. no, svs will not give out the t/s specs on their subs. but the WILL help you design a box if you call or email them. they helped me out.

and jake, the polyfill only tricks the sub into thinking the box is BIGGER than it really is.

jakelm

BIZILL wrote: »

i used my old svs 12 for a truck sub box. no, svs will not give out the t/s specs on their subs. but the WILL help you design a box if you call or email them. they helped me out.

They actually gave me some info, that the 12.1 was the same driver as the TC sounds 500 driver.

Found the specs over @ AVSforum.

Not that it mattered, 'cause I am way over spec anyways.

BIZILL

you and me both. my box was just a bit too small for ported, yet a bit too large for sealed. i went with sealed and it hits low. still wish i had gone ported, though.

ShinAce

BIZILL wrote: »

you and me both. my box was just a bit too small for ported, yet a bit too large for sealed. i went with sealed and it hits low. still wish i had gone ported, though.

It's never too late to operate.

jakelm

ShinAce wrote: »

It's never too late to operate.

And....its easier to cut wood than it is to grow wood.

ShinAce

What kind of wood are we talking about?

jakelm

ShinAce wrote: »

What kind of wood are we talking about?

Partical wood.. MDF.
Very hard to grow it.:D

RSTERN

Bizill
What kind of box did you build? sealed or ported? And how big is it? I was thinking of building one , but not sure if I have enough room.
Thanks
Rob

honda cber

BTW, i wouldnt do this.

You can always try stuffing the box with solid objects to reduce the airspace. Bottles full of water might do the trick, if you have enough of them.

i can think of at least three good reasons that this is a bad idea. maybe some gallon freezer bags filled with sand or something. i would probably double bag it, as well.

OTOH, this technique absolutely works. it also has the added benefit of adding mass to the cabinet, while being acoustically inert.

a