Dual 12" bipolar subwoofer

Systems

jakelm wrote: »

Yeah, thats what I thought, after bracing I would probably be around 4.8cuft.

Thats close enough,you just have to find out what the actual port tuning frequency of the stock SVS is.

Did you get any more accomplished on your project? Or are you letting the glue dry?

Not yet,but Im home with a sick daughter today so I might get some glue on it later today.:)

Systems

jakelm wrote: »

If you can, explain Vas for me. Is that the airspace? What exactly is that? It reads in cuft, but I dont quite understand.

Vas is compliance ratio,it is defined as the amount of air having the same compliance(springiness) as the driver suspension.Yes it is a big part in determing enclosure volume.

jakelm

GV#27 wrote: »

Thats close enough,you just have to find out what the actual port tuning frequency of the stock SVS is.

Well , if I have the same driver A, and the same cuft B, and I know that their speaker rolls off @+/-3 dbs @18hz C, then I can figure out D, the tuning.

Systems

jakelm wrote: »

Well , if I have the same driver A, and the same cuft B, and I know that their speaker rolls off @+/-3 dbs @18hz C, then I can figure out D, the tuning.

What you have to know is the exact diameter and lengths of the ports or ports of the SVS.

Systems

jakelm wrote: »

The only issue i have is the roll off for their xover. Its only a 6db, I would have prefered a 12db stock roll off, with out mods.

They claim the 350 has a 12db LP filter and the 370 can be order with a 12 db or 24 db LP.I need 24 db for my rig.

jakelm

GV#27 wrote: »

What you have to know is the exact diameter and lengths of the ports or ports of the SVS.

Well, yeah.... Like I said, I'll have to wing it.:o

jakelm

GV#27 wrote: »

They claim the 350 has a 12db LP filter and the 370 can be order with a 12 db or 24 db LP.I need 24 db for my rig.

My mistake, your right. Its 24db I would like.

jakelm

It really doesnt matter what they have theirs tuned to so much the same air volume for their driver. I can multi-tune also. Screw them..I can do it too!!!!!:D:D:rolleyes:

Systems

jakelm wrote: »

Well, yeah.... Like I said, I'll have to wing it.:o

Ahhh true unless you were lucky enough to find the specs of the unit and it make mention of the tuning frequency,then it would be easy to figure out port size.

jakelm

GV#27 wrote: »

Ahhh true unless you were lucky enough to find the specs of the unit and it make mention of the tuning frequency,then it would be easy to figure out port size.

True, but I found tuning Fr depends more on my taste and my room than what it "should" be..:p

Currently I am tuned to 21hz, which works very well in my room, 16'W X 24'L x 9'H. I am restricted to that tuning due to my current enclusure design. But will venture a few Hz lower in a bigger cabinet.

jakelm

I know this is an age old question, but your thoughts on down firing vs. front firing. I have noticed a huge transition from front firing to down firing in the past years.

I know you had no choice when going bi/polar. But just wanted to get your thoughts.

Systems

jakelm wrote: »

I know this is an age old question, but your thoughts on down firing vs. front firing. I have noticed a huge transition from front firing to down firing in the past years.

I know you had no choice when going bi/polar. But just wanted to get your thoughts.

Assuming the driver is suited for downfiring(some are not)then I don't think there is any advantage one way or the other and the choice is really because of cosmetics.However one manufafurer claims that downfiring helps to equalize the acoustic load on the front of the driver which linearizes cone motion, supposedly resulting in reduced distortion.

jakelm

GV#27 wrote: »

Assuming the driver is suited for downfiring(some are not).

Whoooo... Dare I ask?

Systems

jakelm wrote: »

Whoooo... Dare I ask?

Some with heavy cones and looser suspensions will sag from the centered position when not placed vertically.

jakelm

GV#27 wrote: »

Some with heavy cones and looser suspensions will sag from the centered position when not placed vertically.

Sounds like ****..lol:eek:

Systems

jakelm wrote: »

Sounds like ****..lol:eek:

he he, excessive sag in either is NOT a good thing.:D

jakelm

I wonder if there is a tell tell sign? The SVS is a very heavy cone based woofer. I wonder if it would suffer from this problem? Also, it was funny, but when I turn my sub on its side and played a 15-18hz sine wave, the whole box would wobble/move. I guess that tells me to leave it down firing, in what ever inclosure I build.

Systems

If SVS used it downfiring then Im sure it will not be an issue.Here is a calculator to determine sag(woofers not ****:D)http://www.parts-express.com/resources/downfire.html

jakelm

GV#27 wrote: »

If SVS used it downfiring then Im sure it will not be an issue.Here is a calculator to determine sag(woofers not ****:D)http://www.parts-express.com/resources/downfire.html

Wow.. Thanks GV, parts express does have everything...:p

Systems

jakelm wrote: »

parts express does have everything...:p

PE are a resourseful bunch.

jakelm

And you see, I though standing a woofer on its side would be a bigger problem. If suspension is not strong enough, after time of hard playing, they could loosen and the coils would sit and rub on top of the magnet.

Learning something new is a wonderfull thing.

Systems

Assuming its not damaged the spider (rear suspension)will always keep the voice coil centered when placed vertically .

jakelm

A blown speaker scratches. Isnt the scratching from over exurting (or breaking) the spider springs and thus the coils are rubbing the magnet.

Systems

jakelm wrote: »

A blown speaker scratches. Isnt the scratching from over exurting (or breaking) the spider springs and thus the coils are rubbing the magnet.

Voicecoils can rub for a couple reasons,when severely overeheated from abuse the coils former can change shape slightly to an oval instead of a circle.With the small amount of clearance in the magnet gap rubbing will occur .Also I have seen coils burned so bad that the varnish coating on coil itself has bubbled enough to scape.Also the end of the coils former can get bent if over excursioned and it hits the back plate hard.Thats the nasty ticking sound when you bottom a woofer.

jakelm

GV#27 wrote: »

Voicecoils can rub for a couple reasons,when severely overeheated from abuse the coils former can change shape slightly to an oval instead of a circle.With the small amount of clearance in the magnet gap rubbing will occur .Also I have seen coils burned so bad that the varnish coating on coil itself has bubbled enough to scape.Also the end of the coils former can get bent if over excursioned and it hits the back plate hard.Thats the nasty ticking sound when you bottom a woofer.

I get a very deffinate "pack" sound when over excursing my subs. Not pleasent at all.

Systems

jakelm wrote: »

Not pleasent at all.

And the level of displeasure goes up proportional to the replacement cost of the woofer.:D

jakelm

GV#27 wrote: »

And the level of displeasure goes up proportional to the replacement cost of the woofer.:D

So True.



I wish I could have got my hands on the SVS 12.2 woofer. Much higher Xmax, from what i was told.

Face

I have one of these in my HT sub, and a spare one sitting around. I may buy a third to use for stereo subs in my 2ch rig. How's a x-max of 18.3mm?
http://www.edesignaudio.com/edv2/product_info.php?t=2&products_id=35

Btw GV, nice design! I may have to copy off of you for my stereo subs.

jakelm

Think Dayton will give it a run for its money?

ShinAce

That pack sound is 'bottoming' of the voice coil former.

I once reassembled an isobarik enclosure with the subs in phase. This caused no sound and lots of wasted power until I finally turned it up loud enough for the voice coils to stress themselves into rubbing against the magnet. I quickly backed off the volume and realized my mistake.

By the way, I meant to say bi polar design but had cracked open a beer before posting. Proofread your posts, ladies and gentlemen.

As GV27 confirmed, Vas is the equivalent air mass that has the same 'stiffness' as the woofer. The cone area affects this value, so stiffness of the cone is not a good indicator. A sealed box that is too large will be overdamped and therefore have fantastic transient response. An oversized ported box will waste space.

When looking for subs that can hit low, also look at Adire audio. When I was still active in this stuff(5 years ago), they had a sub called the tempest. Very respectable performance.