Dual 12" bipolar subwoofer

[GV#27]

Here is the new woofer I'm in the process of building for my combined HT/2 ch system.I wanted to update my aging DIY dual 10" woofer setup with something that would extend deeper into the bass and play louder with less potenial for distortion or over excursion.This sub will be used to augment my main speakers only and will not be used for the LFE channel as I have a pair of woofers already serving that purpose.

The Infinity 1242w car subwoofers I chose are certainly far from exotic but they will work perfectly in my intended enclosure.Using a pair will increase sensitivity by 6 db so they won't need to be driven as hard as a single unit ,plus distortion will be reduced and power handling increased.
I generally prefer the sound of low Q sealed boxes over ported designs so thats what I will be using.

I will be mounting the drivers opposed (one facing forward one back) in a bipolar arrangement that will help cancel cabinet vibrations. As the pics show I also braced the heck out of it so it should be fairly inert and heavy.

[GV#27]

here are some pics.

[anonymouse]

How did you model out that box?

[GV#27]

How did you model out that box?I used Win ISD to do all the response modeling.

[zingo]

Looks good and I still claim that you are the DIY subwoofer king.

[GV#27]

Looks good Thanks and I still claim that you are the DIY subwoofer king.:o uummm definately not ,just an enthusiastic hobbyist.:D

[zingo]

Thanks :o uummm definately not ,just an enthusiastic hobbyist.:D

Well you run circles around me, and I have some fair electronics experience. Cool design for the box, and way to go with the car subs. I like a project that goes outside the box.

[ward91]

i got so fed up of using win isd (both of them, beta pro ? and the other one)to model my box i just built an approximate one coz i got fed up of trying to accurately calculate the volume minus the batons in the sub and the effect of foam ect.
i have always wanted to know how to compensate in the modelling/design about putting foam in the box , my sub (custom) was sealed but at the time i didn't have a decent amp to drive it and id didn't sound much. i went for a rather risky port frequency at 17hz just to seem what it sounded like. the port defiantly changed the sound and yup it did unfortunately boom things up a bit, so i had to be extra careful with placement.

[GV#27]

Cool design for the box, I wanted it to take up as little floor space as possible and I will be placing it in a corner.So it ended up being 48" tall and it only takes up a little more than a square foot.way to go with the car subs. As long as they have the correct T/S parameters there is no reason a driver designed for car use can't be used in a home sub and these ones suited this project.Also I had budgetary contraints impossed by my lovely bank manager/accountant so these were inexpensive Ebay snags.

[jakelm]

What are you driving them with? Subs ran bi/polar does not cause a phase problem? And Ohms will double? Its still sealed, if I understand correctly, stuffed/padded? That is a small Thiel design.

[GV#27]

What are you driving them with? Either a Bryston PP120 or ICE Power ASP 250 classD module,I have both units so I will try and see which I prefer.Subs ran bi/polar does not cause a phase problem? No,they are wired in phase and though they face in opposite directions, both woofers move outward and inward at the same time(push-push) so no cancellation will occur.And Ohms will double? drivers are both 8 ohm but wired in parrallel so impedance will be 4 ohms.Its still sealed, if I understand correctly, stuffed/padded? That is a small Thiel design.Yes it is just a regular sealed designed using the Theile/ Small parameters.There will be some polyfill or fibglass stuffing.

[jakelm]

No,they are wired in phase and though they face in opposite direction both woofers move outward and inward at the same time(push-push) so no cancellation will occur.

Ok, I must be confusing it with di/polar. "di" is out of phase, "bi" is in phase.

I'm curious to hear your thoughts after everything is up and running.

[GV#27]

Ok, I must be confusing it with di/polar. "di" is out of phase, "bi" is in phase.Yes.

I'm curious to hear your thoughts after everything is up and running.
I have to get my butt in gear and get it glued together then veneered.Probably 1-2 weeks.

[jakelm]

Curious, the walls in the middle of the box. Are they for a sonic or purpose or just for bracing?

[GV#27]

Curious, the walls in the middle of the box. Are they for a sonic or purpose or just for bracing?Strictly for bracing.

[jakelm]

Strictly for bracing.

Fairly inert and heavy? I'd say fairly...lol

48" x ? x ? Looks about 14" x 14" x 48"

[GV#27]

Fairly inert and heavy? I'd say fairly...lolWith the drivers added it will be.
48" x ? x ? Looks about 14" x 14" x 48"Close, 13.25" x12" x48".

[jakelm]

Very small footprint. Cloth cover or paint?


You know so many of us are looking into sono tubes. Its nice to see something alittle different and square.

Since I cant seem to find a sonotube anywhere, I was thinking of building something like what you have. And my wife would have yet another place to put a plant...

[GV#27]

It will be veneered like this one.

[jakelm]

Nice,,

[GV#27]

Nice,,Thanks,the new one will be in the opposite corner so visually it equals the room ... atleast thats what I told the Mrs.:D


I removed the bass trap behind it so it actually sits tight into the corner as will the new one.

[ShinAce]

Looks great. I love the fact that you routed or cut channels for the bracing panels. Should come together like lego, if your saw is square.

Let me know how the dipole responds in room, I'm interested to find out if it'll smooth the overall response throughout the room.

[GV#27]

Looks great. ThanksI love the fact that you routed or cut channels for the bracing panels. Should come together like lego, I used a stacking dado blade,and yes it makes assembly much much easier.The pics were taken with it just press fit ,no glue. if your saw is square.Yep,its dead nuts square.:D

Let me know how the dipole responds in room, I'm interested to find out if it'll smooth the overall response throughout the room.
Slight distinction, its bi polar and I'm not sure if it being so will help the in room response or not,but one maker of commercial bi polar subs(Mirage) claims it does.I will let you know after I get a chance to test it out and compare to my non bi polar unit.

[jakelm]

GV, why not slap a nice plate amp in there? Or are you more of an external amp guy?

[GV#27]

GV, why not slap a nice plate amp in there? Or are you more of an external amp guy?http://www.bryston.ca/pp120sst_m.html
The Bryston PP120 I have will bolt right to the back of the box if I decide to use it.It does not have an integral crossover like a plate amp but I already have that and specialized EQ in a separate chassis.

[jakelm]

Ever looked at Rythmik (http://www.rythmikaudio.com/amplifiers.html) plate amps? I am using one for each sub, they are really work horses.

[jakelm]

GV, you might know this answer,

I'm working with an SVS 12.1 driver. I am planning to built an enclosure similar to yours. 16 X 16 X 48... 5.6cuft. The SVS tubes are 16 dia, 46H, 4.2 cuft.

Since there are no prameters for the SVS, how do I know if I am going to have too much air space? There is a point where too much air, is like free air.

Is my enclosure too big? Should I stick with the same cuft as SVS?

[jakelm]

Im really suprized Ben hasnt chimed in

[GV#27]

Should I stick with the same cuft as SVS?Jake, if you want the same response as the stock SVS then yes the internal volume and port size need to be very close to the same on your custom box as in the SVS tube.(Also don't forget to deduct volume for bracing etc). If you want to experiment with different volumes and port tunings then you would need the T/S parameters of that driver and do simulations with Win ISD or Unibox.

[GV#27]

Ever looked at Rythmik (http://www.rythmikaudio.com/amplifiers.html) plate amps?Yes I have and interestingly would likely be my first choice for a plate amp.It is one of the few that have the option of using a customized EQ circuit (Linkwitz Transform)which my design needs.Rythmics 12" and 15" kit designs look to be really good designs as well.

[jakelm]

Jake, if you want the same response as the stock SVS then yes the internal volume and port size need to be very close to the same on your custom box as in the SVS tube.(Also don't forget to deduct volume for bracing etc). If you want to experiment with different volumes and port tunings then you would need the T/S parameters of that driver and do simulations with Win ISD or Unibox.

Yeah, thats what I thought, after bracing I would probably be around 4.8cuft. And instead of 3-3" ports, 1-6" or 1-4" port will do. Unfotunatly SVS dose not provide specs on thier drivers, so I will have to wing it.

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

[jakelm]

Yes I have and interestingly would likely be my first choice for a plate amp.It is one of the few that have the option of using a customized EQ circuit (Linkwitz Transform)which my design needs.Rythmics 12" and 15" kit designs good to be really good designs as well.


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. But I can say i love the "rumble" filter. Saving the life of my drivers. The amp realy has great options for tuning. And dont let the 350watt scare you. My SVS shits when its cranked. The amp can easily over excurse the drivers. I wished the SVS had alittle better Xmax.

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

[GV#27]

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.:)

[GV#27]

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]

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.

[GV#27]

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.

[GV#27]

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]

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]

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:

[GV#27]

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]

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.

[GV#27]

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]

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


Whoooo... Dare I ask?

[GV#27]

Whoooo... Dare I ask?
Some with heavy cones and looser suspensions will sag from the centered position when not placed vertically.

[jakelm]

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

Sounds like boobs..lol:eek:

[GV#27]

Sounds like boobs..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.

[GV#27]

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

[jakelm]

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


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

[GV#27]

parts express does have everything...:pPE 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.

[GV#27]

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.

[GV#27]

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]

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.

[GV#27]

Not pleasent at all.And the level of displeasure goes up proportional to the replacement cost of the woofer.:D

[jakelm]

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? :D
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 (http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=295-404) 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.

[GV#27]

The Dayton jakelm linked to is nice and this one looks real good as well. http://www.diycable.com/main/product_info.php?cPath=24_93&products_id=653 I wish I had the budget for drivers of this quality.:(
... but had cracked open a beer before posting.You should never drink and type.

[GV#27]

Btw GV, nice design! I may have to copy off of you for my stereo subs.
Thanks Face,when are you starting your project.

[Face]

Thanks Face,when are you starting your project.
Hopefully in 2-3 weeks.

[GV#27]

Hopefully in 2-3 weeks.Have you decided on a design?sealed,ported, driver selection?

[jakelm]

I wish I had the budget for drivers of this quality.:(


You wouldnt believe the price I paid for the SVS I have. And one of the best woofers I have ever had.

I think I paid $60 for it when I belong to www.thehometheaterspot.com . Big SVS fans there. Everyone upgraded their woofers and basicaly gave the old ones away.

[GV#27]

You wouldnt believe the price I paid for the SVS I have....I think I paid $60 for it ..Wow nice snag,I wish I could have scored a pair for that price.:(

[jakelm]

Wow nice snag,I wish I could have scored a pair for that price.:(


Yeah, I wanted 2 or 3 even, but the guy only had one. Came out of a PB12 Plus series. Maybe had 40 hours on it, then he upgraded.

You should see the difference in size compared to my Dayton. But I still want something with alittle more excursion, so I dont bottom out so easily.

[GV#27]

. Maybe had 40 hours on it, then he upgraded.

Only 40 hours and he had the urge to upgrade.:confused:What was the cost of the upgrade driver?

[jakelm]

Only 40 hours and he had the urge to upgrade.:confused:What was the cost of the upgrade driver?

Wasnt much...I think $100. Only for SVS owners. It was around 40 hours, he only had it for about a week, maybe 2.

SVS claimed the 12.2 was far superior to the 12.1 and now they claim the same for the 12.3

[GV#27]

OK if it only put him out another $40 it makes sense.

[jakelm]

Here (http://www.svsound.com/products-parts.cfm) you can see the 12.3 is $169 for svs owners

[Face]

Have you decided on a design?sealed,ported, driver selection?
At the moment, I have four of these: http://www.edesignaudio.com/edv2/product_info.php?cPath=37&products_id=183
2 ported boxes, I have the designs saved in WinISD. Going to build two boxes with two subs each. I also have a pair of 6.5 Tannoy dual concentric drivers. I was going to build second enclosure for these and place them on top of each sub to make them full range.

[GV#27]

Going to build two boxes with two subs each.You certainly won't be wanting for more bass with 4 12's. I also have a pair of 6.5 Tannoy dual concentric drivers. I have not listened to any Tannoy dual concentrics but have heard reports that they sound good.