Inverted Subs

Robbie · Post by **Robbie** » Thu Jun 03, 2010 11:26 am

Hi, i am sure this is a huge topic however i am trying to understand the basic theory behind inverting sub's

for example do you use standard sub's? I am guessing that you need one designed for a ported box and not sealed or are they what i remember as free air subs?

would the box volume be the same as one with standard mounting?

Apart from the fact that they look cool is there any benefit to sound quality or power?

Thanks in advance
Robbie

Post by **Bfowler** » Thu Jun 03, 2010 11:38 am

there is surprisingly little to no sound difference!

the front of the cone is still in a enclosure, so you dont need any special or different sub. just make the enclosure to the same air specs as you would have if it was mounted normally. (account for the driver displacement, so .1-.2 cubic feet larger)

Robbie · Post by **Robbie** » Thu Jun 03, 2010 12:19 pm

That is exactly the information i needed, definately the way im going to go

Thanks

Just need to figure out which sub to use now =)

Rob

Post by **ttocs** » Thu Jun 03, 2010 12:26 pm

the only warning I would give is to be sure it is lined up perfectly or else the surround moving will wear out faster rubbing aginst the box. YOu will also get a little more spac out of your box since the motor/magnet is not displacing the air now.

IF you have one sub forward, and one backward you will need to wire on of them out of phase.

Post by **Eric D** » Thu Jun 03, 2010 3:39 pm

ttocs wrote:the only warning I would give is to be sure it is lined up perfectly or else the surround moving will wear out faster rubbing aginst the box. YOu will also get a little more spac out of your box since the motor/magnet is not displacing the air now.

IF you have one sub forward, and one backward you will need to wire on of them out of phase.

Good call. I have seen more than one sub mounted backwards and not aligned properly, then the surround was trashed.

Post by **ttocs** » Thu Jun 03, 2010 5:10 pm

it is amazing how fast they can break down, especially the foam surrounds.

NewOldStock · Post by **NewOldStock** » Thu Jun 03, 2010 9:20 pm

Eric D wrote:
ttocs wrote:the only warning I would give is to be sure it is lined up perfectly or else the surround moving will wear out faster rubbing aginst the box. YOu will also get a little more spac out of your box since the motor/magnet is not displacing the air now.

IF you have one sub forward, and one backward you will need to wire on of them out of phase.
Good call. I have seen more than one sub mounted backwards and not aligned properly, then the surround was trashed.

holy sh*t... isnt that the 6th sign of the apocalypse?

X3 on the alignment... make sure your sub hole is true-round and has the edge rounded off so its not sharp.

Robbie · Post by **Robbie** » Thu Jun 03, 2010 11:46 pm

Now one forward and one back, thats an interesting suggestion. would you use a ported box at double the volume?

Again is it a case of asthetics? or is there a benafit in volume / quality to this design?

Thanks for all of the comments

Robbie

longboard · Post by **longboard** » Fri Jun 04, 2010 8:39 am

and remember to run it out of phase!

paintguy · Post by **paintguy** » Fri Jun 04, 2010 10:36 am

Robbie wrote:Now one forward and one back, thats an interesting suggestion. would you use a ported box at double the volume?

Again is it a case of asthetics? or is there a benafit in volume / quality to this design?

Thanks for all of the comments

Robbie

There are alleged to be sonic advantages in this configuration as any non-linearities in the drivers suspension systems are cancelled out by one moving forward as one moves backwards.

Whether you'd actually hear it or not is another matter. I doubt my dodgy old ears would!

Misfire · Post by **Misfire** » Fri Jun 04, 2010 9:48 pm

Years ago I had 4 JL audio tens in the clam shell configuration running off an M50. Some of the most accurate bass I have ever had. Too bad I didn't keep those tens, I did keep the fiberglass housing though. Would love to run four Ti tens with it..... would be sweet I bet.

Robbie · Post by **Robbie** » Fri Jun 04, 2010 10:50 pm

Thanks again for all of the advice, off to fibreglass my first box today.

Clam shell design, sounds interesting however cant picture it at the moment

Robbie

Post by **ttocs** » Sat Jun 05, 2010 5:44 am

put two subwoofers together, cones facing one another..... looks like a clam shell.

GX3 · Post by **GX3** » Sat Jun 05, 2010 7:50 am

clam shell= Isobaric design If I remember correctly it requires on average half the box volume and produces a lower response

Misfire · Post by **Misfire** » Sat Jun 05, 2010 10:48 am

Well clam shell does kinda fit... gotta love the technical terms! lol. I can't remember the the box dimensions, but it was small. It sounded sweet.

todd217 · Post by **todd217** » Sat Jun 05, 2010 11:08 am

its called isobaric. when you run them isobaric you old need half the box size that 1 needed. so you could run 4 subs in the same size box as only 1. imagine 4 12s in about 1.5 cuft. the motors of the subs also work together allowing for more control and better sound quality but output is reduced.

Post by **stipud** » Sat Jun 05, 2010 11:18 am

todd217 wrote:its called isobaric. when you run them isobaric you old need half the box size that 1 needed. so you could run 4 subs in the same size box as only 1. imagine 4 12s in about 1.5 cuft. the motors of the subs also work together allowing for more control and better sound quality but output is reduced.

That's not how it works. Effectively all running isobaric does is double your power handling. Other than that it makes two drivers take the same box displacement as one driver... but you don't gain any more output. All it does is let you put double the power on it, which gives you an added 3dB at most.

Post by **Bfowler** » Sat Jun 05, 2010 11:31 am

yeah that makes sense. for lower bass i think you are thinking of passive radiator. that makes the cone act heavier which makes for lower (yet slower) output

todd217 · Post by **todd217** » Sat Jun 05, 2010 12:00 pm

what is not right?

Post by **stipud** » Sat Jun 05, 2010 12:20 pm

todd217 wrote:what is not right?

It lets you run TWO subs in the airspace of one sub, not FOUR. Basically it lets two subs act as one, so you can double the power handling... that's it. Your cone area is not doubled so it's no louder on the same power.

Considering the cost of two woofers there is very little benefit to this method, since you can almost always buy better subs with more power handling for the price of two lower power handling woofers if it's really necessary. Mounting the woofers separately with double the airspace is preferred since you gain 3dB in output from having double the displacement.

todd217 · Post by **todd217** » Sat Jun 05, 2010 12:50 pm

no that is right. if 1 sub needs 1.5 then you put it in a isobaric configuration now your down to .75 for those 2 and another 2 gives you 1.5. that is why people used it back in the day to use smaller boxes.

shawn k · Post by **shawn k** » Sat Jun 05, 2010 2:39 pm

There's a lot of good information about the isobaric design here, but also a few myths that should be cleared up.

A small enclosure requirement is the one and only benefit to isobaric: Two identical drivers in an Isobaric configuration requires 1/2 of the internal space of just one driver.

An isobaric does "not": improve SQ, have a lower response, have better control, or improve/double power handling.

In an isobaric configuration only "one" driver is displacing air. Therefore you will have the output and overall performance of "one" driver. Power handling isn't really doubled as you need to power two drivers as apposed to just one(power handling is still for "two" drivers). It's easy to misinterpret this since it makes sense that with two identical drivers power handling would be doubled, but you have to remember that you are limited to the single driver that's displacing air and it's excursion limits.
In fact, an isobaric design requires "double" the power to achieve the same spl as a non-isobaric configuration. This in effect makes it a relatively inefficient design and the more drivers you use, the more ineffiecient the system becomes

todd217

that is why people used it back in the day to use smaller boxes

Absolutely! Back in the late 80's-mid 90's it was common to see 12" drivers needing 2-3 cu ft of internal air space for adequate performance!

paintguy

There are alleged to be sonic advantages in this configuration as any non-linearities in the drivers suspension systems are cancelled out by one moving forward as one moves backwards.

Whether you'd actually hear it or not is another matter. I doubt my dodgy old ears would!

This is true and I'm very glad you brought this up! But as you said, it's highly unlikely to be audibly noticable.

Post by **ttocs** » Sat Jun 05, 2010 4:05 pm

I did one system with 4 12" xmax(2 forwards, 2 backwards) driven off of 2 zx600tis back in the day and it was the loudest system I had ever heard. After tuning it, it vibrated one of the 6ft florescent lights out of its socket, thankfully in the bay next to it and not over it. Funny as hell as me and the other installer cranked it up for a few secs to the point it made our vision blurry and we never saw it fall as it was in both our our blindspots on the passenger side. We were both just confused as hell at what blew up to make all the smoke/fumes.

2 months later he came in complaining that he could no longer open his trunk as it had rattled lock mechanism so violently it broke it. Wouldn't open with the lever, the key or the alarm.

Not sayin it was the mysterious forward-backward phenomina or just dumb luck but that was definitly the best booming system I ever got to build.