Opposed subs?

[RobGMN Premium Member]

In a home-audio discussion room, I mentioned the old-school method of isobarics for getting deeper, lower-distortion bass in a much smaller box. Some young gun shot back that isobarics are a crap solution for cheap woofers, and that the same thing can be achieved by simply putting drivers at opposite ends of the box.

I looked into it, but there is not a ton of info from sources that I would accept as "expert". Anyone familiar with the science?

I'm trying to figure out why simply putting the woofer on opposite ends of a box would allow you to cut the shared internal volume in half, and how it would mechanically reduce distortion.
I did see reference to where it would make the box rattle/flex less due to the directly opposing waves, but even that doesn't make much sense.

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[1aespinoza Premium Member]

Some young gun shot back that isobarics are a crap solution for cheap woofers, and that the same thing can be achieved by simply putting drivers at opposite ends of the box.

I am not versed in this area but if that were true, why would Olson bother with isobarics. Now looking at it from a outside perspective; putting subs in opposing sides of a box would defeat the purpose of a sealed enclosure. The "spring" effect would be lost and the sub's suspensions would be the only excursion control (aside from the amp's damping factor).
Isobaric mounting allows double the power without doubling the box size but the subs are still "protected" by the sealed spring effect.

 

[RobGMN Premium Member]

I am not versed in this area but if that were true, why would Olson bother with isobarics. Now looking at it from a outside perspective; putting subs in opposing sides of a box would defeat the purpose of a sealed enclosure. The "spring" effect would be lost and the sub's suspensions would be the only excursion control (aside from the amp's damping factor).
Isobaric mounting allows double the power without doubling the box size but the subs are still "protected" by the sealed spring effect.

Plus the isobaric cuts Vas in half, and the design reduces distortion naturally (at eh expense of power needed to drive it).

I can't figure out any science that says simply moving the driver around the back is any real difference from having them both on the face of the box.

 

[1aespinoza Premium Member]

I can't figure out any science that says simply moving the driver around the back is any real difference from having them both on the face of the box.

I have never tried that but I assume it would be hard to make it work. Reason is that is similar to a passive rafiator set up. A passive radiator works because of the weight placed on the PR for tuning. If the other sub is placed on the opposing side I would assume cancellation would be the natural outcome since both subs are moving in opposition to each other. After all, that is the wiring method for an isobaric setup.
Only isobaric method where both subs are wired the same is when one sub is mounted on an inside partition facing the same way as the outer sub.

 

[RobGMN Premium Member]

I have never tried that but I assume it would be hard to make it work. Reason is that is similar to a passive rafiator set up. A passive radiator works because of the weight placed on the PR for tuning. If the other sub is placed on the opposing side I would assume cancellation would be the natural outcome since both subs are moving in opposition to each other. After all, that is the wiring method for an isobaric setup.
Only isobaric method where both subs are wired the same is when one sub is mounted on an inside partition facing the same way as the outer sub.

Yes, but they are opposing each other in a dual-forward-facing setup too, simply because of the shared air volume in either design.
Mechanically, the woofers in either setup are fighting against the same static air pressure and volume (sealed setup).

And that's where I'm baffled by the idea that throwing one woofer on the back and one on the front of a box (instead of two on the front) allows you to reduce internal volume by 50% AND it reduces resonance of the box itself.
I could see where a cancellation of waves at very specific frequencies might happen, but not enough to make any real difference.

I've built isobarics with the design you mention, but also with the drivers face-coupled, and one on the outside of the box.
Maybe driver technology and the use of DSP has made the idea/need/use of isobarics a true thing of the past?

 

[Old_Slapper]

I've done it. It doesn't sound the same. Even when you seal the crap out of the box. Instead of sound coming from one speaker, you now have sound from both. Therefore, placement is a huge part of it. Otherwise, it sounds like the typical 2 subs that are out of phase.

 

[Jimi77 Premium Member]

In a home-audio discussion room, I mentioned the old-school method of isobarics for getting deeper, lower-distortion bass in a much smaller box. Some young gun shot back that isobarics are a crap solution for cheap woofers, and that the same thing can be achieved by simply putting drivers at opposite ends of the box.

I looked into it, but there is not a ton of info from sources that I would accept as "expert". Anyone familiar with the science?

I'm trying to figure out why simply putting the woofer on opposite ends of a box would allow you to cut the shared internal volume in half, and how it would mechanically reduce distortion.
I did see reference to where it would make the box rattle/flex less due to the directly opposing waves, but even that doesn't make much sense.

Either this guy didn't know what he's talking about or he did a really poor job describing his solution. That said, I don't see the reason for isobaric with all the small space subs on th market today.

 

[spokey9 5,000+ posts]

Isobaric does look cool but you're losing output in the process

 

[spokey9 5,000+ posts]

Either this guy didn't know what he's talking about or he did a really poor job describing his solution. That said, I don't see the reason for isobaric with all the small space subs on th market today.

You can gain some in sound quality but at the cost of buying 2 subs that are as loud as one. There's too many good subs that do well in tiny boxes these days though...even with old school subs I never saw the point tbh

 

[RobGMN Premium Member]

Either this guy didn't know what he's talking about or he did a really poor job describing his solution. That said, I don't see the reason for isobaric with all the small space subs on th market today.

I remember when they came out with those low Vas subs, there was something else sacrificed, but no clue what it was. Maybe just power?

But the other benefit of the iso design was the natural reduction in distortion. I guess if you can produce a driver that uses 1/2 the volume of a "normal" driver, and also has lower distortion, then iso goes out the window.
Would be interesting to see distortion specs of the old school drivers versus new school, just to see how much things have changed.

And just to clarify, the dual-opposed looks like this

, whereas the standard box would look like this

.

Neither is ported, the drivers are the same, they both share the full internal volume of the box, they are both wired in-phase relative. The only difference is baffle position.

 

[Jimi77 Premium Member]

I remember when they came out with those low Vas subs, there was something else sacrificed, but no clue what it was. Maybe just power?

But the other benefit of the iso design was the natural reduction in distortion. I guess if you can produce a driver that uses 1/2 the volume of a "normal" driver, and also has lower distortion, then iso goes out the window.
Would be interesting to see distortion specs of the old school drivers versus new school, just to see how much things have changed.

Hoffman's Iron law: You can have 2 of the 3. Deep response, small space or efficiency. We sacrificed efficiency, but we power became cheap so nobody cared. There is the distortion advantage of Isobaric, but now you have low distortion designs like XBL and one higher end lower distortion sub is usually easier to deal with than 2 lower end subs mounted isobarically.

 

[RobGMN Premium Member]

Hoffman's Iron law: You can have 2 of the 3. Deep response, small space or efficiency. We sacrificed efficiency, but we power became cheap so nobody cared. There is the distortion advantage of Isobaric, but now you have low distortion designs like XBL and one higher end lower distortion sub is usually easier to deal with than 2 lower end subs mounted isobarically.

I'll have to check out that XBL reference.
Pretty wild to think how far this moderately niche product has come.

 

[Jimi77 Premium Member]

I'll have to check out that XBL reference.
Pretty wild to think how far this moderately niche product has come.

I still have one of the Gen 1 Brahmas. They've even incorporated XBL into some tweeters.

 

[RobGMN Premium Member]

I still have one of the Gen 1 Brahmas. They've even incorporated XBL into some tweeters.

is that brand name or technology?

 

[Jimi77 Premium Member]

is that brand name or technology?

Adire is the company, Brahma is the model name and XBL is the technology. You can look up Dan Wiggins who invented and patented the technology. He has some issues when he first launched Adire. IIRC, he started with building the subs in Brazil and then moved manufacturing to China and got phucked by the Chinese manufacturer who had a crazy failure rate. Adire folded, but then came back, but Dan isn't associated with Adire anymore; he just licenses the XBL technology to other companies. CSS also uses XBL. Adire and CSS are both sold on Parts Express, so you know you'll get good customer service.

XBL has a ridiculously flat BL curve, flatter than the w7 iirc. The downside is you lose a bit of efficiency. The other downside is once you get out of the flat portion of the BL curve, BL drops off like a cliff so the driver goes from ~zero distortion to massive distortion pretty quick. The last downside is clipping is really obvious with XBL drivers, so I have CDs that I can't listen to with my Brahma because there is clipping in the recording and it sounds like arse.

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