Opposed subs?

[1aespinoza Premium Member]

Yes, but they are opposing each other in a dual-forward-facing setup too

Wait, you lost me here. In all setups the subs fire in the same direction. When clamshell mounted or mag to mag, one of the subs is wired in reverse polarity. The air between both subs gets pushed back and forth acting as added "weight" along with the cones.

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 think I see where the confusion is. Both pictures you posted are the same setup. They are a pair of subs sharing an enclosure regardless of direction. If you were to wire one of those subs in reverse polarity, you would get cancellation. In an isobaric setup, the cone area is the same whether you use 2, 3, or 4 subs. Since those subs are all "pistoning" in the same direction, I assume the box has to be smaller to control the extra force presented by multiple subs in the same cone area. May have something to do with the law of hydraulics if that is a thing.

 

[RobGMN Premium Member]

Wait, you lost me here. In all setups the subs fire in the same direction. When clamshell mounted or mag to mag, one of the subs is wired in reverse polarity. The air between both subs gets pushed back and forth acting as added "weight" along with the cones.

Right. I'm talking about compression and rarefaction of the air as both cones move in phase with each other.

AFAIK, the same physics happen no matter how the drivers are mounted, if they share the same air volume.

I think I see where the confusion is. Both pictures you posted are the same setup. They are a pair of subs sharing an enclosure regardless of direction. If you were to wire one of those subs in reverse polarity, you would get cancellation. In an isobaric setup, the cone area is the same whether you use 2, 3, or 4 subs. Since those subs are all "pistoning" in the same direction, I assume the box has to be smaller to control the extra force presented by multiple subs in the same cone area. May have something to do with the law of hydraulics if that is a thing.

That's the rub. The physics you describe is the same understanding I had.

But the young gun was insisting otherwise. I just couldn't think of anything where his claims made sense.

The only guess I have was that he was leaving g out that the hardware (drivers) is also different, eliminating the need for the isobaric setup. Though, his whole comparison was regarding box design itself, not hardware.

 

[Doxquzme Premium Member]

Push-pull and compound (isobaric) are two different things.

Many moons ago, I had a pair of M&K 12" low frequency drivers units, face to face using the full size spare tire well (about 1.65 cu ft) of a 1980 Mustang fastback LX 5.0. powered by a RF Punch 500.2, it putout prestigious amounts of bass, blew people away that it did what it did in such a small sealed box.

I currently have a bass reflex sub in my home theater setup that I built many moons ago, using dual 15" JBL synthesis 15's pulled from an acquired sub pulled from a closed cinema in San diego, in a 6 cu ft box tuned to 24hz and though it's like 25 years old (and soon to be replaced by the same configuration using dual 18" ultimax drive units tuned to 16hz) it puts out and always has.

It is essentially 50% more than a single driver in half the box size as one driver would be in twice the size box, but still 50% less than if you had 1 driver each in their own 12 cu ft cabinets.

There is a place for their use and if you have the money, they can produce some outstanding output in a very small enclosures.

Remember, of course, this was done back when you needed HUGE boxes to get the job done. The JBL's would normally be in their own 10-12 cu ft box each, now doing almost the same amount of work in a 6 cu ft box.

Lots of fun with compound (isobaric)loaded setups - just not that practical anymore as advancements in driver tech have created great drivers that work in some pretty small boxes.

 

[1aespinoza Premium Member]

The only guess I have was that he was leaving g out that the hardware (drivers) is also different, eliminating the need for the isobaric setup. Though, his whole comparison was regarding box design itself, not hardware.

Maybe ask if he has an example whether sketched or pulled from archives?

It is essentially 50% more than a single driver in half the box size as one driver would be in twice the size box, but still 50% less than if you had 1 driver each in their own 12 cu ft cabinets.

Definitely an interesting subject to delve into. They are direct math equations. 2 separate subs= 4 times the box, 1 sub= 2 times the box, 2 iso subs= 1/2 times the box. I do not know if that makes sense but it is catalogued in my mind that way.

 

[shredder1 10+ year member]

2 subs mounted opposing directions inmho is ebay enclosures Inc.
That said...If anyone gets results from an obvious phase issue its thru testing and extensive installation trials. Even then I would wager its a specific bandwidth. User preferred and only viable due to his specific install.

 

[Doxquzme Premium Member]

2 subs mounted opposing directions inmho is ebay enclosures Inc.
That said...If anyone gets results from an obvious phase issue its thru testing and extensive installation trials. Even then I would wager its a specific bandwidth. User preferred and only viable due to his specific install.

?

2 subs mounted in opposite directions or face to face would be wired out of phase, properly wired, phase issues? Not following...

 

[Doxquzme Premium Member]

Maybe ask if he has an example whether sketched or pulled from archives?

Definitely an interesting subject to delve into. They are direct math equations. 2 separate subs= 4 times the box, 1 sub= 2 times the box, 2 iso subs= 1/2 times the box. I do not know if that makes sense but it is catalogued in my mind that way.

Sounds about right.

 

[1aespinoza Premium Member]

But the young gun was insisting otherwise. I just couldn't think of anything where his claims made sense.

I think I just saw a video of what his claim is-

 

[Doxquzme Premium Member]

I think I just saw a video of what his claim is-

There is a lot of information that he boast that are compromises in design here. Ported subs roll off quicker but will play lower. Using isolation feet with ported subs, should not use isolation pads/feet (not spikes) on subs, not so, use spikes to couple as they should absolutely couple with the floor, common misnomer (spikes are great for subs, isolation pads or butcher block/cement slabs for mains).

Internal vibrations can be negated pretty much entirely by good design and build techniques. Don;t get me wrong, I like sealed subs, use them in my car. For home listening in my dual use stereo/7.5.4 Atmos setup, all 5 subs are ported.