subwoofers with dual opposed drivers

[sarumbear]

That is referring to the hydrodynamic pressure inside the cabinet, not acoustic pressure (elastic wave pressure).

Interesting to use the term hydrodynamic for air.

 

[NTK]

Interesting to use the term hydrodynamic for air.

At least air is a fluid. Imagine my bewilderment when I was in school (many many years ago) and my best drinking buddy talked to me about hydrostatic tension in fracture mechanics. Not only the prefix "hydro" was used, and it was used along with "tension", which cannot be supported by any (Newtonian) fluids

Spherical flaw instability in hydrostatic tension - International Journal of Fracture

Fracture initiation due to a hydrostatic tensile stress field is studied by considering an idealized solid containing a small spherical cavity. Finite elastic deformation theory assuming Neo-Hookean material behavior is combined with an energy criterion to determine the critical cavity and...

link.springer.com

 

[q3cpma]

With opposing drivers, there is no (net) change in the internal cabinet volume. Thus, there is no compression and no pressure fluctuation from compression. The air inside the cabinet will slosh back and forth with the cone movements. The effects from this air movement are tiny compared to the compression effects from a single driver. Therefore the pressure loading on the cabinet walls is hugely reduced with opposing drivers.

We are talking about 2 very different effects.

Isn't that isobaric loading? Not the same as "dual opposed" to me.

 

[sarumbear]

Isn't that isobaric loading? Not the same as "dual opposed" to me.

In Isobarik loading only one of the diaphragms emit sound. The other is hidden inside the box and "sealed". That loading simply changes the Vas of the driver (assuming same drivers are used). From a TS point of view dual opposed is simply two drivers in the same box that happen to be mounted on opposing sides of the box.

 

[q3cpma]

In Isobarik loading only one of the diaphragms emit sound.

Are you sure? My understanding is that both receive the same signal (edit: with reverse polarity), the woofer inside isn't a passive radiator; and at subwoofer frequencies, that woofer doesn't care about the box.
Looks like I was indeed mistaken about it, a bit tired. Thought for a moment that the entire point was to maintain the box pressure constant.

 

[sarumbear]

Are you sure? My understanding is that both receive the same signal, the woofer inside isn't a passive radiator; and at subwoofer frequencies, that woofer doesn't care about the box.
Looks like I was indeed mistaken about it, a bit tired. Thought for a moment that the entire point was to maintain the box pressure constant.

There is no woofer inside.

KEF introduces Uni-Core subwoofer technology and its KC62 sub

The KC62 is the first sub to implement KEF's new tech that promises deeper bass from smaller boxes.

www.techhive.com

 

[q3cpma]

There is no woofer inside.

KEF introduces Uni-Core subwoofer technology and its KC62 sub

The KC62 is the first sub to implement KEF's new tech that promises deeper bass from smaller boxes.

www.techhive.com

Yes, as I said, I simplified Isobaric to constant pressure in my tired mind.

 

[sarumbear]

Yes, as I said, I simplified Isobaric to constant pressure in my tired mind.

There is no woofer inside and there is no constant pressure. If the pressure is constant there will be no sound. Sound waves are generated by the pressure waves inside the cabinet. From acoustical point of view it a box with two woofers.

 

[NiagaraPete]

The argument for dual opposed in real life is:
1) wife
2) neighbour's
3) place to put a drink

 

[Chrise36]

In Isobarik loading only one of the diaphragms emit sound. The other is hidden inside the box and "sealed". That loading simply changes the Vas of the driver (assuming same drivers are used). From a TS point of view dual opposed is simply two drivers in the same box that happen to be mounted on opposing sides of the box.

It depends on the order the 6th order emits from both the drivers

 

[Chrise36]

Are you sure? My understanding is that both receive the same signal (edit: with reverse polarity), the woofer inside isn't a passive radiator; and at subwoofer frequencies, that woofer doesn't care about the box.
Looks like I was indeed mistaken about it, a bit tired. Thought for a moment that the entire point was to maintain the box pressure constant.

The box plays a huge role in isobarik you have to measure the drivers to have real thiele small parameters and not rely on the manufacturer data to calculate correctly.You can have a huge dynamic subwoofer in a relatively small box if done properly.

 

[BrokenEnglishGuy]

The argument for dual opposed in real life is:
1) wife
2) neighbour's
3) place to put a drink

Why neighbour's?

 

[sarumbear]

It depends on the order the 6th order emits from both the drivers

No it doesn't. The 2nd driver is inside of the cabinet. There is no emission from that to the outside. Both diaphragms work in the same direction, there is no pressure change in the box more than it will be if one driver exists. Instead of arguing why not reading the textbooks?

 

[sarumbear]

The box plays a huge role in isobarik you have to measure the drivers to have real thiele small parameters and not rely on the manufacturer data to calculate correctly.You can have a huge dynamic subwoofer in a relatively small box if done properly.

Not true.

 

[Chrise36]

No it doesn't. The 2nd driver is inside of the cabinet. There is no emission from that to the outside. Both diaphragms work in the same direction, there is no pressure change in the box more than it will be if one driver exists. Instead of arguing why not reading the textbooks?

6th order isobarik bandpass is this:

 

[Chrise36]

Not true.

Closed box and bass reflex is more immune to box volume changes. In Isobarik 4th order and 6th order volume changes result very different tuning of the system.

 

[sarumbear]

6th order isobarik bandpass is this:
View attachment 161939

That is not Isobarik. The name Isobarik is derived from Iso=equal and Barik=pressure. In an Isobarik design the enclosure between the drivers have no pressure change.

 

[Chrise36]

That is not Isobarik. The name Isobarik is derived from Iso=equal and Barik=pressure. In an Isobarik design the enclosure between the drivers have no pressure change.

No it comes from the equal pressure from the air trapped inside the diaphragm. The air receives rougly equal(iso) pressure from them.

 

[sarumbear]

No it comes from the equal pressure from the air trapped inside the diaphragm. The air receives rougly equal(iso) pressure from them.

Understood. However, I have never seen such a design analysed on a paper or a text book. Nor have I seen used on a speaker on the market. The only Isobaric design on a consumer speaker I know is the old Linn Isobarik. Do you have any examples of the design you posted?

 

[Chrise36]

Understood. However, I have never seen such a design analysed on a paper or a text book. Nor have I seen used on a speaker on the market. The only Isobaric design on a consumer speaker I know is the old Linn Isobarik. Do you have any examples of the design you posted?

It is not used now but it was mainly used in car audio subwoofers. The following is an old Polk design with 4 drivers:

Old School Polk Audio C4 Subwoofer - Four 6x9's in Isobaric Teardrop Enclosure

I wasn't sure if this should go in the Vintage Speaker section or the Car Audio section, but since it's car audio, I decided to put it here.

forum.polkaudio.com

And another one:

Lexus IS-F - 6th order Isobaric Clamshell Bandpass (video page 5)

****DISCLAIMER**** BOX CONFIG SUBJECT TO CHANGE DEPENDING ON HOW IT SOUNDS i am currently ATTEMPTING an oldschool style, Compound (clamshell) Isobaric 6th order Bandpass box. I hope to temporarily put it together outside of the car tomorrow and get and indication of how its going to act. It has t...

www.stevemeadedesigns.com