Perlisten's D212 magic. Isn't it just an Isobaric enclosure?

[aceinc]

In reviewing the Perlisten D212 it looks like a pretty standard Isobaric configuration all be it at 90 degrees.

Am I missing something?

Could I stuff a pair of Ultimax 12s in an appropriately sized box at right angles with a decent amp and achieve similar results, more or less?

 

[shadyJ]

In reviewing the Perlisten D212 it looks like a pretty standard Isobaric configuration all be it at 90 degrees.

Am I missing something?

Could I stuff a pair of Ultimax 12s in an appropriately sized box at right angles with a decent amp and achieve similar results, more or less?

The Ultimax drivers are not on the level of the Perlisten drivers, so no. But If you wanted the advantages of an isobaric enclosure, yes, you could put them in a same style enclosure.

 

[aceinc]

The Ultimax drivers are not on the level of the Perlisten drivers, so no. But If you wanted the advantages of an isobaric enclosure, yes, you could put them in a same style enclosure.

As I relooked at their drawing, I was unsure if the back of bottom driver is open to the air, or enclosed. Do you know how the drivers are configured?

 

[ryanosaur]

True isobaric would have a very tightly sealed chamber between the two drivers. One would be exposed to the outside, one would be exposed to the inside of the cabinet. Both drivers need to operate in phase with each other.
A push-pull enclosure is not the same thing as an isobaric design. The drivers operate in phase with respect to the exposed portion of the Driver, but the Drivers are wired out of phase with respect to the other. The Push Pull configuration is beaded on the idea that when one cone is excusing away from the motor, the other is doing the opposite.

 

[Verdinut]

True isobaric would have a very tightly sealed chamber between the two drivers. One would be exposed to the outside, one would be exposed to the inside of the cabinet. Both drivers need to operate in phase with each other.
A push-pull enclosure is not the same thing as an isobaric design. The drivers operate in phase with respect to the exposed portion of the Driver, but the Drivers are wired out of phase with respect to the other. The Push Pull configuration is beaded on the idea that when one cone is excusing away from the motor, the other is doing the opposite.

An isobaric enclosure can use a push-pull design:

Isobaric Subwoofer Design — VUE Audiotechnik

vue-audiotechnik.com

 

[aceinc]

How would I go about modeling a push pull design similar to the Perlisten D212. Using either the Ultimax 12s or Dayton Audio RSS315HE-22?

 

[ryanosaur]

How would I go about modeling a push pull design similar to the Perlisten D212. Using either the Ultimax 12s or Dayton Audio RSS315HE-22?

Just treat it as a dual driver design.

 

[ryanosaur]

An isobaric enclosure can use a push-pull design:

Isobaric Subwoofer Design — VUE Audiotechnik

vue-audiotechnik.com

I know you know this, so I'm mostly doing this for the plebs out there.

In any isobaric design, the drivers are coupled to each other by that small chamber I mentioned in the earlier post (as small as possible without letting the Drivers touch, especially when excursed). Yes, you can reverse a driver and have magnet to magnet or cone to cone, but for any such design, the two drivers effectively operate as one. In an isobaric build Vas is halved and both drivers are treated as only 1 single Driver, otherwise.
In the Push-pull design of Perlisten or M&k, it is effectively a dual driver design: each Driver is exposed to the outside of the cabinet. Vas is doubled.
Regardless of how you set up the drivers in an isobaric design, one Driver still only sees the inside of the cabinet. In a Push-Pull a la Perlisten and M&K, both Drivers are exposed to open air.
Most of the texts (Alden, Dickinson...) say the only benefit of any Isobaric build is the reduction in Vas which is likely not worth the cost of 2 Drivers. The Non-isobaric Push Pull (Perlisten and M&K) can offer lower distortion and the benefit of Dual Drivers if connected in Parallel.

All of this is to say, Push-Pull is not necessarily isobaric. Isobaric can be Push Pull... But they each have their own specific rules and they are not the same.

 

[aceinc]

If the drivers are acting as one in a push pull environment, wouldn't they effectively act as open baffle with twice the BL?

 

[ryanosaur]

If the drivers are acting as one in a push pull environment, wouldn't they effectively act as open baffle with twice the BL?

They aren’t acting as one Driver. A Push-Pull design like Perlisten and M&K is effectively a Dual Driver build.

 

[aceinc]

They aren’t acting as one Driver. A Push-Pull design like Perlisten and M&K is effectively a Dual Driver build.

If the drivers are wired so that when one goes in (relative to the enclosure) the other goes out, it seems to me as if they would be acting as a single driver.

For visualization purposes assume the two drivers are on opposite sides of the enclosure one facing out one facing in. Wire them in phase. Feed the enclosure a sine wave. One driver will push air into the room while the other driver is pulling air from the room. This seems to have the same effect as a single driver mounted on an open baffle except for a doubling of the motor force.

 

[ryanosaur]

If the drivers are wired so that when one goes in (relative to the enclosure) the other goes out, it seems to me as if they would be acting as a single driver.

For visualization purposes assume the two drivers are on opposite sides of the enclosure one facing out one facing in. Wire them in phase. Feed the enclosure a sine wave. One driver will push air into the room while the other driver is pulling air from the room. This seems to have the same effect as a single driver mounted on an open baffle except for a doubling of the motor force.

That is not how those subs are designed.
In a push-pull, Non-Isobaric, design, both Drivers excurse outwards.
I don’t know how to be more clear in what is happening.

The Perlisten Sub is not isobaric, it is a dual woofer, Push-Pull design.

A lot of this has already been discussed in the review and the supporting thread.

 

[aceinc]

I was unable to find a forum post discussing the push pull aspects of the D212/D215, if you can point me to it I'd appreciate it. I found the review. The wording confuses me somewhat;

One measure that Perlisten has taken in reducing distortion in the D215s and D212s has been to arrange the drivers in a push/pull configuration. This is a sealed dual-driver configuration where one driver is mounted with the cone facing outward and the other with the cone facing inward. The drivers are then wired in opposite phase of each other. So the cones of both drivers are moving inward and outward at the same time with respect to the cabinet, although they are moving inward and outward in opposite phase with respect to each other. The advantage of this is that the non-linear motion that only occurs in one way of travel is mitigated by the other driver since motion is restricted by the increase in air pressure by the inward motion of each cone. In other words, the cones are coupled together by the constant level of air pressure inside the sealed cavity, so the motion of one of the cones in one direction is always modulated by the other cone’s opposite direction of travel. If the cone has uneven excursion with respect to inward and outward oscillation (as all drivers do to some extent), that is balanced out by the interior air pressure change created by the opposite motion by the other driver. This reduces even-order harmonic distortions which are created by nonlinear motion in just one direction of the cone’s travel.

It seems to be saying mostly that the cones are moving in and out in tandem in relation to the cabinet. But it also says the motion is restricted by the increase in pressure by the inward motion of each cone. An increase in pressure should only be observed if the cones are moving in opposite direction in reference to the cabinet.

But it also says there is a constant level of air pressure.

My current interpretation of this is that the cones travel in the same direction relative to the enclosure at all times, a push/pull design.

This leaves me right where I was before, it seems like it would model similar to an open baffle type of enclosure except twice the motor strength.

 

[TLS Guy]

I was unable to find a forum post discussing the push pull aspects of the D212/D215, if you can point me to it I'd appreciate it. I found the review. The wording confuses me somewhat;

One measure that Perlisten has taken in reducing distortion in the D215s and D212s has been to arrange the drivers in a push/pull configuration. This is a sealed dual-driver configuration where one driver is mounted with the cone facing outward and the other with the cone facing inward. The drivers are then wired in opposite phase of each other. So the cones of both drivers are moving inward and outward at the same time with respect to the cabinet, although they are moving inward and outward in opposite phase with respect to each other. The advantage of this is that the non-linear motion that only occurs in one way of travel is mitigated by the other driver since motion is restricted by the increase in air pressure by the inward motion of each cone. In other words, the cones are coupled together by the constant level of air pressure inside the sealed cavity, so the motion of one of the cones in one direction is always modulated by the other cone’s opposite direction of travel. If the cone has uneven excursion with respect to inward and outward oscillation (as all drivers do to some extent), that is balanced out by the interior air pressure change created by the opposite motion by the other driver. This reduces even-order harmonic distortions which are created by nonlinear motion in just one direction of the cone’s travel.

It seems to be saying mostly that the cones are moving in and out in tandem in relation to the cabinet. But it also says the motion is restricted by the increase in pressure by the inward motion of each cone. An increase in pressure should only be observed if the cones are moving in opposite direction in reference to the cabinet.

But it also says there is a constant level of air pressure.

My current interpretation of this is that the cones travel in the same direction relative to the enclosure at all times, a push/pull design.

This leaves me right where I was before, it seems like it would model similar to an open baffle type of enclosure except twice the motor strength.

The drivers compress the air in the enclosure by having a simultaneous compression stroke. So the design formula is standard closed box dual driver in parallel. So Vas is doubled requiring twice the box volume a single driver would.

In an isobaric design, both drivers are coupled in a single space. There is no compression stroke in the coupling space. and only one driver communicates with the enclosure space. So Vas is halved and this halves the enclosure volume, but not quite, as you have to add the volume of the coupling tunnel. The other penalty is you loose 3db of sensitivity compared to a single driver. So the only advantage is a smaller enclosure volume, after that it is all downsides. I have designed and built a couple of isobaric bass designs. I also designed one for this forum, but never built it. My view is that it is more bother and expense than it is worth.

There are variations on the theme ala Bose, with three cavities with two ported and even a port between the cavities. These designs pay the penalty of high distortion and very limited bandwidth. If you are familiar with the sound of Bose bass modules you know what I'm talking about.

 

[ryanosaur]

I was unable to find a forum post discussing the push pull aspects of the D212/D215, if you can point me to it I'd appreciate it. I found the review. The wording confuses me somewhat;

One measure that Perlisten has taken in reducing distortion in the D215s and D212s has been to arrange the drivers in a push/pull configuration. This is a sealed dual-driver configuration where one driver is mounted with the cone facing outward and the other with the cone facing inward. The drivers are then wired in opposite phase of each other. So the cones of both drivers are moving inward and outward at the same time with respect to the cabinet, although they are moving inward and outward in opposite phase with respect to each other. The advantage of this is that the non-linear motion that only occurs in one way of travel is mitigated by the other driver since motion is restricted by the increase in air pressure by the inward motion of each cone. In other words, the cones are coupled together by the constant level of air pressure inside the sealed cavity, so the motion of one of the cones in one direction is always modulated by the other cone’s opposite direction of travel. If the cone has uneven excursion with respect to inward and outward oscillation (as all drivers do to some extent), that is balanced out by the interior air pressure change created by the opposite motion by the other driver. This reduces even-order harmonic distortions which are created by nonlinear motion in just one direction of the cone’s travel.

It seems to be saying mostly that the cones are moving in and out in tandem in relation to the cabinet. But it also says the motion is restricted by the increase in pressure by the inward motion of each cone. An increase in pressure should only be observed if the cones are moving in opposite direction in reference to the cabinet.

But it also says there is a constant level of air pressure.

My current interpretation of this is that the cones travel in the same direction relative to the enclosure at all times, a push/pull design.

This leaves me right where I was before, it seems like it would model similar to an open baffle type of enclosure except twice the motor strength.

I think you are trapping yourself in your own thought exercise.

The Perlisten and M&K Subs, as designed(and stated before) operate no differently than any other Dual Driver design.
There are no special rules here that change any parameters.
The only catch is in the theory that in having the cone excurse away from the motor on one Driver and towards the motor on the second, you will minimize nonlinearities due to multiple drivers both excursing in the same direction (I.e. away from the motor) simultaneously.

Nothing else changes.

I don’t know why you keep insisting that there is something different going on. The wavefronts emanating from the Perlisten Sub would be no different than those emanating from the Monolith 215. It doesn’t even matter that one is ported!

In an Open Baffle build, you have the backwave of the driver exposed to the open air. In a cabinet, those backwave are contained. There is no equivalence between these two designs, an Open Baffle or the Perlisten.

 

[shadyJ]

In other words, the cones are coupled together by the constant level of air pressure inside the sealed cavity, so the motion of one of the cones in one direction is always modulated by the other cone’s opposite direction of travel.

This is my wording, and it is bad wording. Isobaric would have a constant pressure cell on the inner side of the cone within the sealed chamber. instead of constant, I should have said something like a changing level of pressure that offsets each driver's one-way nonlinear travel. Push-pull definitely does not have a constant pressure cell between the drivers, but rather the changes in pressure that occur address each other's irregularities.

 

[aceinc]

This is my wording, and it is bad wording. Isobaric would have a constant pressure cell on the inner side of the cone within the sealed chamber. instead of constant, I should have said something like a changing level of pressure that offsets each driver's one-way nonlinear travel. Push-pull definitely does not have a constant pressure cell between the drivers, but rather the changes in pressure that occur address each other's irregularities.

Since I am of a simple mind, and not too good with graphics I put the drawing below together. In the drawing there is a sine wave and two "enclosures," A & B. The triangles 1 & 2 are two drivers in each enclosure. The red & blue arrows signify which way the cone of the drivers move when the portion of the sine wave excites them.

Does the Perlisten subwoofer work like example A or B?

 

[ryanosaur]

Since I am of a simple mind, and not too good with graphics I put the drawing below together. In the drawing there is a sine wave and two "enclosures," A & B. The triangles 1 & 2 are two drivers in each enclosure. The red & blue arrows signify which way the cone of the drivers move when the portion of the sine wave excites them.

Does the Perlisten subwoofer work like example A or B?

View attachment 66635

I don’t really follow those images.

in the Perlisten Subs, both Drivers excurse outwards, in phase with each other.

if I really try to interpret those images, you need “C:”
Red arrows in phase and both excursing outwards at the same time.

Just one toward the motor, and one away.

So, take “a” and reverse the direction of the arrows for “2” to reflect the actual motion of the Drivers.

 

[TLS Guy]

Since I am of a simple mind, and not too good with graphics I put the drawing below together. In the drawing there is a sine wave and two "enclosures," A & B. The triangles 1 & 2 are two drivers in each enclosure. The red & blue arrows signify which way the cone of the drivers move when the portion of the sine wave excites them.

Does the Perlisten subwoofer work like example A or B?

View attachment 66635

B

 

[ryanosaur]

B

Forgive if I am being daft, but both red arrows should be pointing outward at the same time, and both blue arrows should be pointing inward at the same time, correct? That is the physical action and represents both Drivers excusing together in-phase.