Isobaric back to back lowers sf up to 10 Hz ?

[Tangband]

Investigation of the isobaric principle bring interesting facts, and I found some in this video .

He is adding 14 gram weight to a single subwoofer driver .
The sf is lowered almost 10 Hz .
This is logical. Now, think of this :

The weight of air is 1,18 gram/liters.

A back to back isobaric chamber with two 12 inch drivers will have an isobaric-chamber volume of about 20 liters air = 23,6 gram.

This chamber air weight will add to the twin driver cones and thus lower sf about 5 -10 Hz .

It will then dig deeper than a conventional driver setup.

Conventional wisdom is that isobaric dont change any parametres other than Vas, which will be half .

Is there any weaknesses with my theory in this matter ?

 

[jhaider]

You don't get "more bass," you get "a different frequency response curve" combined with less bass output compared to a normal deployment of the two woofers because you're tossing the volume displacement of one away.

Basically this is an obsolete way of doing things. Best practices now - use a driver with tons of motor and EQ it to your target response.

 

[tomtoo]

Investigating of the isobaric principle bring interesting facts, and I found it in this video .

He is adding 14 gram weight to a single subwoofer driver .
The sf is lowered almost 10 Hz .
This is logical. Now, think of this :

The weight of air is one gram/liters.

An back to back isobaric chamber with two 12 inch drivers will have an isobaric-chamber volume of about 20 liters air = 20 gram.

This chamber air weight will add to the twin driver cones and thus lower sf about 5 -10 Hz .

It will dig then deeper than a conventional driver setup.

Conventional wisdom is that isobaric dont change any parametres other than Vas, which will be half .

Is there any weaknesses with my theory in this matter ?

View attachment 217896

Adding mass, lowers efficience.

 

[digitalfrost]

I wrote soimething about this here: https://www.audiosciencereview.com/...al-opposed-subwoofer-theory.19186/post-795840

 

[Tangband]

I wrote soimething about this here: https://www.audiosciencereview.com/...al-opposed-subwoofer-theory.19186/post-795840

Thank you, really interesting.

 

[Tangband]

Adding mass, lowers efficience.

Yes, but you do get lower freq response ( with no eq involved )

 

[Tangband]

You don't get "more bass," you get "a different frequency response curve" combined with less bass output compared to a normal deployment of the two woofers because you're tossing the volume displacement of one away.

Basically this is an obsolete way of doing things. Best practices now - use a driver with tons of motor and EQ it to your target response.

Ok, thats the modern way to do it , it makes sense since there are now drivers with big motors and high Xmas one can buy.

Another question - is there any advantage at all that the isobaric chamber is pressure constant - thus protects the driver on the outside from the usual case, with a single driver , delayed back pressure sound from the box, with this sound coming out from the front drivers cone ?

Anyway, two driver cones in isobaric coupling would be twice as thick as a single driver - This would also protect the front driver somewhat from the back pressure of the box ?

Am I missing something ?

 

[tomtoo]

Yes, but you do get lower freq response ( with no eq involved )

Sure, but its a inefficient way

 

[Lambda]

Another question - is there any advantage at all that the isobaric chamber is pressure constant - thus protects the driver on the outside from the usual case, with a single driver , delayed back pressure sound from the box, with this sound coming out from the front drivers cone ?

The Advantage is you can uses a smaller box volume.

but those days you can get speakers like this

18IPAL 2Ω - LF Drivers - B&C Speakers

bcspeakers.com

You can make them play as low as you want in basically any enclosure and your only xmax limited

 

[bigjacko]

I think the common wisdom for nowaday is iosbaric is for people don't use dsp. Isobaric require two drivers to play SPL equal to one driver, although digs deeper, but only add 3db at subbass compare to two driver that will add 6db across the board. You do get smaller enclosure, but you can also use dsp to shape the driver to the same frequency response. The only benefit will be less odd order non linear distortion, but not sure how much, need some measurement to know if its worth.

 

[Duke]

Another question - is there any advantage at all that the isobaric chamber is pressure constant - thus protects the driver on the outside from the usual case, with a single driver , delayed back pressure sound from the box, with this sound coming out from the front drivers cone ?

Anyway, two driver cones in isobaric coupling would be twice as thick as a single driver - This would also protect the front driver somewhat from the back pressure of the box ?

My observation of the effect of isobaric loading on the bass region is along similar lines to what you described earlier. The measured (and audible) improvement was more than the "textbook" theory (halving of Vas) would predict.

If you are thinking about running a pair of isobaric midwoofers up into the midrange region, my experience was that the midrange sound quality was dreadful (KEF B110 woofers, 5 1/4" Bextrene cones). I'd want to aggressively roll off the inner woofer north of the bass region, if I were to ever try that again (which is extremely unlikely).

As I'm sure you know, the pressure in the isochamber is not really held constant by the inner woofer, because the inner woofer's movement is constrained by the air behind it.

One effect of the outer woofer effectively "seeing" the greatly reduced backpressure in the isochamber is that it is more susceptible to over-excursion. I smacked the voice coil of one of my KEF B139 woofers against the backplate like that, scared the crap out of me, sounded like a machine gun.

 

[ryanosaur]

You can make them play as low as you want in basically any enclosure and your only xmax limited

And Power. Pushing those drivers below resonance requires much more power the lower you try to go, until you exceed safe excursion. That always seems to be the point left out of conversations about pushing Pro Drivers in that manner. You need a stout Amp and good Household electricity.

 

[Lambda]

And Power. Pushing those drivers below resonance requires much more power the lower you try to go, until you exceed safe excursion. That always seems to be the point left out of conversations about pushing Pro Drivers in that manner. You need a stout Amp and good Household electricity.

Nop it it's not needing mush "power" at all. you need some VA.
Especially Voltage but tats not power. especially not power draw from the grid.

its like kompresing a spring.

 

[Tangband]

Nop it it's not needing mush "power" at all. you need some VA.
Especially Voltage but tats not power. especially not power draw from the grid.

its like kompresing a spring.

Yes. Linkwitz has shown that one dont need big power to make a Linkwitz transformer box . Its all the balance between the xmas, the drivers power rating, the size of the box and the slope of the transformer filter. A really small box with a big size driver need less power than a big box - above the LT compensation frequency. Below, its another story.

————-

Back to isobaric. I have made a couple of those DIY in the ninethies. The results were always sounding better than my expectations, but it was with normal drive units and nothing with great xmas. I did compare one driveunit in a twice as big box than the isobaric one, and this resulted in a less tauth, less deep bass. Like Duke has discovered, this made me wonder why, because people always said that the advantage were only a half as big box with isobaric - no sound quality gain.

My experience with Linn isobarik active, Linn Keltik, and Linn melodik was of outstanding bass quality . Those were all isobaric boxes , and the melodik was a clamshell isobaric construction.

Im still a (slightly) believer that there is something with the constant pressure inside the isobaric box - This would make the job easier for the front driver to perform, especially at higher spl. The search for building optimal bass quality goes on….

 

[jhaider]

but only add 3db at subbass compare to two driver that will add 6db across the board

Why would isobaric add any headroom compared to a single driver? You’re throwing away the volume displacement of one driver.

Another question - is there any advantage at all that the isobaric chamber is pressure constant - thus protects the driver on the outside from the usual case, with a single driver , delayed back pressure sound from the box, with this sound coming out from the front drivers cone ?

That sounds like marketing, not engineering, to me.

The funny thing about audio is that old, dumb ideas seem to forever be recycled in the so called high end. Especially if they’re expensive and useless.

 

[Tangband]

My observation of the effect of isobaric loading on the bass region what you described earlier. The measured (and audible) improvement was more than the "textbook" theory (halving of Vas) would predict.

If you are thinking about running a pair of isobaric midwoofers up into the midrange region, my experience was that the midrange sound quality was dreadful (KEF B110 woofers, 5 1/4" Bextrene cones). I'd want to aggressively roll off the inner woofer north of the bass region, if I were to ever try that again (which is extremely unlikely).

As I'm sure you know, the pressure in the isochamber is not really held constant by the inner woofer, because the inner woofer's movement is constrained by the air behind it.

One effect of the outer woofer effectively "seeing" the greatly reduced backpressure in the isochamber is that it is more susceptible to over-excursion. I smacked the voice coil of one of my KEF B139 woofers against the backplate like that, scared the crap out of me, sounded like a machine gun.

Very interesting . I wonder how they did it with the Totem Mani isobaric loudspeakers ? Those were two ways isobaric loudspeakers, back to back . Maybe they crossed the inside driver below 200 Hz ?

Those loudspeakers have really good extension in the bass for 6 1/2 drivers in a standmount.
The air weight inside the back to back isobaric chamber would lower the dynaudio drivers sf with 5-10 Hz .

Totem Acoustic Mani-2 loudspeaker

Following my review of two high-performance minimonitors last November (footnote 1), I received a letter asking why I recommended a stand-mounted speaker at all when it was possible to buy a floorstanding design with more bass for the same amount of money. Furthermore, the correspondent went on...

www.stereophile.com

 

[Tangband]

By the way - here is Linn products patent from the seventies :

http://www.mickandviv.com/pfm/GB1500711.pdf

There are claims by Ivor Tiefenbrun that the constant pressure inside the isobaric chamber is the main reason for better sound, with less distortion with real music material.

Olson invented the concept earlier.

 

[Duke]

Very interesting . I wonder how they did it with the Totem Mani isobaric loudspeakers ? Those were two ways isobaric loudspeakers, back to back . Maybe they crossed the inside driver below 200 Hz ?

Those loudspeakers have really good extension in the bass for 6 1/2 drivers in a standmount.
The air weight inside the back to back isobaric chamber would lower the dynaudio drivers sf with 5-10 Hz .

Totem Acoustic Mani-2 loudspeaker

Following my review of two high-performance minimonitors last November (footnote 1), I received a letter asking why I recommended a stand-mounted speaker at all when it was possible to buy a floorstanding design with more bass for the same amount of money. Furthermore, the correspondent went on...

www.stereophile.com

View attachment 218082

Thinking back on it now, I just had a handful or so of fluff (either Polyfill or long-haired wool) in the isochamber, and it was clearly inadequate for absorbing the midrange energy off the back of the front cone, and off the front of the back cone. In retrospect a geometry more like Tiefenbrun's in the patent application, with a thick slab of high-quality foam in the isochamber and separating the two woofers, probably would have worked a lot better. Maybe THAT is what makes the Totem Mani successful, or is at least part of it.

Linn made an isobaric two-way called the SARA and so presumably they found a solution to the midrange issue that de-railed my efforts to do something similar.

The search for building optimal bass quality goes on….

Back in the 90's I tried to design a subwoofer "fast enough" to keep up with Maggies and Quads, my theory being that there would be a market for such (I was still an amateur at that stage, but with aspirations). I tried just about everything except horns, including an amp with circuitry which allowed adjustment of the effective driver electrical Q, and eventually gave up. Years later Earl Geddes taught me that the dominant issue regarding sound quality in the bass region was room interaction, and so I started using his ideas with his permission, manufacturing a commercial distributed mult-sub system (having crossed over to the "dark side" by then). NOT trying to dissuade you from your quest! Just relating my own experience.

 

[JustJones]

Maybe they just need to weigh 200lbs

SuperMon Isobaric – MonAcoustic USA

Majestic Performance Meets Unparalleled Engineering The SuperMon Isobaric was created to bring about a revolution in the audio industry. Our latest innovation not only offers impeccable sound quality, but it combines it with a level of never-seen-before construction and engineering. The...

monacoustic.us

 

[Tangband]

Maybe they just need to weigh 200lbs

SuperMon Isobaric – MonAcoustic USA

Majestic Performance Meets Unparalleled Engineering The SuperMon Isobaric was created to bring about a revolution in the audio industry. Our latest innovation not only offers impeccable sound quality, but it combines it with a level of never-seen-before construction and engineering. The...

monacoustic.us

Interesting.
They aparently use a eton bassdriver inside the cabinett, and a Audiotechnolocy 6A77 on the outside , - different drivers in isobaric coupling ? This is a 2,5 way loudspeaker.