I don't think so. The pressure(s) are seen by both drivers in tandem, or as a system. They see the pressure together, like a set of super-twins. they are wired together and see the same load. The pressure seen by both woofers is the same as that seen by one woofer in an enclosure twice the size. You can't create energy. The isobaric chamber has constant pressure and links the two woofers together as a physical bar would.
The higher articulation comes from more voice coil wire in the gap of more magnets. Thought experiment: reduce the isobaric chamber - the result is nothing, reduce it again - no difference, keep it up until the two speaker cones become one heavy cone and the magnets and voice coils are somehow two in piggyback configuration. Vas is cut in half, power handling doubles.
I think the only way to get what you say to happen is to have bi-amplified isobaric woofers. A separate amp for each woofer. Hmmmm.....
Simulation is as accurate as the design of the simulation.
Someone already pointed out this isn't strictly true, but it's close enough in the bass.
Why is the simplest explanation not accepted? The thickness of two cones isolates us from the corrupted back wave inside the main box? Compare aluminum cones with paper cones: Not as much reflected back wave gets back through the cone....
It always surprises me how little basics "specialists" in the audio and speaker building sector knew, just a few decades ago.
Putting damping material in a coupling champer is an absolute no. You want to transfer a maximum of energy and not loose it to processes in damping material.
Many of these older patent scripts show that the inventor had his own fantasys how the world of physics may work.
Today anything around speaker building is just science. If you know soem basic physic, you can understand about anything involved.
It is a little like the electric system you have in an average house today. For someone who lived 100 years ago this may be close to a miracle, today any apprentice in the electric field can explain it to you.
Putting damping material in a coupling champer is an absolute no. You want to transfer a maximum of energy and not loose it to processes in damping material.
Many of these older patent scripts show that the inventor had his own fantasys how the world of physics may work.
Today anything around speaker building is just science. If you know soem basic physic, you can understand about anything involved.
It is a little like the electric system you have in an average house today. For someone who lived 100 years ago this may be close to a miracle, today any apprentice in the electric field can explain it to you.
I have never put any damping material inside the chamber . The isobarik chamber only works up to ( practical use ) about 250 Hz anyway if using fourth order crossover . Ivor Tiefenbrun talks about 500-600 Hz and thats true if using infinite steep crossovers . In the Sara isobarik speaker Linn uses this absorbent to damp the resonanses because the driver plays up to 3 kHz in that speaker. A compromise.
In the end of the lifespan of the big Isobarik loudspeaker from Linn , they used Kustone panels do damp structural resonanses in the chamber.
Biggest advantages with the isobarik principle is, the usual thing publicly known = halv the box and the same deep bass, + plus the two important things = the air in the chamber is adding to the weight of the cones , if its 10 liters of air its 13 grams extra lowering the fb in the whole system = lower bass .
The other big advantage is that the front driver is protected by the driver inside the box , from the backpressure from the whole box. You can compare this with the advantage of using metal cones thats stiffer than paper in an ordinary box, as andersonix already wrote.
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If you use cone to cone isobarik coupling ( making the chamber really small ) the fB of the whole system will be slightly higher compared to the Linn coupling , cone to magnet - adding the weight of the air inside the chamber to the two drivers cone weight.
Adding mass reduces the resonant frequency, but also the efficiency. The membrane stroke is longer, and with it, distortions. Those are sacrifices that can probably be made for better and deeper bass.
I'm not sure if it's good to connect two 4ohm drivers in series to get 8ohm impedances? Or are they usually connected in parallel (8//8=4ohm)? Got some 8" 4ohm drivers for testing, that's why I'm asking.
I'm not sure if it's good to connect two 4ohm drivers in series to get 8ohm impedances? Or are they usually connected in parallel (8//8=4ohm)? Got some 8" 4ohm drivers for testing, that's why I'm asking.
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Conventional parallel Isobaric arrangements allow for a net zero change in sensitivity over a single driver. If you run the woofers in series, it will net a loss in sensitivity. Of course, efficiency is a loss over a single in both cases.
Yes, I meant efficiency and wrote sensitivity. English is not my native language.
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one question
Does anybody know if there would be a problem in isobarik clamshell arrangement to glue the two paper cones together with some expanding foam?
Only a drop of it just to fix them together taking care the foam does not reach the surround.
The drivers would have only little distance to each other just to omit the surrounds are touching each other.
The idea is to bind both drivers really together.
Or is that a bad idea introducing some other problem(s)?
or would it be a great idea?
Does anybody know if there would be a problem in isobarik clamshell arrangement to glue the two paper cones together with some expanding foam?
Only a drop of it just to fix them together taking care the foam does not reach the surround.
The drivers would have only little distance to each other just to omit the surrounds are touching each other.
The idea is to bind both drivers really together.
Or is that a bad idea introducing some other problem(s)?
or would it be a great idea?
You will run into problems because the cones are not centered similar on both drivers. The cheaper the driver, the worse. Why not use that chamber with all it's advantages and make the thing even more problematic? I know it doesn't matter with your builds, but how do you plan to ever get a driver out again?
No good idea. Setzen, 4 minus, aber nur weil Christmas ist.
No good idea. Setzen, 4 minus, aber nur weil Christmas ist.
I see - thanks @Audentid14 !
The FC of Isobaric section of my 475L is 300Hz, but I use a Serial-Parallel 6 to 12dB/Oct. crossover, so there could be some higher frequencies to more or less absorb, hence the Cotton Wool I installed... Emprically... But it may be detrimental for a proper Isobaric operation ? Since the chamber volume is reputedly constant, it should not... 🤔
T
The only high frequency sounds that should be in there are distortion sounds from the drivers themselves. The woofers should be crossed over pretty low, but they don't have to be. I don't think it will hurt anything in your speaker because you don't cover the drivers with damping.
The pressure in the isobaric chamber theoretical varies exactly as the pressure would in a box of twice the size with a single driver. The pressure in the box of the isobaric system is theoretically twice the pressure of the single box system. Thus, the pressure force on the rear driver is (Pbox - Pchhambe). The pressure on the front driver is just Pchamber. Now, with Pchamber being equal to the pressure for a single box system, call it Psb, and with Pbox = 2 x Pchamber = 2 x Psb, P on the rear driver = 2 Psb - Psb = Psb and the pressure on the front driver is just Psb.
The two driver move with slightly different excursions resulting in the pressure variation in the chamber. Gluing, or mechanically coupling the driver would eliminate the isobaric effect.
Note the obvious: If the pressure in the isobaric chamber did not vary the same as the pressure in the single driver box then the response of the isobaric system would not be the same as the single box system with twice the box volume.
https://musicanddesign.speakerdesign.net/Isobaric.html
The two driver move with slightly different excursions resulting in the pressure variation in the chamber. Gluing, or mechanically coupling the driver would eliminate the isobaric effect.
Note the obvious: If the pressure in the isobaric chamber did not vary the same as the pressure in the single driver box then the response of the isobaric system would not be the same as the single box system with twice the box volume.
https://musicanddesign.speakerdesign.net/Isobaric.html
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The mass of air at STP is 1.225 kg/m3 (0.0765 lb/cu ft)
Adding a blanket or curtain of damping material between the woofers also increases the mass and I think it would be an effective, if not dramatic, way to lower Fs. It may also result in the destruction of the woofers if too much excursion is encountered.
Since that isobaric principle works up to a few hundred Hz, what is the effect on the baffle step compensation?
That "blanket or curtain" you describe is exactly what I incorporated into my ( lower part ) bass boxes using a front firing 12" woofer and
rear reverse mounted 15" subwoofer > using a custom designed crossover network > THE RESULTS ARE ASTONISHING !
PS.
My 'lower boxes' = 114 Litres
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