Isobaric frequency limits?

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
I'm aware that isobaric loading is mainly frowned upon here, but there's one driver id like to try it with, when funds allow, clamshell
Here Satori WO24P-8 Woofer

Several reasons why this driver may suit; it is fairly sensitive, it goes down to 25hz f3, it needs a big cabinet and the basket looks alot nicer than the cone!

Main question is, if front facing with floor gain, where roughly would I need to cross?
 
Terrible sketch but this is kind of how it would be. A 3 way with the clamshell recessed slightly into the cab. I want the baffle to continue down and over the front of the bass driver magnet, with enough of a gap to install the two bass drivers. Then the down firing port would run down the back of the cab.
8fbc68094bd80b20aeec7796a64ed5ec.jpg
 
I've never figured out the drive behind using an isobaric configuration. Sure you get 1/2 the volume for the rear enclosure, plus the volume of the isobaric chamber so it's not really 1/2 the total volume. It is, on the other hand, 3dB less efficient, whether you connect the drivers in series or parallel. makes more sense just to find a driver with the same Fs, Qms, Qes, 1/2 the Vas. You will have truly 1/2 the box volume and the same 3dB lower efficiency.
 
Just mount a 10 or 12 on the side...Qtc up to 1 or so for a sealed is fine, and a sealed with Fc ~35 goes a lot deeper than you think. Venting any small box tuned low is problematic. You can get a lot of driver for $400 that will work better in the application.
 
I've never figured out the drive behind using an isobaric configuration. Sure you get 1/2 the volume for the rear enclosure, plus the volume of the isobaric chamber so it's not really 1/2 the total volume. It is, on the other hand, 3dB less efficient, whether you connect the drivers in series or parallel. makes more sense just to find a driver with the same Fs, Qms, Qes, 1/2 the Vas. You will have truly 1/2 the box volume and the same 3dB lower efficiency.
Pretty sure two in parallel will give the same output but requires more power to do so ie 4 instead of 8 ohm load. Thats what I've read, correct me if wrong
 
If mounted in reverse there is some canceling of non-linearity distortions

That is pretty much a myth. I've analyzed the isobaric system and it depends on many factors. In general if there is reduction in distortion is it slight. However, some distortion components can actually increase slightly. It is a completely different situation that the calculation of even order distortion with a push-pull pair of conventional woofers (separate boxes). In the case of isolated push pull system it is the sum of the output of the two system and that the even order distortion is out of phase and cancels. In the case of an isobaric system it is not the isolated outputs that sum. It is two nonlinear devices directly interacting. The motion of one is a driving force to the other. The bottom line is that a blanket statement that isobaric system reduce distortion can not be made.
 
I have always wondered how the outer driver can handle the extra cone movement from double force... Having double radiating cone area would be more beneficial, but of cource the box gets bigger too.

The pressure in the isobaric chamber actually varies as the pressure in the normal sized, single driver box. Thinks about it. The only way the outer driver will behave as if it is in a normal box is if the force on the back side is the same as it would be in a normal box. The rear driver sees a pressure force on the back side which is twice what it would be in a normal sized box, bot on the front side it sees the pressure in the isobaric volume, which is, again, the same as in a normal box. This both the front and rear drivers have the same net pressure force acting on them; that which they would have in a normal sized box. (Minor differences do occur.)
 
The pressure in the isobaric chamber actually varies as the pressure in the normal sized, single driver box. Thinks about it. The only way the outer driver will behave as if it is in a normal box is if the force on the back side is the same as it would be in a normal box. The rear driver sees a pressure force on the back side which is twice what it would be in a normal sized box, bot on the front side it sees the pressure in the isobaric volume, which is, again, the same as in a normal box. This both the front and rear drivers have the same net pressure force acting on them; that which they would have in a normal sized box. (Minor differences do occur.)
Suppose a small upside is that a lower Q is easily attained with a slight increase in box volume and will lessen pressure on the back of that cone.

Why tf am I so obsessed with isobarics..
 
Suppose a small upside is that a lower Q is easily attained with a slight increase in box volume and will lessen pressure on the back of that cone.

Why tf am I so obsessed with isobarics..

Simply because the sound moves you like no other you can taste it. I went one step further and loaded the rear speaker into a transmission line. I drive it with a massive 7 watt class A JLH amp in a listening room of 300 cu m.
 

Attachments

  • DSC00138-2.jpg
    DSC00138-2.jpg
    244 KB · Views: 154
Last edited:
I had both Saras and Linn's big Isobariks. I loved the Saras, but they tended to eat amps. The big Isobariks were a bit easier to drive. Never liked the midrange on them, though, and finally moved to Magnepans. But God, what delicious bass those Isobariks had.

And hey, this is DIY. You should build whatever takes your fancy.

Cheers,
Jeff.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.