Isobaric with dissimilar drivers.

[Circlotron]

Has anyone ever tried a clamshell isobaric setup with two same sized but otherwise different drivers e.g. one with 30Hz and the other with 40Hz resonance? Or some other combination of parameters? Maybe even combined a really good and a really cheap driver to get some particular property like a specific Vas?

[Nappylady]

(remember that I only know HS physics!)

I suspect that any difference in drivers will only reduce the isobarik effect, and possibly provide a kind of "soft knee" effect to whatever port loading or whatever else might be happening in the box.

If you did a lot of research and testing, I bet you could come up with some formulas to make it an optimal thing, or gain some advantages over straight isobarik.

People out there make lots of money by making crazy ideas like this work better than sane ideas like crossovers.

Did you hear someone say manger? I didn't hear anyone say manger. Must've been the wind.

[sreten]

Its possible but probably not a good idea.

The close coupling will form a driver of combined parameters.

The important thing to get right would be matching excursion
capability (assuming Sd is the same) otherwise distortion would
be poor.

Even different size drivers is possible with matching volume
displacement, but the parameters would not combine the
same way as two same sized drivers.

One possibility that would work but I've not seen used is
using an ABR or slave diaphragm instead of the rear driver.

sreten.

[Circlotron]

Originally posted by sreten
One possibility that would work but I've not seen used is
using an ABR or slave diaphragm instead of the rear driver.

Mmmm.... that sounds like fun! So if I bung in an ABR, how do I calculate the composite T/S parameters?

[sreten]

You need a program that calculates the T/S parameters from
more fundamental parameters such as cone mass and suspension
stiffness.

for close coupling of a same size ABR you just add the extra mass
and stiffness to the drivers basic parameters.

(Asumming Q stuff is too high to make much difference,
I don't know how to add this if its applicable.)

sreten.

[7V]

Assuming the diameters were the same you'd probably want to equalize the efficiencies so that cone excursions would be the same throughout most of the range.

In the early days of car suspension, before shock absorbers, they used two different springs and each damped the other. I imagine that the same thing would happen with the bass drivers so the resonances would be muted.

I think it would be well worth trying, great fun. No guarantees though.

[sreten]

Originally posted by 7V
Assuming the diameters were the same you'd probably want to equalize the efficiencies so that cone excursions would be the same throughout most of the range.

In the early days of car suspension, before shock absorbers, they used two different springs and each damped the other. I imagine that the same thing would happen with the bass drivers so the resonances would be muted.

I think it would be well worth trying, great fun. No guarantees though.

Hi 7V,

point 1 : the close coupling would automatically do this IMO.
Series or parallel connection of the voice coils could be very different.

point 2 : sounds more like using two different drivers in parallel in the same box to me.
Again i think the close coupling would not allow this to happen.

sreten.

[phase_accurate]

All I can say: It has (almost) been done.

Speaker Model: Dynaudio Confidence 5

You just can't call it a "clamshell" setup since there is considerable air volume between the outer 8" and the inner 6" driver.

Regards

Charles

[SY]

Go back even further. Dynaudio DA-500 from the 1970s. Inner driver was a 21W54, outer was a 30W54. Worked great, maybe the most natural bass I've heard in a box speaker.

[Nappylady]

Circlotron, I think you're on to something.

I've got these 5" car speakers here, full-rangers, and they sound *eh* okay. A bit harsh, a bit dark, a bit bass-shy, nothing a little EQ doesn't take care of. (If you're interested, parts express #269-912, very good cheap speakers!)

I have this idea.

I've fallen in love with the idea of a bipole, since the magnetic fields of the two speakers cancel each other out, as well as the 2nd-order harmonic distortion of the drivers.

Anyway... these speakers have a resonance around 90-100hz (not sure, can't measure) so everything below 100 just kinda drops off slowly... but I was thinking, two of them in a bipole-isobarik-4th order bandpass box could probably get some decent extension!

And then I thought--what if you added mass to the back driver, reducing the driver resonance? Hey, I bet you could get usable output down to 30hz!

I've still got 7 (and a half) of these drivers just doing... nothing... so I'll try to find someone who can help me measure them and throw together a box and let you know what it sounds like.

Thanks for the idea!!!