Is an open baffle isobarik alignment possible or useful?

[Brisso57]

I'm embarking on building the MJK open baffle with Eminence 15A Alpha bass drivers.

I started to wonder what the effect would be if the baffle were thickened sufficently for two (2) 15A drivers to be mounted nose-to-tail (with sufficient clearance for excursion!) in "isobarik" fashion.

The front driver would experience isobarik loading when the cone moved backward and the rear driver would experience isobarik loading when it cone moves forward. I'm thinking the net "work" done by each driver per cycle would be reduced, compared to the effort of a single cone.

What would the net effect be?

1. Would the cones be better controlled near resonance? If so, could we cadge a few more Hz lower than the standard MJK system?
2. Also, would the choice of upper freq limit be affected? ie could we XO higher?
3. If there is any real and useful effect, what is the implication for driver selection? (The useful characteristic of the 15 Alpha is the high Qts. Would "faux isobarik" loading mean a rethink on the best Qts?)

cheers

Doug

[cuibono]

Hi there - I've tried just what your talking about, and I've seen someone do it elsewhere too.

You end up with some funny results. If you are doing it the way you're talking about (with drivers close together), for some reason, you get a fairly unusable result. But, if you give the drivers enough volume between them (>5" between cones?), you actually get the predicted increase in output. I don't know why one way works, and another doesn't, but I've tried these arrangements a few times, and this seems to be the way it is...

[Brian Oshman]

Isobaric setup is designed to use a cabinet half the size and have equal output as that of one driver in the optimum sized cabinet. Using it on an open baffle is pointless. You will get better results just using both drivers in traditional OB fashion.

[Rudolf]

Originally Posted by Brisso57

1. Would the cones be better controlled near resonance? If so, could we cadge a few more Hz lower than the standard MJK system?
2. Also, would the choice of upper freq limit be affected? ie could we XO higher?
3. If there is any real and useful effect, what is the implication for driver selection? (The useful characteristic of the 15 Alpha is the high Qts. Would "faux isobarik" loading mean a rethink on the best Qts?)

ad 1.
If the parameters of both drivers are sufficiently close (which they should), they simply work as one. Isobarik mounting will increase the depth of the dipole, increasing the dipole length. This will give some gain - exactly the same as when mounting one driver in a H frame of the same depth.

ad 2.
On the contrary. The volume between the two drivers will set a new upper frequency limit, appr. at 2 kHz.

ad 3.
There is no useful effect in case of a woofer.

Rudolf

[sreten]

Hi,

Adding a further two drivers isobaric style is pointless you get very liitle
in return and halve the load impedance, doubling them up on the baffle
is very different and possibly more worthwhile for maximum bass SPL
rather the senstivity increase it will cause.

rgds, sreten.

[wjlamp]

Originally Posted by Brisso57

I'm embarking on building the MJK open baffle with Eminence 15A Alpha bass drivers.

I started to wonder what the effect would be if the baffle were thickened sufficently for two (2) 15A drivers to be mounted nose-to-tail (with sufficient clearance for excursion!) in "isobarik" fashion.

The front driver would experience isobarik loading when the cone moved backward and the rear driver would experience isobarik loading when it cone moves forward. I'm thinking the net "work" done by each driver per cycle would be reduced, compared to the effort of a single cone.

What would the net effect be?

1. Would the cones be better controlled near resonance? If so, could we cadge a few more Hz lower than the standard MJK system?
2. Also, would the choice of upper freq limit be affected? ie could we XO higher?
3. If there is any real and useful effect, what is the implication for driver selection? (The useful characteristic of the 15 Alpha is the high Qts. Would "faux isobarik" loading mean a rethink on the best Qts?)

cheers

Doug

Hi,

some time ago I read a " relatively" same thought in a patent applied for,design.

The designer uses two indentical low frequency drivers ,mounted in tandem, with the front driver in an open baffle.The second driver is mounted in a smaller area baffle with an acoustic suspension round enclosure.The whole thing (front open baffle and back closed box) is separated by rods of a calculated distance.The claimed response is of a controlled radiation in front and the back is a combined response of the back wave of the front woofer and the front wave of the second closed back woofer.Claimed also is the smaller size. Kind like your isobaric thinking,and interesting to boot.
Sorry I am not able to guide you directly to the patent,but a little google search on open baffle patents will take you there.


B.L

[cuibono]

Hmmm, everyone seems to be saying, "NO" it won't work. But I've done it - and it will work, provided you leave enough volume between the drivers.

If you just sandwich the drivers face-to-face, then, no, it won't work.

[john k...]

Originally Posted by cuibono

Hmmm, everyone seems to be saying, "NO" it won't work. But I've done it - and it will work, provided you leave enough volume between the drivers.

If you just sandwich the drivers face-to-face, then, no, it won't work.

It will work, it's just pointless.

[cuibono]

What makes it pointless? When done properly, I've been able to get 4-5dB greater output (in the bass), for only a small increase in total space used. For OB designs, that seems like a good thing.

[sreten]

Originally Posted by cuibono

What makes it pointless? When done properly, I've been able to get 4-5dB
greater output (in the bass), for only a small increase in total space used.
For OB designs, that seems like a good thing.

Hi, its pointless because your numbers are wrong, output is not greater, rgds, sreten.

FWIW face to face works as well as any other arrangement, here its pointless.