You loose 6dB not 9. Purely due to cone area.
Not sure about efficiency. You do get double motor strength but also double mass. But it's the box that keeps the cone back so you should gain some when keeping the box the same. Or no difference if you half the box volume.
Halving the box volume is the only benefit I see of isobarik. If you don't need that I would go with the PPSL shown above ore something else.
Not sure about efficiency. You do get double motor strength but also double mass. But it's the box that keeps the cone back so you should gain some when keeping the box the same. Or no difference if you half the box volume.
Halving the box volume is the only benefit I see of isobarik. If you don't need that I would go with the PPSL shown above ore something else.
I'm going to simplify this for anyone who's not following well:
Isobaric in a parallel driver configuration drops 3dB of efficiency, but retains the same voltage sensitivity. The bonus you get is a box volume requirement half as large, and a potential for even-order distortion cancellation because you arrange them (when done right) with the cones moving in opposite physical direction with respect to the magnet. The cone motion is averaged out so you get equal force whether the cones are rarefying the air in the room or compressing it.
With a push-pull sub, if you arrange it so that one cone fires into the room and the other magnet side faces out, you get a similar benefit, partially limited by the physical spacing of the drivers (at highs where this method falls apart anyway- for subs it's not much of an issue). You also have 2x the cone so +3dB and 2x the current through so +3dB more--- VOLTAGE SENSITIVITY. The efficiency is 3dB higher than a single driver.
For voltage sensitivity, the push pull arrangement is 6dB higher due to the doubling of cone area. The efficiency is 6dB higher. And the box 4x as large.
To simplify, you can just compare box volumes. 4x the box is 6dB. For a nominal 90dB driver the push pull will be 96dB 2.83V, 2W. The Isobaric will be 90dB 2.83V, 2W.
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PPSL, up to 400, what relationship:
From one of your previous posts:
"You can push the frequency high depending upon the distance between the drivers and depth of the slot."
If I would like to run a set of these up to 400Hz, does the plennum, or "slot" need to be deeper, or only as short as required for the diameter of the woofers, which in my case are 12" Emmience 4012 HO? And then again, what about the actual space between the boards that hold the woofers?
From one of your previous posts:
"You can push the frequency high depending upon the distance between the drivers and depth of the slot."
If I would like to run a set of these up to 400Hz, does the plennum, or "slot" need to be deeper, or only as short as required for the diameter of the woofers, which in my case are 12" Emmience 4012 HO? And then again, what about the actual space between the boards that hold the woofers?
This would be my response to the question posted by Tosh/Andersonix earlier, which I have only just noticed.
There is an old monitor design that uses 2 midrange drivers, though in quite a different way. The drivers are coupled such that an equal and opposite mechanical force acts on the radiating driver by using an identical driver, which I think is enclosed and not contributing to the acoustic output. It's because when any cone moves forward, the rest must move back by some degree and vica-versa, the amount depends on the mass ratio. I think this arrangement gives the effect of the midrange being mounted to an infinite mass. Must require very rigid coupling between the drivers to be effective and I don't know how necessary it is really, interesting though.
apology, this ? is O/T to the OP
I like slot loaded push pull. The area is double what 1 driver needs but you pick up 6db (+3 for double drivers, +3 from 8 phm to a 4 ohm load). You can push the frequency high depending upon the distance between the drivers and depth of the slot.
almost no vibration also, very clean
Norman[/QUOTE]
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My question is :
If I would like to run a set of these up to 400Hz, does the plennum, or "slot" need to be deeper, or only as short as required for the diameter of the woofers, which in my case are 12" Emmience 4012 HO? And then again, what about the actual space between the boards that hold the woofers?
I like slot loaded push pull. The area is double what 1 driver needs but you pick up 6db (+3 for double drivers, +3 from 8 phm to a 4 ohm load). You can push the frequency high depending upon the distance between the drivers and depth of the slot.
An externally hosted image should be here but it was not working when we last tested it.
almost no vibration also, very clean
Norman[/QUOTE]
_________________________________________________________________
My question is :
If I would like to run a set of these up to 400Hz, does the plennum, or "slot" need to be deeper, or only as short as required for the diameter of the woofers, which in my case are 12" Emmience 4012 HO? And then again, what about the actual space between the boards that hold the woofers?
_________________________________________________________________
My question is :
If I would like to run a set of these up to 400Hz, does the plennum, or "slot" need to be deeper, or only as short as required for the diameter of the woofers, which in my case are 12" Emmience 4012 HO? And then again, what about the actual space between the boards that hold the woofers?[/QUOTE]
Hi Scott,
I'm not an expert on PPSL, but from djk I know that the smaller the slot, the higher up in frequency they will work. So you want to make the cavity as small as possible. The distance between the drivers should not be much larger than just allowing both drivers to be mounted. Les Hudson, who posts at the High efficiency AA board have made the cavity even smaller than just the smallest possible rectangular box surrounding the drivers by inserting small "brackets" mounted in a 45 degree angle inside the cavity, where they take up a bit of space in the two (or actually four) corners.
Best regards
Peter
a bit note on isobaric setup, with woofers wired back-to-back. It actualy has an advantage, other than reduced volume, or in some cases better impedance matching. Isobaric setups like that cancel out non-linearity between cone movement backwards and forwards. Cones do not behave the same when moving backwards and forwards. This actualy reduces distorsion, at high cone excursion levels. One must allso account a drawback too, as the chamber that is holding the drivers magnets is small, voice coil heating can become a problem in some cases. I have used isobaric setup many times, for sealed and for ported designs. It actualy works quite well, when it is affordable i can only advice to use it. The speaker's cone is a cone, try pushing it at one side, then at the opposite side. Due to it's shape, it will be harder to deform it from the front. When the cone is moving backkwards, it can deform with less effort. In case the chamber that holds the drivers is realy small, the 2 cones will help eatch other to maintian their form regardles of movement direction. Suposedly the result of an isobaric setup is not just reduced volume, but improves cone "stiffnes/rigidity" whatever is the proper english word, and linearity at lage signal lvl is better for the combined driver than a single one. Allso, since the volume is less, standing waves / resonances will occur at higher freqvency then for a single woofer. Absorbing that is easyer. One might allso mention that the basket of the woofer does interact with air. The hole in the magnet ment to aid the voicecoil cooling allso makes strange noises, those are contained in the sealed chamber holding the drivers. I personaly do not think those noises can be significant, but who knows, i never mesured anything, i can only verify that an isobaric setup plays cleaner, specialy at high excursion lvl. There are no identical drivers, drivers have some unique peaks and dips in response curve. The ones i think of are in the magnitude of a dBL or so. But since those are unqique, and does not occur at the verry same freqvency for both drivers in the isobaric load, these peaks have to face 2 times the mass to move compared to if only 1 driver would be used. So suposedly differences between the 2 drivers get a damping. Thisone is allso not vierifyed by me, it is something i read, but i think it seems logical. Not sure if this is an advantage, as suposedly dips not common to the 2 drivers would be larger by the same factor. The problem of the voicecoil cooling hole in the magnet can become a HUGE one, if the drivers are back to back exactly. Since the hot air pushed out by one driver will go directly into the other. Some suggest that drivers should be offset. I prefer that too, as it enables the construction of a smaller volume of coupling chamber between the drivers. Some use a mesh and wool to even further reduce the volume between the drivers, i would not go that far if I would push the unit with high power. Voice coil overheating / changes in parameters due to heat would be problematic. A nother downside is box-rumble. 2x the moving mass, and 2x the power to movie it. For the same SPL lvl as a single unit. This means the box will tend to rezonate more than with a single driver. Well, I think this is all I can add 
I built a isobarik "face to face" subwoofer using two 15" woofers from a PA cabinet and a 18" passive radiator. It does work well but is about 3 dB lower in volume compared to the single driver.
My reason for the alignment was the pair of speakers were laying around and the 3.4 cubic feet PA cabinets are 3/4" plywood and built like tanks. The numbers indicated 5.2 cubic feet for one woofer and 10.4 cf for the pair. Isobarik required 2.6 cubic feet so with space taken up by the Exodus Audio 18" PR and cross braces--the Isobarik was very close.
I have more power than a single 15 could handle so the pair give me the 3dB I lost with Isobarik. So after all that work I have the output of one driver by using twice the power. Total cost was $100 for the PR, $20 for a half-sheet of plywood to make a 2.25" thick flush panel on the back to mount the passive and $10 in glue.
My wife gained getting rid of one of those PA speaker boxes--I got a much stronger sub than the old AR 12.
I would not build an Isobarik if I was buying the drivers but it is a great option to reuse PA speakers and cabinets that were just sitting in the garage. The trick also works well for car audio, once you get sick of the loss of trunk space with your pair of 12's...cut the box in half and mount the pair face to face on one side. If you want to keep the same tuning, make the box 1/4 of the original size. You'll lose 6dB but your wife won't file for divorce if you don't get rid of the thing.
Isobarik--endorsed by long suffering spouses of DIY'ers everywhere.
My reason for the alignment was the pair of speakers were laying around and the 3.4 cubic feet PA cabinets are 3/4" plywood and built like tanks. The numbers indicated 5.2 cubic feet for one woofer and 10.4 cf for the pair. Isobarik required 2.6 cubic feet so with space taken up by the Exodus Audio 18" PR and cross braces--the Isobarik was very close.
I have more power than a single 15 could handle so the pair give me the 3dB I lost with Isobarik. So after all that work I have the output of one driver by using twice the power. Total cost was $100 for the PR, $20 for a half-sheet of plywood to make a 2.25" thick flush panel on the back to mount the passive and $10 in glue.
My wife gained getting rid of one of those PA speaker boxes--I got a much stronger sub than the old AR 12.
I would not build an Isobarik if I was buying the drivers but it is a great option to reuse PA speakers and cabinets that were just sitting in the garage. The trick also works well for car audio, once you get sick of the loss of trunk space with your pair of 12's...cut the box in half and mount the pair face to face on one side. If you want to keep the same tuning, make the box 1/4 of the original size. You'll lose 6dB but your wife won't file for divorce if you don't get rid of the thing.
Isobarik--endorsed by long suffering spouses of DIY'ers everywhere.
Yup, isobaric is costly. You need 2x the woofer, 2x the power.
Bt it is SOO sexy to have the response of a mutch larger box...
Magical, You have a -for its sound- tiny box, and yet it can produce deep tones..
DIY audio is sorthof not more than a set of compromises.
DIYer's call what to choose.
Bt it is SOO sexy to have the response of a mutch larger box...
Magical, You have a -for its sound- tiny box, and yet it can produce deep tones..
DIY audio is sorthof not more than a set of compromises.
DIYer's call what to choose.
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