I cant really figure out if a line of 4 woofers would have "4x the virtual surface area" or the ones between the outside world ones would actually do nothing much because the outside drivers would be doing most of the work.
on the one hand there is "the 2 outside woofers" doing all the work and the inside ones not doing anything, on the other hand the air has to be moved and the inside ones might help the outside ones.
i got 4 half decent TB woofers i bought on a whim here but they are only 25 w RMS. i just got them to try experiments with
i want to put them all in a line with a fairly small enclosure.
on the one hand there is "the 2 outside woofers" doing all the work and the inside ones not doing anything, on the other hand the air has to be moved and the inside ones might help the outside ones.
i got 4 half decent TB woofers i bought on a whim here but they are only 25 w RMS. i just got them to try experiments with
i want to put them all in a line with a fairly small enclosure.
I by no means am an expert, and maybe someone with better knowledge can give you a more techincal explanation of this, but let me at least take a stab at it. When you put woofers in an isobaric configuration it has a few affects, one is that you can get a similar response in about half the volume, at least based on models I have run in programs like WinISD. However, its at the expense of efficiency, which lowers drasticly in my experience. I believe you lose about 6 decibles of efficiency.
Just as an exercise, I took and modeled a single Brahma Subwoofer in a 3 cubic foot sealed box, and a pair mounted isobaricly. The response was about the same, however the cone excursion was considerably less at any given power level, but so was output. As I said, about 6 decibles compared to the single woofer.
Now my guess based on what I'm seeing in WinISD, and based one what I think I have read about Isobaric mounting is that they share the load pretty evenly, and actually the benefit is that you get a large reduction in distortion, and a large increase in power handeling. However you end up needing it given the reduction in effeciency. In the case of the Brahma, you go from the 1600watt power handeling of the single driver to 3200 watts, effecticly doubling its power handeling.
Doing a quick web search I found that Isobarics couples the woofers as one causing them to act the same as a single driver in twice the volume of the box. It reduces the VAS, and allows the same output in half the box volume, but at the expense of a 3db loss in efficiency. I modeled 6, but who knows. It goes on the mention that you could potentially get an increase in output by using 4 woofers and 4 times the power and get about 6 decibles more ouput in the same size box as a single woofer. It sounds like a great space saving method, but somewhat cost prohibitive for most.
I speculate still about the reduced distortion, I would imagine that any nonlinear movement of one cone might be canceled, at least to a point, but the other. However, I'm guessing, I havne't read that. As I said, maybe someone more knowing will be able to chime in.
Just as an exercise, I took and modeled a single Brahma Subwoofer in a 3 cubic foot sealed box, and a pair mounted isobaricly. The response was about the same, however the cone excursion was considerably less at any given power level, but so was output. As I said, about 6 decibles compared to the single woofer.
Now my guess based on what I'm seeing in WinISD, and based one what I think I have read about Isobaric mounting is that they share the load pretty evenly, and actually the benefit is that you get a large reduction in distortion, and a large increase in power handeling. However you end up needing it given the reduction in effeciency. In the case of the Brahma, you go from the 1600watt power handeling of the single driver to 3200 watts, effecticly doubling its power handeling.
Doing a quick web search I found that Isobarics couples the woofers as one causing them to act the same as a single driver in twice the volume of the box. It reduces the VAS, and allows the same output in half the box volume, but at the expense of a 3db loss in efficiency. I modeled 6, but who knows. It goes on the mention that you could potentially get an increase in output by using 4 woofers and 4 times the power and get about 6 decibles more ouput in the same size box as a single woofer. It sounds like a great space saving method, but somewhat cost prohibitive for most.
I speculate still about the reduced distortion, I would imagine that any nonlinear movement of one cone might be canceled, at least to a point, but the other. However, I'm guessing, I havne't read that. As I said, maybe someone more knowing will be able to chime in.
I posted a very similar post to this yesterday on a swedish forum:
Compared to one driver:
Using isobaric halves Vas and the box can be made to have half the volume. The efficiency drops to half (-3 dB) but the thermal power limit is doubled as a whole. The maximum output level in the half-as-big box will therefore be identical* to the single driver in the original volume.
If the drivers are mounted side-by-side, Vas is doubled and the box needs to be twice as big. The power limit will double and the efficiency is increased by 3 dB. As a result, the maximum output level increases by 6 dB.
Example:
Thick line= frequency response, thin line= maximum output level, dashed line= electrical impedance. All designs have the same length for the vent, ie the diameter varies. This results in a too small tube for this isobaric design, which in turn results in a lower maximum output level around the vent tuning.
*Apart from potential problems with overloading the vent.
Compared to one driver:
Using isobaric halves Vas and the box can be made to have half the volume. The efficiency drops to half (-3 dB) but the thermal power limit is doubled as a whole. The maximum output level in the half-as-big box will therefore be identical* to the single driver in the original volume.
If the drivers are mounted side-by-side, Vas is doubled and the box needs to be twice as big. The power limit will double and the efficiency is increased by 3 dB. As a result, the maximum output level increases by 6 dB.
Example:
Thick line= frequency response, thin line= maximum output level, dashed line= electrical impedance. All designs have the same length for the vent, ie the diameter varies. This results in a too small tube for this isobaric design, which in turn results in a lower maximum output level around the vent tuning.
An externally hosted image should be here but it was not working when we last tested it.
*Apart from potential problems with overloading the vent.
neutron7 said:
Yes, true, apart from the overloading effects of the vent if the box is bass-reflex. Sensitivity*, efficiency, frequency response remains the same, max power quadruples and max output level increases by 6 dB**.
* Given series-parallel connection
** Again apart from around vent resonance.
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