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Old 15th March 2013, 03:33 PM   #11
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Quote:
Originally Posted by Zero D View Post
@ Smeneice
Half the volume required of the box.
Right, box size can be half for a given low frequency cutoff, while using double the drivers and power for roughly the same output as a single driver in a larger box.
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Old 17th March 2013, 06:02 AM   #12
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I can't say I see any reason to do isobaric.

If you mount the same number or drivers in the same size vented box you will get 6dB more output an octave above Fb. The output a half-octave above Fb will be equal, and at F3 it will have about 3dB less output than isobaric.

The simulation I used had a pair of 15s in 5.627 cu ft tuned to 22hz. Both designs had equal output at 31hz, the non-isobaric had 3dB more output at 40hz, and 6dB more output at 55hz and above. 55hz is the peak output frequency in typical dance music.

I would rather have the same size box and the extra output available with non-isobaric.
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Old 17th March 2013, 04:54 PM   #13
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Thank you for this. That's very interesting. I'm starting to think that isobaric designs should only be used when absolutely nessasary. Vented flush mount is my usual build. They all seem to do well.
When you say "The same number of drivers in the same size box" I assume you mean the four drivers on the face plate. I could build two such cabs, non isobaric. You can imagine having eight drivers just sitting on the shelf makes you want to do something with them. Thought I'd get creative. Perhaps I'll come up with something else. Thanks again DJK for the info!
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Old 24th March 2013, 06:52 PM   #14
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if you are looking for an experiment and have the drivers I would highly recommend trying a passive radiator.

with isobaric you mainly gain 1/2 vas. however at the cost of efficiency.

with a passive radiator you have soo many options to get creative. such a single/dual reflex. an awesome design is a fourth order bandpass with a pr. --- would be intense
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Old 24th March 2013, 10:33 PM   #15
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I have seen passive radiators but never in use. I have lots of power. Would it be better to make all the drivers active? If you have an example of the cab design I'd love to see it. Thank you for the suggestion.
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Old 24th March 2013, 10:55 PM   #16
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You could try them in the slutted open baffle Pass came up with.
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Old 25th March 2013, 01:32 AM   #17
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Quote:
Originally Posted by weltersys View Post
If the drivers are not back vented, or the vents do not make noise, I would suggest mounting the drivers cone to cone, reversing the polarity of the drivers with the magnets out.
Simplifies construction, reduces even order harmonic distortion, and the reduced enclosed area makes the output sound "tighter".
I second that, especially for ported (vented / reflex) type enclosures. You need to minimise the volume between the driver cones. I've posted a graph elsewhere on diyaudio to show this:

Isobaric tapped horns

It shows the differences in excursion between the two drivers of an isobaric pair in a tapped horn design. The same thing happens in a ported enclosure at the enclosure resonant frequency. It's less of an issue in sealed enclosures.
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Old 25th March 2013, 04:08 AM   #18
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@smeneice



how many woofers? you said 8-10 inches I assumed. could you be more specific?
also how much power, and how much space.

can't post any pr designs until morning.
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Old 25th March 2013, 09:33 AM   #19
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Getting rid of eight 8" woofers in place of a pair of 15s in a pair of vented Klipsch LaScala.

Click the image to open in full size.
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