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In Reply to: RE: For my clarity please, posted by sober1 on May 26, 2015 at 07:05:58
The shortest path between front of cone to the rear is what limits bass extension.
The sound wave doesn't care if its around the sides or over the top of the baffle as bass is omnidirectional but if you sit the baffles on the floor at least one pathway is blocked as hitsware said below.
Of course if you were to use a box all paths are blocked and thus no acoustic short circuit occurs.
Boosting bass via eq stresses the driver and limits its dynamic range.
For OB 12dB boost is not unheard of to achieve a flat output and a 3dB boost equals a doubling of input power.
Consequently 6dB is a quadrupling, 9dB equals 8x the power and 12dB 16 times compared to a box speaker!
So to get the same bass output from an OB as a box speaker using the same woofer at 10W you might need 160W.
That's what I mean by 'not very elegant' as you produce sound only to waste most of it before it reaches your ears. A transmission line is a much more elegant way IMO.
Follow Ups:
"So to get the same bass output from an OB as a box speaker using the same woofer at 10W you might need 160W"
That is the most common mistake/misconception, you should not be using a woofer designed for a box in a dipole speaker system to produce bass. Use a woofer with a high Qts, which is not really suitable for a box, to offset the dipole roll-off of an OB. You need to think outside the box and throw away the years of box thinking. The resulting SPL will be in the same league as a boxed woofer system, and to head off the next arguement the bass will not be boomy because of a Qts value > = to 1.0 (that again is box thinking).
How exactly does a high Qts stop the acoustical short circuit?
It doesn't.
But combine a 6 dB per octave loss due to the OB with a peaking SPL response from the high Qts driver and you can end up with a system response that is just right. It is all in the combination of driver, baffle, and crossover.
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