Acoustic Crossover

[kspv]

What are the benefits and limitations/pitfalls of an acoustic crossover with reference to subwoofers, vis a vis an electronic crossover?

[bobolix]

In general, they are two main types of the "acoustic crossovers" - in fact they are the boxes behaving as a band bass filter. The first one, so called "one port", performs similarly to bassreflex at the bottom, but with lower steepness (12 dB per octave) and without excessive raising the diaphragm displacement below box resonance frequency. The second one, the "two ported", is very similar to the bassreflex including the steepness and displacement raising, but at proper design it can achieve better sensitivity in the passband.

The pitfalls: it is very hard to damp the standing waves inside the boxes, so that the function would be not degraded and the parasitic coupling of higher modes would be suppressed (usually between 500-1000 Hz). Usually a simple electric crossover is needed (a lowpass filter), but the phasing between the bandpass box and the rest of the system is very critical. Also the sensitivity to the driver tolerances is quite critical. At the two port design the tuning of the ports can be difficiult, as the lower resonance frequency is quite low, usually below 30 Hz, and at reasonable volumes and port crossection the length of the port can be unacceptably big - above one feet e.g.

In general, this construction is suitable only for right selected drivers, having the parameters under tight control. By my opinion, the positives are not very serious - the classical vented box could work at least similarly effective without said pitfalls.

[BillFitzmaurice]

To simplify, an acoustic crossover as seen in bandpass boxes does nothing to efficiently utilize amplifier power; even though the sub rolls off acoustically frequencies outside its passband the amp is still working those frequencies, which is a waste of power for both the amp and the speaker and also leads to IM distortion.

[hunter audio]

hi

other than the above factors mentioned above in an electronic c/o you will have total control over the cross over frequency with a total freedom to tune and boost the signals you would like to hear from that singular design

where as in a band pass the box needs to be rock solid , then even with carefully measured drivers a design may yet fail to give you the tuning or the frequencies you desired

again unless as mentioned above you have tight control over the drive units - that means driver design

in the indian context

- taking the loss of efficiency in a band pass , one requires higher power ratings for the drive units for eg a 6 inch rated at 100 w
Rms or above , plus a good mosfet amp to push it

I guess linear high exscursion high power drive units are not available easily -

suranjan das gupta

transducer design engineer