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Here is one that would pique my interest if I had an appropriate room for open baffles:
http://musicanddesign.com/NaO_Note_II_RS.html
http://musicanddesign.com/NaO_Note_II_RS.html
What about ported boxes? And sealed speakers that lack perfect cabinets?An ordinary monopole speaker doesn't leak *any* anti-phase into the room...
What about ported boxes? And sealed speakers that lack perfect cabinets?
More seriously, the classic BBC cabinet paper showed cabinet inaudibility around -20dB or so, IIRC. That's a long way from no output at all. Aren't the modern cardioids getting 12-15dB attenuation to the rear?
The theory is quite simpel. When you place a speaker in a tube, you displace the front and back wave cancellation towards the rear. Only now you have introduced a resonance which affects the amplitude response of the backwave. Hence the damping which acts as low pass filter. The depth of the "tube" behind the driver dictates the resonance frequency but also allows more dampening material depth.Can anyone fill us in on the theory of the cardioid cancellation?
I think it would very well be possible to make this into a mathlab model, which would simplify design. However, as a mathlab nitwit and not being an engineer, i won't be the one making it .The way I see it, such a system can be optimised purely through trial-and-error (with a more scientific name, possibly). You would start out by saying that there must be some arrangement of slots that means that the backwave from the driver meets the front wave at different times and places and cancels out. With trial and error, an optimal set of slots can be found based on some criteria you specify e.g. minimal SPL measured with (possibly simulated) microphones arrayed around the rear of the (possibly simulated) speaker and summed, over some range of frequencies.
I tried different densities of absorption (Akotherm D20 and D40), it didn't even matter that much, but D40 won.
i can use a gate of 5,5ms. However, the mic is at less than a meter distance, which makes it sensitive to variation in distance to the woofer when making measurements at the rear.
But we have more vacation to work on DIY projects
I have tried nearfield. But not sure what it helps.
Measuring at the "slots"; it's not really nearfield. It's just the sum of front and back.
^Not me, just some articles in magazines and forum comments. A cardioid radiation pattern helps only for front wall cancellation, sidewall get as much energy as a standard monopole loudspeaker gives. Dipole pattern or horn helps for sidewalls, but a dipole of course suffers from front wall... A bass horn must be terribly huge.
Choose your poison...
Thank you for your reply. Im referring to the transition zone, say 200 - 700hz, rather than bass frequencies (modal zone). The question then is; does the spectral content of reflections matter in the transition zone as it does for >700hz.^Not me, just some articles in magazines and forum comments. A cardioid radiation pattern helps only for front wall cancellation, sidewall get as much energy as a standard monopole loudspeaker gives. Dipole pattern or horn helps for sidewalls, but a dipole of course suffers from front wall... A bass horn must be terribly huge.
Choose your poison...