The Linkwitz Transform is absolutely appropriate - why do you not like it?
You want to produce a boost complimentary to the woofer's natural rolloff, and get a new cutoff of around 30Hz? Forgive me, but this is what the LT is for! In addition to correcting magnitude, the LT perfectly corrects phase, so there are no issues with group delay.
From the graph you posted, there only needs to be 6dB or so of boost at the highest point, which isn't going to overload anything. If you want a faster rolloff below 30Hz, maybe to minimise excess excursion, you can even use a highpass filter below the LT.
What's not to like?
Ok Wingfeather, you are absolutely correct . I hadn't really realised the potential of the LT circuit, I was paying too much attention to the examples. When I applied it in WinISD I saw what it could do; a -3db point at 23hz seems to work well. It also reduces group delay (especially over the high pass circuit). My design has just under 11db dc boost with the driver in a 78L box, should work ok. Look forward to experimenting!
Got some ideas for box construction too. Trying to draw in sketchup but it keeps pausing and getting lines everywhere, think my passive GFX card is overheating in this hot weather . I'll try to describe, the outer box will be made from MDF (18mm say) with plywood (mabye 12mm) backed onto it, I believe its called constrained layer damping. But also, leaving some spacings between the internal plywood layers I can have a groove for the internal "swiss cheese" bracing to slot into. I also thought about having an angled deflector at the back behind the woofer, to reduce reflected sound coming back through its cone (as per my mid box). Don't know if this is worth doing with only below 400hz being handled.
. I hadn't really realised the potential of the LT circuit, I was paying too much attention to the examples. When I applied it in WinISD I saw what it could do; a -3db point at 23hz seems to work well. It also reduces group delay (especially over the high pass circuit). My design has just under 11db dc boost with the driver in a 78L box, should work ok. Look forward to experimenting! Got some ideas for box construction too. Trying to draw in sketchup but it keeps pausing and getting lines everywhere, think my passive GFX card is overheating in this hot weather
. I'll try to describe, the outer box will be made from MDF (18mm say) with plywood (mabye 12mm) backed onto it, I believe its called constrained layer damping. But also, leaving some spacings between the internal plywood layers I can have a groove for the internal "swiss cheese" bracing to slot into. I also thought about having an angled deflector at the back behind the woofer, to reduce reflected sound coming back through its cone (as per my mid box). Don't know if this is worth doing with only below 400hz being handled.
These little beasties turned up yesterday . Only really been as far as to test for faults and they seem fine. Not got any box yet but they seem to handle power well and kick pretty hard. There is some motor noise at the higher excursions but I doubt this will be audible with the rear (where it eminates) in its box and the mids playing too, may become less obvious with wearing in period too, hear they take a fair bit of wearing in.
. Only really been as far as to test for faults and they seem fine. Not got any box yet but they seem to handle power well and kick pretty hard. There is some motor noise at the higher excursions but I doubt this will be audible with the rear (where it eminates) in its box and the mids playing too, may become less obvious with wearing in period too, hear they take a fair bit of wearing in.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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