Josh Ricci wrote on Fri, 05 November 2010 13:44 |
Phil, I used hornresponse mostly for the modeling with some investigation in akabak but I am still on the learning curve for akabak. Anyway I used a 10" port with 0.75" roundover at both exits. The proximity to the back wall is the cause of the large shift down over the model. I had left only about 9" clearance if memory serves and the port is also baffled internally as part o fthe bracing. I thought it would drop the tune at most only marginally. Wrong!
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I use Akabak very infrequently, fantastic manual for high level learning, though! Hornresponse is powerful and fairly useful, though it rarely seems to nail port tunings. It is FAST for just playing around.
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Unfortunately I did not do impedance measurement at varying power levels but I did do power compression tests using sine waves of long duration and I did get a base impedance curve. Port compression and some shift was evident at the highest drive levels.
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I am curious which way the tuning shifted. If I had to guess, based on the state port area of 500 cm^2 (per driver?) is that it first went up, and then back down slightly at very high power levels?
The Le(x) curve variation for these high power professional drivers is usually so small that the impedance data, even at large excursions, will give you more information about the port Q and tuning frequency than almost any other measurement.
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I am curious why would I want to downgrade slightly to the lighter duty sw115.? (If you could possibly call it that in seriousness) The 21sw152 is their top of the line with the 15mm xmax rating and 6" split wind coil.
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Oh, my mistake, I was under the impression that the 6" VC 21 did not have the variable "split" vc winding, but it appears that it does. Thus it should should have the excellent Bl(x) behavior of the SW115 with more power handling. Oops! Apparently there was a discontinued 21" driver that did not have the split coil.
That would now make the 21SW152 the top dog
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Btw a 18sw115 was tested in vc mag and did very well. Id expect similar or better with the 21's.
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The test in VC is how I became aware of the split winding drives. Fantastically even and symmetrical Bl(x) and kms(x). Good Le(x), too.