Posted by Duke [ 208.98.184.25 ] on November 30, 2007 at 00:51:57:
In Reply to: Impedance, Qts, VAS, efficiency and box tuning? posted by Norris Wilson on November 29, 2007 at 06:35:45:
Hi Norris,
Well I'll be able to answer your questions more accurately once I can test the prototypes, which is being held up right now by slow delivery of the custom voice coil(s).
I gather you are asking what would happen if instead of using a plate amp to drive the second voice coil, you simply wired the two voice coils in series to produce a 16 ohm driver. Is this correct?
Here is my understanding (someone correct me if I'm wrong) of the way it works for a dual voice coil woofer:
With both coils active, whether in series or in parallel, Qes would decrease to 1/2 of the Qes value for only one coil active. Qms would stay the same. So Qts for both coils active would be a little bit more than 1/2 the Qts value for only one coil active.
Vas stays the same.
The efficiency will go up by 3 dB for both coils active in comparison with only a single coil being active. This is predicted by the change in Qes.
With both coils active (driven by the same amplifier) whether wired in series or in parallel, I think my woofer would become in effect a high efficiency midrange driver with excess x-max. With the two voice coils wired in series, the load would probably be easier on most tube amps because of the increased efficiency but that might be offset by the need to now come up with a woofer section to do the deep bass.
Duke
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