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In Reply to: RE: MG 3.7i exposed posted by neolith on August 26, 2015 at 12:25:28
Very nice
Are you sure you can reproduce this in a parallel XO without increasing the complexity?
Are you going to run FR sweeps on the drivers? The mids seem to be done differently this time so it would be interesting to see if that overlap works with the drivers' FR (actually just the mid's rolloff)
Looks like they managed to lower the XO of the mid to 400 hz or perhaps below.
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I plan to biamp leaving the tweeter and mid in series. This may compensate for the anomalies and fortunately the "deviations" are at low db so it may not make that much difference using a "clean" parallel crossover. We will see.
I put the socks back on without taking individual measurements of the drivers -- I had to do this while the wife was away playing as I think she would have had a heart attack if she saw brand new $6K speakers in pieces :).
Rather it's certain folks at Magnepan who might be having 'the big one' (as in "Elizabeth I'm coming to join ya").
In that case, I think you should reconfigure the mid/tweet crossover to parallel. That will give you complete (separate) control of the two electrical responses, and it will place a capacitor in series with the tweeter for DC-blocking and transient on/off protection (should you need it.)
When you remove L1/C1 you separate the woofer and its "protection" from the overall series configuration scheme. This is most likely a minor issue if your power amplifier is well-behaved, but it might be something to consider.
Dave.
It is not necessary to convert the mid-tweeter to a parallel config since the cap (mid-tweet hp) will protect the tweeter. In any case, my W4S amps are really well-behaved and there are not thumps and bumps in the night.
At this point however I am not sure how to simulate the "weird" effect of the 8 ohm mid on the series woofer.
It doesn't block DC though, is what I'm saying......as it would in a parallel network. Yes, you do have the coil in shunt, but a good amplifier could still source/sink constant DC current to the tweeter driver.
However, I'm sure you'll be okay either way.
If the 8 ohm midrange measurement is correct....through the frequency range....then your simulation is correct. Ideally, you'd want to impedance sweep all three drivers and incorporate that into your simulation vice just a DCR measurement.
Cheers,
Dave.
Wendell confirmed the 8 ohm impedance and since the driver is essentially purely resistive, the impedance is essentially constant independent of frequency.
While I agree with you that in my case the concern about DC is somewhat moot, I would think that the HP capacitor of the parallel circuit that feeds into the combined mid-tweeter series network, should be sufficient protection. The woofer is paralleled via the inductor.
As for the wife, thankfully mine doesn't care what I do. Pull apart brand new speakers, OK. Rip apart the car I just bought, sure.
That should be much easier..
Too bad you had to cover your tracks before you got to measure the drivers. Reminds me of hiding the pieces left over from reassembling my grandfather's watch when I was 8.
Brave and wonderful soul. The Odysseus of the 3.7i ...Have a great journey in the 'black boat'.
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