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In Reply to: RE: Snell and Spica Rebuild - ESR Consideration? posted by tvr2500m on February 09, 2009 at 21:24:08
...will be of much use because their values likely have shifted with age. Inductors aren't going to change and it's not likely the resistors will either. I'd start with the tweeter circuit first and replace caps and resistors, then re-assemble the speaker and listen for a while. You might even experiment by doing only one speaker and leave the other original. Compare the two my listening while your electronics are switched to mono. Use the balance control to change between the two and see if there's a noticeable difference. Take your time. By doing one branch of the crossover at a time you can spot potential problems much easier.As far as ESR, better quality film caps won't create problems.
Tuning the crossover to a reference, as I understand it, involves changing resistor values or unwinding inductors, which also changes resistance to some degree.
Edits: 02/10/09Follow Ups:
Thanks for the reply. The measured approach you suggest is such a good one. Sober, scientific. I just have to find the patience for it (for the Snells, it's more like my brother does; they're his speakers and he's up for some tweaking, but how much is the question).
Okay, so I won't sweat the ESR values.
On the tuning to a reference, I'm good with the top level of the concept, but I'm lost re: the tactical details. I'd like to see this done. What's measured? How are measurements made? What responses are made to the measurements when changes are indicated? For the Spicas, I'd like to know the exact process/methodology used to grade the midwoofers. Inquiring minds want to know ;)
- SJ
For the Snells, the sliding resistor was the tuning device. It's the only adjustment in the xover. I expect it simply balanced the spl outputs of the drivers.
Peter Snell was famous for bundling NPE caps and bypassing the bundle with a small disc shaped nF cap.
Some EE's suggest adding a low value resistor (.25-.5 ohms in series) when replacing NPE's to compensate for NPE's inherent ESR. That's another route you can try with your single speaker upgrade experiments. NPE's are cheap enough. If your old NPE's have drifted significantly (i.e. ESR risen well above 1 ohm) then replacing with film will be quite noticeable. It's like removing a series resistor from the tweeter circuit.
Check the link below for more information on the Spicas.
It's all about the music
I would imagine measurements would include impedance plots and anechoic chamber frequency response measurements.
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