Parallel Capacitor Question

[Oracle2000]

I am restoring an old Pyramid PS/1 speaker which has a switchable built-in crossover for use with the RTR subwoofer module. I just picked these up at a garage sale and am digging in to replace rotted surround and questionable old capacitors. I wonder if anyone knows why Pyramid elected to bundle 4 75mfd 75VNP's in parallel & right next to them install a single 300mfd 50VNP. Both speaker crossovers look identical, neatly glued together as manufactured. They're all NP axials, and the difference is that the bundled 75mfd's are in the series circuit to the drivers, whereas the 300mfd singletons are paired with a choke in a tuning shunt. I decided to launch a search (unsuccessful thus far) before replacing the bundled 75mfd's with singleton 300s.

There are hopefully some thoughts out there on this . . . . .

[Inductor]

Just to mention the fact that the 4(?) caps can accept a higher voltage (4x75V?) than a single one of 50/75V.

[stratus46]

Originally Posted by Inductor

Just to mention the fact that the 4(?) caps can accept a higher voltage (4x75V?) than a single one of 50/75V.

Not in parallel they can't. Has the XO been modified or is it 'stock'?

G²

[DavidL]

The reasons for the bundled caps might be simply that they got a good deal cost wise on caps and just used what they had on hand. As long as the single cap equals the capacitance of the bundled caps and equals or exceeds the voltage rating then it makes no difference.Perhaps the ESR would be lower for the bundled caps in total but shouldn't be an issue anyway unless they are really bad to begin with.

[AndrewT]

4 off paralleled 75uF caps will have many differences from a 300uF cap.
These differences could be ESR, Ripple capacity, volume, cost, etc...................
ESR and ripple capacity are possibly the most important. Packaging space and cost will come into the productionising decisions at some point.

BTW,
do you think that 75uF equals 75mfd?
I am not sure.

[speakerdoctor]

Peter Snell, innovative founder of Snell Acoustics commonly used bundles of NPE's bypassed by a single pF disk cap (at bottom to glue the bundle to the xo board) to attain a value he needed. Below is a pic of just one example found in his famous Snell Model A.

[jcx]

BTW,
do you think that 75uF equals 75mfd?
I am not sure.

we've had that discussion

mfd = micro and not milli farads?

[AndrewT]

mfd = milli femto deci
But, from the context, I'm guessing the manufacturer meant uF.

[Oracle2000]

Thanks for your input, gentlemen. I am certain the identical glued-up crossover blocks are as factory built - the fellow I bought the speakers from acquired them new.

OK, OK, it's microfarads.

The bundled caps look like the typical Callins I've seen in many 60s & 70s speakers, and the 300uF singletons are the really cheap no-name Al-clad cans. I'm just trying to figure out, after all the crossovers I've seen, whether designers knowingly would have chosen higher-quality caps for the in-line signal and thought so much less of the shunted signal that it warranted a decidedly lesser cap quality. I guess I've never encountered a crossover with 2 paths having such high capacitance. These fellas from Canoga Park weren't going toe-to-toe with Dave Wilson, but this speaker combo was their showpiece at the time.

[LafeEric]

I'm with DavidL.