Resistor change altering crossover point?

[Joe6805]

Hi guys,

Have a pair of Optimus 1000s that I’ve swapped a Peerless silk dome into, and they sound great overall. Redid the crossovers with stock values, and will be going back in soon to swap caps and tweeter resistor again. Here is the schematic (courtesy of @Stuart Pedaso):


As you can see, the 6 ohm tweeter uses a 4 ohm resistor in series. I’m considering a change in value to better match the Peerless’ output to the other drivers.

I know a change of resistance moves the crossover point, but my question is…how much will it move for a small change in that resistor? I may go to say, a 4.2 or 4.5 ohm. Will that be enough of a change to necessitate making an l-pad circuit instead, or not enough to worry about?

Thanks!
Joe

 

[Lavane]

most resistors used in crossovers tend to have 5% to 10% tolerances.
I've seen a lot if ceramic wire wound resistors used that have a 10% tolerance used in crossovers. So the value can be 10% high, or low of the value of the resistor. So if your withing that range I would think you would be ok? Even electrolytic caps.ysed in many speakers are just general purposes caps with + or - 50% tolerances. I've run across fairly new caps that were around 20% low.
Hopefully someone with more experience with crossovers will.chime in.

 

[toddalin]

If you put the resistor between the split for the other two drivers and the 2.2 NPE, it will lower the tweeter's volume, but will not adversly affect the crossover frequency or slope. The value will be small and even a couple ohms rated at 10 watts should be more than enough.

 

[Rick Owen]

If you put the resistor between the split for the other two drivers and the 2.2 NPE, it will lower the tweeter's volume, but will not adversly affect the crossover frequency or slope. The value will be small and even a couple ohms rated at 10 watts should be more than enough.

Wouldn't moving the resistor from it's current location effect the crossover point.
I get what your saying, and adding a reisistor (if more is wanted) in the location you suggest might not effect crossover frequency much, if at all, but the moving of the exisiting resisitor would?

 

[toddalin]

Wouldn't moving the resistor from it's current location effect the crossover point.
I get what your saying, and adding a reisistor (if more is wanted) in the location you suggest might not effect crossover frequency much, if at all, but the moving of the exisiting resisitor would?

Yes, moving the existing resistor would change the crossover slope and no placing an additional resistor in the noted position won't.

https://audiokarma.org/forums/index...or-is-placed-in-the-crossover-network.926881/

 

[Stuart Pedaso]

I ran a mock-up of the circuit in XSim to test some resistor value changes.


Resistor of 4Ω, 4.7Ω, 6Ω and 12Ω made very small changes in slope at the low frequency side of the tweeter response curve (where crossover occurs), and more profound changes on the high frequency side. Crossover frequency change itself is so slight it barely registers within pixel resolution of the graphic, with cursor centered on the crossover point (not the red arrow -- that just indicates the crossover point under test).








So in this exercise, we go from a crossover point of 4.6kHz to just over 4.7kHz by tripling the series resistor value.

I'm feeling some relief to realize that 5% resistors are quite good enough for the typical crossover application.

 

[Joe6805]

I ran a mock-up of the circuit in XSim to test some resistor value changes.
View attachment 3118769

Resistor of 4Ω, 4.7Ω, 6Ω and 12Ω made very small changes in slope at the low frequency side of the tweeter response curve (where crossover occurs), and more profound changes on the high frequency side. Crossover frequency change itself is so slight it barely registers within pixel resolution of the graphic, with cursor centered on the crossover point (not the red arrow -- that just indicates the crossover point under test).
View attachment 3118760

View attachment 3118762

View attachment 3118763

View attachment 3118764

So in this exercise, we go from a crossover point of 4.6kHz to just over 4.7kHz by tripling the series resistor value.

I'm feeling some relief to realize that 5% resistors are quite good enough for the typical crossover application.

Again, sir, you are awesome. Thanks!

Will that program show the crossover frequency of both the mid and tweeter? Have tried plugging the values into the online calculators, but never seems to jive.

Mids are 6 ohm also, FWIW.

Thanks,
Joe

 

[Coolhandjjl]

Why not use an "L pad" that does not alter the crossover point?

The 6 ohm tweeter complicates things. L-Pads are designed for an 8 ohm tweeter (and some for a 4 ohm tweeter)

 

[toddalin]

Why not use an "L pad" that does not alter the crossover point?

Also, cost and ease of mounting may come into play. And, over time (sometimes a very short time), the L-pad will become scratchy/noisy and the resistor never will.