# How 2 figure out xover freq of unknown xovers?

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#### Bull

got given and have various x overs, but all of them the xover point is unknown.

1st is an active mains plug in RCF high pass filter with RCA outputs for the RCF monitor series [I think 8] anyone know it's cut off point?

2nd is a 12/db octave subwoofer passive xover. How would I work out the xover point?

3rd is 3x 12/db octave 2 way[I think] xovers, with a resistor, cap and inductor.

4th is 2x high quality Link Dynamics 2 way xovers, with 5 caps[polyester type] and 2 inductors per crossover board. I swear that would be a 24/db octave one.

Want to use at least the last ones, so need to know.

Thanks.

#### Cal Weldon

Paid Member
Hi Bull,

It will be difficult to analyze the XO points without more info. Are there no numbers on any of the components?

Are you trying to fit an existing XO into a design? That's very hard to do and not recommended. Every XO is matched to the system and can't just be swapped over at will.

A fourth order, 24 dB requires four coils and four caps per board. You have enough components for an 18 dB cut off for the high pass but only a 12dB cut off of the woofer, plus a couple extra caps. Can you draw a schematic and show us a pic?

EDIT: Moved to loudspeakers

#### Cloth Ears

Photos of front and back might give us an indication of what sort of set-up they are. But, as Cal said, we really need some figures (numbers) from the components or we're simply guessing (badly).

#### Ron E

for a 12dB crossover:

Find the L and C that resonate,
Put L in Henries and C in Farads
e.g 1mH = 0.001 Henries

Fc = sqrt(1/(L*C))/(2*pi)

for the example
Fc= sqrt(1/5e-8)/(2*pi) = 712Hz

#### Bull

Cal Weldon said:
Hi Bull,

It will be difficult to analyze the XO points without more info. Are there no numbers on any of the components?

Are you trying to fit an existing XO into a design? That's very hard to do and not recommended. Every XO is matched to the system and can't just be swapped over at will.

A fourth order, 24 dB requires four coils and four caps per board. You have enough components for an 18 dB cut off for the high pass but only a 12dB cut off of the woofer, plus a couple extra caps. Can you draw a schematic and show us a pic?

EDIT: Moved to loudspeakers

Nope, just want to find it's xover point. To [a] see if I can use it with the enclosures I want to build.
And if I can't, then will know what xover point it has if I need to sell them.

Will dig out my camera tommorrow and take some pics.

Also I don't think I half any inductor measuring equipment.

I just checked my Fluke multimeter, and it doesn't do inductor measuring, a shame. Ain't got an oscilloscope either.
As it's got a capacitor tester, transistor tester and the rest of the normal multimeter type functions though.

My friend thinks I can connect the xover to an amp and drivers and run a low level swept frequency through them with like a freeware signal generator on the PC. And tells me to listen to where the signal starts to roll off.

That seems ok, but I don't recognise very close frequencies to each other to make an accurate guess. I'm not that good at all at recognizing different frequencies apart from random quessing.

If I use the wrong xover in project, it would definatly blow the compression driver if the xover point is too low.

So need an accurate way of testing the unknown xovers.

#### augerpro

Paid Member
The true crossover frequency will dependent on the response of the drivers. So knowing the crossover frequency of just the filter is of limited usefulness.

#### Bull

augerpro said:
The true crossover frequency will dependent on the response of the drivers. So knowing the crossover frequency of just the filter is of limited usefulness.

Well the plan says use a xover point of 1.6khz, 18db/octave.

And a high pass at 200hz.

It's basically a plan for horn loaded mid/high. Will find a suitable bass bin for it, when built.

Drivers I wish to use are the Fane Studio 8M[ Fs 81hz] and Selenium D205Ti [800hz-18khz].
The xover I use might have to built from scratch I just thought.

Selenium D205Ti has an SPL of 108 dB at 1W/1m and 75w rms handling.

Fane Studio 8M has an SPL of 101db at 1W/1m and 100w rms handling.

So definatly some dampening resistors on the HF would be needed.

#### ZilchLab

Bull said:
My friend thinks I can connect the xover to an amp and drivers and run a low level swept frequency through them with like a freeware signal generator on the PC. And tells me to listen to where the signal starts to roll off.
Don't hafta listen; use the appropriate load resistors and measure the voltage drives.

First determine what frequency range your Fluke can accurately measure AC from its specs....

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