Question about xover parts and values

[kgveteran]

This all started in the Dayton WTMW center channel thread, but I thought that some xover help was needed and apart from the project thread.

Inductors: In schematics I see ohm values and mH values.The mH values are easy to find and by adding together in series or parallel they work.The problem I seem to be having is the ohm value as stated on the published schematic.When ordering the parts, the catalog does not jive with the values of the project.A little explaination on the values and how to select proper chokes.Should I also choose a coil based on ga./watt rating or does the ga. indicate the ohm value ? I would like to stay faithful to the great designs in this forum, but sticking to it is tough when I'm unsure on these questions.

I think I read in the other thread that resistors add value in series and divided by two when in parallel.Is there any way to use odd values to create the desired value for the project ? If so what formula is used ?

About values, if the desired value of a capacitor is 9.5uF for a xover, can I use a 10uF cap with little change in the sound ? How far can I deviate from the project value before I cause real problems.

Last, caps are the oposite from resistors, they add value in parallel and divide by two when run in series.Do I always use equal value to get the desired cap or is there a formula to using odd values in series.

I know these are basic questions from a xover newbie , but I'm trying.If you guys feel this is better left in the Dayton RS center channel thread than by all means move it.Thanx.

KG

[Paul H]

Inductors: In schematics I see ohm values and mH values.The mH values are easy to find and by adding together in series or parallel they work.The problem I seem to be having is the ohm value as stated on the published schematic.When ordering the parts, the catalog does not jive with the values of the project.A little explaination on the values and how to select proper chokes.Should I also choose a coil based on ga./watt rating or does the ga. indicate the ohm value ? I would like to stay faithful to the great designs in this forum, but sticking to it is tough when I'm unsure on these questions.

Most air-cored coils (the ones with no metal in the middle) suggested by designs in this forum are going to be in the 14 gauge to 18 gauge range. Some lower frequency crossovers may use 10 or 12 gauge (ie the Arvo woofer crossover). Generally larger wire (lower gauge number) is better, due to increased power handling, but of course the cost, weight and overall size goes up with the wire size.

The resistance is often given by manufacturer's websites and noted as DCR (Direct Current Resistance).

The audible difference between say a 14 gauge and 16 gauge inductor will be very minimal - attempting to match resistance of the inductor with the published design gets into tweaking in the n'th degree.

A decent balance between quality and thrift may be to use 14 gauge inductors for the low pass crossover (woofer portion) and 16-18 gauge for any inductors in the high pass (tweeter portion).

I think I read in the other thread that resistors add value in series and divided by two when in parallel.Is there any way to use odd values to create the desired value for the project ? If so what formula is used ?

Resistor value in parallel only divides by two if you're using two resistors of the same value. Formulas are as follows:

Resistors in series - R total = R1 + R2 + R3 .....

ie Three 8 Ohm resistors in series gives 8+8+8=24 Ohms

Resistors in parallel - 1/R total = 1/R1 + 1/R2 + 1/R3 ....

ie Three 8 Ohm resistors in parallel : 1/8 + 1/8 + 1/8 = 3/8
Total R = 1 / (3/8) = 8/3 =~ 2.67 Ohms

About values, if the desired value of a capacitor is 9.5uF for a xover, can I use a 10uF cap with little change in the sound ? How far can I deviate from the project value before I cause real problems.

I was advised way back by Thomas as I recall that the 5% variance on the meter I was using to measure capacitors was no problem. Simulations in LSPCad indicate the same thing (ie minimal effect with 5% change).

Last, caps are the oposite from resistors, they add value in parallel and divide by two when run in series.Do I always use equal value to get the desired cap or is there a formula to using odd values in series.

See resistor comment & formulas above, but reverse series and parallel for caps.


Paul

[kgveteran]

Paul,
Will you be my new "xover best friend".Thank you so much for taking the time to address each concern I had.

So, if i'm to understand the DRC value is suggested but may fall into the 5% rule, and to get as close as possible but not to scrap the whole project because the DRC value does not match to the "T".

I hope you check in time to time in the RS center channel thread to assist if needed.I'm looking forward to hearing this center channel in action.

KG

[Dennis H]

Another thing, when shopping for component values, check more than one supplier if you don't find what you need. Sometimes Parts Express will have something Madisound doesn't and vice versa.

[kgveteran]

Dennis,

I just finished my parts list.Total xover parts came to 95.00 .

For the tweeter xover all parts match 100%.The woofer parts all match, even the combined value parts for a 100% match.

The midrange had two value mismatches and I'll list them.

The 57uF cap can be made from a 50.0uF and a 6.8uF run in parallel for a combined value of 56.8uF .This is well within the 5% deviation.

The 0.08mH coil can be made from two .15 coils run in parallel for a combined value of 0.75mH . I calculated a 6% deviation from the schematic.

Not that any part is less important than another, but do you feel that this is within our conversation of variables that this design can live with.

Can our patient moderators move this to the Dewaro RS center channel thread, sorry.

[Dennis H]

Sounds good.