Inductors & L Pad resistors

Two questions in one thread, all part of my ongoing quest for knowlege about passive crossovers.

1). What diameter wire should I be using for inductors. I bought 1.2mm but eminence seem to use about 0.9mm on their crossovers, which (obviously is a lot lighter and cheaper.

2). Resistors for L pads. Resistors seem to only come in certain values 1R8, 2R2, 3R3, 3R9, 4R7, 5R6, 6R8, etc, so is it simply a case of using the nearest value available for L Pads. For example a 3dB pad requires a 2.4ohm and a 20 ohm. The nearest available values are 2R2 and 22R, so will they do the job??

Mark,
With inductors there is no one suitable size for the wire. It is preferable to keep the resistance of the coil to no more than 10% of the driver value. So for a typical 8 ohm driver try to keep the coil below 0.8 ohms. So you will need to know the resistance of the wire used per metre and do a little maths.

This can be relaxed on comp drivers where L-pads are used as long as the overall effect is measured.

With resisters I use the the nearest available value to the one calculated. If you are worried that it needs to be more accurate the make the adjustments using further parallel or series components .

Tony

Edited by: AJW

There is lots of good information on the Elliott Sound Products web page. The link takes you to the main articles index. The one you want is passive crossovers. Take care not to get distracted. [img]smileys/smiley2.gif[/img]

sound.westhost.com/articles.htm

Regarding values, you will find that, as the change in effect is very gradual, when it comes to caps, coils and resistors, it won't matter if the values are a little bit out. Once you start to know how to play with the parts, you can make things very flat. When you wind a coils for instance, if you are supposed to wind 300 turns, it won't matter whether it turns out to be 295 turns or 305. When it comes to the sound you will never hear the difference. The same goes for resistors. Caps are a tiny bit more sensitive. one mic. may produce an audible in the hf region, but lower down would have less effect.
In the end it's knowing what matters and what doesn't that's important.

Thanks for the input guys. I've been working on building my own coil winder. I found a couple of hand wound ones on the net but they were about £400.00 and obviously the motor driven ones are more.

I started with one based around an old hand drill......... went on to a cordless drill and am now on the Mk 5 version based on a foot controlled sewing machine motor. I still need to gear it down more and that will involve making a longer drive belt, but when/if I get it finished I'll post some pics.Edited by: markie

Markie, I paid £600.00 for mine after I designed the Spektra range. David at Volt supplied me at first but I needed them on tap, so I had to get one. Mine is based on a sewing machine stand. I'll take some photos tomorrow and post them. So you can compare. It's a great machine.

Tony I'd be really interested to see your pics.

Markie, here's the pics of my coil winder. Enjoy. Did you know there is a mag called coil winder monthly. It's a riveting read.

i know a man with one of those! he builds transformers for a living.

Wow, serious piece of kit. I'll post some pics of my DIY effort when it's finished.

COIL WINDER MONTHLY.............. YOU'RE 'AVIN A LAUGH