DIY speaker question

[nm2285]

I'm designing a speaker that uses a tweeter with an efficiency rating of 91.5 db and a midrange with 91 db. I calculated an L-Pad attenuator and it said I'd need a resistor in series with the tweeter at .22 ohms and a resistor in parallel at 67.5 ohms. The for the resistor in parallel, I could wire 2 resistors in series (a 25 and a 40), but for the .22, I've don't see any non-inductive resistors I could use. Is there any problem using regular wire-wound?

Also, the resistors I'm buying are 10W. I don't really see many rated much higher, will they be ok? I drive my speakers with an amp rated at 120W RMS, 210 dynamic.

This is my first DIY project. Help if you can, please!

Thanks,
Nick

 

[Rip Van Woofer]

No problem with wire wound resistors. Also no problem with 10 or even 5 watt resistors. The resistors don't take all the wattage of your amp themselves; the rest of the xover circuit kind of divvies it up so nothing goes 'poof'*. I'm driving my DIY speakers with a 100 watt/channel amp and have 5 or 10 watt resistors throughout my crossovers, depending only on what was available from Parts Express for a given resistance. No problems. Nothing even gets warm in the xover (my xovers are externally mounted due to the shallow cabinet).

For that matter, not all of your amp's power even makes it to the drivers. Your crossover circuit (a 'passive' circuit) soaks up a considerable amount of it. I have read that the 'insertion loss' of a typical passive crossover is 3db which, if true, means that only half of your amp's wattage makes it to the drivers, all else being perfect which it probably ain't. That's one reason among many I'm going to go to active crossovers.

*Since my electrical knowledge is that of a trained chimpanzee I don't know exactly why. A basic electronics book will explain it; mine does but I don't have it handy and haven't yet mastered the relevant concepts. Go ahead and snicker, you EE types! (Before I started in DIY, my knowledge was that of an untrained chimpanzee so I've made some progress!)