Passive Crossover Design

[altoncustomtech 773]

I'm working on a project for a buddy of mine and I've come across a bit of a hold up.  I'm more than familiar enough with circuit design, crossover components and such to build crossovers.  I've been doing it for quite a few years with results that I felt were what I needed.  I've come across something different with this as my buddies tweeter is significantly louder than the midrange or the woofer in his 3 way floor standing speakers.  The speakers haven't been used in several years and when we hooked them up to test and tune the system for his mom's upcoming birthday party that we were going to DJ ourselves the old tweeters didn't work.  Instead of waiting for me to help him find some he just ordered what he thought looked good/cool and they're way too loud.  He did manage to make sure they were 8 ohm like the old ones and fit the hole in the enclosure, so he didn't do all bad.  I've got a box full of 5 and 10 watt resistors all kinds of values that I can use to build an attenuation circuit to quiet the thing down, we don't have time to order better suited tweeters.  

 

My question is, does the resistors in the attenuation circuit change the impedance of the circuit as a whole enough to need to change the capacitor and inductor in the Lw-R crossover?  Would it affect it enough to matter?  If it does what's the best way to calculate or measure for the difference so I know what the change is and can get the components in the crossover changed to values that will keep the crossover point close to where it was supposed to be?

 

 

Thanks for the help guys, this is the first time I've actually put an attenuation circuit to use and was just wondering how it affects the crossover point.  I am assuming it doesn't change anything, or not enough to matter since they make L-PAD resistors that are variable and would change the crossover point every time it's adjusted.

[95Honda 486]

You need to do an L-network (series and parallel resistors) instead of a single resistor in series or you will alter the crossover frequency.

 

There are a ton L-attenuator calculators online, just choose one and run with it.

 

By the way, if this is going to get a bunch of power (like a DJ rig) make sure you combine a few of the resistors in parallel (at least in the series component) to increase heat dissipation...  You can easily burn up a 10 watt resistor in minutes.  I you have powerful pro audio amps try and get at least 30+ watts of resistors on the series portion and 20+ on parallel portion...

[altoncustomtech 773]

I have looked at several of those calculators and was planning on doing the L-network I just wasn't sure if it would alter the crossover frequency or not.

 

It's not a high powered DJ rig at all.  It's just a pair of Matrix 12" 3 ways with a Crown XL200 amp running them, nothing spectacularly powerful at all and it's not going to be cranked to the moon.  I've got plenty of them so adding them together to increase wattage wouldn't be an issue, though I could swear that connecting them in parallel was the way to add their heat dissipation together, not series.  No matter, at least it won't affect the crossover frequency, that was the important thing. 

[95Honda 486]

The whole point of an L-network is not to effect the impedance the crossover network sees.  So you'll be good...  Just make sure you use the appropriate L-network (it should have you input driver impedance).

 

I would shoot for at least 20-30 watts rated dissipation, with that amp.  Just gang them up and you'll be fine.  Better safe than sorry...