I made my first crossover- and it works

[JonW]

Frankly, I’m a little amazed. And quite relieved. If it didn’t work, I don’t know how I would have gone about fixing it. This is for the RS28a version of the Modula MT’s. I have zero electronics experience (not to mention few woodworking skills). So putting together a crossover was the most daunting process of making speakers. But also exactly why I wanted to do it- to try and learn some electronics. I hooked up the crossover and used test tones from the computer. Measured output at each of the tweeter and woofer with a DMM (never used one before). Sure enough, they each drop off in voltage as they approached the crossover frequency. Amazing.

Tons of thanks to you all for the help- especially Chuck, chasw98. I owe you some beers.

Here’s the crossover:

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And the testing setup:

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[chasw98]

Hey, hey, hey! Looking good there! Congratulations. Wait till you get them assembled and listen to some music through them.

[ThomasW]

Good going Jon, glad to see you're back to speaker building again.... :T

[cobbpa]

Hmmm...hey jon..how soon will these be up for a demo? :T We're going to be building some Modulas soon & maybe a sonosub. It just so happens in about a month we'll be going through Lafayette too. ehh? ehhhh?? :P

[JonW]

Hey, hey, hey! Looking good there! Congratulations. Wait till you get them assembled and listen to some music through them.

I can hardly wait. I really appreciate all the help. :T

Good going Jon, glad to see you're back to speaker building again.... :T

Yup. It’s really lots of fun- when I can get some time to do it. And much thanks to you as well, for all the help. :T

Hmmm...hey jon..how soon will these be up for a demo? :T We're going to be building some Modulas soon & maybe a sonosub. It just so happens in about a month we'll be going through Lafayette too. ehh? ehhhh?? :P

Yes, you’re quite welcome to stop by for a listen. Drop me an email when/if you want to coordinate a visit. Hopefully I won’t be traveling when you’re here.

My sub is already done, so you can hear that. Not sure when I’ll finish the speakers. Work has been incredibly busy. And I’m about to submerge back into a month of really intense work. I’m hoping to have the speakers done in a month or so, but I really can’t tell. I progress slowly on these DIY projects because spare time is rare- my sub, some shelves for the audio gear, and these speakers, in total, will probably add up to about 10 months or more.

[JonW]

Hey Fellas,

I've got a pretty basic crossover question, just for better understanding things...

When testing the crossover, I measured the voltage at the + and - of the tweeter when playing various frequencies. And then at the woofer. And also at the input + and - from the amp. The tweeter and woofer voltages were quite low. And they did not add up to what I saw straight from the amp. So, umm, where is the missing voltage going? I think I'm just misunderstanding something here. Thanks.

[Dennis H]

So, umm, where is the missing voltage going?

Short version, it's being dissipated by the crossover components.

When you stop and think about it, the crossover can't put out more voltage than is put into it. So, the only way it can shape the response is to cut the voltage going to the driver at certain frequencies. If you measure the output of the woofer network at say 20 Hz, it's probably putting out about the same as what goes in. As you move higher in frequency, the baffle step shaping has to reduce voltage. The tweeter has reduced voltage across the band because the driver is more sensitive than the woofer and its SPL output has to match the reduced output of the woofer above the baffle step.

Clear as mud?

Edit: a pic is worth 1000 words. Here's the transfer function JonMarsh posted for the RS tweeter version of the Modula MT. Transfer function is just a fancy way of saying output volts on a log scale, expressed in dB. Every time you cut 6 dB, you have cut the voltage in half. Max output is at about 120 Hz and everything else is a form of passive EQ that cuts voltage to shape the response. So, there's more going on than just cutting the highs from the woofer and cutting the lows from the tweeter.

[chasw98]

Jon:
You must also take into account the meter you are using to measure with. You will find that the frequency response of your average DMM is somewhat lacking in the high frequency department and probably at the low end. It probably is nominally flat from 60 Hz to 1 KHz. But outside of that band, response can drop sharply. I used to own 5 different AC voltmeters specifically for measuring various ranges of frequency from Hz to MHz. OTOH, this is not a scientific test you are conducting and the meter told you enough to know that lows are going to the woofer and high's to the tweeter. Swipe an expensive meter out of the lab one weekend and take it home to play with

Chuck

[Licinius]

Nifty, slighty OT, where can you pick up those little white terminal pieces?

- Thanks chasw, that would make sense, doh

[chasw98]

Radio Shack

[JonW]

Thanks for the explanations- you guys are excellent. :T

That's pretty much what I figured, but thought I'd ask. Now that I've muddled my way through a crossover, I'll go back and reread the speaker books I have. Things will probably make a little more sense.

Yup, Radio Shack for the white terminals. I got the idea from someone else (JonMarsh?) and I like them. Helps to keep things cleaner.