HELP: Best crossover choice

[coxy1214]

Hello everyone. I'm designing a loudspeaker project for a communications electronics course. I'm stuck with designing a crossover network. Of course, I want one best suited for offering maximum protection for the tweeter. Projected drivers:

Eminence BETA-12CX
**RMS 250W, 8 ohms, 43Hz resonance, range 66Hz~5kHz
Eminence APT-50
**RMS 35W@3.5kHz/85W@kHz (some explanation wanted on these two aspects), 8 ohms, 1.6kHz resonance, range 3.5kHz-20kHz

I was thinking a crossover frequency at around 4kHz? Any and all help is appreciated!

[jerome69]

Hi,

Originally Posted by coxy1214

**RMS 35W@3.5kHz/85W@kHz

Power with a crossover 3.5kHz@12dB electrical.

Originally Posted by coxy1214

I was thinking a crossover frequency at around 4kHz? Any and all help is appreciated!

Yes for 4kHz

Try this one ? DESIGNED TO WORK IN HIGH

Don't forget to buy a LPAD for the tweeter : Pro-Tech L-Pad 100-8. This L-Pad will adjust volume of highs.

[coxy1214]

Thanks for the reply! I hadn't gotten to researching L-Pads yet but I assume that these are necessary for ideal performance?

To the recommended crossover: I have to build it... That's where I require lots of help

[tinitus]

you may need a quite big inductor in series with woofer

[jerome69]

Originally Posted by coxy1214

Thanks for the reply! I hadn't gotten to researching L-Pads yet but I assume that these are necessary for ideal performance?

Yes because the woofer have 95dB and the tweeter 104dB. You must reduce the tweeter level. You can use two resistors but a LPAD is more flexible.

Originally Posted by coxy1214

To the recommended crossover: I have to build it... That's where I require lots of help

For the tweeter positive polarity, a 18dB 3.5kHz : C=3.9uF L=0.22mH C=10uF LPAD Rs=4.7ohm Rp=4.7ohm

For the woofer first order, positive polarity L=0.47mH. Need a RLC in parallel with the woofer after the inductor, to suppress the 2kHz resonance peak R=4.7ohm L=0.47mH C=10uF.

Hope this Helps.

[coxy1214]

Great help! And this will offer appropriate protection for my tweeter?

[jerome69]

Yes a 18dB crossover offers higher power handling, 45W instead 35W with a 12dB. If you want a higher level of protection you can add a 2A fuse but I think it's unnecessary.

[Soundminded]

If protecting the tweeter is the main criteria be guided by these principles;

The steeper the filter the better. Steeper filters restrict LF out band energy from reaching it. A third order filter is better than a secod order filter. A fourth order filter is better than a third order filter.

The higher the low cutoff frequency the better. A tweeter crossed over at 5khz will be required to handle less energy than one crossed over at 4 khz. A 3 way design facillitates a higher crossover for the tweeter than a 2 way system.

Fuses help too. A combination of both a fast blow and slow blow fuse in series offers the best protection.

A low pass filter operating just above 20 khz will protect the tweeter from damage due to accidental ultrasonic oscillation either from the source signal or due to amplifier failure.

Use series caps rated at 200 VDC to protect the tweeter best if the amplifier output stage fails and there is DC at the speaker terminals.

This belt and suspenders design will protect a tweeter from electrical abuse under most conceivable forms of abuse. I am not aware of any commercially available speaker system which incorporates all of these elements in its design.

[tinitus]

Originally Posted by Soundminded

A third order filter is better than a secod order filter. A fourth order filter is better than a third order filter.

just a short note

'electrical' 18db might as a acoustical result give either
or something completely different in between
depends on impedance variation and actual frequency response without xo

your filter might be just fine and work ok
but if very critical its really not this simple
if it was anyone could calculate or sim a perfect filter
but I guess it could be worse
well, even with measurements you might have problems to tell 100% what kind of slopes you have
its more important to know phase and impulse behaviour
which fortunately is possible with measurements
and unfortunately even harder without

[Soundminded]

Originally Posted by tinitus

just a short note

'electrical' 18db might as a acoustical result give either
or something completely different in between
depends on impedance variation and actual frequency response without xo

your filter might be just fine and work ok
but if very critical its really not this simple
if it was anyone could calculate or sim a perfect filter
but I guess it could be worse
well, even with measurements you might have problems to tell 100% what kind of slopes you have
its more important to know phase and impulse behaviour
which fortunately is possible with measurements
and unfortunately even harder without

Where the sole criteria is preventing tweeter burnout, I'll stick with what I said about higher order filters. However, as soon as sound quality becomes a factor, all bets are off and a second order filter is probably a better choice. The third order filter provides a steeper slope for frequencies below the corner frequency. This reduces the risk of damage. For best sound, an array of tweeters using first order filters strikes me as even better.