Crossover logic validation

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Sixto

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Joined 2014
#1
I’m Building a 3-way with the following drivers:

Mid-Woofer: Silver Flute W14RC25-04 ohm 5-1/2" Wool Cone
Subwoofer: SB Acoustics SB34NRX75-6 12" Woofer
Tweeter: Fountek Neo X 2.0 Ribbon Tweeter Black

Question is crossover frequency between woofer and sub... my theory is to cross as low as possible, but at least one octave above the mid/woofer's F3 which in this case would be 120 Hz for a sealed mid/woofer box (resulting in crossover design of 240 Hz).

Does that sound like a good strategy? Should I lower the crossover closer to 120 Hz by building a vented woofer enclosure?

Thanks! Six in Minneapolis
 
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#2
Are you using a passive or active crossover? What reasons have you thought of that the crossover should be at least one octave above the woofer f3?

For passive crossovers: a reason to base the crossover frequency on the f3 is that around that frequency there usually are impedance peaks, which need to be flattened (= expensive crossover components) if the crossover frequency is close. Another reason is that the frequency response starts to fall off at the f3.

For active crossovers, especially DSPs, impedance and frequency response are not important. Then factors like dispersion, driver distortion and power handling are more important.

Mid-woofers usually are mounted in a closed box to avoid midrange frequencies leaking through the port.
 
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#4
"Mid-woofers usually are mounted in a closed box to avoid midrange frequencies leaking through the port."

Um...no. Midrange drivers are isolated because you don't want your woofer giving your midrange a reach around every time the bass drops.
 
#5
TBTL said:
Are you using a passive or active crossover? What reasons have you thought of that the crossover should be at least one octave above the woofer f3?.
Click to expand...

I am planning to build active x-o, but thought that basing the x-o point on a 1st order rule of thumb (overlap frequencies by 1 octave) might be a safe bet, since the drivers have so much overlap. I guess I could use a 4th order L/R and set the crossover point at f3 or 120. Hz for a sealed mid/woofer enclosure.

Thanks! Six
 
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#7
Smirkr said:
"Mid-woofers usually are mounted in a closed box to avoid midrange frequencies leaking through the port."

Um...no. Midrange drivers are isolated because you don't want your woofer giving your midrange a reach around every time the bass drops.
Click to expand...

Not sure I follow either response... the sub enclosure would be isolated from the mid/woof in all cases. I would prefer to go sealed for the mid and vented for the sub to get more extended low-end. The mid/woofer driver has a recommendation for either (sealed or vented enclosure) though I've never seen a 3-way with a vented mid/woofer enclosure to bring the crossover lower, it seemed possible, so I thought I'd ask if it may be beneficial to do so and get the X/O closer to 80 Hz so that when the sub kicks in it's at a less directional (lower) frequency

Thanks, Six
 
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#8
You want to incorporate the sealed/2nd order behavior of the midwoofer into your design. It's not independent.



You can also do some tricks with using a much smaller enclosure, bumping up the response, and accelerating drop off. You need to deal with it in your crossover, but it's a useful way to save cabinet space.
 
#9
eriksquires said:
You want to incorporate the sealed/2nd order behavior of the midwoofer into your design. It's not independent.

You can also do some tricks with using a much smaller enclosure, bumping up the response, and accelerating drop off. You need to deal with it in your crossover, but it's a useful way to save cabinet space.
Click to expand...

So I'm reading between the lines here, but I get the sense that a sealed mid/woof enclosure is generally preferred over a vented design, and also to set the X/O frequency as low the drivers and X/O design allows for the enclosure type... or in other words, if there is room for driver overlap at this point, give more bandwidth to the mid-woof instead of the sub. I hope I'm not oversimplifying.

Thanks! Six.
 
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